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Sample records for early earth mantle

  1. Global-scale water circulation in the Earth's mantle: Implications for the mantle water budget in the early Earth

    NASA Astrophysics Data System (ADS)

    Nakagawa, Takashi; Spiegelman, Marc W.

    2017-04-01

    We investigate the influence of the mantle water content in the early Earth on that in the present mantle using numerical convection simulations that include three processes for redistribution of water: dehydration, partitioning of water into partially molten mantle, and regassing assuming an infinite water reservoir at the surface. These models suggest that the water content of the present mantle is insensitive to that of the early Earth. The initial water stored during planetary formation is regulated up to 1.2 OMs (OM = Ocean Mass; 1.4 ×1021 kg), which is reasonable for early Earth. However, the mantle water content is sensitive to the rheological dependence on the water content and can range from 1.2 to 3 OMs at the present day. To explain the evolution of mantle water content, we computed water fluxes due to subducting plates (regassing), degassing and dehydration. For weakly water dependent viscosity, the net water flux is almost balanced with those three fluxes but, for strongly water dependent viscosity, the regassing dominates the water cycle system because the surface plate activity is more vigorous. The increased convection is due to enhanced lubrication of the plates caused by a weak hydrous crust for strongly water dependent viscosity. The degassing history is insensitive to the initial water content of the early Earth as well as rheological strength. The degassing flux from Earth's surface is calculated to be approximately O (1013) kg /yr, consistent with a coupled model of climate evolution and mantle thermal evolution.

  2. Numerical Mantle Convection Models of Crustal Formation in an Oceanic Environment in the Early Earth

    NASA Astrophysics Data System (ADS)

    van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.

    2001-12-01

    The generation of basaltic crust in the early Earth by partial melting of mantle rocks, subject to investigation in this study, is thought to be a first step in the creation of proto-continents (consisting largely of felsic material), since partial melting of basaltic material was probably an important source for these more evolved rocks. In the early Archean the earth's upper mantle may have been hotter than today by as much as several hundred degrees centigrade. As a consequence, partial melting in shallow convective upwellings would have produced a layering of basaltic crust and underlying depleted (lherzolitic-harzburgitic) mantle peridotite which is much thicker than found under modern day oceanic ridges. When a basaltic crustal layer becomes sufficiently thick, a phase transition to eclogite may occur in the lower parts, which would cause delamination of this dense crustal layer and recycling of dense eclogite into the upper mantle. This recycling mechanism may have contributed significantly to the early cooling of the earth during the Archean (Vlaar et al., 1994). The delamination mechanism which limits the build-up of a thick basaltic crustal layer is switched off after sufficient cooling of the upper mantle has taken place. We present results of numerical modelling experiments of mantle convection including pressure release partial melting. The model includes a simple approximate melt segregation mechanism and basalt to eclogite phase transition, to account for the dynamic accumulation and recycling of the crust in an upper mantle subject to secular cooling. Finite element methods are used to solve for the viscous flow field and the temperature field, and lagrangian particle tracers are used to represent the evolving composition due to partial melting and accumulation of the basaltic crust. We find that this mechanism creates a basaltic crust of several tens of kilometers thickness in several hundreds of million years. This is accompanied by a cooling of

  3. A model for the evolution of the Earth's mantle structure since the Early Paleozoic

    NASA Astrophysics Data System (ADS)

    Zhang, Nan; Zhong, Shijie; Leng, Wei; Li, Zheng-Xiang

    2010-06-01

    Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., superplumes) and circum-Pacific seismically fast anomalies (i.e., a globally spherical harmonic degree 2 structure). However, the cause for and time evolution of the African and Pacific superplumes and the degree 2 mantle structure remain poorly understood with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Myr and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma) and the mantle in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree 1 structure before the Pangea formation). Here, we construct a proxy model of plate motions for the African hemisphere for the last 450 Myr since the Early Paleozoic using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations. Coupled with assumed oceanic plate motions for the Pacific hemisphere, this proxy model for the plate motion history is used as time-dependent surface boundary condition in three-dimensional spherical models of thermochemical mantle convection to study the evolution of mantle structure, particularly the African mantle structure, since the Early Paleozoic. Our model calculations reproduce well the present-day mantle structure including the African and Pacific superplumes and generally support the second proposal with a dynamic cause for the superplume structure. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of

  4. Accessory Mineral Records of Early Earth Crust-Mantle Systematics: an Example From West Greenland

    NASA Astrophysics Data System (ADS)

    Storey, C. D.; Hawkesworth, C. J.

    2008-12-01

    Conditions for the formation and the nature of Earth's early crust are enigmatic due to poor preservation. Before c.4 Ga the only archives are detrital minerals eroded from earlier crust, such as the Jack Hills zircons in western Australia, or extinct isotope systematics. Zircons are particularly powerful since they retain precise records of their ages of crystallisation, and the Lu-Hf radiogenic isotope and O stable isotope systematics of the reservoir from which they crystallised. In principle, this allows insight into the nature of the crust, the mantle reservoir from which the melt was extracted and any reworked material incorporated into that melt. We have used in situ methods to measure U-Pb, O and Lu-Hf within single zircon crystals from tonalitic gneisses from West Greenland in the vicinity of the Isua Supracrustal Belt. They have little disturbed ages of c.3.8 Ga, mantle-like O isotope signatures and Lu-Hf isotope signatures that lie on the CHUR evolution line at 3.8 Ga. These samples have previously been subjected to Pb isotope feldspar and 142Nd whole rock analysis and have helped constrain models in which early differentiation of a proto-crust must have occurred. The CHUR-like Lu-Hf signature, along with mantle-like O signature from these zircons suggests juvenile melt production at 3.8 Ga from undifferentiated mantle, yet the other isotope systems preclude this possibility. Alternatively, this is further strong evidence for a heterogeneous mantle in the early Earth. Whilst zircons afford insight into the nature of the early crust and mantle, it is through the Sm-Nd system that the mantle has traditionally been viewed. Titanite often contains several thousand ppm Nd, making it amenable to precise analysis, and is a common accessory phase. It has a reasonably high closure temperature for Pb and O, and it can retain cores with older ages and distinct REE chemistry. It is often the main accessory phase alongside zircon, and it is the main carrier of Nd

  5. The Earth's Mantle.

    ERIC Educational Resources Information Center

    McKenzie, D. P.

    1983-01-01

    The nature and dynamics of the earth's mantle is discussed. Research indicates that the silicate mantle is heated by the decay of radioactive isotopes and that the heat energizes massive convention currents in the upper 700 kilometers of the ductile rock. These currents and their consequences are considered. (JN)

  6. On the temporal evolution of long-wavelength mantle structure of the Earth since the early Paleozoic

    NASA Astrophysics Data System (ADS)

    Zhong, Shijie; Rudolph, Maxwell L.

    2015-05-01

    The seismic structure of the Earth's lower mantle is characterized by a dominantly degree-2 pattern with the African and Pacific large low shear velocity provinces (i.e., LLSVP) that are separated by circum-Pacific seismically fast anomalies. It is important to understand the origin of such a degree-2 mantle structure and its temporal evolution. In this study, we investigated the effects of plate motion history and mantle viscosity on the temporal evolution of the lower mantle structure since the early Paleozoic by formulating 3-D spherical shell models of thermochemical convection. For convection models with realistic mantle viscosity and no initial structure, it takes about ˜50 Myr to develop dominantly degree-2 lower mantle structure using the published plate motion models for the last either 120 Ma or 250 Ma. However, it takes longer time to develop the mantle structure for more viscous mantle. While the circum-Pangea subduction in plate motion history models promotes the formation of degree-2 mantle structure, the published pre-Pangea plate motions before 330 Ma produce relatively cold lower mantle in the African hemisphere and significant degree-1 structure in the early Pangea (˜300 Ma) or later times, even if the lower mantle has an initially degree-2 structure and a viscosity as high as 1023 Pas. This suggests that the African LLSVP may not be stationary since the early Paleozoic. With the published plate motion models and lower mantle viscosity of 1022 Pas, our mantle convection models suggest that the present-day degree-2 mantle structure may have largely been formed by ˜200 Ma.

  7. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth

    NASA Astrophysics Data System (ADS)

    van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.

    2004-12-01

    Important constituents of Archean cratons, formed in the early and hot history of the Earth, are Tonalite-Trondhjemite-Granodiorite (TTG) plutons and greenstone belts. The formation of these granite-greenstone terrains is often ascribed to plate-tectonic processes. Buoyancy considerations, however, do not allow plate tectonics to take place in a significantly hotter Earth. We therefore propose an alternative mechanism for the coeval and proximate production of TTG plutons and greenstone-like crustal successions. That is, when a locally anomalously thick basaltic crust has been produced by continued addition of extrusive or intrusive basalts due to partial melting of the underlying convecting mantle, the transition of a sufficient amount of basalt in the lower crust to eclogite may trigger a resurfacing event, in which a complete crustal section of over 1000 km long sinks into the mantle in less than 2 million years. Pressure release partial melting in the complementary upwelling mantle produces large volumes of basaltic material replacing the original crust. Partial melting at the base of this newly produced crust may generate felsic melts which are added as intrusives and/or extrusives to the generally mafic crustal succession, adding to what resembles a greenstone belt. Partial melting of metabasalt in the sinking crustal section produces a significant volume of TTG melt which is added to the crust directly above the location of 'subduction', presumably in the form of a pluton. This scenario is self-consistently produced by numerical thermochemical mantle convection models, presented in this paper, including partial melting of mantle peridotite and crustal (meta)basalt. The metamorphic p, T conditions under which partial melting of metabasalt takes place in this scenario are consistent with geochemical trace element data for TTGs, which indicate melting under amphibolite rather than eclogite facies. Other geodynamical settings which we have also investigated

  8. Origin of the Early Sial Crust and U-Pb Isotope-Geochemical Heterogeneity of the Earth's Mantle

    NASA Astrophysics Data System (ADS)

    Mishkin, M. A.; Nozhkin, A. D.; Vovna, G. M.; Sakhno, V. G.; Veldemar, A. A.

    2018-02-01

    It is shown that presence of the Early Precambrian sial crust in the Indo-Atlantic segment of the Earth and its absence in the Pacific has been caused by geochemical differences in the mantle underlying these segments. These differences were examined on the basis of Nd-Hf and U-Pb isotopes in modern basalts. The U-Pb isotope system is of particular interest, since uranium is a member of a group of heat-generating radioactive elements providing heat for plumes. It is shown that in the Indo-Atlantic segment, a distribution of areas of the modern HIMU type mantle is typical, while it is almost completely absent in the Pacific segment. In the Archean, in the upper HIMU type paleo-mantle areas, plume generation and formation of the primordial basic crust occurred; this was followed by its remelting resulting in the appearance of an early sial crust forming cratons of the Indo-Atlantic segment.

  9. Variation in 142Nd/144Nd of Archean rocks from southwest Greenland : Implications for early Earth mantle dynamics

    NASA Astrophysics Data System (ADS)

    Rizo, H.; Boyet, M.; Blichert-Toft, J.; Rosing, M.; Paquette, J. L.

    2012-04-01

    The short-lived 146Sm-142Nd chronometer (half-life = 103 Ma) has proven successful in bringing constraints on the dynamics of the early Earth mantle. Since the parent isotope, 146Sm, was extant only during the first 300 Ma of the history of the Solar System, the positive 142Nd anomalies measured in southwest Greenland Archean rocks imply that their incompatible element-depleted mantle source formed during the Hadean. Interestingly, the magnitude of these anomalies seems to decrease over time. 3.7-3.8 Ga old rocks from the Amitsoq Complex have revealed +10 to +20 ppm 142Nd anomalies [1, 2, 3, 4, 5, 6, 7], whereas younger 3.0 Ga old samples from the Ivisaartoq greenstone belt yield smaller positive anomalies, ranging from +5.5 to +8.5 ppm [8]. Thus, the chemical heterogeneities detected in the southwest Greenland mantle were formed during the first 150 Ma of Earth's history, and seem to have resisted re-mixing by mantle convection until 3.0 Ga. In this study, we investigate the evolution of the southwest Greenland mantle during the time period of 3.3-3.4 Ga. The samples analyzed come from both the ~3.3 Ga amphibolite unit and the ~3.4 Ga Ameralik basic dyke swarm from the Amitsoq Complex. Coupled Sm-Nd and Lu-Hf bulk-rock ages obtained for seven amphibolites are in good agreement (3351 ± 210 Ma and 3302 ± 260 Ma, respectively) and consistent with the minimum age found by Nutman and Friend (2009) [9] for this formation. We further obtained coherent bulk-rock 147Sm-143Nd and zircon+baddeleyite 207Pb/206Pb ages for the Ameralik dykes (3428 ± 250 Ma and 3421 ± 34 Ma, respectively), in line with ages suggested by Nielsen at al., (2002) [10] and Nutman et al., (2004) [11]. We are currently in the process of analyzing these samples for 142Nd isotopic compositions and the results will be compared with the existing southwest Greenland data in order to shed new light on the evolution and destruction of heterogeneities in the early Earth mantle. [1] Rizo et al., (2011

  10. A Mercury-like component of early Earth yields uranium in the core and high mantle 142Nd

    NASA Astrophysics Data System (ADS)

    Wohlers, Anke; Wood, Bernard J.

    2015-04-01

    Recent 142Nd isotope data indicate that the silicate Earth (its crust plus the mantle) has a samarium to neodymium elemental ratio (Sm/Nd) that is greater than that of the supposed chondritic building blocks of the planet. This elevated Sm/Nd has been ascribed either to a `hidden' reservoir in the Earth or to loss of an early-formed terrestrial crust by impact ablation. Since removal of crust by ablation would also remove the heat-producing elements--potassium, uranium and thorium--such removal would make it extremely difficult to balance terrestrial heat production with the observed heat flow. In the `hidden' reservoir alternative, a complementary low-Sm/Nd layer is usually considered to reside unobserved in the silicate lower mantle. We have previously shown, however, that the core is a likely reservoir for some lithophile elements such as niobium. We therefore address the question of whether core formation could have fractionated Nd from Sm and also acted as a sink for heat-producing elements. We show here that addition of a reduced Mercury-like body (or, alternatively, an enstatite-chondrite-like body) rich in sulfur to the early Earth would generate a superchondritic Sm/Nd in the mantle and an 142Nd/144Nd anomaly of approximately +14 parts per million relative to chondrite. In addition, the sulfur-rich core would partition uranium strongly and thorium slightly, supplying a substantial part of the `missing' heat source for the geodynamo.

  11. A Mercury-like component of early Earth yields uranium in the core and high mantle (142)Nd.

    PubMed

    Wohlers, Anke; Wood, Bernard J

    2015-04-16

    Recent (142)Nd isotope data indicate that the silicate Earth (its crust plus the mantle) has a samarium to neodymium elemental ratio (Sm/Nd) that is greater than that of the supposed chondritic building blocks of the planet. This elevated Sm/Nd has been ascribed either to a 'hidden' reservoir in the Earth or to loss of an early-formed terrestrial crust by impact ablation. Since removal of crust by ablation would also remove the heat-producing elements--potassium, uranium and thorium--such removal would make it extremely difficult to balance terrestrial heat production with the observed heat flow. In the 'hidden' reservoir alternative, a complementary low-Sm/Nd layer is usually considered to reside unobserved in the silicate lower mantle. We have previously shown, however, that the core is a likely reservoir for some lithophile elements such as niobium. We therefore address the question of whether core formation could have fractionated Nd from Sm and also acted as a sink for heat-producing elements. We show here that addition of a reduced Mercury-like body (or, alternatively, an enstatite-chondrite-like body) rich in sulfur to the early Earth would generate a superchondritic Sm/Nd in the mantle and an (142)Nd/(144)Nd anomaly of approximately +14 parts per million relative to chondrite. In addition, the sulfur-rich core would partition uranium strongly and thorium slightly, supplying a substantial part of the 'missing' heat source for the geodynamo.

  12. Chondritic xenon in the Earth's mantle.

    PubMed

    Caracausi, Antonio; Avice, Guillaume; Burnard, Peter G; Füri, Evelyn; Marty, Bernard

    2016-05-05

    Noble gas isotopes are powerful tracers of the origins of planetary volatiles, and the accretion and evolution of the Earth. The compositions of magmatic gases provide insights into the evolution of the Earth's mantle and atmosphere. Despite recent analytical progress in the study of planetary materials and mantle-derived gases, the possible dual origin of the planetary gases in the mantle and the atmosphere remains unconstrained. Evidence relating to the relationship between the volatiles within our planet and the potential cosmochemical end-members is scarce. Here we show, using high-precision analysis of magmatic gas from the Eifel volcanic area (in Germany), that the light xenon isotopes identify a chondritic primordial component that differs from the precursor of atmospheric xenon. This is consistent with an asteroidal origin for the volatiles in the Earth's mantle, and indicates that the volatiles in the atmosphere and mantle originated from distinct cosmochemical sources. Furthermore, our data are consistent with the origin of Eifel magmatism being a deep mantle plume. The corresponding mantle source has been isolated from the convective mantle since about 4.45 billion years ago, in agreement with models that predict the early isolation of mantle domains. Xenon isotope systematics support a clear distinction between mid-ocean-ridge and continental or oceanic plume sources, with chemical heterogeneities dating back to the Earth's accretion. The deep reservoir now sampled by the Eifel gas had a lower volatile/refractory (iodine/plutonium) composition than the shallower mantle sampled by mid-ocean-ridge volcanism, highlighting the increasing contribution of volatile-rich material during the first tens of millions of years of terrestrial accretion.

  13. Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics?

    NASA Astrophysics Data System (ADS)

    Kerrich, Robert; Polat, Ali

    2006-03-01

    Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone-granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then "resurfaced" by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41-65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111-124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite-basalt plateau sequences erupted from deep mantle plumes and bimodal basalt-dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites-Mg andesites- and Nb-enriched basalts. Archean cratons

  14. Early Earth slab stagnation

    NASA Astrophysics Data System (ADS)

    Agrusta, R.; Van Hunen, J.

    2016-12-01

    At present day, the Earth's mantle exhibits a combination of stagnant and penetrating slabs within the transition zone, indicating a intermittent convection mode between layered and whole-mantle convection. Isoviscous thermal convection calculations show that in a hotter Earth, the natural mode of convection was dominated by double-layered convection, which may imply that slabs were more prone to stagnate in the transition zone. Today, slab penetration is to a large extent controlled by trench mobility for a plausible range of lower mantle viscosity and Clapeyron slope of the mantle phase transitions. Trench mobility is, in turn, governed by slab strength and density and upper plate forcing. In this study, we systematically investigate the slab-transition zone internation in the Early Earth, using 2D self-consistent numerical subduction models. Early Earth's higher mantle temperature facilitates decoupling between the plates and the underlying asthenosphere, and may result in slab sinking almost without trench retreat. Such behaviour together with a low resistance of a weak lower mantle may allow slabs to penetrate. The ability of slab to sink into the lower mantle throughout Earth's history may have important implications for Earth's evolution: it would provide efficient mass and heat flux through the transition zone therefore provide an efficient way to cool and mix the Earth's mantle.

  15. Evidence from coupled (Sm-147)-(Nd-143) and (Sm-146)-(Nd-142) systematics for very early (4.5-Gyr) differentiation of the earth's mantle

    NASA Technical Reports Server (NTRS)

    Harper, Charles L., Jr.; Jacobsen, Stein B.

    1992-01-01

    Evidence for early differentiation of the earth's mantle is presented based on measurements of Nd-143/Nd-144 and Nd-142/Nd-144 ratios in an approximately 3.8 Gyr-old supracrustal rock from Isua, West Greenland. Coupled (Sm-146,147)-(Nd-142,143) systematics suggest that the fractionation of Sm/Nd took place 4.44-4.54 Gyr ago, due to extraction of a light rare earth element-enriched primordial crust.

  16. Structure and dynamics of Earth's lower mantle.

    PubMed

    Garnero, Edward J; McNamara, Allen K

    2008-05-02

    Processes within the lowest several hundred kilometers of Earth's rocky mantle play a critical role in the evolution of the planet. Understanding Earth's lower mantle requires putting recent seismic and mineral physics discoveries into a self-consistent, geodynamically feasible context. Two nearly antipodal large low-shear-velocity provinces in the deep mantle likely represent chemically distinct and denser material. High-resolution seismological studies have revealed laterally varying seismic velocity discontinuities in the deepest few hundred kilometers, consistent with a phase transition from perovskite to post-perovskite. In the deepest tens of kilometers of the mantle, isolated pockets of ultralow seismic velocities may denote Earth's deepest magma chamber.

  17. Primary differentiation in the early Earth: Nd and Sr isotopic evidence from diamondiferous eclogites for both old depleted and old enriched mantle, Yakutia, Siberia

    NASA Technical Reports Server (NTRS)

    Snyder, Gregory A.; Jerde, Eric A.; Taylor, Lawrence A.; Halliday, Alex N.; Sobolev, Vladimir N.; Sobolev, Nickolai V.; Clayton, Robert N.; Mayeda, Toshiko K.; Deines, Peter

    1993-01-01

    Ancient, stable, continental cratons possess thick, subcontinental-lithospheric mantle 'keels' which favor particularly the emplacement of diamondiferous kimberlites and included peridotites and eclogites. These refractory mantle samples of the roots provide hard constraints on the theories of formation, growth, and evolution of these cratons. Xenoliths containing only primary garnet and clinopyroxene (eclogites), although rare in most kimberlites, can retain the geochemical signatures of their parent protoliths (e.g., subducted oceanic crust, ancient mantle) thus offering the opportunity to address mantle processes which may have taken place at earlier times in the Earth's history. In fact, it has been postulated that some eclogites are residues from the accretion of the early Earth. Nd and Sr isotopic data are presented which may be interpreted as evidence of an early (greater than 4 Ga) mantle differentiation event. The kimberlites of Yakutia are located both marginal and central to the Siberian craton, and a wide variety of xenoliths are present within them. The Siberian mantle samples have received little attention in the western world, largely because suitable suites of Yakutian samples have not been readily available. Importantly, there is evidence that metasomatism of the Siberian lithosphere has been considerably less intense or extensive than for the Kaapvaal craton. Therefore, it should be considerably easier to elicit the igneous/metamorphic histories of Siberian kimberlitic xenoliths. One of the notable features of the Siberian eclogites is the common appearance of diamonds, especially in the Mir and Udachnaya pipes. In all, eight eclogite samples (eight garnet separates and eight clinopyroxene separates) have been analyzed to date on the Udachnaya pipe, seven from our group.

  18. Sulfur in Earth's Mantle and Its Behavior During Core Formation

    NASA Technical Reports Server (NTRS)

    Chabot, Nancy L.; Righter,Kevin

    2006-01-01

    The density of Earth's outer core requires that about 5-10% of the outer core be composed of elements lighter than Fe-Ni; proposed choices for the "light element" component of Earth's core include H, C, O, Si, S, and combinations of these elements [e.g. 1]. Though samples of Earth's core are not available, mantle samples contain elemental signatures left behind from the formation of Earth's core. The abundances of siderophile (metal-loving) elements in Earth's mantle have been used to gain insight into the early accretion and differentiation history of Earth, the process by which the core and mantle formed, and the composition of the core [e.g. 2-4]. Similarly, the abundance of potential light elements in Earth's mantle could also provide constraints on Earth's evolution and core composition. The S abundance in Earth's mantle is 250 ( 50) ppm [5]. It has been suggested that 250 ppm S is too high to be due to equilibrium core formation in a high pressure, high temperature magma ocean on early Earth and that the addition of S to the mantle from the subsequent accretion of a late veneer is consequently required [6]. However, this earlier work of Li and Agee [6] did not parameterize the metalsilicate partitioning behavior of S as a function of thermodynamic variables, limiting the different pressure and temperature conditions during core formation that could be explored. Here, the question of explaining the mantle abundance of S is revisited, through parameterizing existing metal-silicate partitioning data for S and applying the parameterization to core formation in Earth.

  19. Water partitioning in the Earth's mantle

    NASA Astrophysics Data System (ADS)

    Inoue, Toru; Wada, Tomoyuki; Sasaki, Rumi; Yurimoto, Hisayoshi

    2010-11-01

    We have conducted H2O partitioning experiments between wadsleyite and ringwoodite and between ringwoodite and perovskite at 1673 K and 1873 K, respectively. These experiments were performed in order to constrain the relative distribution of H2O in the upper mantle, the mantle transition zone, and the lower mantle. We successfully synthesized coexisting mineral assemblages of wadsleyite-ringwoodite and ringwoodite-perovskite that were large enough to measure the H2O contents by secondary ion mass spectrometry (SIMS). Combining our previous H2O partitioning data (Chen et al., 2002) with the present results, the determined water partitioning between olivine, wadsleyite, ringwoodite, and perovskite under H2O-rich fluid saturated conditions are 6:30:15:1, respectively. Because the maximum H2O storage capacity in wadsleyite is ∼3.3 wt% (e.g. Inoue et al., 1995), the possible maximum H2O storage capacity in the olivine high-pressure polymorphs are as follows: ∼0.7 wt% in olivine (upper mantle just above 410 km depth), ∼3.3 wt% in wadsleyite (410-520 km depth), ∼1.7 wt% in ringwoodite (520-660 km depth), and ∼0.1 wt% in perovskite (lower mantle). If we assume ∼0.2 wt% of the H2O content in wadsleyite in the mantle transition zone estimated by recent electrical conductivity measurements (e.g. Dai and Karato, 2009), the estimated H2O contents throughout the mantle are as follows; ∼0.04 wt% in olivine (upper mantle just above 410 km depth), ∼0.2 wt% in wadsleyite (410-520 km depth), ∼0.1 wt% in ringwoodite (520-660 km depth) and ∼0.007 wt% in perovskite (lower mantle). Thus, the mantle transition zone should contain a large water reservoir in the Earth's mantle compared to the upper mantle and the lower mantle.

  20. Iron Isotopic Fractionation in Earth's Lower Mantle

    NASA Astrophysics Data System (ADS)

    Yang, H.; Lin, J. F.; Hu, M. Y.; Bi, W.; Zhao, J.; Alp, E. E.; Roskosz, M.; Dauphas, N.; Okuchi, T.

    2017-12-01

    The Earth's bulk chemical composition is vital for deciphering the origin of this planet. Our estimation of the iron isotopic composition of the bulk Earth relies on the iron isotopic composition difference between the metallic core and silicate mantle. Previous studies1,2,3 on this fractionation scale have mostly focused on the alloying effects of light elements in the iron metal phases, while the pressure effects of the silicate mantle phases especially due to iron partitioning4 in the lower mantle minerals have not been fully addressed. For instance, Polyakov (2009) simply assumed equal iron distribution between ferropericlase and post-perovskite in his model. Shahar et al. (2016) only used bridgmanite as a proxy for the mantle while another lower mantle mineral ferropericlase was neglected. Here we have investigated the force constant of iron bonds in lower-mantle ferropericlase and bridgmanite crystals up to 104GPa using NRIXS(Nuclear Resonant Inelastic X-ray Scattering) and SMS(Synchrotron Mössbauer Spectroscopy) in a diamond anvil cell at sector-3 of the Advance Photon Source. These results are used to evaluate the pressure effects as well as the spin/valence states of iron5,6 on the force constant of iron bonds and the iron isotope distributions within the lower mantle and at the core-mantle boundary. We found that the liquid-solid iron isotopic fractionation during magma ocean crystallization was limited, however, the inter-mineral fractionation between ferropericlase and bridgmanite could be significant influenced by the spin/valence states at the lowermost mantle conditions. 1.Polyakov, V. B. Science 323, 912-914 (2009). 2.Shahar, A. et al. Science 352, 580-582 (2016). 3.Liu, J. et al. Nat. Commun. 8, 14377 (2017). 4.Irifune, T. et al. Science 327, 193-195 (2010). 5.Lin, J. F., Speziale, S., Mao, Z. & Marquardt, Rev. Geophys. 51, 244-275 (2013). 6.Mao, Z. et al. Am. Mineral. 102 (2017).

  1. Hydrogen in Earths Lowermost Mantle

    NASA Astrophysics Data System (ADS)

    Townsend, J. P.; Tsuchiya, J.; Bina, C. R.; Jacobsen, S. D.; Liu, Z.

    2013-12-01

    The lowermost mantle (D') is characterized by pronounced elastic anisotropy and elevated seismic attenuation. The presence of the post-perovskite (PPv) phase in the D' layer would contribute to these seismic observables, and therefore the influence of compositional variability on the physical properties of PPv should be explored to test mineralogical models of D' against the observed seismic structure. Here, we explore the influence of hydrogen on the physical properties of the PPv phase by first-principles calculations using density functional theory. The presence of hydrogen in the core-mantle boundary region, either as primordial H diffused from the liquid outer core or added by deeply subducted slabs, could potentially influence PPv physical properties and its phase stability. The OH-storage capacity of perovskite is likely much lower than PPv so the presence of OH could also influence the structure of D'. In the upper mantle, even small amounts of OH at concentrations less than 0.1 wt% can influence elastic properties and lattice preferred orientation. To study the possible influence of hydrogen on the physical properties of PPv, we have determined a stable hydrogen defect structure for PPv and its associated elastic properties, thermal stability, and IR signature. We will present a comparison of the observed elastic properties of the D' region with the calculated elastic properties of hPPv, as well as calculated FTIR spectra for comparison to ongoing experiments using a new CO2 laser-heating system and synchrotron-FTIR spectroscopy at the National Synchrotron Light Source.

  2. Convective Differentiation of the Earth's Mantle

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Schmalzl, J.; Stemmer, K.

    2007-05-01

    The differentiation of the Earth is likely to be influenced by convective motions within the early mantle. Double- diffusive convection (d.d.c), driven by thermally and compositionally induced density differences is considered as a vital mechanism behind the dynamic differentiation of the early mantle.. We demonstrate that d.d.c can lead to layer formation on a planetary scale in the diffusive regime where composition stabilizes the system whil heat provides the destabilizing force. Choosing initial conditions in which a stable compositional gradient overlies a hot reservoir we mimic the situation of a planet in a phase after core formation. Differently from earlier studies we fixed the temperature rather than the heat flux at the lower boundary, resembling a more realistic condition for the core-mantle boundary. We have carried out extended series of numerical experiments, ranging from 2D calculations in constant viscosity fluids to fully 3D experiments in spherical geometry with strongly temperature dependent viscosity. The buoyancy ratio R and the Lewis number Le are the important dynamical parameters. In all scenarios we could identify a parameter regime where the non-layered initial structure developed into a state consisting of several, mostly two layers. Initially plumes from the bottom boundary homogenize a first layer which subsequently thickens. The bottom layer heats up and then convection is initiated in the top layer. This creates dynamically (i.e. without jump in the material behavior) a stack of separately convecting layers. The bottom layer is significantly thicker than the top layer. Strongly temperature dependent viscosity leads to a more complex evolution The formation of the bottom layer is followed by the generation of several layers on top. Finally the uppermost layer starts to convect. In general, the multilayer structure collapses into a two layer system. We employed a numerical technique, allowing for a diffusion free treatment of the

  3. The origin of volatiles in the Earth's mantle

    NASA Astrophysics Data System (ADS)

    Hier-Majumder, Saswata; Hirschmann, Marc M.

    2017-08-01

    The Earth's deep interior contains significant reservoirs of volatiles such as H, C, and N. Due to the incompatible nature of these volatile species, it has been difficult to reconcile their storage in the residual mantle immediately following crystallization of the terrestrial magma ocean (MO). As the magma ocean freezes, it is commonly assumed that very small amounts of melt are retained in the residual mantle, limiting the trapped volatile concentration in the primordial mantle. In this article, we show that inefficient melt drainage out of the freezing front can retain large amounts of volatiles hosted in the trapped melt in the residual mantle while creating a thick early atmosphere. Using a two-phase flow model, we demonstrate that compaction within the moving freezing front is inefficient over time scales characteristic of magma ocean solidification. We employ a scaling relation between the trapped melt fraction, the rate of compaction, and the rate of freezing in our magma ocean evolution model. For cosmochemically plausible fractions of volatiles delivered during the later stages of accretion, our calculations suggest that up to 77% of total H2O and 12% of CO2 could have been trapped in the mantle during magma ocean crystallization. The assumption of a constant trapped melt fraction underestimates the mass of volatiles in the residual mantle by more than an order of magnitude.Plain Language SummaryThe <span class="hlt">Earth</span>'s deep interior contains substantial amounts of volatile elements like C, H, and N. How these elements got sequestered in the <span class="hlt">Earth</span>'s interior has long been a topic of debate. It is generally assumed that most of these elements escaped the interior of the <span class="hlt">Earth</span> during the first few hundred thousand years to create a primitive atmosphere, leaving the <span class="hlt">mantle</span> reservoir nearly empty. In this work, we show that the key to this paradox involves the very <span class="hlt">early</span> stages of crystallization of the <span class="hlt">mantle</span> from a global</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1816723C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1816723C"><span>Chondritic Xenon in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>: new constrains on a <span class="hlt">mantle</span> plume below central Europe</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caracausi, Antonio; Avice, Guillaume; Bernard, Peter; Furi, Evelin; Marty, Bernard</p> <p>2016-04-01</p> <p> data support the notion that the fraction of plutonium-derived Xe in plume sources (oceanic as well as continental) is higher than in the MORB source reservoir. Hence, the MORB - type reservoirs appear to be well distinguished and more degassed than the plume sources (oceanic as well as continental) supporting the heterogeneity of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Finally this study highlights that xenon isotopes in the Eifel gas have preserved a chemical signature that is characteristic of other <span class="hlt">mantle</span> plume sources. This is very intriguing because the presence of a <span class="hlt">mantle</span> plume in this sector of Central Europe was already inferred from geophysical and geochemical studies(Buikin et al., 2005; Goes et al., 1999). Notably, tomographic images show a low-velocity structure down to 2000 km depth, representing deep <span class="hlt">mantle</span> upwelling under central Europe, that may feed smaller upper-<span class="hlt">mantle</span> plumes (Eifel volcanic district-Germany). References Buikin A., Trieloff M., HoppJ., Althaus T., Korochantseva E., Schwarz W.H. &Altherr R., (2005), Noble gas isotopessuggestdeepmantleplume source of late Cenozoicmaficalkalinevolcanism in Europe, <span class="hlt">Earth</span> Planet. Sci. Lett. 230, 143-162. Goes S., Spakman W. &BijwaardH., (1999), A lowermantle source for centraleuropeanvolcanism, Science, 286, 1928-1931.G. Holland, M. Cassidy, C.J. Ballentine, Meteorite Kr in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> suggests a late accretionary source for the atmosphere, Science, 326, 1522-1525, (2009). Marty, B. Neon and xenon isotopes in MORB: implications for the <span class="hlt">Earth</span>-atmosphere evolution. <span class="hlt">Earth</span> Planet. Sci. Lett. 94, 45-56 (1989). Mukhopadhyay S., <span class="hlt">Early</span> differentiation and volatile accretion recorded in deep-<span class="hlt">mantle</span> neon and xenon Nature, 486, 101-106, (2013).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P54A..06O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P54A..06O"><span>Evolution of the earliest <span class="hlt">mantle</span> caused by the magmatism-<span class="hlt">mantle</span> upwelling feedback: Implications for the Moon and the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ogawa, M.</p> <p>2017-12-01</p> <p>The two most important agents that cause <span class="hlt">mantle</span> evolution are magmatism and <span class="hlt">mantle</span> convection. My earlier 2D numerical models of a coupled magmatism-<span class="hlt">mantle</span> convection system show that these two agents strongly couple each other, when the Rayleigh number Ra is sufficiently high: magmatism induced by a <span class="hlt">mantle</span> upwelling flow boosts the upwelling flow itself. The <span class="hlt">mantle</span> convection enhanced by this positive feedback (the magmatism-<span class="hlt">mantle</span> upwelling, or MMU, feedback) causes vigorous magmatism and, at the same time, strongly stirs the <span class="hlt">mantle</span>. I explored how the MMU feedback influences the evolution of the earliest <span class="hlt">mantle</span> that contains the magma ocean, based on a numerical model where the <span class="hlt">mantle</span> is hot and its topmost 1/3 is partially molten at the beginning of the calculation: The evolution drastically changes its style, as Ra exceeds the threshold for onset of the MMU feedback, around 107. At Ra < 107, basaltic materials generated by the initial widespread magmatism accumulate in the deep <span class="hlt">mantle</span> to form a layer; the basaltic layer is colder than the overlying shallow <span class="hlt">mantle</span>. At Ra > 107, however, the <span class="hlt">mantle</span> remains compositionally more homogeneous in spite of the widespread magmatism, and the deep <span class="hlt">mantle</span> remains hotter than the shallow <span class="hlt">mantle</span>, because of the strong convective stirring caused by the feedback. The threshold value suggests that the <span class="hlt">mantle</span> of a planet larger than Mars evolves in a way substantially different from that in the Moon does. Indeed, in my earlier models, magmatism makes the <span class="hlt">early</span> <span class="hlt">mantle</span> compositionally stratified in the Moon, but the effects of strong convective stirring overwhelms that of magmatism to keep the <span class="hlt">mantle</span> compositionally rather homogeneous in Venus and the <span class="hlt">Earth</span>. The MMU feedback is likely to be a key to understanding why vestiges of the magma ocean are so scarce in the <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMDI31A1952L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMDI31A1952L"><span>Subducting Slabs: Jellyfishes in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Loiselet, C.; Braun, J.; Husson, L.; Le Carlier de Veslud, C.; Thieulot, C.; Yamato, P.; Grujic, D.</p> <p>2010-12-01</p> <p>The constantly improving resolution of geophysical data, seismic tomography and seismicity in particular, shows that the lithosphere does not subduct as a slab of uniform thickness but is rather thinned in the upper <span class="hlt">mantle</span> and thickened around the transition zone between the upper and lower <span class="hlt">mantle</span>. This observation has traditionally been interpreted as evidence for the buckling and piling of slabs at the boundary between the upper and lower <span class="hlt">mantle</span>, where a strong contrast in viscosity may exist and cause resistance to the penetration of slabs into the lower <span class="hlt">mantle</span>. The distribution and character of seismicity reveal, however, that slabs undergo vertical extension in the upper <span class="hlt">mantle</span> and compression near the transition zone. In this paper, we demonstrate that during the subduction process, the shape of low viscosity slabs (1 to 100 times more viscous than the surrounding <span class="hlt">mantle</span>) evolves toward an inverted plume shape that we coin jellyfish. Results of a 3D numerical model show that the leading tip of slabs deform toward a rounded head skirted by lateral tentacles that emerge from the sides of the jellyfish head. The head is linked to the body of the subducting slab by a thin tail. A complete parametric study reveals that subducting slabs may achieve a variety of shapes, in good agreement with the diversity of natural slab shapes evidenced by seismic tomography. Our work also suggests that the slab to <span class="hlt">mantle</span> viscosity ratio in the <span class="hlt">Earth</span> is most likely to be lower than 100. However, the sensitivity of slab shapes to upper and lower <span class="hlt">mantle</span> viscosities and densities, which remain poorly constrained by independent evidence, precludes any systematic deciphering of the observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GGG....11.8016L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GGG....11.8016L"><span>Subducting slabs: Jellyfishes in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Loiselet, Christelle; Braun, Jean; Husson, Laurent; Le Carlier de Veslud, Christian; Thieulot, Cedric; Yamato, Philippe; Grujic, Djordje</p> <p>2010-08-01</p> <p>The constantly improving resolution of geophysical data, seismic tomography and seismicity in particular, shows that the lithosphere does not subduct as a slab of uniform thickness but is rather thinned in the upper <span class="hlt">mantle</span> and thickened around the transition zone between the upper and lower <span class="hlt">mantle</span>. This observation has traditionally been interpreted as evidence for the buckling and piling of slabs at the boundary between the upper and lower <span class="hlt">mantle</span>, where a strong contrast in viscosity may exist and cause resistance to the penetration of slabs into the lower <span class="hlt">mantle</span>. The distribution and character of seismicity reveal, however, that slabs undergo vertical extension in the upper <span class="hlt">mantle</span> and compression near the transition zone. In this paper, we demonstrate that during the subduction process, the shape of low viscosity slabs (1 to 100 times more viscous than the surrounding <span class="hlt">mantle</span>) evolves toward an inverted plume shape that we coin jellyfish. Results of a 3D numerical model show that the leading tip of slabs deform toward a rounded head skirted by lateral tentacles that emerge from the sides of the jellyfish head. The head is linked to the body of the subducting slab by a thin tail. A complete parametric study reveals that subducting slabs may achieve a variety of shapes, in good agreement with the diversity of natural slab shapes evidenced by seismic tomography. Our work also suggests that the slab to <span class="hlt">mantle</span> viscosity ratio in the <span class="hlt">Earth</span> is most likely to be lower than 100. However, the sensitivity of slab shapes to upper and lower <span class="hlt">mantle</span> viscosities and densities, which remain poorly constrained by independent evidence, precludes any systematic deciphering of the observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004E%26PSL.225..253W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004E%26PSL.225..253W"><span><span class="hlt">Early</span> <span class="hlt">Earth</span> differentiation [rapid communication</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walter, Michael J.; Trønnes, Reidar G.</p> <p>2004-09-01</p> <p>The birth and infancy of <span class="hlt">Earth</span> was a time of profound differentiation involving massive internal reorganization into core, <span class="hlt">mantle</span> and proto-crust, all within a few hundred million years of solar system formation ( t0). Physical and isotopic evidence indicate that the formation of iron-rich cores generally occurred very <span class="hlt">early</span> in planetesimals, the building blocks of proto-<span class="hlt">Earth</span>, within about 3 million years of t0. The final stages of terrestrial planetary accretion involved violent and tremendously energetic giant impacts among core-segregated Mercury- to Mars-sized objects and planetary embryos. As a consequence of impact heating, the <span class="hlt">early</span> <span class="hlt">Earth</span> was at times partially or wholly molten, increasing the likelihood for high-pressure and high-temperature equilibration among core- and <span class="hlt">mantle</span>-forming materials. The <span class="hlt">Earth</span>'s silicate <span class="hlt">mantle</span> harmoniously possesses abundance levels of the siderophile elements Ni and Co that can be reconciled by equilibration between iron alloy and silicate at conditions comparable to those expected for a deep magma ocean. Solidification of a deep magma ocean possibly involved crystal-melt segregation at high pressures, but subsequent convective stirring of the <span class="hlt">mantle</span> could have largely erased nascent layering. However, primitive upper <span class="hlt">mantle</span> rocks apparently have some nonchondritic major and trace element refractory lithophile element ratios that can be plausibly linked to <span class="hlt">early</span> <span class="hlt">mantle</span> differentiation of ultra-high-pressure <span class="hlt">mantle</span> phases. The geochemical effects of crystal fractionation in a deep magma ocean are partly constrained by high-pressure experimentation. Comparison between compositional models for the primitive convecting <span class="hlt">mantle</span> and bulk silicate <span class="hlt">Earth</span> generally allows, and possibly favors, 10-15% total fractionation of a deep <span class="hlt">mantle</span> assemblage comprised predominantly of Mg-perovskite and with minor but geochemically important amounts of Ca-perovskite and ferropericlase. Long-term isolation of such a crystal pile is generally</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009E%26PSL.282..306H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009E%26PSL.282..306H"><span>Magnesium stable isotope composition of <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.</p> <p>2009-05-01</p> <p>The <span class="hlt">mantle</span> is <span class="hlt">Earth</span>'s largest reservoir of Mg containing > 99% of <span class="hlt">Earth</span>'s Mg inventory. However, no consensus exists on the stable Mg isotope composition of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> or how variable it is and, in particular, whether the <span class="hlt">mantle</span> has the same stable Mg isotope composition as chondrite meteorites. We have determined the Mg isotope composition of olivine from 22 <span class="hlt">mantle</span> peridotites from eastern Australia, west Antarctica, Jordan, Yemen and southwest Greenland by pseudo-high-resolution MC-ICP-MS on Mg purified to > 99%. The samples include fertile lherzolites, depleted harzburgites and dunites, cryptically metasomatised ('dry') peridotites and modally metasomatised apatite ± amphibole-bearing harzburgites and wehrlites. Olivine from these samples of <span class="hlt">early</span> Archaean through to Permian lithospheric <span class="hlt">mantle</span> have δ25Mg DSM-3 = - 0.22 to - 0.08‰. These data indicate the bulk upper <span class="hlt">mantle</span> as represented by peridotite olivine is homogeneous within current analytical uncertainties (external reproducibility ≤ ± 0.07‰ [2 sd]). We find no systematic δ25Mg variations with location, lithospheric age, peridotite fertility, or degree or nature of <span class="hlt">mantle</span> metasomatism. Although pyroxene may have slightly heavier δ25Mg than coexisting olivine, any fractionation between <span class="hlt">mantle</span> pyroxene and olivine is also within current analytical uncertainties with a mean Δ25Mg pyr-ol = +0.06 ± 0.10‰ (2 sd; n = 5). Our average <span class="hlt">mantle</span> olivine δ25Mg DSM-3 = - 0.14 ± 0.07‰ and δ26Mg DSM-3 = - 0.27 ± 0.14‰ (2 sd) are indistinguishable from the average of data previously reported for terrestrial basalts, confirming that basalts have stable Mg isotope compositions representative of the <span class="hlt">mantle</span>. Olivine from five pallasite meteorites have δ25Mg DSM-3 = - 0.16 to - 0.11‰ that are identical to terrestrial olivine and indistinguishable from the average δ25Mg previously reported for chondrites. These data provide no evidence for measurable heterogeneity in the stable Mg isotope</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150009507','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150009507"><span>Evolution of the Oxidation State of the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Danielson, L. R.; Righter, K.; Keller, L.; Christoffersen, E.; Rahman, Z.</p> <p>2015-01-01</p> <p>The oxidation state of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3(+) at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. In our previous experiments on shergottite compositions, variable fO2, T, and P less than 4 GPa, Fe3(+)/sigma Fe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3(+)/sigma Fe decreased as well, but it's unclear from previous modelling whether the deeper <span class="hlt">mantle</span> could retain significant Fe3(+). Our current experiments expand our pressure range deeper into the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and focus on compositions and conditions relevant to the <span class="hlt">early</span> <span class="hlt">Earth</span>. Preliminary multi-anvil experiments with Knippa basalt as the starting composition were conducted at 5-7 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal to Fe3(+)/2(+). Experiments are underway to produce glassy samples that can be measured by EELS and XANES, and are conducted at higher pressures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR21C..07F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR21C..07F"><span>Melting behavior of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> minerals at high pressures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fu, S.; Yang, J.; Prakapenka, V. B.; Zhang, Y.; Greenberg, E.; Lin, J. F.</p> <p>2017-12-01</p> <p>Melting behavior of the most abundant lower <span class="hlt">mantle</span> minerals, bridgmanite and ferropericlase, at high pressure-temperature (P-T) conditions is of critical importance to understand the dynamic evolution of the <span class="hlt">early</span> <span class="hlt">Earth</span> and to explain the seismological and geochemical signatures in the present lowermost <span class="hlt">mantle</span>. Theoretical calculations [1] and geodynamical models [2] suggested that partial melting of <span class="hlt">early</span> <span class="hlt">Earth</span> among MgO-FeO-SiO2 ternary could be located at the eutectic point where a pyrolitic composition formed for the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> and the eutectic crystallization process could provide a plausible mechanism to the origin of the ultra-low velocity zones (ULVZs) near the core-<span class="hlt">mantle</span> boundary. Here we have investigated the melting behavior of ferropericlase and Al,Fe-bearing bridgmanite in laser-heated diamond anvil cells coupled with in situ X-ray diffraction up to 120 GPa. Together with chemical and texture characterizations of the quenched samples, these results are analyzed using thermodynamic models to address the effects of iron on the liquidus and solidus temperatures as well as solid-liquid iron partitioning and the eutectic point in ferropericlase-bridgmanite existing system at lower-<span class="hlt">mantle</span> pressure. In this presentation, we discuss the application of these results to better constrain the seismic observations of the deep lowermost <span class="hlt">mantle</span> such as large low shear wave velocity provinces (LLSVPs) and ULVZs. We will also discuss the geochemical consequences of the ferropericlase-bridgmanite melting due to the changes in the electronic spin and valence states of iron in the system. ADDIN EN.REFLIST 1. Boukaré, C.E., Y. Ricard, and G. Fiquet, Thermodynamics of the MgO-FeO-SiO2 system up to 140 GPa: Application to the crystallization of <span class="hlt">Earth</span>'s magma ocean. Journal of Geophysical Research: Solid <span class="hlt">Earth</span>, 2015. 120(9): p. 6085-6101. 2. Labrosse, S., J. Hernlund, and N. Coltice, A crystallizing dense magma ocean at the base of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Nature, 2007</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9572726','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9572726"><span>Plutonium-fission xenon found in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kunz; Staudacher; Allegre</p> <p>1998-05-08</p> <p>Data from mid-ocean ridge basalt glasses indicate that the short-lived radionuclide plutonium-244 that was present during an <span class="hlt">early</span> stage of the development of the solar system is responsible for roughly 30 percent of the fissiogenic xenon excesses in the interior of <span class="hlt">Earth</span> today. The rest of the fissiogenic xenon can be ascribed to the spontaneous fission of still live uranium-238. This result, in combination with the refined determination of xenon-129 excesses from extinct iodine-129, implies that the accretion of <span class="hlt">Earth</span> was finished roughly 50 million to 70 million years after solar system formation and that the atmosphere was formed by <span class="hlt">mantle</span> degassing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4757760','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4757760"><span><span class="hlt">Earth</span>'s oldest <span class="hlt">mantle</span> fabrics indicate Eoarchaean subduction</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kaczmarek, Mary-Alix; Reddy, Steven M.; Nutman, Allen P.; Friend, Clark R. L.; Bennett, Vickie C.</p> <p>2016-01-01</p> <p>The extension of subduction processes into the Eoarchaean era (4.0–3.6 Ga) is controversial. The oldest reported terrestrial olivine, from two dunite lenses within the ∼3,720 Ma Isua supracrustal belt in Greenland, record a shape-preferred orientation of olivine crystals defining a weak foliation and a well-defined lattice-preferred orientation (LPO). [001] parallel to the maximum finite elongation direction and (010) perpendicular to the foliation plane define a B-type LPO. In the modern <span class="hlt">Earth</span> such fabrics are associated with deformation of <span class="hlt">mantle</span> rocks in the hanging wall of subduction systems; an interpretation supported by experiments. Here we show that the presence of B-type fabrics in the studied Isua dunites is consistent with a <span class="hlt">mantle</span> origin and a supra-subduction <span class="hlt">mantle</span> wedge setting, the latter supported by compositional data from nearby mafic rocks. Our results provide independent microstructural data consistent with the operation of Eoarchaean subduction and indicate that microstructural analyses of ancient ultramafic rocks provide a valuable record of Archaean geodynamics. PMID:26879892</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950015396&hterms=hydrogen+storage&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dhydrogen%2Bstorage','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950015396&hterms=hydrogen+storage&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dhydrogen%2Bstorage"><span>Hydrogen storage in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and core</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Prewitt, Charles T.</p> <p>1994-01-01</p> <p>Two different approaches to explaining how hydrogen might be stored in the <span class="hlt">mantle</span> are illustrated by a number of papers published over the past 25-30 years, but there has been little attempt to provide objective comparisons of the two. One approach invokes the presence in the <span class="hlt">mantle</span> of dense hydrous magnesium silicates (DHMS) stable at elevated pressures and temperatures. The other involves nominally anhydrous minerals (NAM) that contain hydrogen as a minor constituent on the ppm level. Experimental studies on DHMS indicate these phases may be stable to pressures and temperatures as high at 16 GPa and 1200 C. This temperature is lower than that indicated by a <span class="hlt">mantle</span> geotherm at 16 GPa, but may be reasonable for a subducting slab. It is possible that other DHMS could be stable to even higher pressures, but little is known about maximum temperature limits. For NAM, small amounts of hydrogen (up to several hundred ppm) have been detected in olivine, orthopyroxene, clinopyroxene, and garnet recovered from xenoliths in kimberlites, eclogites, and alkali basalts; it has been demonstrated that synthetic wadsleyite and perovskite can accommodate significant amounts of hydrogen. A number of problems are associated with each possibility. For NAM originating in the <span class="hlt">mantle</span>, one would like to assume that the hydrogen measured in samples recovered on <span class="hlt">Earth</span>'s surface was incorporated when the phase-crystallized at high temperatures and pressures, but it could have been introduced during transport to the surface. Major problems for the DHMS proponents are that none of these phases have been found as minerals and little is yet known about their stabilities in systems containing other cations such as Fe, Al, and Ca.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005GMS...160..117V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005GMS...160..117V"><span>Numerical study of the origin and stability of chemically distinct reservoirs deep in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Thienen, P.; van Summeren, J.; van der Hilst, R. D.; van den Berg, A. P.; Vlaar, N. J.</p> <p></p> <p>Seismic tomography is providing mounting evidence for large scale compositional heterogeneity deep in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>; also, the diverse geochemical and isotopic signatures observed in oceanic basalts suggest that the <span class="hlt">mantle</span> is not chemically homogeneous. Isotopic studies on Archean rocks indicate that <span class="hlt">mantle</span> inhomogeneity may have existed for most of the <span class="hlt">Earth</span>'s history. One important component may be recycled oceanic crust, residing at the base of the <span class="hlt">mantle</span>. We investigate, by numerical modeling, if such reservoirs may have been formed in the <span class="hlt">early</span> <span class="hlt">Earth</span>, before plate tectonics (and subduction) were possible, and how they have survived—and evolved—since then. During <span class="hlt">Earth</span>'s <span class="hlt">early</span> evolution, thick basaltic crust may have sunk episodically into the <span class="hlt">mantle</span> in short but vigorous diapiric resurfacing events. These sections of crust may have resided at the base of the <span class="hlt">mantle</span> for very long times. Entrainment of material from the enriched reservoirs thus produced may account for enriched <span class="hlt">mantle</span> and high-μ signatures in oceanic basalts, whereas deep subduction events may have shaped and replenished deep <span class="hlt">mantle</span> reservoirs. Our modeling shows that (1) convective instabilities and resurfacing may have produced deep enriched <span class="hlt">mantle</span> reservoirs before the era of plate tectonics; (2) such formation is qualitatively consistent with the geochemical record, which shows multiple distinct ocean island basalt sources; and (3) reservoirs thus produced may be stable for billions of years.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23486061','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23486061"><span>Water and hydrogen are immiscible in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bali, Enikő; Audétat, Andreas; Keppler, Hans</p> <p>2013-03-14</p> <p>In the deep, chemically reducing parts of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>, hydrous fluids contain significant amounts of molecular hydrogen (H2). Thermodynamic models of fluids in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> so far have always assumed that molecular hydrogen and water are completely miscible. Here we show experimental evidence that water and hydrogen can coexist as two separate, immiscible phases. Immiscibility between water and hydrogen may be the cause of the formation of enigmatic, ultra-reducing domains in the <span class="hlt">mantle</span> that contain moissanite (SiC) and other phases indicative of extremely reducing conditions. Moreover, the immiscibility between water and hydrogen may provide a mechanism for the rapid oxidation of <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> immediately following core formation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR54A..05B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR54A..05B"><span>Large-scale compositional heterogeneity in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ballmer, M.</p> <p>2017-12-01</p> <p>Seismic imaging of subducted Farallon and Tethys lithosphere in the lower <span class="hlt">mantle</span> has been taken as evidence for whole-<span class="hlt">mantle</span> convection, and efficient <span class="hlt">mantle</span> mixing. However, cosmochemical constraints point to a lower-<span class="hlt">mantle</span> composition that has a lower Mg/Si compared to upper-<span class="hlt">mantle</span> pyrolite. Moreover, geochemical signatures of magmatic rocks indicate the long-term persistence of primordial reservoirs somewhere in the <span class="hlt">mantle</span>. In this presentation, I establish geodynamic mechanisms for sustaining large-scale (primordial) heterogeneity in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> using numerical models. <span class="hlt">Mantle</span> flow is controlled by rock density and viscosity. Variations in intrinsic rock density, such as due to heterogeneity in basalt or iron content, can induce layering or partial layering in the <span class="hlt">mantle</span>. Layering can be sustained in the presence of persistent whole <span class="hlt">mantle</span> convection due to active "unmixing" of heterogeneity in low-viscosity domains, e.g. in the transition zone or near the core-<span class="hlt">mantle</span> boundary [1]. On the other hand, lateral variations in intrinsic rock viscosity, such as due to heterogeneity in Mg/Si, can strongly affect the mixing timescales of the <span class="hlt">mantle</span>. In the extreme case, intrinsically strong rocks may remain unmixed through the age of the <span class="hlt">Earth</span>, and persist as large-scale domains in the mid-<span class="hlt">mantle</span> due to focusing of deformation along weak conveyor belts [2]. That large-scale lateral heterogeneity and/or layering can persist in the presence of whole-<span class="hlt">mantle</span> convection can explain the stagnation of some slabs, as well as the deflection of some plumes, in the mid-<span class="hlt">mantle</span>. These findings indeed motivate new seismic studies for rigorous testing of model predictions. [1] Ballmer, M. D., N. C. Schmerr, T. Nakagawa, and J. Ritsema (2015), Science Advances, doi:10.1126/sciadv.1500815. [2] Ballmer, M. D., C. Houser, J. W. Hernlund, R. Wentzcovitch, and K. Hirose (2017), Nature Geoscience, doi:10.1038/ngeo2898.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI44A..03H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI44A..03H"><span>Core-exsolved SiO2 Dispersal in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Helffrich, G. R.; Ballmer, M.; Hirose, K.</p> <p>2017-12-01</p> <p>SiO2 may have been expelled from the core following its formation in the <span class="hlt">early</span> stages of <span class="hlt">Earth</span>'s accretion and onwards through the present day. On account of SiO2's low density with respect to both the core and the lowermost <span class="hlt">mantle</span>, we examine the process of SiO2 accumulation at the core-<span class="hlt">mantle</span> boundary (CMB) and its incorporation into the <span class="hlt">mantle</span> by buoyant rise. Today, the if SiO2 is 100-10000 times more viscous than lower <span class="hlt">mantle</span> material, the dimensions of SiO2 diapirs formed by the viscous Rayleigh-Taylor instability at the CMB would cause them to be swept into the <span class="hlt">mantle</span> as inclusions of 100 m - 10 km diameter. Under <span class="hlt">early</span> <span class="hlt">Earth</span> conditions of rapid heat loss after core formation, SiO2 diapirs of 5-80 km diameter could have risen independently of <span class="hlt">mantle</span> flow to their level of neutral buoyancy in the <span class="hlt">mantle</span>, trapping them there due to a combination of high viscosity and neutral buoyancy. We examine the SiO2 yield by assuming Si+O saturation at the conditions found at the base of a magma ocean and find that for a range of conditions, dispersed bodies could reach as high as 2 volume percent in shallow parts of the lower <span class="hlt">mantle</span>, with their abundance decreasing with depth. At such low concentrations, their effect on aggregate seismic wavespeeds would be within the uncertainty of the radial <span class="hlt">Earth</span> model PREM. However, their presence would be revealed by small-scale scattering in the lower <span class="hlt">mantle</span> due to the bodies' large velocity contrast. We conclude that the shallow lower <span class="hlt">mantle</span> (700-1500 km depth) could harbor SiO2 released in <span class="hlt">early</span> <span class="hlt">Earth</span> times.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P53F..04A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P53F..04A"><span>Thermal Evolution of <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> During the Accretion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arkani-Hamed, J.; Roberts, J. H.</p> <p>2017-12-01</p> <p><span class="hlt">Earth</span> is likely formed by accreting Moon to Mars size embryos. The impact heating by an embryo melts the embryo and the upper <span class="hlt">mantle</span> of the <span class="hlt">Earth</span> beneath the impact site. The iron core of the embryo sinks and merges with the core of the <span class="hlt">Earth</span>, while the <span class="hlt">mantle</span> of the embryo mixes with the upper <span class="hlt">mantle</span> of the <span class="hlt">Earth</span>, producing a buoyant molten/partially molten magma pond. Strong but localized <span class="hlt">mantle</span> dynamics results in fast lithostatic adjustment that pours out a huge amount of molten and partially molten magma which spread on the <span class="hlt">Earth</span>, and together with impact ejecta creates a globe encircling magma ocean. The lithostatic adjustment diminishes as the magma ocean becomes globe encircling within 104 to 105 yr. The major part of the thermal evolution of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> after an impact takes place in the presence of a thick and hot magma ocean, which hampers heat loss from the <span class="hlt">mantle</span> and suppresses global <span class="hlt">mantle</span> dynamics. Because the impact velocity of an embryo increases as the <span class="hlt">Earth</span> grows, a given magma ocean is hotter than the previous ones. We investigated this scenario using 25 Moon to Mars size embryos. Due to random geographic impact sites we considered vertical impacts since no information is available about the impact angles. This may over estimate the impact heating by a factor of 1.4 with respect to the most probable impact angle of 45o. The thermal structure of the <span class="hlt">Earth</span> at the end of accretion is layered, aside from the localized magma ponds that are distributed randomly due to the random geographic impact sites. We also take into account the impact heating of the solid lower <span class="hlt">mantle</span>, the heating of the lower <span class="hlt">mantle</span> by the gravitational energy released through sinking of an embryo's core. We then follow the thermal evolution of the <span class="hlt">mantle</span> of a growing <span class="hlt">Earth</span> using a 3D convection model. The <span class="hlt">Earth</span> grows due to merging of the impactor iron core with the <span class="hlt">Earth</span>'s core, and the accumulating magma ocean on the surface. The growth enhances the lithostatic pressure</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JGRB..123..176H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGRB..123..176H"><span>Core-Exsolved SiO2 Dispersal in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Helffrich, George; Ballmer, Maxim D.; Hirose, Kei</p> <p>2018-01-01</p> <p>SiO2 may have been expelled from the core directly following core formation in the <span class="hlt">early</span> stages of <span class="hlt">Earth</span>'s accretion and onward through the present day. On account of SiO2's low density with respect to both the core and the lowermost <span class="hlt">mantle</span>, we examine the process of SiO2 accumulation at the core-<span class="hlt">mantle</span> boundary (CMB) and its incorporation into the <span class="hlt">mantle</span> by buoyant rise. Today, if SiO2 is 100-10,000 times more viscous than lower <span class="hlt">mantle</span> material, the dimensions of SiO2 diapirs formed by the viscous Rayleigh-Taylor instability at the CMB would cause them to be swept into the <span class="hlt">mantle</span> as inclusions of 100 m-10 km diameter. Under <span class="hlt">early</span> <span class="hlt">Earth</span> conditions of rapid heat loss after core formation, SiO2 diapirs of ˜1 km diameter could have risen independently of <span class="hlt">mantle</span> flow to their level of neutral buoyancy in the <span class="hlt">mantle</span>, trapping them there due to a combination of intrinsically high viscosity and neutral buoyancy. We examine the SiO2 yield by assuming Si + O saturation at the conditions found at the base of a magma ocean and find that for a range of conditions, dispersed bodies could reach as high as 8.5 vol % in parts of the lower <span class="hlt">mantle</span>. At such low concentration, their effect on aggregate seismic wave speeds is within observational seismology uncertainty. However, their presence can account for small-scale scattering in the lower <span class="hlt">mantle</span> due to the bodies' large-velocity contrast. We conclude that the shallow lower <span class="hlt">mantle</span> (700-1,500 km depth) could harbor SiO2 released in <span class="hlt">early</span> <span class="hlt">Earth</span> times.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li class="active"><span>2</span></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_2 --> <div id="page_3" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="41"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910038883&hterms=homogenization&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhomogenization','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910038883&hterms=homogenization&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dhomogenization"><span>Evidence for extreme <span class="hlt">mantle</span> fractionation in <span class="hlt">early</span> Archaean ultramafic rocks from northern Labrador</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Collerson, Kenneth D.; Campbell, Lisa M.; Weaver, Barry L.; Palacz, Zenon A.</p> <p>1991-01-01</p> <p>Samarium-neodymium isotope data for tectonically interleaved fragments of lithospheric <span class="hlt">mantle</span> and meta-komatiite from the North Atlantic craton provide the first direct record of <span class="hlt">mantle</span> differentiation before 3,800 Myr ago. The results confirm the magnitude of light-rare-<span class="hlt">earth</span>-element depletion in the <span class="hlt">early</span> <span class="hlt">mantle</span>, and also its depleted neodymium isotope composition. The <span class="hlt">mantle</span> fragments were able to retain these ancient geochemical signatures by virtue of having been tectonically incorporated in buoyant felsic crust, thus escaping recycling and homogenization by <span class="hlt">mantle</span> convection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22364075-vigor-mantle-convection-super-earths','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22364075-vigor-mantle-convection-super-earths"><span>ON THE VIGOR OF <span class="hlt">MANTLE</span> CONVECTION IN SUPER-<span class="hlt">EARTHS</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Miyagoshi, Takehiro; Tachinami, Chihiro; Kameyama, Masanori</p> <p>2014-01-01</p> <p>Numerical models are presented to clarify how adiabatic compression affects thermal convection in the <span class="hlt">mantle</span> of super-<span class="hlt">Earths</span> ten times the <span class="hlt">Earth</span>'s mass. The viscosity strongly depends on temperature, and the Rayleigh number is much higher than that of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. The strong effect of adiabatic compression reduces the activity of <span class="hlt">mantle</span> convection; hot plumes ascending from the bottom of the <span class="hlt">mantle</span> lose their thermal buoyancy in the middle of the <span class="hlt">mantle</span> owing to adiabatic decompression, and do not reach the surface. A thick lithosphere, as thick as 0.1 times the depth of the <span class="hlt">mantle</span>, develops along the surface boundary, and themore » efficiency of convective heat transport measured by the Nusselt number is reduced by a factor of about four compared with the Nusselt number for thermal convection of incompressible fluid. The strong effect of adiabatic decompression is likely to inhibit hot spot volcanism on the surface and is also likely to affect the thermal history of the <span class="hlt">mantle</span>, and hence, the generation of magnetic field in super-<span class="hlt">Earths</span>.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V21C3041D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V21C3041D"><span>Iron-carbonate interaction at <span class="hlt">Earth</span>'s core-<span class="hlt">mantle</span> boundary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dorfman, S. M.; Badro, J.; Nabiei, F.; Prakapenka, V.; Gillet, P.</p> <p>2015-12-01</p> <p>Carbon storage and flux in the deep <span class="hlt">Earth</span> are moderated by oxygen fugacity and interactions with iron-bearing phases. The amount of carbon stored in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> versus the core depends on carbon-iron chemistry at the core-<span class="hlt">mantle</span> boundary. Oxidized carbonates subducted from <span class="hlt">Earth</span>'s surface to the lowermost <span class="hlt">mantle</span> may encounter reduced Fe0 metal from disproportionation of Fe2+ in lower <span class="hlt">mantle</span> silicates or mixing with the core. To understand the fate of carbonates in the lowermost <span class="hlt">mantle</span>, we have performed experiments on sandwiches of single-crystal (Ca0.6Mg0.4)CO3 dolomite and Fe foil in the laser-heated diamond anvil cell at lower <span class="hlt">mantle</span> conditions of 49-110 GPa and 1800-2500 K. Syntheses were conducted with in situ synchrotron X-ray diffraction to identify phase assemblages. After quench to ambient conditions, samples were sectioned with a focused Ga+ ion beam for composition analysis with transmission electron microscopy. At the centers of the heated spots, iron melted and reacted completely with the carbonate to form magnesiowüstite, iron carbide, diamond, magnesium-rich carbonate and calcium carbonate. In samples heated at 49 and 64 GPa, the two carbonates exhibit a eutectoid texture. In the sample heated at 110 GPa, the carbonates form rounded ~150-nm-diameter grains with a higher modal proportion of interspersed diamonds. The presence of reduced iron in the deep lower <span class="hlt">mantle</span> and core-<span class="hlt">mantle</span> boundary region will promote the formation of diamonds in carbonate-bearing subducted slabs. The complete reaction of metallic iron to oxides and carbides in the presence of <span class="hlt">mantle</span> carbonate supports the formation of these phases at the <span class="hlt">Earth</span>'s core-<span class="hlt">mantle</span> boundary and in ultra-low velocity zones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950015385&hterms=recycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Drecycling','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950015385&hterms=recycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Drecycling"><span>Subduction and volatile recycling in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>King, S. D.; Ita, J. J.; Staudigel, H.</p> <p>1994-01-01</p> <p>The subduction of water and other volatiles into the <span class="hlt">mantle</span> from oceanic sediments and altered oceanic crust is the major source of volatile recycling in the <span class="hlt">mantle</span>. Until now, the geotherms that have been used to estimate the amount of volatiles that are recycled at subduction zones have been produced using the hypothesis that the slab is rigid and undergoes no internal deformation. On the other hand, most fluid dynamical <span class="hlt">mantle</span> flow calculations assume that the slab has no greater strength than the surrounding <span class="hlt">mantle</span>. Both of these views are inconsistent with laboratory work on the deformation of <span class="hlt">mantle</span> minerals at high pressures. We consider the effects of the strength of the slab using two-dimensional calculations of a slab-like thermal downwelling with an endothermic phase change. Because the rheology and composition of subducting slabs are uncertain, we consider a range of Clapeyron slopes which bound current laboratory estimates of the spinel to perovskite plus magnesiowustite phase transition and simple temperature-dependent rheologies based on an Arrhenius law diffusion mechanism. In uniform viscosity convection models, subducted material piles up above the phase change until the pile becomes gravitationally unstable and sinks into the lower <span class="hlt">mantle</span> (the avalanche). Strong slabs moderate the 'catastrophic' effects of the instabilities seen in many constant-viscosity convection calculations; however, even in the strongest slabs we consider, there is some retardation of the slab descent due to the presence of the phase change.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29144451','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29144451"><span>Tidal tomography constrains <span class="hlt">Earth</span>'s deep-<span class="hlt">mantle</span> buoyancy.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lau, Harriet C P; Mitrovica, Jerry X; Davis, James L; Tromp, Jeroen; Yang, Hsin-Ying; Al-Attar, David</p> <p>2017-11-15</p> <p><span class="hlt">Earth</span>'s body tide-also known as the solid <span class="hlt">Earth</span> tide, the displacement of the solid <span class="hlt">Earth</span>'s surface caused by gravitational forces from the Moon and the Sun-is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the <span class="hlt">mantle</span> and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain <span class="hlt">Earth</span>'s deep-<span class="hlt">mantle</span> buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average <span class="hlt">mantle</span> density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the <span class="hlt">mantle</span>. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with <span class="hlt">Earth</span>'s formation. Because the dynamics of the <span class="hlt">mantle</span> is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the <span class="hlt">Earth</span> system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V11D..02P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V11D..02P"><span><span class="hlt">Early</span> Terrestrial <span class="hlt">Mantle</span> Differentiation Recorded in Paleoarchean Komatiites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Puchtel, I. S.; Blichert-Toft, J.; Touboul, M.; Horan, M. F.; Walker, R. J.</p> <p>2016-12-01</p> <p>Geochmical signatures generated in the manle as a result of radioactive decay of short- and long-lived nuclides can be used to constrain the timing of formation and the nature of now mostly vanished <span class="hlt">early</span> terrestrial reservoirs. The 3.55 Ga komatiites from the Schapenburg Greenstone Remnant (SGR) located in the Barberton Greenstone Belt in South Africa have a unique combination of trace element abundances and isotopic compositions that place strong constraints on the origin of these reservoirs. The SGR komatiites define a Re-Os isochron with an age of 3550±87 Ma and an initial γ187Os = +3.7±0.2 (2SD). The absolute HSE abundances in the <span class="hlt">mantle</span> source of the SGR komatiite system are estimated to be only 29±5% of those in the present-day bulk silicate <span class="hlt">Earth</span> (BSE) estimates. The SGR komatiites show coupled depletion, relative to the modern <span class="hlt">mantle</span>, in 142Nd and 182W (μ142Nd = -5.0±2.8, μ182W = -8.4±4.5), the decay products of the short-lived 146Sm and 182Hf nuclides, respectively, indicating derivation from a <span class="hlt">mantle</span> domain that was enriched in incompatible elements 30 Ma after Solar System formation. <span class="hlt">Early</span> Hadean contributors to this <span class="hlt">mantle</span> domain could include high-pressure fractionates from a primordial magma ocean. By contrast, the long-lived Sm-Nd and Lu-Hf isotope systems (ɛ143Nd = +2.4±0.1, ɛ176Hf = +5.7±0.3) indicate that the <span class="hlt">mantle</span> domain that the SGR komatiites were ultimately derived from underwent additional processing after the <span class="hlt">early</span> Hadean, including melt depletion at lower pressures. The preservation of <span class="hlt">early</span>-formed 182W and 142Nd anomalies in the <span class="hlt">mantle</span> until at least 3.55 Ga indicates that the products of <span class="hlt">early</span> planetary differentiation survived both later planetary accretion and convective <span class="hlt">mantle</span> mixing during the Hadean. This study lends further support to the notion that variable late accretion, by itself, cannot account for all of the observed W isotope and absolute and relative HSE abundance variations in the Archean <span class="hlt">mantle</span> recorded by</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813558F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813558F"><span>Predicting lower <span class="hlt">mantle</span> heterogeneity from 4-D <span class="hlt">Earth</span> models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Flament, Nicolas; Williams, Simon; Müller, Dietmar; Gurnis, Michael; Bower, Dan J.</p> <p>2016-04-01</p> <p>The <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> is characterized by two large-low-shear velocity provinces (LLSVPs), approximately ˜15000 km in diameter and 500-1000 km high, located under Africa and the Pacific Ocean. The spatial stability and chemical nature of these LLSVPs are debated. Here, we compare the lower <span class="hlt">mantle</span> structure predicted by forward global <span class="hlt">mantle</span> flow models constrained by tectonic reconstructions (Bower et al., 2015) to an analysis of five global tomography models. In the dynamic models, spanning 230 million years, slabs subducting deep into the <span class="hlt">mantle</span> deform an initially uniform basal layer containing 2% of the volume of the <span class="hlt">mantle</span>. Basal density, convective vigour (Rayleigh number Ra), <span class="hlt">mantle</span> viscosity, absolute plate motions, and relative plate motions are varied in a series of model cases. We use cluster analysis to classify a set of equally-spaced points (average separation ˜0.45°) on the <span class="hlt">Earth</span>'s surface into two groups of points with similar variations in present-day temperature between 1000-2800 km depth, for each model case. Below ˜2400 km depth, this procedure reveals a high-temperature cluster in which <span class="hlt">mantle</span> temperature is significantly larger than ambient and a low-temperature cluster in which <span class="hlt">mantle</span> temperature is lower than ambient. The spatial extent of the high-temperature cluster is in first-order agreement with the outlines of the African and Pacific LLSVPs revealed by a similar cluster analysis of five tomography models (Lekic et al., 2012). Model success is quantified by computing the accuracy and sensitivity of the predicted temperature clusters in predicting the low-velocity cluster obtained from tomography (Lekic et al., 2012). In these cases, the accuracy varies between 0.61-0.80, where a value of 0.5 represents the random case, and the sensitivity ranges between 0.18-0.83. The largest accuracies and sensitivities are obtained for models with Ra ≈ 5 x 107, no asthenosphere (or an asthenosphere restricted to the oceanic domain), and a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PEPI..265...67A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PEPI..265...67A"><span>Toward a coherent model for the melting behavior of the deep <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.; Boujibar, A.; Garbarino, G.; Manthilake, G.; Mezouar, M.; Monteux, J.; Parisiades, P.; Pesce, G.</p> <p>2017-04-01</p> <p>Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep <span class="hlt">mantle</span>. <span class="hlt">Early</span> in the <span class="hlt">Earth</span>'s history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost <span class="hlt">mantle</span> as well as at mid upper-<span class="hlt">mantle</span> depths, which control important aspects of <span class="hlt">mantle</span> dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of <span class="hlt">mantle</span> melting. For example, the liquidus of the <span class="hlt">mantle</span> was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high <span class="hlt">mantle</span> depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower <span class="hlt">mantle</span> mineral) and a melt was reported between ∼0.1 and ∼0.5, for a <span class="hlt">mantle</span> depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep <span class="hlt">mantle</span>. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and <span class="hlt">mantle</span> composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower <span class="hlt">mantle</span> as a function of pressure</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.V22A..04H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.V22A..04H"><span>The Ins and Outs of Water in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hauri, E. H.; Gaetani, G. A.; Shaw, A. M.; Kelley, K. A.; Saal, A. E.</p> <p>2005-12-01</p> <p>Most of the hydrogen in the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> is dissolved in nominally anhydrous minerals such as olivine, orthopyroxene, clinopyroxene and garnet as structural OH [e.g. 1 ]. Considering the significant influence of hydrogen on <span class="hlt">mantle</span> properties such as solidus temperature, rheology, conductivity and seismic velocity, it is important to understand both the distribution of water among <span class="hlt">mantle</span> phases and the mass transfer processes that influence water distribution in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Despite the important role of water in the <span class="hlt">mantle</span>, experimental determinations of the equilibrium distribution of trace amounts of hydrogen among coexisting silicate phases remain extremely limited. Improved analytical techniques have recently paved the way for quantitative investigations of water partitioning and abundances in nominally anhydrous <span class="hlt">mantle</span> minerals [e.g. 2]. Several studies of submarine glasses have revealed correlated increases in incompatible elements and water contents along segments of mid-ocean ridges approaching hotspots [e.g. 3,4]. A source-related increase in the water content of the <span class="hlt">mantle</span> is typically postulated to explain such observations, but elevated hotspot H2O contents may also relate to pressure differences in partitioning of water, analogous to the case for rare-<span class="hlt">earth</span> elements (e.g. the "garnet signature"). New experimental water partitioning data illuminate these differences. Hydrogen isotope ratios vary in submarine glasses from ocean ridges, back-arc basins and hotspots, and in hydrous phases from arcs and hotspots, suggesting significant hydrogen isotopic variability in the <span class="hlt">mantle</span>, which may be related to the subduction of water. Water clearly enters the upper <span class="hlt">mantle</span> at subduction zones, however the full water budget for any single subduction zone is highly uncertain [e.g. 5]. This uncertainty in the water budget at convergent margins indicates that we do not even know whether the present-day net flux of water is into or out of the <span class="hlt">Earth</span>. This</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940011863','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940011863"><span>Water in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>: Hydrogen analysis of <span class="hlt">mantle</span> olivine, pyroxenes and garnet using the SIMS</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kurosawa, Masanori; Yurimoto, Hisayoshi; Sueno, Shigeho</p> <p>1993-01-01</p> <p>Hydrogen (or water) in the <span class="hlt">Earth</span>'s interior plays a key role in the evolution and dynamics of the planet. However, the abundance and the existence form of the hydrogen have scarcely been clear in practice. Hydrogen in the <span class="hlt">mantle</span> was incorporated in the interior during the formation of the <span class="hlt">Earth</span>. The incorporated hydrogen was hardly possible to concentrate locally inside the <span class="hlt">Earth</span> considering its high mobility and high reactivity. The hydrogen, preferably, could be distributed homogeneously over the <span class="hlt">mantle</span> and the core by the subsequent physical and chemical processes. Therefore, hydrogen in the <span class="hlt">mantle</span> could be present in the form of trace hydrogen in nominally anhydrous <span class="hlt">mantle</span> minerals. The hydrogen and the other trace elements in <span class="hlt">mantle</span> olivines, orthopyroxenes, clinopyroxenes, and garnets were determined using secondary ion mass spectrometry (SIMS) for elucidating (1) the exact hydrogen contents, (2) the correlation between the hydrogen and the other trace elements, (3) the dependence of the hydrogen contents on the depth, and (4) the dependence of the whole rock water contents on the depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI51B0312H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI51B0312H"><span>Tomographic and Geodynamic Constraints on Convection-Induced Mixing in <span class="hlt">Earth</span>'s Deep <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hafter, D. P.; Forte, A. M.; Bremner, P. M.; Glisovic, P.</p> <p>2017-12-01</p> <p>Seismological studies reveal two large low-shear-velocity provinces (LLSVPs) in the lowermost <span class="hlt">mantle</span> (e.g., Su et al. 1994; Wang & Wen 2007; He & Wen 2012), which may represent accumulations of subducted slabs at the CMB (Tan & Gurnis 2005; Christensen & Hoffman 1994) or primordial material generated in the <span class="hlt">early</span> differentiation of <span class="hlt">Earth</span> (e.g. Li et al. 2014). The longevity or stability of these large-scale heterogeneities in the deep <span class="hlt">mantle</span> depends on the vigor and spatial distribution of the convective circulation, which is in turn dependent on the distribution of <span class="hlt">mantle</span> buoyancy and viscosity (e.g. Glisovic & Forte 2015). Here we explore the state of convective mixing in the <span class="hlt">mantle</span> using the ASPECT convection code (Kronbichler et al. 2012). A series of experiments are conducted to consider the geochemical and dynamical contributions of LLSVPs to deep-<span class="hlt">mantle</span> upwellings and corresponding plume-sourced volcanism. The principal feature of these experiments is the use of particle tracers to track geochemical changes in the LLSVPs and <span class="hlt">mantle</span> plumes in addition to identifying those parts of the <span class="hlt">mantle</span> that may remain unmixed. We employ 3-D <span class="hlt">mantle</span> density anomalies derived from joint inversions of seismic, geodynamic and mineral physics constraints and geodynamically-constrained viscosity distributions (Glisovic et al. 2015) to ensure that the predicted flow fields yield a good match to key geophysical constraints (e.g. heat flow, global gravity anomalies and plate velocities).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912224M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912224M"><span>Understanding the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> Through Advanced Elasticity Measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marquardt, Hauke; Schulze, Kirsten; Kurnosov, Alexander; Buchen, Johannes; Frost, Daniel; Boffa Ballaran, Tiziana; Marquardt, Katharina; Kawazoe, Takaaki</p> <p>2017-04-01</p> <p>Constraints on the inner structure, chemical and mineralogical composition as well as dynamics of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> can be derived through comparison of laboratory elasticity data to seismological observables. A quantitative knowledge of the elastic properties of <span class="hlt">mantle</span> minerals, and their variations with chemical composition, at pressure and temperature conditions of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> is key to construct reliable synthetic mineral physics-based seismic velocity models to be compared to seismic observables. We will discuss results of single-crystal elasticity measurements on <span class="hlt">Earth</span> <span class="hlt">mantle</span> minerals that have been conducted using the combined Brillouin scattering and x-ray diffraction (XRD) system at BGI Bayreuth in combination with advanced sample preparation using the focused ion beam (FIB) technique [1] that allows for tailoring sizes and shapes of tiny single-crystals. In our experiments, multiple FIB-prepared single-crystals were loaded in a single sample chamber of a resistively-heated diamond-anvil cell (DAC). The possiblity to measure simultaneously acoustic wave velocities and density (unit-cell parameters) in the DAC in combination with the multi-sample approach facilitates direct quantification of the effects of chemical substitution on the elasticity and seismic wave velocities at non-ambient conditions. Our experimental approach eliminates uncertainties arising from the combination of data collected under (potentially) different conditions in several DAC runs, in different laboratories and/or from using different pressure-temperature sensors. We will present our recent experiments on the elasticity of single-crystal Fe-Al-bearing bridgmanite in the lower <span class="hlt">mantle</span> and discuss implications for the composition and oxidation state of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. We will further discuss our laboratory data on the effects of 'water' and iron on the seismic wave velocities of ringwoodite in <span class="hlt">Earth</span>'s transition zone and outline implications for mapping 'water' in the transition</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PhDT.......181H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PhDT.......181H"><span>Free and forced convection in <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hall, Paul S.</p> <p></p> <p>Convective motion within <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> occurs as a combination of two primary modes: (1) buoyant upwelling due to the formation of gravitational instabilities at thermochemical boundary layers, and (2) passive flow associated with the divergence of lithospheric plates at mid-ocean ridges and their re-entry into the <span class="hlt">mantle</span> at subduction zones. The first mode is driven by variations in density and is therefore classified as 'free' convection. Examples of free convection within the <span class="hlt">Earth</span> include the diapiric flow of hydrous and/or partially molten <span class="hlt">mantle</span> at subduction zones and <span class="hlt">mantle</span> plumes. The second mode, while ultimately driven by density on a global scale, can be treated kinematically on the scale of the upper <span class="hlt">mantle</span>. This type of flow is designated 'forced' convection. On the scale of individual buoyant upwellings in the upper <span class="hlt">mantle</span>, the forced convection associated with plate tectonics acts to modify the morphology of the flow associated with free convection. Regions in which such interactions occur are typically associated with transfer of significant quantities of both mass and energy (i.e., heat) between the deep interior and the surface of the <span class="hlt">Earth</span> and thus afford a window into the dynamics of the <span class="hlt">Earth</span>'s interior. The dynamics and the consequences of the interaction between these two modes of convection is the focus of this dissertation. I have employed both laboratory and numerical modeling techniques to investigate the interaction between free and forced convection in this study. Each of these approaches has its own inherent strengths and weaknesses. These approaches are therefore complementary, and their use in combination is particularly powerful. I have focused on two examples interaction between free and forced convection in the upper <span class="hlt">mantle</span> in this study. Chapter I considers the interaction between ascending diapirs of hydrous and/or partially molten <span class="hlt">mantle</span> and flow in the <span class="hlt">mantle</span> wedge at subduction zones using laboratory models. Chapter</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998PhDT........11S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998PhDT........11S"><span>Properties of the Plasma <span class="hlt">Mantle</span> in the <span class="hlt">Earth</span>'s Magnetotail</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shodhan-Shah, Sheela</p> <p>1998-04-01</p> <p>The plasma <span class="hlt">mantle</span> is the site where the solar wind enters the <span class="hlt">Earth</span>'s magnetosphere. As yet, the <span class="hlt">mantle</span> in the magnetotail (downstream part of the magnetosphere) has remained an enigma, for this region is remote and inaccessible. However, new results from the GEOTAIL spacecraft have yielded data on the <span class="hlt">mantle</span>, making its study possible. The research reported in this dissertation uses the measurements made by the GEOTAIL spacecraft when it was beyond 100 Re (1 Re = <span class="hlt">Earth</span> radius) in the magnetotail to determine the global geometrical and dynamical properties of the <span class="hlt">mantle</span>. The model and the data together provide a cross-sectional picture of the <span class="hlt">mantle</span>, as well as its extent into the tail and along the circumference of the tail. The model assesses the mass and momentum flux flowing through the <span class="hlt">mantle</span> and merging with the plasma sheet (a relatively dense region that separates the oppositely directed fields of the tail lobes). In this way, the thesis examines the importance of the <span class="hlt">mantle</span> as a source that replenishes and moves the plasma sheet. Moreover, it addresses the relative importance of the global dynamical modes of the tail. The analysis finds that the tail's 'breathing' mode, of shape change, occurs on a timescale of tens of minutes while a windsock-type motion, responding to changes in the solar wind direction, occurs on a scale of hours. The <span class="hlt">mantle</span> extends about 140o around the circumference of the tail rather than 90o as previously thought and is about 20 ± 9 Re thick. It is capable of feeding the plasma sheet with sufficient particles to make up for those lost and can drag it away with a force that compares with the Earthward force on it. The rate at which the energy flows through the tail at 100 Re is about 10% of that in the solar wind and is a factor of 10 higher than the energy dissipated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70019067','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70019067"><span>A migratory <span class="hlt">mantle</span> plume on Venus: Implications for <span class="hlt">Earth</span>?</span></a></p> <p><a target="_blank" href=""></a></p> <p>Chapman, M.G.; Kirk, R.L.</p> <p>1996-01-01</p> <p>A spatially fixed or at least internally rigid hotspot reference frame has been assumed for determining relative plate motions on <span class="hlt">Earth</span>. Recent 1:5,000,000 scale mapping of Venus, a planet without terrestrial-style plate tectonics and ocean cover, reveals a systematic age and dimensional progression of corona-like arachnoids occurring in an uncinate chain. The nonrandom associations between arachnoids indicate they likely formed from a deep-seated <span class="hlt">mantle</span> plume in a manner similar to terrestrial hotspot features. However, absence of expected convergent "plate" margin deformation suggests that the arachnoids are the surface expression of a migratory <span class="hlt">mantle</span> plume beneath a stationary surface. If <span class="hlt">mantle</span> plumes are not stationary on Venus, what if any are the implications for <span class="hlt">Earth</span>?</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815198B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815198B"><span>Subduction History and the Evolution of <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bull, Abigail; Shephard, Grace; Torsvik, Trond</p> <p>2016-04-01</p> <p>Understanding the complex structure, dynamics and evolution of the deep <span class="hlt">mantle</span> is a fundamental goal in solid <span class="hlt">Earth</span> geophysics. Close to the core-<span class="hlt">mantle</span> boundary, seismic images reveal a <span class="hlt">mantle</span> characterised by (1) higher than average shear wave speeds beneath Asia and encircling the Pacific, consistent with sub ducting lithosphere beneath regions of ancient subduction, and (2) large regions of anomalously low seismic wavespeeds beneath Africa and the Central Pacific. The anomalously slow areas are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. The origin, composition and long-term evolution of the LLSVPs remain enigmatic. Geochemical inferences of multiple chemical reservoirs at depth, strong seismic contrasts, increased density, and an anticorrelation of shear wave velocity to bulk sound velocity in the anomalous regions imply that heterogeneities in both temperature and composition may be required to explain the seismic observations. Consequently, heterogeneous <span class="hlt">mantle</span> models place the anomalies into the context of thermochemical piles, characterised by an anomalous component whose intrinsic density is a few percent higher relative to that of the surrounding <span class="hlt">mantle</span>. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale <span class="hlt">mantle</span> convection. One end member scenario suggests that the LLSVPs are relatively mobile features over short timescales and thus are strongly affected by supercontinent cycles and <span class="hlt">Earth</span>'s plate motion history. In this scenario, the African LLSVP formed as a result of return flow in the <span class="hlt">mantle</span> due to circum-Pangean subduction (~240 Ma), contrasting a much older Pacific LLSVP, which may be linked to the Rodinia supercontinent and is implied to have remained largely unchanged since Rodinian breakup (~750-700 Ma). This propounds that <span class="hlt">Earth</span>'s plate motion history plays a controlling role in LLSVP development, suggesting that the location</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V24A..08V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V24A..08V"><span>An Impaired View of <span class="hlt">Earth</span>'s <span class="hlt">Early</span> History</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vervoort, J. D.; Kemp, A. I.; Bauer, A.; Bowring, S. A.; Fisher, C.</p> <p>2014-12-01</p> <p>The Hf and Nd isotope records of <span class="hlt">Earth</span>'s <span class="hlt">early</span> history are sparse, difficult to interpret, and controversial, much like the few remnants of crust older than 4 Ga. New analytical techniques have been brought to bear on this problem but despite this recent work­-or, perhaps, because of it-the record is no clearer than it was 15 years ago. Several studies, based on highly variable calculated initial isotopic compositions, have argued for highly heterogeneous crust and <span class="hlt">mantle</span> reservoirs in the <span class="hlt">early</span> <span class="hlt">Earth</span>1,2 and an ultra-depleted Eoarchean <span class="hlt">mantle</span>3. These data come mostly from two sources: Hf-Nd isotope analyses of ultramafic rocks and Hf isotope analyses of zircons by solution or laser ablation. An important question for understanding the chemical evolution of the <span class="hlt">early</span> <span class="hlt">Earth</span> is: Do these data offer a unique window into the <span class="hlt">early</span> <span class="hlt">Earth</span> or are they artefacts not representative of crust/<span class="hlt">mantle</span> evolution, giving an impaired view of the <span class="hlt">Earth</span>'s <span class="hlt">early</span> history? In complex samples, measured isotopic compositions can result from open-system behavior in easily altered ultramafic compositions, in multicomponent, polymetamorphic gneisses, or in zircons with multiple generations of growth. Perhaps most importantly, accurate age assignment is often lacking, compromised, or impossible in these rocks, making calculation of initial epsilon Hf and Nd values ambiguous at best. In order to gain insight into crust <span class="hlt">mantle</span> evolution in the <span class="hlt">early</span> <span class="hlt">Earth</span> we need, above all, a robust and unambiguous isotopic record to work with. This can be achieved by integrating zircon U-Pb and Hf and whole-rock Hf and Nd isotope compositions in relatively undisturbed igneous rocks with well-constrained ages. When this approach is used apparent isotopic heterogeneity decreases and a simpler model for crust-<span class="hlt">mantle</span> evolution in the <span class="hlt">early</span> <span class="hlt">Earth</span> emerges. Careful screening of geological relationships, petrology, and geochemistry of samples from the <span class="hlt">early</span> <span class="hlt">Earth</span> should be done before interpreting isotopic data</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009PhDT........57A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009PhDT........57A"><span>Teleseismic tomography for imaging <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aktas, Kadircan</p> <p></p> <p>Teleseismic tomography is an important imaging tool in earthquake seismology, used to characterize lithospheric structure beneath a region of interest. In this study I investigate three different tomographic techniques applied to real and synthetic teleseismic data, with the aim of imaging the velocity structure of the upper <span class="hlt">mantle</span>. First, by applying well established traveltime tomographic techniques to teleseismic data from southern Ontario, I obtained high-resolution images of the upper <span class="hlt">mantle</span> beneath the lower Great Lakes. Two salient features of the 3D models are: (1) a patchy, NNW-trending low-velocity region, and (2) a linear, NE-striking high-velocity anomaly. I interpret the high-velocity anomaly as a possible relict slab associated with ca. 1.25 Ga subduction, whereas the low-velocity anomaly is interpreted as a zone of alteration and metasomatism associated with the ascent of magmas that produced the Late Cretaceous Monteregian plutons. The next part of the thesis is concerned with adaptation of existing full-waveform tomographic techniques for application to teleseismic body-wave observations. The method used here is intended to be complementary to traveltime tomography, and to take advantage of efficient frequency-domain methodologies that have been developed for inverting large controlled-source datasets. Existing full-waveform acoustic modelling and inversion codes have been modified to handle plane waves impinging from the base of the lithospheric model at a known incidence angle. A processing protocol has been developed to prepare teleseismic observations for the inversion algorithm. To assess the validity of the acoustic approximation, the processing procedure and modelling-inversion algorithm were tested using synthetic seismograms computed using an elastic Kirchhoff integral method. These tests were performed to evaluate the ability of the frequency-domain full-waveform inversion algorithm to recover topographic variations of the Moho under a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V51D0384B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V51D0384B"><span>The record of <span class="hlt">mantle</span> heterogeneity preserved in <span class="hlt">Earth</span>'s oceanic crust</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burton, K. W.; Parkinson, I. J.; Schiano, P.; Gannoun, A.; Laubier, M.</p> <p>2017-12-01</p> <p><span class="hlt">Earth</span>'s oceanic crust is produced by melting of the upper <span class="hlt">mantle</span> where it upwells beneath mid-ocean ridges, and provides a geographically widespread elemental and isotopic `sample' of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. The chemistry of mid-ocean ridge basalts (MORB), therefore, holds key information on the compositional diversity of the upper <span class="hlt">mantle</span>, but the problem remains that mixing and reaction during melt ascent acts to homogenise the chemical variations they acquire. Nearly all isotope and elemental data obtained thus far are for measurements of MORB glass, and this represents the final melt to crystallise, evolving in an open system. However, the crystals that are present are often not in equilibrium with their glass host. Melts trapped in these minerals indicate that they crystallised from primitive magmas that possess diverse compositions compared to the glass. Therefore, these melt inclusions preserve information on the true extent of the <span class="hlt">mantle</span> that sources MORB, but are rarely amenable to precise isotope measurement. An alternative approach is to measure the isotope composition of the primitive minerals themselves. Our new isotope data indicates that these minerals crystallised from melts with significantly different isotope compositions to their glass host, pointing to a <span class="hlt">mantle</span> source that has experienced extreme melt depletion. These primitive minerals largely crystallised in the lower oceanic crust, and our preliminary data for lower crustal rocks and minerals shows that they preserve a remarkable range of isotope compositions. Taken together, these results indicate that the upper <span class="hlt">mantle</span> sampled by MORB is extremely heterogeneous, reflecting depletion and enrichment over much of <span class="hlt">Earth</span>'s geological history.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V24A..01H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V24A..01H"><span>By Permission of the <span class="hlt">Mantle</span>: Modern and Ancient Deep <span class="hlt">Earth</span> Volatile Cycles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hirschmann, M. M.</p> <p>2011-12-01</p> <p>The principle volatile elements, H and C, are of surpassing importance to processes and conditions in the interiors and the surfaces of terrestrial planets, affecting everything from <span class="hlt">mantle</span> dynamics and large scale geochemical differentiation to climate and habitability. The storage of these volatiles in planetary interiors, their inventory in the near-surface environment and exchange between the interiors and the exosphere are governed by petrologic processes. Were it not for the effective incompatibility of these components in <span class="hlt">mantle</span> lithologies, there might be no oceans, no habitable climate, and no biosphere on the surface. Consequently, deep <span class="hlt">Earth</span> volatile cycles represent one of the best examples of how petrology influences nearly all other aspects of <span class="hlt">Earth</span> science. The exosphere of the modern <span class="hlt">Earth</span> has a high H/C ratio compared to that of the interior sampled by oceanic basalts. A potential explanation for this is that C is subducted to the deep <span class="hlt">mantle</span> more efficiently than H, such that the exosphere C reservoir shrinks through geologic time. Unfortunately this hypothesis conflicts with the sedimentary record, which suggests that carbonate storage on the continents has increased rather than decreased with time. It also may not be applicable to the first 3 Ga of <span class="hlt">Earth</span> history, when hotter typical subduction geotherms greatly reduced the efficiency of C subduction. An important question regarding deep <span class="hlt">Earth</span> volatile cycles is the inventory of H and C in the interior and the exosphere that descend from <span class="hlt">Earth</span>'s earliest differentiation processes. Originally, much of <span class="hlt">Earth</span>'s volatile inventory was presumably present as a thick atmosphere, in part because volatiles were probably delivered late in the accretion history and owing to both the efficiency of impact degassing and of volatile release from <span class="hlt">early</span> magma ocean(s). <span class="hlt">Early</span> <span class="hlt">mantle</span> H2O may descend from the magma ocean, in which portions of a steam atmosphere are dissolved in the magma and then precipitated with</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_3 --> <div id="page_4" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="61"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V13C2051A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V13C2051A"><span>Eutectic melting temperature of the lowermost <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.</p> <p>2009-12-01</p> <p>Partial melting of the <span class="hlt">Earth</span>'s deep <span class="hlt">mantle</span> probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-<span class="hlt">mantle</span> boundary. Melts are important because they dominate the chemical evolution of the different <span class="hlt">Earth</span>'s reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep <span class="hlt">Earth</span>, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep <span class="hlt">Earth</span> at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower <span class="hlt">mantle</span> region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-<span class="hlt">mantle</span> boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower <span class="hlt">mantle</span> in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower <span class="hlt">mantle</span> materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMMR43A2364K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMMR43A2364K"><span>High Resolution Global Electrical Conductivity Variations in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kelbert, A.; Sun, J.; Egbert, G. D.</p> <p>2013-12-01</p> <p>Electrical conductivity of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> is a valuable constraint on the water content and melting processes. In Kelbert et al. (2009), we obtained the first global inverse model of electrical conductivity in the <span class="hlt">mantle</span> capable of providing constraints on the lateral variations in <span class="hlt">mantle</span> water content. However, in doing so we had to compromise on the problem complexity by using the historically very primitive ionospheric and magnetospheric source assumptions. In particular, possible model contamination by the auroral current systems had greatly restricted our use of available data. We have now addressed this problem by inverting for the external sources along with the electrical conductivity variations. In this study, we still focus primarily on long period data that are dominated by quasi-zonal source fields. The improved understanding of the ionospheric sources allows us to invert the magnetic fields directly, without a correction for the source and/or the use of transfer functions. It allows us to extend the period range of available data to 1.2 days - 102 days, achieving better sensitivity to the upper <span class="hlt">mantle</span> and transition zone structures. Finally, once the source effects in the data are accounted for, a much larger subset of observatories may be used in the electrical conductivity inversion. Here, we use full magnetic fields at 207 geomagnetic observatories, which include mid-latitude, equatorial and high latitude data. Observatory hourly means from the years 1958-2010 are employed. The improved quality and spatial distribution of the data set, as well as the high resolution modeling and inversion using degree and order 40 spherical harmonics mapped to a 2x2 degree lateral grid, all contribute to the much improved resolution of our models, representing a conceptual step forward in global electromagnetic sounding. We present a fully three-dimensional, global electrical conductivity model of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> as inferred from ground geomagnetic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010E%26PSL.298..175J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010E%26PSL.298..175J"><span>Chlorine isotope evidence for crustal recycling into the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>John, Timm; Layne, Graham D.; Haase, Karsten M.; Barnes, Jaime D.</p> <p>2010-09-01</p> <p>Subduction of oceanic lithosphere is a key feature of terrestrial plate tectonics. However, the effect of this recycled crustal material on <span class="hlt">mantle</span> composition is debated. Ocean island basalts (OIB) provide direct insights into the composition of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. The distinct composition of the HIMU (high 238U/ 204Pb)- and EM (enriched <span class="hlt">mantle</span>)-type OIB <span class="hlt">mantle</span> sources may be due to either recycling of oceanic crust and sediment into the <span class="hlt">mantle</span> or metasomatic processes within the <span class="hlt">mantle</span>. Chlorine derived from seawater or crustal fluids potentially provides a tracer for recycled material. Previously reported δ 37Cl values for mid-ocean ridge basalts (MORB) range from ca. - 3.0 to near 0‰. In contrast to MORB, we find a larger variation in OIB glasses representing HIMU- and EM-type <span class="hlt">mantle</span> sources based on replicate SIMS analyses with δ 37Cl values ranging from - 1.6 to + 1.1‰ for HIMU-type and - 0.4 to + 2.9‰ for EM-type lavas. These δ 37Cl values correlate positively with 87Sr/ 86Sr ratios for both the HIMU- and EM-type samples. The negative δ 37Cl values of some HIMU-type lavas overlap with those of altered oceanic lithosphere, which is assumed to be present in the HIMU source. The EM lavas have high 87Sr/ 86Sr and primarily positive δ 37Cl values. We hypothesize that subducting sediments may have developed high δ 37Cl values by expelling 37Cl-depleted pore fluids, thus accounting for the positive δ 37Cl values recorded in the EM-type lavas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFMMR44A..03K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFMMR44A..03K"><span>Constraints from <span class="hlt">Earth</span>'s heat budget on <span class="hlt">mantle</span> dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kellogg, L. H.; Ferrachat, S.</p> <p>2006-12-01</p> <p>Recent years have seen an increase in the number of proposed models to explain <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> dynamics: while two end-members, pure layered convection with the upper and lower <span class="hlt">mantle</span> convecting separately from each other, and pure, whole <span class="hlt">mantle</span> convection, appear not to satisfy all the observations, several addition models have been proposed. These models include and attempt to characterize least one reservoir that is enriched in radiogenic elements relative to the mid-ocean ridge basalt (MORB) source, as is required to account for most current estimates of the <span class="hlt">Earth</span>'s heat budget. This reservoir would also be responsible for the geochemical signature in some ocean island basalts (OIBs) like Hawaii, but must be rarely sampled at the surface. Our current knowledge of the mass- and heat-budget for the bulk silicate <span class="hlt">Earth</span> from geochemical, cosmochemical and geodynamical observations and constraints enables us to quantify the radiogenic heat enrichment required to balance the heat budget. Without assuming any particular model for the structure of the reservoir, we first determine the inherent trade-off between heat production rate and mass of the reservoir. Using these constraints, we then investigate the dynamical inferences of the heat budget, assuming that the additional heat is produced within a deep layer above the core-<span class="hlt">mantle</span> boundary. We carry out dynamical models of layered convection using four different fixed reservoir volumes, corresponding to deep layers of thicknesses 150, 500 1000 and 1600 km, respectively, and including both temperature-dependent viscosity and an instrinsic viscosity jump between upper and lower <span class="hlt">mantle</span>. We then assess the viability of these cases against 5 criteria: stability of the deep layer through time, topography of the interface, effective density profile, intrinsic chemical density and the heat flux at the CMB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.U21A0002B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.U21A0002B"><span>A New Carbonate Chemistry in the <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boulard, E.; Gloter, A.; Corgne, A.; Antonangeli, D.; Auzende, A.; Perrillat, J.; Guyot, F. J.; Fiquet, G.</p> <p>2010-12-01</p> <p> explanation for the coexistence of oxidized and reduced C species observed on natural samples [4, 5], but also a new diamond formation mechanism at lower <span class="hlt">mantle</span> conditions. [1] Sleep, N. H., and K. Zahnle (2001) J. Geophys. Res.-Planets 106(E1), 1373-1399. [2] Javoy, M. (1997) Geophys. Res. Lett. 24(2), 177-180. [3] Lecuyer et al. (2000) <span class="hlt">Earth</span> Planet. Sci. Lett. 181(1-2), 33-40. [4] Brenker et al. (2007) <span class="hlt">Earth</span> Planet. Sci. Lett. 260(1-2), 1-9. [5] Stachel et al. (2000) Contrib. Mineral. Petrol. 140(1), 16-27.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.475...94F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.475...94F"><span>Long-term preservation of <span class="hlt">early</span> formed <span class="hlt">mantle</span> heterogeneity by mobile lid convection: Importance of grainsize evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Foley, Bradford J.; Rizo, Hanika</p> <p>2017-10-01</p> <p>The style of tectonics on the Hadean and Archean <span class="hlt">Earth</span>, particularly whether plate tectonics was in operation or not, is debated. One important, albeit indirect, constraint on <span class="hlt">early</span> <span class="hlt">Earth</span> tectonics comes from observations of <span class="hlt">early</span>-formed geochemical heterogeneities: 142Nd and 182W anomalies recorded in Hadean to Phanerozoic rocks from different localities indicate that chemically heterogeneous reservoirs, formed during the first ∼500 Myrs of <span class="hlt">Earth</span>'s history, survived their remixing into the <span class="hlt">mantle</span> for over 1 Gyrs. Such a long mixing time is difficult to explain because hotter <span class="hlt">mantle</span> temperatures, expected for the <span class="hlt">early</span> <span class="hlt">Earth</span>, act to lower <span class="hlt">mantle</span> viscosity and increase convective vigor. Previous studies found that mobile lid convection typically erases heterogeneity within ∼100 Myrs under such conditions, leading to the hypothesis that stagnant lid convection on the <span class="hlt">early</span> <span class="hlt">Earth</span> was responsible for the observed long mixing times. However, using two-dimensional Cartesian convection models that include grainsize evolution, we find that mobile lid convection can preserve heterogeneity at high <span class="hlt">mantle</span> temperature conditions for much longer than previously thought, because higher <span class="hlt">mantle</span> temperatures lead to larger grainsizes in the lithosphere. These larger grainsizes result in stronger plate boundaries that act to slow down surface and interior convective motions, in competition with the direct effect temperature has on <span class="hlt">mantle</span> viscosity. Our models indicate that mobile lid convection can preserve heterogeneity for ≈0.4-1 Gyrs at <span class="hlt">early</span> <span class="hlt">Earth</span> <span class="hlt">mantle</span> temperatures when the initial heterogeneity has the same viscosity as the background <span class="hlt">mantle</span>, and ≈1-4 Gyrs when the heterogeneity is ten times more viscous than the background <span class="hlt">mantle</span>. Thus, stagnant lid convection is not required to explain long-term survival of <span class="hlt">early</span> formed geochemical heterogeneities, though these heterogeneities having an elevated viscosity compared to the surrounding <span class="hlt">mantle</span> may be essential for their</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26564850','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26564850"><span>Evidence for primordial water in <span class="hlt">Earth</span>'s deep <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hallis, Lydia J; Huss, Gary R; Nagashima, Kazuhide; Taylor, G Jeffrey; Halldórsson, Sæmundur A; Hilton, David R; Mottl, Michael J; Meech, Karen J</p> <p>2015-11-13</p> <p>The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of <span class="hlt">Earth</span> can be used to constrain the origin of its water. However, the most accessible reservoir, <span class="hlt">Earth</span>'s oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define <span class="hlt">Earth</span>'s original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep <span class="hlt">mantle</span> has a low D/H ratio (δD more negative than -218 per mil). Such strongly negative values indicate the existence of a component within <span class="hlt">Earth</span>'s interior that inherited its D/H ratio directly from the protosolar nebula. Copyright © 2015, American Association for the Advancement of Science.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR43C0475Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR43C0475Q"><span>Effects of spin crossover on iron isotope fractionation in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Qin, T.; Shukla, G.; Wu, Z.; Wentzcovitch, R.</p> <p>2017-12-01</p> <p>Recent studies have revealed that the iron isotope composition of mid-ocean ridge basalts (MORBs) is +0.1‰ richer in heavy Fe (56Fe) relative to chondrites, while basalts from Mars and Vesta have similar Fe isotopic composition as chondrites. Several hypotheses could explain these observations. For instance, iron isotope fractionation may have occurred during core formation or <span class="hlt">Earth</span> may have lost some light Fe isotope during the high temperature event in the <span class="hlt">early</span> <span class="hlt">Earth</span>. To better understand what drove these isotopic observations, it is important to obtain accurate Fe isotope fractionation factors among <span class="hlt">mantle</span> and core phases at the relevant P-T conditions. In bridgmanite, the most voluminous mineral in the lower <span class="hlt">mantle</span>, Fe can occupy more than one crystalline site, be in ferrous and/or ferric states, and may undergo a spin crossover in the lower <span class="hlt">mantle</span>. Iron isotopic fractionation properties under spin crossover are poorly constrained, while this may be relevant to differentiation of <span class="hlt">Earth</span>'s magma ocean. In this study we address the effect of these multiple states on the iron isotope fractionation factors between <span class="hlt">mantle</span> and core phases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20120001984&hterms=oceans+tide&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Doceans%2Btide','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20120001984&hterms=oceans+tide&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Doceans%2Btide"><span>Fortnightly <span class="hlt">Earth</span> Rotation, Ocean Tides, and <span class="hlt">Mantle</span> Anelasticity</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ray, Richard D.; Egbert, Gary D.</p> <p>2011-01-01</p> <p>Sustained accurate measurements of <span class="hlt">earth</span> rotation are one of the prime goals of Global Geodetic Observing System (GGOS). We here concentrate on the fortnightly (Mf) tidal component of <span class="hlt">earth</span>-rotation data to obtain new results concerning anelasticity of the <span class="hlt">mantle</span> at this period. The study comprises three parts: (1) a new determination of the Mf component of polar motion and length-of-day from a multi-decade time series of space-geodetic data; (2) the use of the polar-motion determination as one constraint in the development of a hydrodynamic ocean model of the Mf tide; and (3) the use of these results to place new constraints on <span class="hlt">mantle</span> anelasticity. Our model of the Mf ocean tide assimilates more than fourteen years of altimeter data from the Topex/Poseidon and Jason-1 satellites. The polar motion data, plus tide-gauge data and independent altimeter data, give useful additional information, with only the polar motion putting constraints on tidal current velocities. The resulting ocean-tide model, plus the dominant elastic body tide, leaves a small residual in observed length-of-day caused by <span class="hlt">mantle</span> anelasticity. The inferred effective tidal 0 of the anelastic body tide is 90 and is in line with a omega-alpha frequency dependence with alpha in the range 0.2--0.3.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050155260&hterms=1074&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3D%2526%25231074','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050155260&hterms=1074&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3D%2526%25231074"><span>Biosignatures of <span class="hlt">early</span> <span class="hlt">earths</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pilcher, Carl B.</p> <p>2003-01-01</p> <p>A major goal of NASA's Origins Program is to find habitable planets around other stars and determine which might harbor life. Determining whether or not an extrasolar planet harbors life requires an understanding of what spectral features (i.e., biosignatures) might result from life's presence. Consideration of potential biosignatures has tended to focus on spectral features of gases in <span class="hlt">Earth</span>'s modern atmosphere, particularly ozone, the photolytic product of biogenically produced molecular oxygen. But life existed on <span class="hlt">Earth</span> for about 1(1/2) billion years before the buildup of atmospheric oxygen. Inferred characteristics of <span class="hlt">Earth</span>'s earliest biosphere and studies of modern microbial ecosystems that share some of those characteristics suggest that organosulfur compounds, particularly methanethiol (CH(3)SH, the sulfur analog of methanol), may have been biogenic products on <span class="hlt">early</span> <span class="hlt">Earth</span>. Similar production could take place on extrasolar <span class="hlt">Earth</span>-like planets whose biota share functional chemical characteristics with <span class="hlt">Earth</span> life. Since methanethiol and related organosulfur compounds (as well as carbon dioxide) absorb at wavelengths near or overlapping the 9.6-microm band of ozone, there is potential ambiguity in interpreting a feature around this wavelength in an extrasolar planet spectrum.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/14678658','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/14678658"><span>Biosignatures of <span class="hlt">early</span> <span class="hlt">earths</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pilcher, Carl B</p> <p>2003-01-01</p> <p>A major goal of NASA's Origins Program is to find habitable planets around other stars and determine which might harbor life. Determining whether or not an extrasolar planet harbors life requires an understanding of what spectral features (i.e., biosignatures) might result from life's presence. Consideration of potential biosignatures has tended to focus on spectral features of gases in <span class="hlt">Earth</span>'s modern atmosphere, particularly ozone, the photolytic product of biogenically produced molecular oxygen. But life existed on <span class="hlt">Earth</span> for about 1(1/2) billion years before the buildup of atmospheric oxygen. Inferred characteristics of <span class="hlt">Earth</span>'s earliest biosphere and studies of modern microbial ecosystems that share some of those characteristics suggest that organosulfur compounds, particularly methanethiol (CH(3)SH, the sulfur analog of methanol), may have been biogenic products on <span class="hlt">early</span> <span class="hlt">Earth</span>. Similar production could take place on extrasolar <span class="hlt">Earth</span>-like planets whose biota share functional chemical characteristics with <span class="hlt">Earth</span> life. Since methanethiol and related organosulfur compounds (as well as carbon dioxide) absorb at wavelengths near or overlapping the 9.6-microm band of ozone, there is potential ambiguity in interpreting a feature around this wavelength in an extrasolar planet spectrum.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JGRB..114.1205R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JGRB..114.1205R"><span>Water-induced convection in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> transition zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Richard, Guillaume C.; Bercovici, David</p> <p>2009-01-01</p> <p>Water enters the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> by subduction of oceanic lithosphere. Most of this water immediately returns to the atmosphere through arc volcanism, but a part of it is expected as deep as the <span class="hlt">mantle</span> transition zone (410-660 km depth). There, slabs can be deflected and linger before sinking into the lower <span class="hlt">mantle</span>. Because it lowers the density and viscosity of the transition zone minerals (i.e., wadsleyite and ringwoodite), water is likely to affect the dynamics of the transition zone <span class="hlt">mantle</span> overlying stagnant slabs. The consequences of water exchange between a floating slab and the transition zone are investigated. In particular, we focus on the possible onset of small-scale convection despite the adverse thermal gradient (i.e., <span class="hlt">mantle</span> is cooled from below by the slab). The competition between thermal and hydrous effects on the density and thus on the convective stability of the top layer of the slab is examined numerically, including water-dependent density and viscosity and temperature-dependent water solubility. For plausible initial water content in a slab (≥0.5 wt %), an episode of convection is likely to occur after a relatively short time delay (5-20 Ma) after the slab enters the transition zone. However, water induced rheological weakening is seen to be a controlling parameter for the onset time of convection. Moreover, small-scale convection above a stagnant slab greatly enhances the rate of slab dehydration. Small-scale convection also facilitates heating of the slab, which in itself may prolong the residence time of the slab in the transition zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMDI43A..07H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMDI43A..07H"><span>Dynamical Generation of the Transition Zone in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hansen, U.; Stemmer, K.</p> <p>2005-12-01</p> <p>The internal structure of the <span class="hlt">Earth</span> is made up by a series of layers, though it is unclear how many layers exist and if there are layers invisible to remote sensing techniques. The transition zone is likely to be a boundary layer separating the convective systems in the lower and upper <span class="hlt">mantle</span>. It seems likely that currently there is some mass exchange across this boundary, rather than the two systems beeing strictly separated.a Double-diffusive convection(d.d.c) is a vital mechanism which can generate layered structure and may thus be an important mmical machinery behind the formation of the transition zone. Double-diffusive convection determines the dynamics of systems whose density is influenced by at least two components with different molecular diffusivities.In the <span class="hlt">mantle</span>, composition and temperature play the role of those two components. By means of numerical experiments we demonstrate that under <span class="hlt">mantle</span> relevant conditions d.d.c typically leads to the formation of a transition zone. The calculations encompass two- and three dimensional Cartesian geometries as well as fully 3D spherical domains. We have further included strongly temperature dependent viscosity and find that this leads to even more pronounced layering. In most cases a layered flow pattern emerges, where two layers with a transition zone in between resembles a quasistationary state. Thus, the transition zone can be the result of a self organization process of the convective flow in the <span class="hlt">mantle</span>. The presence of a phase transition further helps to stabilize the boundary against overturning, even on a time scale on the order of the age of the <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27872307','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27872307"><span>High-pressure phase of brucite stable at <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> transition zone and lower <span class="hlt">mantle</span> conditions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hermann, Andreas; Mookherjee, Mainak</p> <p>2016-12-06</p> <p>We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH) 2 , using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> transition zone and lower <span class="hlt">mantle</span>. This prediction implies that brucite can play a much more important role in water transport and storage in <span class="hlt">Earth</span>'s interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO 6 octahedral units arranged in the anatase-TiO 2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep <span class="hlt">Earth</span> possible with geophysical methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040089381&hterms=Biosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DBiosphere','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040089381&hterms=Biosphere&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DBiosphere"><span><span class="hlt">Earth</span>'s <span class="hlt">early</span> biosphere</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Des Marais, D. J.</p> <p>1998-01-01</p> <p>Understanding our own <span class="hlt">early</span> biosphere is essential to our search for life elsewhere, because life arose on <span class="hlt">Earth</span> very <span class="hlt">early</span> and rocky planets shared similar <span class="hlt">early</span> histories. The biosphere arose before 3.8 Ga ago, was exclusively unicellular and was dominated by hyperthermophiles that utilized chemical sources of energy and employed a range of metabolic pathways for CO2 assimilation. Photosynthesis also arose very <span class="hlt">early</span>. Oxygenic photosynthesis arose later but still prior to 2.7 Ga. The transition toward the modern global environment was paced by a decline in volcanic and hydrothermal activity. These developments allowed atmospheric O2 levels to increase. The O2 increase created new niches for aerobic life, most notably the more advanced Eukarya that eventually spawned the megascopic fauna and flora of our modern biosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI13B..01H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI13B..01H"><span>Evidence for Primordial Water in <span class="hlt">Earths</span> Deep <span class="hlt">Mantle</span>: D/h Ratios in Baffin Island and Icelandic Picrites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hallis, L. J.; Huss, G. R.; Nagashima, K.; Taylor, J.; Hilton, D. R.; Mottl, M. J.; Meech, K. J.; Halldorsson, S. A.</p> <p>2016-12-01</p> <p>Experimentally based chemical models suggest Jeans escape could have caused an increase in <span class="hlt">Earth</span>'s atmospheric D/H ratio of between a factor of 2 and 9 since the planets formation1. Plate tectonic mixing ensures this change has been incorporated into the <span class="hlt">mantle</span>. In addition, collisions with hydrogen bearing planetesimals or cometary material after <span class="hlt">Earth</span>'s accretion could have altered the D/H ratio of the planet's surface and upper <span class="hlt">mantle</span>2. Therefore, to determine <span class="hlt">Earth</span>'s original D/H ratio, a reservoir that has been completely unaffected by these surface and upper <span class="hlt">mantle</span> changes is required. Most studies suggest that high 3He/4He ratios in some OIBs indicate the existence of relatively undegassed regions in the deep <span class="hlt">mantle</span> compared to the upper <span class="hlt">mantle</span>, which retain a greater proportion of their primordial He3-4. <span class="hlt">Early</span> Tertiary (60-million-year-old) picrites from Baffin Island and west Greenland, which represent volcanic rocks from the proto/<span class="hlt">early</span> Iceland <span class="hlt">mantle</span> plume, contain the highest recorded terrestrial 3He/4He ratios3-4. These picrites also have Pb and Nd isotopic ratios consistent with primordial <span class="hlt">mantle</span> ages (4.45 to 4.55 Ga)5, indicating the persistence of an ancient, isolated reservoir in the <span class="hlt">mantle</span>. The undegassed and primitive nature6of this reservoir suggests that it could preserve <span class="hlt">Earth</span>'s initial D/H ratio. We measured the D/H ratios of olivine-hosted glassy melt inclusions in Baffin Island and Icelandic picrites to establish whether their deep <span class="hlt">mantle</span> source region exhibits a different D/H ratio to known upper <span class="hlt">mantle</span> and surface reservoirs. Baffin Island D/H ratios were found to extend lower than any previously measured <span class="hlt">mantle</span> values (δD -97 to -218 ‰), suggesting that areas of the deep <span class="hlt">mantle</span> do preserve a more primitive hydrogen reservoir, hence are unaffected by plate tectonic mixing. Comparing our measured low D/H ratios to those of known extra-terrestrial materials can help determine where <span class="hlt">Earths</span> water came from. References: [1] Genda and Ikoma</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017CoMP..172...51U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017CoMP..172...51U"><span>Fluorine and chlorine in <span class="hlt">mantle</span> minerals and the halogen budget of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Urann, B. M.; Le Roux, V.; Hammond, K.; Marschall, H. R.; Lee, C.-T. A.; Monteleone, B. D.</p> <p>2017-07-01</p> <p>The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB <span class="hlt">mantle</span> (DMM). Yet, the F and Cl budget of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (≥0.4 µg/g F and ≥0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of <span class="hlt">mantle</span> minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The <span class="hlt">mantle</span> wedge is likely enriched in F compared to un-metasomatized <span class="hlt">mantle</span>, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite <span class="hlt">mantle</span> contains 1.4-31 µg/g F and 0.14-0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1-9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMDI11A2133K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMDI11A2133K"><span>First Principles Analysis of Convection in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span>, Eustatic Sea Level and <span class="hlt">Earth</span> Volume</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kinsland, G. L.</p> <p>2011-12-01</p> <p>Steady state convection (convection whereby heat leaving the <span class="hlt">mantle</span> at the top is equal to the heat entering the <span class="hlt">mantle</span> across the core <span class="hlt">mantle</span> boundary and that created within the <span class="hlt">mantle</span>) of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> is, to a very good approximation, both a constant mass and constant volume process. Mass or volume which moves to one place; e.g., an oceanic ridge; must be accompanied by mass or volume removed from another place. The location of removal, whether from underneath of an ocean or a continent, determines the relationship between oceanic ridge volume and eustatic sea level. If all of the volume entering a ridge were to come from under an oceanic basin then the size of the ridge would not affect eustatic sea level as it would be compensated by a lowering of the sea floor elsewhere. If the volume comes from under a continent then the hypsometry of the continent becomes important. Thus, eustatic sea level is not simply related to convection rate and oceanic ridge volume as posited by Hays and Pitman(1973). Non-steady state convection is still a constant mass process but is not a constant volume process. The <span class="hlt">mantle</span> experiences a net gain of heat, warms and expands during periods of relatively slow convection (that being convection rate which is less than that necessary to transport incoming and internally created heat to the surface). Conversely, the <span class="hlt">mantle</span> has a net loss of heat, cools and contracts during periods of relatively rapid convection. The <span class="hlt">Earth</span> itself expands and contracts as the <span class="hlt">mantle</span> does. During rapid convection more volume is delivered from the interior of the <span class="hlt">mantle</span> to the <span class="hlt">Earth</span>'s ridge system than during slow convection. The integral of the difference of ridge system volume between fast and slow convection over a fast-slow convection cycle is a measure of the difference in volume of the <span class="hlt">mantle</span> over a cycle. The magnitude of the <span class="hlt">Earth</span>'s volume expansion and contraction as calculated from published values for the volume of ocean ridges and is about</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004Tectp.386...41V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004Tectp.386...41V"><span>Production and recycling of oceanic crust in the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.</p> <p>2004-08-01</p> <p>Because of the strongly different conditions in the <span class="hlt">mantle</span> of the <span class="hlt">early</span> <span class="hlt">Earth</span> regarding temperature and viscosity, present-day geodynamics cannot simply be extrapolated back to the <span class="hlt">early</span> history of the <span class="hlt">Earth</span>. We use numerical thermochemical convection models including partial melting and a simple mechanism for melt segregation and oceanic crust production to investigate an alternative suite of dynamics which may have been in operation in the <span class="hlt">early</span> <span class="hlt">Earth</span>. Our modelling results show three processes that may have played an important role in the production and recycling of oceanic crust: (1) Small-scale ( x×100 km) convection involving the lower crust and shallow upper <span class="hlt">mantle</span>. Partial melting and thus crustal production takes place in the upwelling limb and delamination of the eclogitic lower crust in the downwelling limb. (2) Large-scale resurfacing events in which (nearly) the complete crust sinks into the (eventually lower) <span class="hlt">mantle</span>, thereby forming a stable reservoir enriched in incompatible elements in the deep <span class="hlt">mantle</span>. New crust is simultaneously formed at the surface from segregating melt. (3) Intrusion of lower <span class="hlt">mantle</span> diapirs with a high excess temperature (about 250 K) into the upper <span class="hlt">mantle</span>, causing massive melting and crustal growth. This allows for plumes in the Archean upper <span class="hlt">mantle</span> with a much higher excess temperature than previously expected from theoretical considerations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22678288','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22678288"><span><span class="hlt">Early</span> differentiation and volatile accretion recorded in deep-<span class="hlt">mantle</span> neon and xenon.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mukhopadhyay, Sujoy</p> <p>2012-06-06</p> <p>The isotopes (129)Xe, produced from the radioactive decay of extinct (129)I, and (136)Xe, produced from extinct (244)Pu and extant (238)U, have provided important constraints on <span class="hlt">early</span> <span class="hlt">mantle</span> outgassing and volatile loss from <span class="hlt">Earth</span>. The low ratios of radiogenic to non-radiogenic xenon ((129)Xe/(130)Xe) in ocean island basalts (OIBs) compared with mid-ocean-ridge basalts (MORBs) have been used as evidence for the existence of a relatively undegassed primitive deep-<span class="hlt">mantle</span> reservoir. However, the low (129)Xe/(130)Xe ratios in OIBs have also been attributed to mixing between subducted atmospheric Xe and MORB Xe, which obviates the need for a less degassed deep-<span class="hlt">mantle</span> reservoir. Here I present new noble gas (He, Ne, Ar, Xe) measurements from an Icelandic OIB that reveal differences in elemental abundances and (20)Ne/(22)Ne ratios between the Iceland <span class="hlt">mantle</span> plume and the MORB source. These observations show that the lower (129)Xe/(130)Xe ratios in OIBs are due to a lower I/Xe ratio in the OIB <span class="hlt">mantle</span> source and cannot be explained solely by mixing atmospheric Xe with MORB-type Xe. Because (129)I became extinct about 100 million years after the formation of the Solar System, OIB and MORB <span class="hlt">mantle</span> sources must have differentiated by 4.45 billion years ago and subsequent mixing must have been limited. The Iceland plume source also has a higher proportion of Pu- to U-derived fission Xe, requiring the plume source to be less degassed than MORBs, a conclusion that is independent of noble gas concentrations and the partitioning behaviour of the noble gases with respect to their radiogenic parents. Overall, these results show that <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> accreted volatiles from at least two separate sources and that neither the Moon-forming impact nor 4.45 billion years of <span class="hlt">mantle</span> convection has erased the signature of <span class="hlt">Earth</span>'s heterogeneous accretion and <span class="hlt">early</span> differentiation.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_4 --> <div id="page_5" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="81"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhDT........50A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhDT........50A"><span>Teleseismic Array Studies of <span class="hlt">Earth</span>'s Core-<span class="hlt">Mantle</span> Boundary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alexandrakis, Catherine</p> <p>2011-12-01</p> <p>The core <span class="hlt">mantle</span> boundary (CMB) is an inaccessible and complex region, knowledge of which is vital to our understanding of many <span class="hlt">Earth</span> processes. Above it is the heterogeneous lower-<span class="hlt">mantle</span>. Below the boundary is the outer-core, composed of liquid iron, and/or nickel and some lighter elements. Elucidation of how these two distinct layers interact may enable researchers to better understand the geodynamo, global tectonics, and overall <span class="hlt">Earth</span> history. One parameter that can be used to study structure and limit potential chemical compositions is seismic-wave velocity. Current global-velocity models have significant uncertainties in the 200 km above and below the CMB. In this thesis, these regions are studied using three methods. The upper outer core is studied using two seismic array methods. First, a modified vespa, or slant-stack method is applied to seismic observations at broadband seismic arrays, and at large, dense groups of broadband seismic stations dubbed 'virtual' arrays. Observations of core-refracted teleseismic waves, such as SmKS, are used to extract relative arrivaltimes. As with previous studies, lower -<span class="hlt">mantle</span> heterogeneities influence the extracted arrivaltimes, giving significant scatter. To remove raypath effects, a new method was developed, called Empirical Transfer Functions (ETFs). When applied to SmKS waves, this method effectively isolates arrivaltime perturbations caused by outer core velocities. By removing raypath effects, the signals can be stacked further reducing scatter. The results of this work were published as a new 1D outer-core model, called AE09. This model describes a well-mixed outer core. Two array methods are used to detect lower <span class="hlt">mantle</span> heterogeneities, in particular Ultra-Low Velocity Zones (ULVZs). The ETF method and beam forming are used to isolate a weak P-wave that diffracts along the CMB. While neither the ETF method nor beam forming could adequately image the low-amplitude phase, beam forms of two events indicate precursors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19950041672&hterms=Manga&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DManga','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19950041672&hterms=Manga&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DManga"><span>The interaction of plume heads with compositional discontinuities in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Manga, Michael; Stone, Howard A.; O'Connell, Richard J.</p> <p>1993-01-01</p> <p>The effects of compositional discontinuities of density and viscosity in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> on the ascent of <span class="hlt">mantle</span> plume heads is studied using a boundary integral numerical technique. Three specific problems are considered: (1) a plume head rising away from a deformable interface, (2) a plume head passing through an interface, and (3) a plume head approaching the surface of the <span class="hlt">Earth</span>. For the case of a plume attached to a free-surface, the calculated time-dependent plume shapesare compared with experimental results. Two principle modes of plume head deformation are observed: plume head elingation or the formation of a cavity inside the plume head. The inferred structure of <span class="hlt">mantle</span> plumes, namely, a large plume head with a long tail, is characteristic of plumes attached to their source region, and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high- to low-viscosity region. As a rising plume head approaches the upper <span class="hlt">mantle</span>, most of the lower <span class="hlt">mantle</span> will quickly drain from the gap between the plume head and the upper <span class="hlt">mantle</span> if the plume head enters the upper <span class="hlt">mantle</span>. If the plume head moves from a high- to low-viscosity region, the plume head becomes significantly elongated and, for the viscosity contrasts thought to exist in the <span class="hlt">Earth</span>, could extend from the 670 km discontinuity to the surface. Plume heads that are extended owing to a viscosity decrease in the upper <span class="hlt">mantle</span> have a cylindrical geometry. The dynamic surface topography induced by plume heads is bell-shaped when the top of the plume head is at depths greater than about 0.1 plume head radii. As the plume head approaches the surface and spreads, the dynamic topography becomes plateau-shaped. The largest stresses are produced in the <span class="hlt">early</span> stages of plume spreading when the plume head is still nearly spherical, and the surface expression of these stresses is likely to be dominated by radial extension. As the plume spreads, compressional</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI43B0353F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI43B0353F"><span>Quantifying apparent anisotropy in a chemically heterogeneous <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Faccenda, M.; Ferreira, A. M.; Lithgow-Bertelloni, C. R.; Stixrude, L. P.; Pennacchioni, G.</p> <p>2017-12-01</p> <p>The interpretation of seismic observations of anisotropy is not straightforward. For example, it is well established that a finely layered, purely isotropic medium is equivalent at large scale to a homogeneous anisotropic medium (Backus, 1962) and there is seismological evidence for fine layered media, such as quasi-laminated structures constrained from high-frequency scattered waves (e.g., Furumura and Kennett, 2005; Kennett and Furumura, 2008). Thus, when imaging fine layering with seismic wave data with wavelength larger than the layer's thickness may result in artificial (also called apparent) anisotropy. Recent studies identified families of stable fine scale models that are equivalent to long-wavelength, vertically transversely isotropic (VTI) models (Fichtner et al., 2013; Wang et al., 2013; Bodin et al., 2015), and efforts to consider more general media are currently under way (e.g., Capdeville et al., 2010a,b). However, it is not clear whether the equivalent fine scale models are compatible with the properties of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> materials. In this contribution, we quantify apparent anisotropy arising from fine layering by considering a range of realistic <span class="hlt">Earth</span>'s compositions both at grain and rock scale. We show that significant apparent anisotropy can be formed in ideal conditions only in very narrow regions, while in most of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> apparent anisotropy will hardly be detectable. ReferencesBackus, G.E., 1962. J. Geophys. Res. 67, 4427-4440. Bodin, T., Capdeville, Y., Romanowicz, B. & Montagner, J.-P., 2015. In The <span class="hlt">Earth</span>'s Heterogeneous <span class="hlt">Mantle</span>, pp. 105-144, eds Khan, A. & Deschamps, F., Springer. Capdeville, Y., Guillot, L., Marigo, J.J., 2010a. Geophys. J. Int. 182, 903-922. Capdeville, Y., Guillot, L., Marigo, J.J., 2010b. Geophys. J. Int. 181, 897-910. Fichtner, A., B. Kennett, and J. Trampert, 2013. Phys. <span class="hlt">Earth</span> Planet. Inter., 219, 11-20. Furumura, T., Kennett, B.L.N., 2005. J. Geophys. Res. 110, 10.129/2004JB003486. Kennett, B.L.N., Furumura</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24695310','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24695310"><span>Highly siderophile elements in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> as a clock for the Moon-forming impact.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jacobson, Seth A; Morbidelli, Alessandro; Raymond, Sean N; O'Brien, David P; Walsh, Kevin J; Rubie, David C</p> <p>2014-04-03</p> <p>According to the generally accepted scenario, the last giant impact on <span class="hlt">Earth</span> formed the Moon and initiated the final phase of core formation by melting <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. A key goal of geochemistry is to date this event, but different ages have been proposed. Some argue for an <span class="hlt">early</span> Moon-forming event, approximately 30 million years (Myr) after the condensation of the first solids in the Solar System, whereas others claim a date later than 50 Myr (and possibly as late as around 100 Myr) after condensation. Here we show that a Moon-forming event at 40 Myr after condensation, or earlier, is ruled out at a 99.9 per cent confidence level. We use a large number of N-body simulations to demonstrate a relationship between the time of the last giant impact on an <span class="hlt">Earth</span>-like planet and the amount of mass subsequently added during the era known as Late Accretion. As the last giant impact is delayed, the late-accreted mass decreases in a predictable fashion. This relationship exists within both the classical scenario and the Grand Tack scenario of terrestrial planet formation, and holds across a wide range of disk conditions. The concentration of highly siderophile elements (HSEs) in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> constrains the mass of chondritic material added to <span class="hlt">Earth</span> during Late Accretion. Using HSE abundance measurements, we determine a Moon-formation age of 95 ± 32 Myr after condensation. The possibility exists that some late projectiles were differentiated and left an incomplete HSE record in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Even in this case, various isotopic constraints strongly suggest that the late-accreted mass did not exceed 1 per cent of <span class="hlt">Earth</span>'s mass, and so the HSE clock still robustly limits the timing of the Moon-forming event to significantly later than 40 Myr after condensation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1664683','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1664683"><span>Physical conditions on the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lunine, Jonathan I</p> <p>2006-01-01</p> <p>The formation of the <span class="hlt">Earth</span> as a planet was a large stochastic process in which the rapid assembly of asteroidal-to-Mars-sized bodies was followed by a more extended period of growth through collisions of these objects, facilitated by the gravitational perturbations associated with Jupiter. The <span class="hlt">Earth</span>'s inventory of water and organic molecules may have come from diverse sources, not more than 10% roughly from comets, the rest from asteroidal precursors to chondritic bodies and possibly objects near <span class="hlt">Earth</span>'s orbit for which no representative class of meteorites exists today in laboratory collections. The final assembly of the <span class="hlt">Earth</span> included a catastrophic impact with a Mars-sized body, ejecting <span class="hlt">mantle</span> and crustal material to form the Moon, and also devolatilizing part of the <span class="hlt">Earth</span>. A magma ocean and steam atmosphere (possibly with silica vapour) existed briefly in this period, but terrestrial surface waters were below the critical point within 100 million years after <span class="hlt">Earth</span>'s formation, and liquid water existed continuously on the surface within a few hundred million years. Organic material delivered by comets and asteroids would have survived, in part, this violent <span class="hlt">early</span> period, but frequent impacts of remaining debris probably prevented the continuous habitability of the <span class="hlt">Earth</span> for one to several hundred million years. Planetary analogues to or records of this <span class="hlt">early</span> time when life began include Io (heat flow), Titan (organic chemistry) and Venus (remnant <span class="hlt">early</span> granites). PMID:17008213</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17008213','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17008213"><span>Physical conditions on the <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lunine, Jonathan I</p> <p>2006-10-29</p> <p>The formation of the <span class="hlt">Earth</span> as a planet was a large stochastic process in which the rapid assembly of asteroidal-to-Mars-sized bodies was followed by a more extended period of growth through collisions of these objects, facilitated by the gravitational perturbations associated with Jupiter. The <span class="hlt">Earth</span>'s inventory of water and organic molecules may have come from diverse sources, not more than 10% roughly from comets, the rest from asteroidal precursors to chondritic bodies and possibly objects near <span class="hlt">Earth</span>'s orbit for which no representative class of meteorites exists today in laboratory collections. The final assembly of the <span class="hlt">Earth</span> included a catastrophic impact with a Mars-sized body, ejecting <span class="hlt">mantle</span> and crustal material to form the Moon, and also devolatilizing part of the <span class="hlt">Earth</span>. A magma ocean and steam atmosphere (possibly with silica vapour) existed briefly in this period, but terrestrial surface waters were below the critical point within 100 million years after <span class="hlt">Earth</span>'s formation, and liquid water existed continuously on the surface within a few hundred million years. Organic material delivered by comets and asteroids would have survived, in part, this violent <span class="hlt">early</span> period, but frequent impacts of remaining debris probably prevented the continuous habitability of the <span class="hlt">Earth</span> for one to several hundred million years. Planetary analogues to or records of this <span class="hlt">early</span> time when life began include Io (heat flow), Titan (organic chemistry) and Venus (remnant <span class="hlt">early</span> granites).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890054376&hterms=convection+currents&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dconvection%2Bcurrents','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890054376&hterms=convection+currents&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dconvection%2Bcurrents"><span>Three-dimensional spherical models of convection in the <span class="hlt">earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bercovici, Dave; Schubert, Gerald; Glatzmaier, Gary A.</p> <p>1989-01-01</p> <p>Three-dimensional spherical models of <span class="hlt">mantle</span> convection in the <span class="hlt">earth</span> reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of <span class="hlt">mantle</span> circulation. Thus subduction zones and descending sheetlike slabs in the <span class="hlt">mantle</span> are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding <span class="hlt">mantle</span>. Cylindrical <span class="hlt">mantle</span> plumes that cause hot spots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale <span class="hlt">mantle</span> circulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150023256','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150023256"><span>Evolution of the Oxidation State of the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span>: Challenges of High Pressure Quenching</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Danielson, L. R.; Righter, K.; Keller, L.; Christoffersen, R.; Rahman, Z.</p> <p>2015-01-01</p> <p>The oxidation state of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3+ at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Experiments of more mafic compositions and at higher pressures commonly form a polyphase quench intergrowth composed primarily of pyroxenes, with interstitial glass which hosts nearly all of the more volatile minor elements. In our previous experiments on shergottite compositions, variable fO2, T, and P is less than 4 GPa, Fe3+/TotFe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3+/TotFe decreased as well, but it's unclear from previous modelling whether the deeper <span class="hlt">mantle</span> could retain significant Fe3+. Our current experiments expand our pressure range deeper into the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and focus on compositions and conditions relevant to the <span class="hlt">early</span> <span class="hlt">Earth</span>. Experiments with Knippa basalt as the starting composition were conducted at 1-8 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products from 7-8 GPa quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal Fe3+/2+. A number of different approaches have been employed to produce glassy samples that can be measured by EELS and XANES. A more intermediate andesite was used in one experiment, and decompression during quenching was attempted after, but both resulted in a finer grained polyphase texture. Experiments are currently underway to test different capsule materials may affect quench texture. A preliminary experiment using liquid nitrogen to greatly enhance the rate of cooling of the assembly has also been attempted and this technique will be</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1980PEPI...23..314A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1980PEPI...23..314A"><span>The thermodynamic properties of the <span class="hlt">earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anderson, Orson L.; Sumino, Yoshio</p> <p>1980-12-01</p> <p>The thermodynamic properties of the lower <span class="hlt">mantle</span> are determined from the seismic profile, where the primary thermodynamic variables are the bulk modulus K and density ρ. It is shown that the Bullen law ( K ∝ P) holds in the lower <span class="hlt">mantle</span> with a high correlation coefficient for the seismic parametric <span class="hlt">Earth</span> model (PEM). Using this law produces no ambiguity or trade-off between ρ0 and K0, since both K0 and K' 0 are exactly determined by applying a linear K- ρ relationship to the data. On the other hand, extrapolating the velocity data to zero pressure using a Birch-Murnaghan equation of state (EOS) results in an ambiguous answer because there are three unknown adjustable parameters ( ρ0, K0, K' 0) in the EOS. From the PEM data, K = 232.4 + 3.19 P (GPa). The PEM yields a hot uncompressed density of 3.999 ± 0.0026 g cm -3 for material decompressed from all parts of the lower <span class="hlt">mantle</span>. Even if the hot uncompressed density were uniform for all depths in the lower <span class="hlt">mantle</span>, the cold uncompressed <span class="hlt">mantle</span> would be inhomogeneous because the decompression given by the Bullen law crosses isotherms; for example, the temperature is different at different depths. To calculate the density distribution correctly, an isothermal EOS must be used along an isotherm, and temperature corrections must be placed in the thermal pressure PTH. The thermodynamic parameters of the lower <span class="hlt">mantle</span> are found by iteration. Values of the three uncompressed anharmonic parameters are first arbitrarily selected: α0 (hot), the coefficient of thermal expansion; γ0, the Grüneisen parameter; and δ, the second Grüneisen parameter. Using γ0 and the measured ρ0 (hot) and K0 (hot), the values of θ0 (Debye temperature) and q = dln γ/dln ρ are found from the measured seismic velocities. Then from ( αKT) 0 and q the thermal pressure PTH at all high temperatures is found. Correlating PTH against T to the geotherm for the lower <span class="hlt">mantle</span>, PTH is found at all depths Z. The isothermal pressure, along the 0 K</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMMR23A2663F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMMR23A2663F"><span>Abnormal Elasticity of Single-Crystal Magnesiosiderite across the Spin Transition in <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fu, S.; Yang, J.; Lin, J. F.</p> <p>2016-12-01</p> <p>Carbon can be transported into deep <span class="hlt">Earth</span>'s interior via subduction of carbonated oceanic crust, hosted as Mg-Fe bearing carbonates. The existence of stable carbonate can significantly affect our understanding on geochemical and geophysical properties of the planet. <span class="hlt">Early</span> studies have shown that iron spin-pairing transition could occur in the iron-enriched carbonates, generally called magnesiosiderite, under lower <span class="hlt">mantle</span> conditions. The pressure-induced spin state change is accompanied by a sudden volume collaps. However, the effects of the spin-pairing transition on single-crystal elasticity of magnesiosiderite under high pressure conditions are still unclear. Understanding the elasticity of single-crystal magnesiosiderite at relevant lower <span class="hlt">mantle</span> conditions plays an important role in better understanding the seismic signatures in the carbon-enriched region, and to constrain carbon storage and recycling in the <span class="hlt">mantle</span>. In order to solve all individual elastic constants (C11, C22, C33, C44, C55, C66, C12, C23, and C13) of magnesiosiderite at high pressures via Christoffel's equations, we employed Brillouin Light Scattering (BLS) to measure shear wave (Vs) and compressional wave velocities (Vp) as a function of the azimuthal angle under lower <span class="hlt">mantle</span> pressures, accompanied by Impulsive Stimulate Light Scattering (ISS) to measure the Vp when pressures are too high to measure it by BLS. A general thermoelastic modelling was developed to fit the elastic softening within the spin transition. We will further discuss the effects of pressures, as well as iron spin states, on the single-crystal elasticity and seismic parameters (Vp and Vs anisotropy AVp, AVs, etc) at lower <span class="hlt">mantle</span> conditions. These results could provide clues in explaining regional seismic heterogeneities in deep <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.S43B1008M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.S43B1008M"><span>Seismological Signature of Chemical Differentiation of <span class="hlt">Earth</span>'s Upper <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matsukage, K. N.; Nishihara, Y.; Karato, S.</p> <p>2004-12-01</p> <p>Chemical differentiation from a primitive rock (such as pyrolite) to harzburgite due to partial melting and melt extraction is one of the most important mechanisms that causes the chemical heterogeneity in <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>. In this study, we investigate the seismic signature of chemical differentiation that helps mapping chemical heterogeneity in the upper <span class="hlt">mantle</span>. The relation between chemical differentiation and its seismological signature is not straightforward because a large number of unknown parameters are involved although the seismological observations provide only a few parameters (e.g., VP, VS, QP). Therefore it is critical to identify a small number of parameters by which the gross trend of chemical evolution can be described. The variation in major element composition in natural samples reflect complicated processes that include not only partial melting but also other complex processes (e.g., metasomatism, influx melting). We investigate the seismic velocities of hypothetical but well-defined simple chemical differentiation processes (e.g., partial melting of various pressure conditions, addition of Si-rich melt or fluid), which cover the chemical variation of the natural <span class="hlt">mantle</span> peridotites with various tectonic settings (mid ocean ridge, island arc and continent). The seismic velocities of the peridotites were calculated to 13 GPa and 1730 K. We obtained two major conclusions. First is that the variations of seismic velocities of upper <span class="hlt">mantle</span> peridotites can be interpreted in terms of a few distinct parameters. For one class of peridotites which is formed by simple partial melting (e.g. mid-ocean ridges peridotites), seismic velocities can be described in terms of one parameter, namely Mg# (=Mg/(Mg+Fe) atomic ratio). In contrast, some of the peridotites in the continental (cratonic) environment with high silica content and high Mg# need at least two parameters (such as Mg# and Opx# (the volume fraction of orthopyroxene)) are needed to characterize</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V23E..05M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V23E..05M"><span><span class="hlt">Early</span> and long-term <span class="hlt">mantle</span> processing rates derived from xenon isotopes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukhopadhyay, S.; Parai, R.; Tucker, J.; Middleton, J. L.; Langmuir, C. H.</p> <p>2015-12-01</p> <p>Noble gases, particularly xenon (Xe), in <span class="hlt">mantle</span>-derived basalts provide a rich portrait of <span class="hlt">mantle</span> degassing and surface-interior volatile exchange. The combination of extinct and extant radioactive species in the I-Pu-U-Xe systems shed light on the degassing history of the <span class="hlt">early</span> <span class="hlt">Earth</span> throughout accretion, as well as the long-term degassing of the <span class="hlt">Earth</span>'s interior in association with plate tectonics. The ubiquitous presence of shallow-level air contamination, however, frequently obscures the <span class="hlt">mantle</span> Xe signal. In a majority of the samples, shallow air contamination dominates the Xe budget. For example, in the gas-rich popping rock 2ΠD43, 129Xe/130Xe ratios reach 7.7±0.23 in individual step-crushes, but the bulk composition of the sample is close to air (129Xe/130Xe of 6.7). Thus, the extent of variability in <span class="hlt">mantle</span> source Xe composition is not well-constrained. Here, we present new MORB Xe data and explore constraints placed on <span class="hlt">mantle</span> processing rates by the Xe data. Ten step-crushes were obtained on a depleted popping glass that was sealed in ultrapure N2 after dredge retrieval from between the Kane-Atlantis Fracture Zone of the Mid Atlantic Ridge in May 2012. 9 steps yielded 129Xe/130Xe of 7.50-7.67 and one yielded 7.3. The bulk 129Xe/130Xe of the sample is 7.6, nearly identical to the estimated <span class="hlt">mantle</span> source value of 7.7 for the sample. Hence, the sample is virtually free of shallow-level air contamination. Because sealing the sample in N2upon dredge retrieval largely eliminated air contamination, for many samples, contamination must be added after sample retrieval from the ocean bottom. Our new high-precision Xe isotopic measurements in upper <span class="hlt">mantle</span>-derived samples provide improved constraints on the Xe isotopic composition of the <span class="hlt">mantle</span> source. We developed a forward model of <span class="hlt">mantle</span> volatile evolution to identify solutions that satisfy our Xe isotopic data. We find that accretion timescales of ~10±5 Myr are consistent with I-Pu-Xe constraints, and the last</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI14A..08R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI14A..08R"><span>Using the heterogeneity distribution in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> to study structure and flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rost, S.; Frost, D. A.; Bentham, H. L.</p> <p>2016-12-01</p> <p>The <span class="hlt">Earth</span>'s interior contains heterogeneities on many scale-lengths ranging from continent sized structures such as Large-Low Shear Velocity Provinces (LLSVPs) to grain-sized anomalies resolved using geochemistry. Sources of heterogeneity in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> are for example the recycling of crustal material through the subduction process as well as partial melting and compositional variations. The subduction and recycling of oceanic crust throughout <span class="hlt">Earth</span>'s history leads to strong heterogeneities in the <span class="hlt">mantle</span> that can be detected using seismology and geochemistry. Current models of <span class="hlt">mantle</span> convection show that the subducted crustal material can be long-lived and is transported passively throughout the <span class="hlt">mantle</span> by convective flows. Settling and entrainment is dependent on the density structure of the heterogeneity. Imaging heterogeneities throughout the <span class="hlt">mantle</span> therefore allows imaging <span class="hlt">mantle</span> flow especially in areas of inhibited flow due to e.g. viscosity changes or changes in composition or dynamics. The short-period seismic wavefield is dominated by scattered seismic energy partly originating from scattering at small-scale heterogeneities in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Using specific raypath configurations we are able to sample different depths throughout <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> for the existence and properties of heterogeneities. These scattering probes show distinct variations in energy content with frequency indicating dominant heterogeneity length-scales in the <span class="hlt">mantle</span>. We detect changes in heterogeneity structure both in lateral and radial directions. The radial heterogeneity structure requires changes in <span class="hlt">mantle</span> structure at depths of 1000 km and 1800 to 2000 km that could indicate a change in viscosity structure in the mid <span class="hlt">mantle</span> partly changing the flow of subducted crustal material into the deep <span class="hlt">mantle</span>. Lateral changes in heterogeneity structure close to the core <span class="hlt">mantle</span> boundary indicate lateral transport inhibited by the compositional anomalies of the LLSVPs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005APS..MARL11002B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005APS..MARL11002B"><span>Elasticity of Deep-<span class="hlt">Earth</span> Materials at High P and T: Implication for <span class="hlt">Earths</span> Lower <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bass, Jay; Sinogeikin, S. V.; Mattern, Estelle; Jackson, J. M.; Matas, J.; Wang, J.; Ricard, Y.</p> <p>2005-03-01</p> <p>Brillouin spectroscopy allows measurements of sound velocities and elasticity on phases of geophysical interest at high Pressures and Temperatures. This technique was used to measure the properties of numerous important phases of <span class="hlt">Earths</span> deep interior. Emphasis is now on measurements at elevated P-T conditions, and measurements on dense polycrystals. Measurements to 60 GPa were made using diamond anvil cells. High temperature is achieved by electrical resistance and laser heating. Excellent results are obtained for polycrystalline samples of dense oxides such as silicate spinels, and (Mg,Al)(Si,Al)O3 --perovskites. A wide range of materials can now be characterized. These and other results were used to infer <span class="hlt">Earths</span> average lower <span class="hlt">mantle</span> composition and thermal structure by comparing mineral properties at lower <span class="hlt">mantle</span> P-T conditions to global <span class="hlt">Earth</span> models. A formal inversion procedure was used. Inversions of density and bulk sound velocity do not provide robust compositional and thermal models. Including shear properties in the inversions is important to obtain unique solutions. We discuss the range of models consistent with present lab results, and data needed to further refine lower <span class="hlt">mantle</span> models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120009846','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120009846"><span>Fortnightly Ocean Tides, <span class="hlt">Earth</span> Rotation, and <span class="hlt">Mantle</span> Anelasticity</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ray, Richard; Egbert, Gary</p> <p>2012-01-01</p> <p>The fortnightly Mf ocean tide is the largest of the long-period tides (periods between 1 week and 18.6 years), but Mf is still very small, generally 2 cm or less. All long-period tides are thought to be near equilibrium with the astronomical tidal potential, with an almost pure zonal structure. However, several lines of evidence point to Mf having a significant dynamic response to forcing. We use a combination of numerical modeling, satellite altimetry, and observations of polar motion to determine the Mf ocean tide and to place constraints on certain global properties, such as angular momentum. Polar motion provides the only constraints on Mf tidal currents. With a model of the Mf ocean tide in hand, we use it to remove the effects of the ocean from estimates of fortnightly variations in length-of-day. The latter is dominated by the <span class="hlt">earth</span>'s body tide, but a small residual allows us to place new constraints on the anelasticity of the <span class="hlt">earth</span>'s <span class="hlt">mantle</span>. The result gives the first experimental confirmation of theoretical predictions made by Wahr and Bergen in 1986.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMPP21D..02H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMPP21D..02H"><span>Continental Growth and <span class="hlt">Mantle</span> Hydration as <span class="hlt">Earth</span> System Feedback Cycles and possible Effects of the Biosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Höning, D.; Spohn, T.</p> <p>2016-12-01</p> <p>The evolution of <span class="hlt">Earth</span> is charcterized by intertwined feedback cycles. We focus on two feedback cycles that include the <span class="hlt">mantle</span> water budget and the continental crust and study possible effects of the <span class="hlt">Earth</span>'s biosphere. The first feedback loop includes cycling of water into the <span class="hlt">mantle</span> at subduction zones and outgassing at volcanic chains and mid-ocean ridges. Water will reduce the viscosity of <span class="hlt">mantle</span> rock, and therefore the speed of <span class="hlt">mantle</span> convection and plate subduction will increase with the <span class="hlt">mantle</span> water concentration, eventually enhancing the rates of <span class="hlt">mantle</span> water regassing and outgassing. A second feedback loop includes the production and erosion of continental crust. Continents grow by volcanism above subduction zones, whose total length is determined by the total area of the continents. Furthermore, the erosion rate of the continents is proportional to the total surface area of continental crust. The rate of sediment subduction affects the rate of transport of water to the <span class="hlt">mantle</span> and the production rate of new continental crust. We present a model that includes both cycles and show how the system develops stable and unstable fixed points in a plane defined by <span class="hlt">mantle</span> water concentration and surface are of continents. The stable points represent either an <span class="hlt">Earth</span> mostly covered by continents and a wet <span class="hlt">mantle</span> or an <span class="hlt">Earth</span> mostly covered by oceans with a dry <span class="hlt">mantle</span>. The presently observed <span class="hlt">Earth</span> is inbetween these extreme states but the state is intrinsically unstable. We couple the feedback model to a parameterized thermal evolution model. We show how <span class="hlt">Earth</span> evolved towards its present unstable state. We argue that other feedback cycles such as the carbonate silicate cycle may act to stabilize the present state, however. By enhancing continental weathering and erosion, and eventually the sediment transport into subduction zones, the biosphere impacts both feedback cycles and might play a crucial role in regulating <span class="hlt">Earth</span>'s system and keep continental crust coverage and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMDI43B..05R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMDI43B..05R"><span>Memories of <span class="hlt">Earth</span> Formation in the Modern <span class="hlt">Mantle</span>: W Isotopic Composition of Flood Basalt Lavas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Horan, M. F.; Mukhopadhyay, S.; Francis, D.; Jackson, M. G.</p> <p>2015-12-01</p> <p>Four and a half billion years of geologic activity has overprinted much of the direct evidence for processes involved in <span class="hlt">Earth</span>'s formation and its initial chemical differentiation. Xenon isotopic ratios [1] and 3He/22Ne ratios [2] suggest that heterogeneities formed during <span class="hlt">Earth</span>'s accretion have been preserved to the present time. New opportunities to learn about <span class="hlt">early</span> <span class="hlt">Earth</span> history have opened up with the development of analytical techniques that allow high precision analysis of short-lived isotopic systems. The Hf-W system (t½ = 8.9 Ma) is particularly valuable for studying events that occurred during the first ~50 Ma of Solar System history. Here we report new data for ~ 60 Ma Baffin Bay and ~ 120 Ma Ontong Java Plateau lava samples. Both are large igneous provinces that may have sampled a primitive, less degassed deep <span class="hlt">mantle</span> reservoir that has remained isolated since shortly after <span class="hlt">Earth</span> formation [3,4]. Three samples analyzed have 182W/184W ratios that are 10 to 48 ppm higher than our terrestrial standard. These excesses in 182W are the highest ever measured in terrestrial rocks, and may reflect 182W ingrowth in an <span class="hlt">early</span>-formed high Hf/W <span class="hlt">mantle</span> domain that was produced by magma ocean differentiation [5]. Long and short-lived Sm-Nd systematics in these samples, however, are inconsistent with this hypothesis. The 182W excessses could rather reflect the derivation of these lavas from a <span class="hlt">mantle</span> reservoir that was isolated from late accretionary additions [6]. The chondritic initial Os isotopic compositions and highly siderophile element abundances of these samples, however, are inconsistent with this interpretation. Tungsten concentrations for the Baffin Bay and Ontong Java Plateau samples range from 23 ppb to 62 ppb, and are negatively correlated with their 182W/184W ratios. We propose that the source reservoirs for these flood basalts likely formed through Hf/W fractionation caused by core-forming events occuring over a protacted time interval during <span class="hlt">Earth</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFM.T12E..09K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFM.T12E..09K"><span>Electrochemistry and the <span class="hlt">Earth</span>'s Core-<span class="hlt">Mantle</span> Boundary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kavner, A.; Walker, D.</p> <p>2001-12-01</p> <p>The <span class="hlt">Earth</span>'s core-<span class="hlt">mantle</span> boundary consists of a highly heterogeneous metal-oxide interface subjected to high temperatures, pressures, and additionally, to the presence of a temporally- and spatially-varying electrical field generated by the outer core dynamo. An understanding of the core-<span class="hlt">mantle</span> boundary should include the nature of its electrical behavior, its electrically induced chemical partitioning, and any resultant core-<span class="hlt">mantle</span> dynamic coupling. To this end, we have developed a method to measure the electrical behavior of metal-silicate interfaces at high pressures (15-25 kbar) and temperatures (1300-1400° C) in a piston-cylinder apparatus. Platinum electrical leads are placed at each end of the sample, which consists of a layer of iron and/or iron alloy below a layer of silicate. The sample is enclosed in a sintered MgO chamber which is then surrounded by a metal Faraday cage, allowing the sample to be electrically insulated from the AC field of the graphite heater. The platinum electric leads are threaded through the thermocouple tube and connected with an HP4284A LCR meter to measure AC impedance, or to a DC power supply to apply a field such that either the silicate or the metal end is the anode (+). AC impedance measurements performed in-situ on samples consisting of Fe, Fe-Ni-S, and a basalt-olivine mixture in series show that conductivity is strongly dependent on the electrical polarization of the silicate relative to the sulfide. When the silicate is positively charged (silicate is the anode) and when there is no applied charge, the probe-to-probe resistance displays semiconductor behavior, with conductivity ( ~10-2 S/cm) strongly thermally activated. However, when the electrical polarity is reversed, and the sulfide is the anode, the electrical conductivity between the two probes increases dramatically (to ~1 S/cm) over timescales of minutes. If the polarity is removed or reversed, the conductivity returns to its original values over similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMDI43C..08M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMDI43C..08M"><span>Visualizing <span class="hlt">Earth</span>'s Core-<span class="hlt">Mantle</span> Interactions using Nanoscale X-ray Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mao, W. L.; Wang, J.; Yang, W.; Hayter, J.; Pianetta, P.; Zhang, L.; Fei, Y.; Mao, H.; Hustoft, J. W.; Kohlstedt, D. L.</p> <p>2010-12-01</p> <p><span class="hlt">Early</span>-stage, core-<span class="hlt">mantle</span> differentiation and core formation represent a pivotal geological event which defined the major geochemical signatures. However current hypotheses of the potential mechanism for core-<span class="hlt">mantle</span> separation and interaction need more experimental input which has been awaiting technological breakthroughs. Nanoscale x-ray computed tomography (nanoXCT) within a laser-heated diamond anvil cell has exciting potential as a powerful 3D petrographic probe for non-destructive, nanoscale (<40nm) resolution of multiple minerals and amorphous phases (including melts) which are synthesized under the high pressure-temperature conditions found deep within the <span class="hlt">Earth</span> and planetary interiors. Results from high pressure-temperature experiments which illustrate the potential for this technique will be presented. By extending measurements of the texture, shape, porosity, tortuosity, dihedral angle, and other characteristics of molten Fe-rich alloys in relation to silicates and oxides, along with the fracture systems of rocks under deformation by high pressure-temperature conditions, potential mechanisms of core formation can be tested. NanoXCT can also be used to investigate grain shape, intergrowth, orientation, and foliation -- as well as mineral chemistry and crystallography at core-<span class="hlt">mantle</span> boundary conditions -- to understand whether shape-preferred orientation is a primary source of the observed seismic anisotropy in Earth’s D” layer and to determine the textures and shapes of the melt pockets and channels which would form putative partial melt which may exist in ultralow velocity zones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014hwat.confP..24M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014hwat.confP..24M"><span><span class="hlt">Early</span> <span class="hlt">Earth(s</span>) Across Time and Space</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mojzsis, S.</p> <p>2014-04-01</p> <p>The geochemical and cosmochemical record of our solar system is the baseline for exploring the question: "when could life appear on a world similar to our own?" Data arising from direct analysis of the oldest terrestrial rocks and minerals from the first 500 Myr of <span class="hlt">Earth</span> history - termed the Hadean Eon - inform us about the timing for the establishment of a habitable silicate world. Liquid water is the key medium for life. The origin of water, and its interaction with the crust as revealed in the geologic record, guides our exploration for a cosmochemically <span class="hlt">Earth</span>-like planets. From the time of primary planetary accretion to the start of the continuous rock record on <span class="hlt">Earth</span> at ca. 3850 million years ago, our planet experienced a waning bolide flux that partially or entirely wiped out surface rocks, vaporized oceans, and created transient serpentinizing atmospheres. Arguably, "<span class="hlt">Early</span> <span class="hlt">Earths</span>" across the galaxy may start off as ice planets due to feeble insolation from their young stars, occasionally punctuated by steam atmospheres generated by cataclysmic impacts. Alternatively, <span class="hlt">early</span> global environments conducive to life spanned from a benign surface zone to deep into crustal rocks and sediments. In some scenarios, nascent biospheres benefit from the exogenous delivery of essential bio-elements via leftovers of accretion, and the subsequent establishment of planetary-scale hydrothermal systems. If what is now known about the <span class="hlt">early</span> dynamical regime of the <span class="hlt">Earth</span> serves as any measure of the potential habitability of worlds across space and time, several key boundary conditions emerge. These are: (i) availability and long-term stability of liquid water; (ii) presence of energy resources; (iii) accessibility of organic raw materials; (iv) adequate inventory of radioisotopes to drive internal heating; (v) gross compositional parameters such as <span class="hlt">mantle</span>/core mass ratio, and (vi) P-T conditions at or near the surface suitable for sustaining biological activity. Life could</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.195..142K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.195..142K"><span>Open system models of isotopic evolution in <span class="hlt">Earth</span>'s silicate reservoirs: Implications for crustal growth and <span class="hlt">mantle</span> heterogeneity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kumari, Seema; Paul, Debajyoti; Stracke, Andreas</p> <p>2016-12-01</p> <p>An open system evolutionary model of the <span class="hlt">Earth</span>, comprising continental crust (CC), upper and lower <span class="hlt">mantle</span> (UM, LM), and an additional isolated reservoir (IR) has been developed to study the isotopic evolution of the silicate <span class="hlt">Earth</span>. The model is solved numerically at 1 Myr time steps over 4.55 Gyr of <span class="hlt">Earth</span> history to reproduce both the present-day concentrations and isotope ratios of key radioactive decay systems (Rb-Sr, Sm-Nd, and U-Th-Pb) in these terrestrial reservoirs. Various crustal growth scenarios - continuous versus episodic and <span class="hlt">early</span> versus late crustal growth - and their effect on the evolution of Sr-Nd-Pb isotope systematics in the silicate reservoirs have been evaluated. Modeling results where the present-day UM is ∼60% of the total <span class="hlt">mantle</span> mass and a lower <span class="hlt">mantle</span> that is non-primitive reproduce the estimated geochemical composition and isotope ratios in <span class="hlt">Earth</span>'s silicate reservoirs. The isotopic evolution of the silicate <span class="hlt">Earth</span> is strongly affected by the mode of crustal growth; only an exponential crustal growth pattern with crustal growth since the <span class="hlt">early</span> Archean satisfactorily explains the chemical and isotopic evolution of the crust-<span class="hlt">mantle</span> system and accounts for the so-called Pb paradoxes. Assuming that the OIB source is located in the deeper <span class="hlt">mantle</span>, our model could, however, not reproduce its target ɛNd of +4.6 for the UM, which has been estimated from the average isotope ratios of 32 individual ocean island localities. Hence, either <span class="hlt">mantle</span> plumes sample the LM in a non-representative way, or the simplified model set-up does not capture the full complexity of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> (Nd isotope) evolution. Compared to the results obtained for a 4.55 Ga <span class="hlt">Earth</span>, a model assuming a protracted U-Pb evolution of silicate <span class="hlt">Earth</span> by ca. 100 Myr reproduces a slightly better fit for the Pb isotope ratios in <span class="hlt">Earth</span>'s silicate reservoirs. One notable feature of successful models is the <span class="hlt">early</span> depletion of incompatible elements (as well as rapid decrease in Th/U) in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870012888','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870012888"><span><span class="hlt">Mantle</span> convection and the state of the <span class="hlt">Earth</span>'s interior</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hager, Bradford H.</p> <p>1987-01-01</p> <p>During 1983 to 1986 emphasis in the study of <span class="hlt">mantle</span> convection shifted away from fluid mechanical analysis of simple systems with uniform material properties and simple geometries, toward analysis of the effects of more complicated, presumably more realistic models. The important processes related to <span class="hlt">mantle</span> convection are considered. The developments in seismology are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V51B2521P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V51B2521P"><span>The Xenon record of <span class="hlt">Earth</span>'s <span class="hlt">early</span> differentiaiton</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peto, M. K.; Mukhopadhyay, S.; Kelley, K. A.</p> <p>2011-12-01</p> <p>Xenon isotopes in <span class="hlt">mantle</span> derived rocks provide information on the <span class="hlt">early</span> differentiation of the silicate <span class="hlt">mantle</span> of our planet. {131,132 134,136}Xe isotopes are produced by the spontaneous fission of two different elements: the now extinct radionuclide 244Pu, and the long-lived 238U. These two parent nuclides, however, yield rather different proportion of fissiogenic Xenon isotopes. Hence, the proportion of Pu- to U-derived fission xenon is indicative of the degree and rate of outgassing of a <span class="hlt">mantle</span> reservoir. Recent data obtained from Iceland in our lab confirm that the Xenon isotopic composition of the plume source(s) is characterized by lower 136Xe/130Xe ratios than the MORB source and the Iceland plume is more enriched in the Pu-derived Xenon component. These features are interpreted as reflecting different degrees of outgassing and appear not to be the result of preferential recycling of Xenon to the deep <span class="hlt">mantle</span>. To further investigate how representative the Icelandic measurements might be of other <span class="hlt">mantle</span> plumes, we measured noble gases (He, Ne, Ar, Xe) in gas-rich basalt glasses from the Rochambeau Ridge (RR) in the Northern Lau Basin. Recent work suggests the presence of a "Samoan-like" OIB source in the northern Lau Basin and our measurements were performed on samples with plume-like 3He/4He ratios (15-28 RA) [1]. The Xenon isotopic measurements indicate that the maximum measured 136Xe/130Xe ratios in the Rochambeau samples are similar to Iceland. In particular, for one of the gas rich samples we were able to obtain 77 different isotopic measurements through step-crushing. Preliminary investigation of this sample suggests higher Pu- to U-derived fission Xenon than in MORBs. To quantitatively evaluate the degree and rate of outgassing of the plume and MORB reservoirs, particularly during the first few hundred million years of <span class="hlt">Earth</span>'s history, we have modified a geochemical reservoir model that was previously developed to investigate <span class="hlt">mantle</span> overturn and mixing</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17731881','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17731881"><span>Three-Dimensional Spherical Models of Convection in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bercovici, D; Schubert, G; Glatzmaier, G A</p> <p>1989-05-26</p> <p>Three-dimensional, spherical models of <span class="hlt">mantle</span> convection in the <span class="hlt">earth</span> reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of <span class="hlt">mantle</span> circulation. Thus, subduction zones and descending sheetlike slabs in the <span class="hlt">mantle</span> are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding <span class="hlt">mantle</span>. Cylindrical <span class="hlt">mantle</span> plumes that cause hotspots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale <span class="hlt">mantle</span> circulation. Active sheetlike upwellings that could be associated with mid-ocean ridges did not develop in the model simulations, a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.482..556M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.482..556M"><span>Nitrogen evolution within the <span class="hlt">Earth</span>'s atmosphere-<span class="hlt">mantle</span> system assessed by recycling in subduction zones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mallik, Ananya; Li, Yuan; Wiedenbeck, Michael</p> <p>2018-01-01</p> <p>Understanding the evolution of nitrogen (N) across <span class="hlt">Earth</span>'s history requires a comprehensive understanding of N's behaviour in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> - a massive reservoir of this volatile element. Investigation of terrestrial N systematics also requires assessment of its evolution in the <span class="hlt">Earth</span>'s atmosphere, especially to constrain the N content of the Archaean atmosphere, which potentially impacted water retention on the post-accretion <span class="hlt">Earth</span>, potentially causing enough warming of surface temperatures for liquid water to exist. We estimated the proportion of recycled N in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> today, the isotopic composition of the primitive <span class="hlt">mantle</span>, and the N content of the Archaean atmosphere based on the recycling rates of N in modern-day subduction zones. We have constrained recycling rates in modern-day subduction zones by focusing on the mechanism and efficiency of N transfer from the subducting slab to the sub-arc <span class="hlt">mantle</span> by both aqueous fluids and slab partial melts. We also address the transfer of N by aqueous fluids as per the model of Li and Keppler (2014). For slab partial melts, we constrained the transfer of N in two ways - firstly, by an experimental study of the solubility limit of N in melt (which provides an upper estimate of N uptake by slab partial melts) and, secondly, by the partitioning of N between the slab and its partial melt. Globally, 45-74% of N introduced into the <span class="hlt">mantle</span> by subduction enters the deep <span class="hlt">mantle</span> past the arc magmatism filter, after taking into account the loss of N from the <span class="hlt">mantle</span> by degassing at mid-ocean ridges, ocean islands and back-arcs. Although the majority of the N in the present-day <span class="hlt">mantle</span> remains of primordial origin, our results point to a significant, albeit minor proportion of <span class="hlt">mantle</span> N that is of recycled origin (17 ± 8% or 12 ± 5% of N in the present-day <span class="hlt">mantle</span> has undergone recycling assuming that modern-style subduction was initiated 4 or 3 billion years ago, respectively). This proportion of recycled N is enough to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29610319','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29610319"><span>Effects of iron on the lattice thermal conductivity of <span class="hlt">Earth</span>'s deep <span class="hlt">mantle</span> and implications for <span class="hlt">mantle</span> dynamics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo; Lin, Jung-Fu</p> <p>2018-04-17</p> <p>Iron may critically influence the physical properties and thermochemical structures of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. Its effects on thermal conductivity, with possible consequences on heat transfer and <span class="hlt">mantle</span> dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-<span class="hlt">mantle</span> ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8-10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-<span class="hlt">mantle</span> thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower <span class="hlt">mantle</span>. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PNAS..115.4099H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PNAS..115.4099H"><span>Effects of iron on the lattice thermal conductivity of <span class="hlt">Earth</span>'s deep <span class="hlt">mantle</span> and implications for <span class="hlt">mantle</span> dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo; Lin, Jung-Fu</p> <p>2018-04-01</p> <p>Iron may critically influence the physical properties and thermochemical structures of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. Its effects on thermal conductivity, with possible consequences on heat transfer and <span class="hlt">mantle</span> dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-<span class="hlt">mantle</span> ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8–10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-<span class="hlt">mantle</span> thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower <span class="hlt">mantle</span>. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930037357&hterms=Magnetic+energy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DMagnetic%2Benergy','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930037357&hterms=Magnetic+energy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DMagnetic%2Benergy"><span>Constraints on magnetic energy and <span class="hlt">mantle</span> conductivity from the forced nutations of the <span class="hlt">earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Buffett, Bruce A.</p> <p>1992-01-01</p> <p>The possibility of a presence of a conducting layer at the base of the <span class="hlt">mantle</span>, as suggested by Knittle and Jeanloz (1986, 1989), was examined using observations of the <span class="hlt">earth</span>'s nutations. Evidence favoring the presence of a conducting layer is found in the effect of ohmic dissipation, which can cause the amplitude of the <span class="hlt">earth</span>'s nutation to be out-of-phase with tidal forcings. It is shown that the <span class="hlt">earth</span>'s magnetic field can produce observable signatures in the forced nutations of the <span class="hlt">earth</span> when a thin conducting layer is located at the base of the <span class="hlt">mantle</span>. The present theoretical calculations are compared with VLBI determinations of forced nutations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26439346','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26439346"><span>Photosynthesis and <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shih, Patrick M</p> <p>2015-10-05</p> <p>Life has been built on the evolution and innovation of microbial metabolisms. Even with our scant understanding of the full diversity of microbial life, it is clear that microbes have become integral components of the biogeochemical cycles that drive our planet. The antiquity of life further suggests that various microbial metabolisms have been core and essential to global elemental cycling for a majority of <span class="hlt">Earth</span>'s history. Copyright © 2015 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI43C..03W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI43C..03W"><span>The Fine Geochemical Structure of the Hawaiian <span class="hlt">Mantle</span> Plume: Relation to the <span class="hlt">Earth</span>'s Lowermost <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weis, D.; Harrison, L.</p> <p>2017-12-01</p> <p>The Hawaiian <span class="hlt">mantle</span> plume has been active for >80 Ma with the highest magmatic flux, also distinctly increasing with time. The identification of two clear geochemical trends (Loa-Kea) among Hawaiian volcanoes in all isotope systems has implications for the dynamics and internal structure of the plume conduit and source in the deep <span class="hlt">mantle</span>. A compilation of modern isotopic data on Hawaiian shield volcanoes and from the Northwest Hawaiian Ridge (NWHR), focusing specifically on high-precision Pb isotopes integrated with Sr, Nd and Hf isotopes, indicates the presence of source differences for Loa- and Kea-trend volcanoes that are maintained throughout the 1 Ma activity of each volcano. These differences extend back in time on all the Hawaiian Islands ( 5 Ma), and as far back as 47 Ma on the NWHR. In all isotope systems, the Loa-trend basalts are more heterogeneous by a factor of 1.5 than the Kea-trend basalts. The Hawaiian <span class="hlt">mantle</span> plume overlies the boundary between ambient Pacific lower <span class="hlt">mantle</span> on the Kea side and the Pacific LLSVP on the Loa side. Geochemical differences between Kea and Loa trends reflect preferential sampling of these two distinct sources of deep <span class="hlt">mantle</span> material, with additional contribution of ULVZ material sporadically on the Loa side. Plume movement up the gently sloping edge of the LLSVP resulted in entrainment of greater amounts of LLSVP-enriched material over time, and explains why the Hawaiian <span class="hlt">mantle</span> plume dramatically strengthens over time, contrary to plume models. Similar indications of preferential sampling at the edges of the African LLSVP are found in Kerguelen and Tristan da Cunha basalts in the Indian and Atlantic oceans, respectively. The anomalous low-velocity zones at the core-<span class="hlt">mantle</span> boundary store geochemical heterogeneities that are enriched in recycled material (EM-I type) with different compositions under the Pacific and under Africa, and that are sampled by strong <span class="hlt">mantle</span> plumes such as Hawaii and Kerguelen.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26037825','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26037825"><span>Magma Ocean Depth and Oxygen Fugacity in the <span class="hlt">Early</span> <span class="hlt">Earth</span>--Implications for Biochemistry.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Righter, Kevin</p> <p>2015-09-01</p> <p>A large class of elements, referred to as the siderophile (iron-loving) elements, in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> can be explained by an <span class="hlt">early</span> deep magma ocean on the <span class="hlt">early</span> <span class="hlt">Earth</span> in which the <span class="hlt">mantle</span> equilibrated with metallic liquid (core liquid). This stage would have affected the distribution of some of the classic volatile elements that are also essential ingredients for life and biochemistry - H, C, S, and N. Estimates are made of the H, C, S, and N contents of <span class="hlt">Earth</span>'s <span class="hlt">early</span> <span class="hlt">mantle</span> after core formation, considering the effects of variable temperature, pressure, oxygen fugacity, and composition on their partitioning. Assessment is made of whether additional, exogenous, sources are required to explain the observed <span class="hlt">mantle</span> concentrations, and areas are identified where additional data and experimentation would lead to an improved understanding of this phase of <span class="hlt">Earth</span>'s history.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI11A2343D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI11A2343D"><span>Plate Tectonic Cycling and Whole <span class="hlt">Mantle</span> Convection Modulate <span class="hlt">Earth</span>'s 3He/22Ne Ratio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dygert, N. J.; Jackson, C.; Hesse, M. A.; Tremblay, M. M.; Shuster, D. L.; Gu, J.</p> <p>2016-12-01</p> <p>3He and 22Ne are not produced in the <span class="hlt">mantle</span> or fractionated by partial melting, and neither isotope is recycled back into the <span class="hlt">mantle</span> by subduction of oceanic basalt or sediment. Thus, it is a surprise that large 3He/22Ne variations exist within the <span class="hlt">mantle</span> and that the <span class="hlt">mantle</span> has a net elevated 3He/22Ne ratio compared to volatile-rich planetary precursor materials. Depleted subcontinental lithospheric <span class="hlt">mantle</span> and mid-ocean ridge basalt (MORB) <span class="hlt">mantle</span> have distinctly higher 3He/22Ne compared to ocean island basalt (OIB) sources ( 4-12.5 vs. 2.5-4.5, respectively) [1,2]. The low 3He/22Ne of OIBs approaches chondritic ( 1) and solar nebula values ( 1.5). The high 3He/22Ne of the MORB <span class="hlt">mantle</span> is not similar to solar sources or any known family of meteorites, requiring a mechanism for fractionating He from Ne in the <span class="hlt">mantle</span> and suggesting isolation of distinct <span class="hlt">mantle</span> reservoirs throughout geologic time. We model the formation of a MORB source with elevated and variable 3He/22Ne though diffusive exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to <span class="hlt">mantle</span> upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is relatively immobile, producing a regassed, depleted <span class="hlt">mantle</span> lithosphere with elevated 3He/22Ne. Subduction of high 3He/22Ne <span class="hlt">mantle</span> would generate a MORB source with high 3He/22Ne. Regassed, high 3He/22Ne <span class="hlt">mantle</span> lithosphere has He concentrations 2-3 orders of magnitude lower than undegassed <span class="hlt">mantle</span>. To preserve the large volumes of high 3He/22Ne <span class="hlt">mantle</span> required by the MORB source, mixing between subducted and undegassed <span class="hlt">mantle</span> reservoirs must have been limited throughout geologic time. Using the new 3He/22Ne constraints, we ran a model similar to [3] to quantify <span class="hlt">mantle</span> mixing timescales, finding they are on the order of Gyr assuming physically reasonable seafloor spreading rates, and that <span class="hlt">Earth</span>'s convecting <span class="hlt">mantle</span> has lost >99% of its primordial</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830053000&hterms=redox&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dredox','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830053000&hterms=redox&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dredox"><span>Redox state of <span class="hlt">earth</span>'s upper <span class="hlt">mantle</span> from kimberlitic ilmenites</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Haggerty, S. E.; Tompkins, L. A.</p> <p>1983-01-01</p> <p>Temperatures and oxygen fugacities are reported on discrete ilmenite nodules in kimberlites from West Africa which demonstrate that the source region in the upper <span class="hlt">mantle</span> is moderately oxidized, consistent with other nodule suites in kimberlites from southern Africa and the United States. A model is presented for a variety of tectonic settings, proposing that the upper <span class="hlt">mantle</span> is profiled in redox potential, oxidized in the fertile asthenosphere but reduced in the depleted lithosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V33A2737H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V33A2737H"><span>How Irreversible Heat Transport Processes Drive <span class="hlt">Earth</span>'s Interdependent Thermal, Structural, and Chemical Evolution Providing a Strongly Heterogeneous, Layered <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hofmeister, A.; Criss, R. E.</p> <p>2013-12-01</p> <p>Because magmatism conveys radioactive isotopes plus latent heat rapidly upwards while advecting heat, this process links and controls the thermal and chemical evolution of <span class="hlt">Earth</span>. We present evidence that the lower <span class="hlt">mantle</span>-upper <span class="hlt">mantle</span> boundary is a profound chemical discontinuity, leading to observed heterogeneities in the outermost layers that can be directly sampled, and construct an alternative view of <span class="hlt">Earth</span>'s internal workings. <span class="hlt">Earth</span>'s beginning involved cooling via explosive outgassing of substantial ice (mainly CO) buried with dust during accretion. High carbon content is expected from Solar abundances and ice in comets. Reaction of CO with metal provided a carbide-rich core while converting MgSiO3 to olivine via oxidizing reactions. Because thermodynamic law (and buoyancy of hot particles) indicates that primordial heat from gravitational segregation is neither large nor carried downwards, whereas differentiation forced radioactive elements upwards, formation of the core and lower <span class="hlt">mantle</span> greatly cooled the <span class="hlt">Earth</span>. Reference conductive geotherms, calculated using accurate and new thermal diffusivity data, require that heat-producing elements are sequestered above 670 km which limits convection to the upper <span class="hlt">mantle</span>. These irreversible beginnings limit secular cooling to radioactive wind-down, permiting deduction of <span class="hlt">Earth</span>'s inventory of heat-producing elements from today's heat flux. Coupling our estimate for heat producing elements with meteoritic data indicates that <span class="hlt">Earth</span>'s oxide content has been underestimated. Density sorting segregated a Si-rich, peridotitic upper <span class="hlt">mantle</span> from a refractory, oxide lower <span class="hlt">mantle</span> with high Ca, Al and Ti contents, consistent with diamond inclusion mineralogy. <span class="hlt">Early</span> and rapid differentiation means that internal temperatures have long been buffered by freezing of the inner core, allowing survival of crust as old as ca.4 Ga. Magmatism remains important. Melt escaping though stress-induced fractures in the rigid lithosphere imparts a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR24A..04L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR24A..04L"><span>Elasticity of the <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span> Minerals at High Pressures: Implications to Understanding Seismic Observations of the Deep <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lin, J. F.; Yang, J.; Fu, S.</p> <p>2017-12-01</p> <p>Elasticity of the candidate lower-<span class="hlt">mantle</span> minerals at relevant P-T conditions of the region provides critical information in understanding seismic profiles, compositional and mineralogical models, and geodynamic processes of the <span class="hlt">Earth</span>'s interior. Here we will discuss recent major research advances in the investigation of the elasticity of major lower-<span class="hlt">mantle</span> minerals in a high-pressure diamond anvil cell coupled with Brillouin Light Scattering, Impulsive Stimulated Scattering (ISS), and X-ray diffraction. These have permitted direct and reliable measurements of both Vp and Vs to derive full elastic constants of single-crystal ferropericlase and (Fe, Al)-bearing bridgmanite as well as velocity profiles of polycrystalline silicate post-perovskite at relevant lower-<span class="hlt">mantle</span> pressures. The effects of the spin transition on the single-crystal elasticity of ferropericlase are now well understood experimentally and theoretically1,2: the spin transition causes drastic softening in elastic constants involving the compressive stress component (C11 and C12) due to the additional Gibbs free energy term arising from the mixing of the high-spin and low-spin states, while the elastic constant(s) related to the shear stress component (C44) is not affected. This leads to significant reduction in VP/VS ratio within the spin transition of ferropericlase in the mid-lower <span class="hlt">mantle</span>. The derived single-crystal Cij of bridgmanite at lower <span class="hlt">mantle</span> pressures display relatively small elastic Vp and Vs anisotropies as compared to the ferropericlase counterpart. Using thermoelastic modelling, we will discuss the application of the elasticity of ferropericlase, bridgmanite, and silicate post-perovskite at relevant conditions of the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> to differentiate the role of the thermal vs. chemical perturbations as well as the spin transition and iron partitioning effects in the reported seismic lateral heterogeneity in lower <span class="hlt">mantle</span> as well as the D″ zone region3,4. We will address how recent</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI41A2603A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI41A2603A"><span>Iron Speciation in Minerals and Melts at High Pressure: Implications for the Redox Evolution of the <span class="hlt">Early</span> <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Armstrong, K.; Frost, D. J.; McCammon, C. A.; Rubie, D. C.; Boffa Ballaran, T.; Miyajima, N.</p> <p>2016-12-01</p> <p>During the differentiation of the <span class="hlt">early</span> <span class="hlt">Earth</span>, the silicates of the <span class="hlt">mantle</span> must have been in equilibrium with core-forming metal iron, as indicated by the depletion of siderophile elements from the <span class="hlt">mantle</span>. Studies of ancient rocks suggest that by at least 3.9 Ga, the upper <span class="hlt">mantle</span> was 4-5 log units more oxidized than metal saturation implies (Delano 2001). The process(es) by which the <span class="hlt">mantle</span> was oxidized is unclear, but has implications for the timing of accretion, differentiation, and volatile delivery to the <span class="hlt">early</span> <span class="hlt">Earth</span>, as well as evolution of the <span class="hlt">early</span> atmosphere. One plausible oxidation mechanism is suggested by the tendency of high-pressure silicate minerals to favor Fe3+ over Fe2+ in their structures, even at metal saturation. This preference in the lower <span class="hlt">mantle</span> mineral bridgmanite has been proposed to drive the disproportionation reaction of FeO to form Fe­2O3 and iron metal (Frost and McCammon 2008). We have performed experiments at the Ru-RuO2 fO2 buffer which show that silicate melts may mirror this behavior and Fe3+ may be stabilized with pressure for a constant fO2; by 21 GPa, the previously observed trend of Fe3+ decreasing with pressure (O'Neill, 2006) reverses and ferric iron content had increased. If this is also the case at lower oxygen fugacities, FeO disproportionation may have occurred at the base of an <span class="hlt">early</span> magma ocean, establishing a redox gradient similar to what is presumed for the <span class="hlt">mantle</span> today. Here we report results of further multianvil and diamond anvil cell experiments exploring the plausibility of FeO disproportionation driving <span class="hlt">mantle</span> oxidation. Experiments investigating Fe speciation in high pressure melts at variable fO2 will be discussed along with results of diamond anvil cell experiments investigating ferric iron content of lower <span class="hlt">mantle</span> minerals at metal saturation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120001844','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120001844"><span>Core-<span class="hlt">Mantle</span> Partitioning of Volatile Siderophile Elements and the Origin of Volatile Elements in the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nickodem, K.; Righter, K.; Danielson, L.; Pando, K.; Lee, C.</p> <p>2012-01-01</p> <p>There are currently several hypotheses on the origin of volatile siderophile elements in the <span class="hlt">Earth</span>. One hypothesis is that they were added during <span class="hlt">Earth</span> s accretion and core formation and mobilized into the metallic core [1], others claim multiple stage origin [2], while some hypothesize that volatiles were added after the core already formed [3]. Several volatile siderophile elements are depleted in <span class="hlt">Earth</span> s <span class="hlt">mantle</span> relative to the chondrites, something which continues to puzzle many scientists. This depletion is likely due to a combination of volatility and core formation. The <span class="hlt">Earth</span> s core is composed of Fe and some lighter constituents, although the abundances of these lighter elements are unknown [4]. Si is one of these potential light elements [5] although few studies have analyzed the effect of Si on metal-silicate partitioning, in particular the volatile elements. As, In, Ge, and Sb are trace volatile siderophile elements which are depleted in the <span class="hlt">mantle</span> but have yet to be extensively studied. The metal-silicate partition coefficients of these elements will be measured to determine the effect of Si. Partition coefficients depend on temperature, pressure, oxygen fugacity, and metal and silicate composition and can constrain the concentrations of volatile, siderophile elements found in the <span class="hlt">mantle</span>. Reported here are the results from 13 experiments examining the partitioning of As, In, Ge, and Sb between metallic and silicate liquid. These experiments will examine the effect of temperature, and metal-composition (i.e., Si content) on these elements in or-der to gain a greater understanding of the core-<span class="hlt">mantle</span> separation which occurred during the <span class="hlt">Earth</span> s <span class="hlt">early</span> stages. The data can then be applied to the origin of volatile elements in the <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18826925','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18826925"><span><span class="hlt">Early</span> differentiation of the <span class="hlt">Earth</span> and the Moon.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bourdon, Bernard; Touboul, Mathieu; Caro, Guillaume; Kleine, Thorsten</p> <p>2008-11-28</p> <p>We examine the implications of new 182W and 142Nd data for Mars and the Moon for the <span class="hlt">early</span> evolution of the <span class="hlt">Earth</span>. The similarity of 182W in the terrestrial and lunar <span class="hlt">mantles</span> and their apparently differing Hf/W ratios indicate that the Moon-forming giant impact most probably took place more than 60Ma after the formation of calcium-aluminium-rich inclusions (4.568Gyr). This is not inconsistent with the apparent U-Pb age of the <span class="hlt">Earth</span>. The new 142Nd data for Martian meteorites show that Mars probably has a super-chondritic Sm/Nd that could coincide with that of the <span class="hlt">Earth</span> and the Moon. If this is interpreted by an <span class="hlt">early</span> <span class="hlt">mantle</span> differentiation event, this requires a buried enriched reservoir for the three objects. This is highly unlikely. For the <span class="hlt">Earth</span>, we show, based on new mass-balance calculations for Nd isotopes, that the presence of a hidden reservoir is difficult to reconcile with the combined 142Nd-143Nd systematics of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. We argue that a likely possibility is that the missing component was lost during or prior to accretion. Furthermore, the 142Nd data for the Moon that were used to argue for the solidification of the magma ocean at ca 200Myr are reinterpreted. Cumulate overturn, magma mixing and melting following lunar magma ocean crystallization at 50-100Myr could have yielded the 200Myr model age.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.478...40U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.478...40U"><span>Phase transitions in MgSiO3 post-perovskite in super-<span class="hlt">Earth</span> <span class="hlt">mantles</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Umemoto, Koichiro; Wentzcovitch, Renata M.; Wu, Shunqing; Ji, Min; Wang, Cai-Zhuang; Ho, Kai-Ming</p> <p>2017-11-01</p> <p>The highest pressure form of the major <span class="hlt">Earth</span>-forming <span class="hlt">mantle</span> silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-<span class="hlt">Earths</span>-type exoplanets, arguably the most interesting for their similarities with <span class="hlt">Earth</span>. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2 and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed the problem of <span class="hlt">mantle</span> composition, particularly major element abundances usually expressed in terms of three main variables, the Mg/Si and Fe/Si ratios and the Mg#, as in the <span class="hlt">Earth</span>. Here we show that the critical compositional parameter, the Mg/Si ratio, whose value in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> is still debated, is a vital ingredient for modeling phase transitions and internal structure of super-<span class="hlt">Earth</span> <span class="hlt">mantles</span>. Specifically, we have identified new sequences of phase transformations, including new recombination reactions that depend decisively on this ratio. This is a new level of complexity that has not been previously addressed, but proves essential for modeling the nature and number of internal layers in these rocky <span class="hlt">mantles</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR51B..08L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR51B..08L"><span>Release of Nitrogen during Planetary Accretion Explains Missing Nitrogen in <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, J.; Dorfman, S.; Lv, M.; Li, J.; Kono, Y.</p> <p>2017-12-01</p> <p>Nitrogen and carbon are essential elements for life on <span class="hlt">Earth</span>, and their relative abundances in planetary bodies (C/N ratios) are important for understanding planetary evolution and habitability1,2. However, the high C/N ratio in the bulk silicate <span class="hlt">Earth</span> relative to CI chondrites and other volatile-rich chondrites is difficult to explain with partitioning behavior between silicate and metallic liquid or solubility in silicate melt, and has thus been a major unsolved problem in geochemistry1-5. Because core formation does not explain nitrogen depletion in the <span class="hlt">mantle</span>, another process is required to match the observed BSE C/N ratio, such as devolatilization of metallic liquid. Previous studies have examined the Fe-C phase diagram extensively (e.g. ref. 6), but very limited melting data is available for the Fe-N system7. Here we examine melting relations for four Fe-N-C compositions with 1-7 wt% nitrogen up to 7 GPa and 2200 K in the Paris-Edinburgh press by a combination of in-situ X-ray radiography, X-ray diffraction and ex-situ electron microprobe techniques. In striking contrast to the Fe-C system, near-surface melting in all compositions in the Fe-N-C system entails release of nitrogen fluid and depletion of nitrogen from the liquid alloy. This could provide a pathway for nitrogen to escape the magma ocean in the accretion stage while carbon is retained. On the basis of our experimental results, we propose a new quantitative model of <span class="hlt">mantle</span> nitrogen evolution during the core formation stage to explain the high BSE C/N ratios and resolve the paradox of missing <span class="hlt">mantle</span> nitrogen1-5. Although nitrogen itself is not a greenhouse gas, the nitrogen released to the atmosphere from metallic melt <span class="hlt">early</span> in <span class="hlt">Earth</span>'s history could amplify the greenhouse effect through collision-enhanced absorption8,9, which may help to explain warm surface temperatures during the Hadean and Archean eras on <span class="hlt">Earth</span> when the solar luminosity was 25-30% lower than the present10. References1. Bergin et</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.198..151W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.198..151W"><span>Zinc isotope fractionation during <span class="hlt">mantle</span> melting and constraints on the Zn isotope composition of <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Ze-Zhou; Liu, Sheng-Ao; Liu, Jingao; Huang, Jian; Xiao, Yan; Chu, Zhu-Yin; Zhao, Xin-Miao; Tang, Limei</p> <p>2017-02-01</p> <p>The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an initial approach, the terrestrial <span class="hlt">mantle</span>, and by inference, the bulk silicate <span class="hlt">Earth</span> (BSE), have previously been suggested to have an average δ66Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for <span class="hlt">mantle</span> peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during <span class="hlt">mantle</span> melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites (n = 47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ66Zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31 ± 0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ66Zn range of -0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66Zn value of +0.18 ± 0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during <span class="hlt">mantle</span> partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ66ZnSpl-Ol = +0.12 ± 0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11-88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during <span class="hlt">mantle</span> melting plays a key role in generating high Zn concentrations and heavy Zn isotopic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70011540','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70011540"><span>Effects of selective fusion on the thermal history of the <span class="hlt">earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href=""></a></p> <p>Lee, W.H.K.</p> <p>1968-01-01</p> <p>A comparative study on the thermal history of the <span class="hlt">earth</span>'s <span class="hlt">mantle</span> was made by numerical solutions of the heat equation including and excluding selective fusion of silicates. Selective fusion was approximated by melting in a multicomponent system and redistribution of radioactive elements. Effects of selective fusion on the thermal models are (1) lowering (by several hundred degrees centigrade) and stabilizing the internal temperature distribution, and (2) increasing the surface heat-flow. It was found that models with selective fusion gave results more compatible with observations of both present temperature and surface heat-flow. The results therefore suggest continuous differentiation of the <span class="hlt">earth</span>'s <span class="hlt">mantle</span> throughout geologic time, and support the hypothesis that the <span class="hlt">earth</span>'s atmosphere, oceans, and crust have been accumulated throughout the <span class="hlt">earth</span>'s history by degassing and selective fusion of the <span class="hlt">mantle</span>. ?? 1968.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810008127','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810008127"><span>Gravitational field models for study of <span class="hlt">Earth</span> <span class="hlt">mantle</span> dynamics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1979-01-01</p> <p>The tectonic forces or stresses due to the small scale <span class="hlt">mantle</span> flow under the South American plate are detected and determined by utilizing the harmonics of the geopotential field model. The high degree harmonics are assumed to describe the small scale <span class="hlt">mantle</span> convection patterns. The input data used in the derivation of this model is made up of 840,000 optical, electronic, and laser observations and 1,656 5 deg x 5 deg mean free air anomalies. Although there remain some statistically questionable aspects of the high degree harmonics, it seems appropriate now to explore their implications for the tectonic forces or stress field under the crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P42A..05N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P42A..05N"><span>On evolutionary climate tracks in deep <span class="hlt">mantle</span> volatile cycle computed from numerical <span class="hlt">mantle</span> convection simulations and its impact on the habitability of the <span class="hlt">Earth</span>-like planets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakagawa, T.; Tajika, E.; Kadoya, S.</p> <p>2017-12-01</p> <p>Discussing an impact of evolution and dynamics in the <span class="hlt">Earth</span>'s deep interior on the surface climate change for the last few decades (see review by Ehlmann et al., 2016), the <span class="hlt">mantle</span> volatile (particularly carbon) degassing in the mid-oceanic ridges seems to play a key role in understanding the evolutionary climate track for <span class="hlt">Earth</span>-like planets (e.g. Kadoya and Tajika, 2015). However, since the <span class="hlt">mantle</span> degassing occurs not only in the mid-oceanic ridges but also in the wedge <span class="hlt">mantle</span> (island arc volcanism) and hotspots, to incorporate more accurate estimate of <span class="hlt">mantle</span> degassing flux into the climate evolution framework, we developed a coupled model of surface climate-deep <span class="hlt">Earth</span> evolution in numerical <span class="hlt">mantle</span> convection simulations, including more accurate deep water and carbon cycle (e.g. Nakagawa and Spiegelman, 2017) with an energy balance theory of climate change. Modeling results suggest that the evolution of planetary climate computed from a developed model is basically consistent with an evolutionary climate track in simplified <span class="hlt">mantle</span> degassing model (Kadoya and Tajika, 2015), but an occurrence timing of global (snowball) glaciation is strongly dependent on <span class="hlt">mantle</span> degassing rate occurred with activities of surface plate motions. With this implication, the surface plate motion driven by deep <span class="hlt">mantle</span> dynamics would play an important role in the planetary habitability of such as the <span class="hlt">Earth</span> and <span class="hlt">Earth</span>-like planets over geologic time-scale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V33F0578S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V33F0578S"><span>Nitrogen partitioning during <span class="hlt">Earth</span>'s accretion and core-<span class="hlt">mantle</span> differentiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Speelmanns, I. M.; Schmidt, M. W.; Liebske, C.</p> <p>2017-12-01</p> <p>On present day <span class="hlt">Earth</span>, N is one of the key constituents of our atmosphere and forms the basis of life. However, the deep <span class="hlt">Earth</span> geochemistry of N, i.e. its distribution and isotopic fractionation between <span class="hlt">Earth</span>'s deep reservoirs is not well constrained. This study investigates nitrogen partitioning between metal and silicate melts as relevant for core segregation during the accretion of planetesimals into the <span class="hlt">Earth</span>. We have determined N-partitioning coefficients over a wide range of temperatures (1250-2000 °C), pressures (15-35 kbar) and oxygen fugacity's, the latter in the relevant range of core segregation (IW-5 to IW). Centrifuging piston cylinders were used to equilibrate and then gravitationally separate metal-silicate melt pairs. Separation of the two melts is necessary to avoid micro nugget contamination in the silicate melt at reducing conditions < IW-2.5. Complete segregation of the two melts was reached within 1 to 3 hours at 1000 g and 1600-1250 °C respectively, the interface showing a proper meniscus. The applied double capsule technique in all experiments, using an outer metallic (Pt) and inner non-metallic capsule (graphite or Al2O3), minimizes N-loss over the course of the experiments compared to single non-metallic capsules. The two quenched melts were cut apart mechanically, cleaned at the outside, their N concentrations were then analysed on bulk samples by an elemental analyser, the low abslute masses requiring careful development of analytical routines. Despite these difficulties, we were able to determine a DNmetal/silicate of 13±0.3 at IW-1 decreasing to 2.0±0.2 at IW-5.5, at 1250°C and 15 kbar, N partitioning into the core forming metal. Increasing temperature dramatically lowers the DNmetal/silicate to e.g. 0.5±0.15 at IW-4, during <span class="hlt">early</span> core formation N was hence mildly incompatible in the metal. The results suggest that under magma ocean conditions (> 2000 oC and fO2 IW-2.5), N-partition coefficents were within a factor of 2 of unity</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27611737','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27611737"><span>Revealing the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> from the tallest mountains using the Jinping Neutrino Experiment.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Šrámek, Ondřej; Roskovec, Bedřich; Wipperfurth, Scott A; Xi, Yufei; McDonough, William F</p> <p>2016-09-09</p> <p>The <span class="hlt">Earth</span>'s engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of <span class="hlt">Earth</span>'s composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving <span class="hlt">mantle</span> dynamics. Recent measurements of the <span class="hlt">Earth</span>'s flux of geoneutrinos, electron antineutrinos from terrestrial natural radioactivity, reveal the amount of uranium and thorium in the <span class="hlt">Earth</span> and set limits on the residual proportion of primordial energy. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the <span class="hlt">mantle</span>'s radiogenic power. Measurement at an oceanic location, distant from nuclear reactors and continental crust, would best reveal the <span class="hlt">mantle</span> flux, however, no such experiment is anticipated. We predict the geoneutrino flux at the site of the Jinping Neutrino Experiment (Sichuan, China). Within 8 years, the combination of existing data and measurements from soon to come experiments, including Jinping, will exclude end-member models at the 1σ level, define the <span class="hlt">mantle</span>'s radiogenic contribution to the surface heat loss, set limits on the composition of the silicate <span class="hlt">Earth</span>, and provide significant parameter bounds for models defining the mode of <span class="hlt">mantle</span> convection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010068810','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010068810"><span>Gravitational Core-<span class="hlt">Mantle</span> Coupling and the Acceleration of the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rubincam, David Parry; Smith, David E. (Technical Monitor)</p> <p>2001-01-01</p> <p>Gravitational core-<span class="hlt">mantle</span> coupling may be the cause of the observed variable acceleration of the <span class="hlt">Earth</span>'s rotation on the 1000 year timescale. The idea is that density inhomogeneities which randomly come and go in the liquid outer core gravitationally attract density inhomogeneities in the <span class="hlt">mantle</span> and crust, torquing the <span class="hlt">mantle</span> and changing its rotation state. The corresponding torque by the <span class="hlt">mantle</span> on the core may also explain the westward drift of the magnetic field of 0.2 deg per year. Gravitational core-<span class="hlt">mantle</span> coupling would stochastically affect the rate of change of the <span class="hlt">Earth</span>'s obliquity by just a few per cent. Its contribution to polar wander would only be about 0.5% the presently observed rate. Tidal friction is slowing down the rotation of the <span class="hlt">Earth</span>, overwhelming a smaller positive acceleration from postglacial rebound. Coupling between the liquid outer core of the <span class="hlt">Earth</span> and the <span class="hlt">mantle</span> has long been a suspected reason for changes in the length-of-day. The present investigation focuses on the gravitational coupling between the density anomalies in the convecting liquid outer core and those in the <span class="hlt">mantle</span> and crust as a possible cause for the observed nonsecular acceleration on the millenial timescale. The basic idea is as follows. There are density inhomogeneities caused by blobs circulating in the outer core like the blobs in a lava lamp; thus the outer core's gravitational field is not featureless. Moreover, these blobs will form and dissipate somewhat randomly. Thus there will be a time variability to the fields. These density inhomogeneities will gravitationally attract the density anomalies in the <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26333468','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26333468"><span>Broad plumes rooted at the base of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> beneath major hotspots.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>French, Scott W; Romanowicz, Barbara</p> <p>2015-09-03</p> <p>Plumes of hot upwelling rock rooted in the deep <span class="hlt">mantle</span> have been proposed as a possible origin of hotspot volcanoes, but this idea is the subject of vigorous debate. On the basis of geodynamic computations, plumes of purely thermal origin should comprise thin tails, only several hundred kilometres wide, and be difficult to detect using standard seismic tomography techniques. Here we describe the use of a whole-<span class="hlt">mantle</span> seismic imaging technique--combining accurate wavefield computations with information contained in whole seismic waveforms--that reveals the presence of broad (not thin), quasi-vertical conduits beneath many prominent hotspots. These conduits extend from the core-<span class="hlt">mantle</span> boundary to about 1,000 kilometres below <span class="hlt">Earth</span>'s surface, where some are deflected horizontally, as though entrained into more vigorous upper-<span class="hlt">mantle</span> circulation. At the base of the <span class="hlt">mantle</span>, these conduits are rooted in patches of greatly reduced shear velocity that, in the case of Hawaii, Iceland and Samoa, correspond to the locations of known large ultralow-velocity zones. This correspondence clearly establishes a continuous connection between such zones and <span class="hlt">mantle</span> plumes. We also show that the imaged conduits are robustly broader than classical thermal plume tails, suggesting that they are long-lived, and may have a thermochemical origin. Their vertical orientation suggests very sluggish background circulation below depths of 1,000 kilometres. Our results should provide constraints on studies of viscosity layering of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and guide further research into thermochemical convection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI13A0278T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI13A0278T"><span>The role of upper <span class="hlt">mantle</span> mineral phase transitions on the current structure of large-scale <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> convection.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thoraval, C.</p> <p>2017-12-01</p> <p>Describing the large-scale structures of <span class="hlt">mantle</span> convection and quantifying the mass transfer between upper and lower <span class="hlt">mantle</span> request to account for the role played by mineral phase transitions in the transition zone. We build a density distribution within the <span class="hlt">Earth</span> <span class="hlt">mantle</span> from velocity anomalies described by global seismic tomographic models. The density distribution includes thermal anomalies and topographies of the phase transitions at depths of 410 and 660 km. We compute the flow driven by this density distribution using a 3D spherical circulation model, which account for depth-dependent viscosity. The dynamic topographies at the surface and at the CMB and the geoid are calculated as well. Within the range of viscosity profiles allowing for a satisfying restitution of the long wavelength geoid, we perform a parametric study to decipher the role of the characteristics of phase diagrams - mainly the Clapeyron's slopes - and of the kinetics of phase transitions, which may modify phase transition topographies. Indeed, when a phase transition is delayed, the boundary between two mineral phases is both dragged by the flow and interfere with it. The results are compared to recent estimations of surface dynamic topography and to the phase transition topographies as revealed by seismic studies. The consequences are then discussed in terms of structure of <span class="hlt">mantle</span> flow. Comparisons between various tomographic models allow us to enlighten the most robust features. At last, the role played by the phase transitions on the lateral variations of mass transfer between upper and lower <span class="hlt">mantle</span> are quantified by comparison to cases with no phase transitions and confronted to regional tomographic models, which reflect the variability of the behaviors of the descending slabs in the transition zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830031654&hterms=deutsche+forschungsgemeinschaft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Ddeutsche%2Bforschungsgemeinschaft','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830031654&hterms=deutsche+forschungsgemeinschaft&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Ddeutsche%2Bforschungsgemeinschaft"><span>Modes of <span class="hlt">mantle</span> convection and the removal of heat from the <span class="hlt">earth</span>'s interior</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Spohn, T.; Schubert, G.</p> <p>1982-01-01</p> <p>Thermal histories for two-layer and whole-<span class="hlt">mantle</span> convection models are calculated and presented, based on a parameterization of convective heat transport. The model is composed of two concentric spherical shells surrounding a spherical core. The models were constrained to yield the observed present-day surface heat flow and <span class="hlt">mantle</span> viscosity, in order to determine parameters. These parameters were varied to determine their effects on the results. Studies show that whole-<span class="hlt">mantle</span> convection removes three times more primordial heat from the <span class="hlt">earth</span> interior and six times more from the core than does two-layer convection (in 4.5 billion years). <span class="hlt">Mantle</span> volumetric heat generation rates for both models are comparable to that of a potassium-depleted chondrite, and thus surface heat-flux balance does not require potassium in the core. Whole and two-layer <span class="hlt">mantle</span> convection differences are primarily due to lower <span class="hlt">mantle</span> thermal insulation and the lower heat removal efficiency of the upper <span class="hlt">mantle</span> as compared with that of the whole <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI11B..03A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI11B..03A"><span><span class="hlt">Earth</span>'s Core-<span class="hlt">Mantle</span> equilibrium and a heat sink at the Core <span class="hlt">Mantle</span> Boundary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alfe, D.; Pozzo, M.; Davies, C. J.; Gubbins, D.</p> <p>2016-12-01</p> <p>Chemical equilibrium between the two sides of the core <span class="hlt">mantle</span> boundary (CMB) has longbeen debated. If the core is well mixed and in equilibrium with the inner coredisequilibrium at the CMB seems inevitable. Indeed, a number of experiments pointto a possible non-equilibrium configuration in which the core liquid iron mixture wouldbe undersaturated in oxygen. As discussed by several authors, this chemical imbalancecould result in the formation of an oxygen rich layer at the top of the core, and astratification, which could explain a seismic anomaly claimed by some authors.Here we have revisited the core-<span class="hlt">mantle</span> equilibrium by calculating the chemical potentialof FeO in both liquid iron mixtures and solid Periclase at CMB conditions, usingfirst principles methods based on quantum mechanics and standard statistical mechanics.We find that FeO is favoured in the liquid mixture, with an equilibrium O concentrationthat is much larger than that of the bulk core. In addition, we find that the heat ofreaction of the FeO dissolution form the <span class="hlt">mantle</span> to the core is positive, making thereaction endothermic, and therefore providing a heat sink at the top of the core.The power lost in the heat sink depends on the rate of FeO dissolution, and we discussa scenario which could result in a heat sink of several TW. This sink would absorbsome of the heat conducted along the core adiabat and reduce the CMB heat flux.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.P11C3779H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.P11C3779H"><span>A Thermal Evolution Model of the <span class="hlt">Earth</span> Including the Biosphere, Continental Growth and <span class="hlt">Mantle</span> Hydration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Höning, D.; Spohn, T.</p> <p>2014-12-01</p> <p>By harvesting solar energy and converting it to chemical energy, photosynthetic life plays an important role in the energy budget of <span class="hlt">Earth</span> [2]. This leads to alterations of chemical reservoirs eventually affecting the <span class="hlt">Earth</span>'s interior [4]. It further has been speculated [3] that the formation of continents may be a consequence of the evolution life. A steady state model [1] suggests that the <span class="hlt">Earth</span> without its biosphere would evolve to a steady state with a smaller continent coverage and a dryer <span class="hlt">mantle</span> than is observed today. We present a model including (i) parameterized thermal evolution, (ii) continental growth and destruction, and (iii) <span class="hlt">mantle</span> water regassing and outgassing. The biosphere enhances the production rate of sediments which eventually are subducted. These sediments are assumed to (i) carry water to depth bound in stable mineral phases and (ii) have the potential to suppress shallow dewatering of the underlying sediments and crust due to their low permeability. We run a Monte Carlo simulation for various initial conditions and treat all those parameter combinations as success which result in the fraction of continental crust coverage observed for present day <span class="hlt">Earth</span>. Finally, we simulate the evolution of an abiotic <span class="hlt">Earth</span> using the same set of parameters but a reduced rate of continental weathering and erosion. Our results suggest that the origin and evolution of life could have stabilized the large continental surface area of the <span class="hlt">Earth</span> and its wet <span class="hlt">mantle</span>, leading to the relatively low <span class="hlt">mantle</span> viscosity we observe at present. Without photosynthetic life on our planet, the <span class="hlt">Earth</span> would be geodynamical less active due to a dryer <span class="hlt">mantle</span>, and would have a smaller fraction of continental coverage than observed today. References[1] Höning, D., Hansen-Goos, H., Airo, A., Spohn, T., 2014. Biotic vs. abiotic <span class="hlt">Earth</span>: A model for <span class="hlt">mantle</span> hydration and continental coverage. Planetary and Space Science 98, 5-13. [2] Kleidon, A., 2010. Life, hierarchy, and the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910046523&hterms=high+reaction+chemicals&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dhigh%2Breaction%2Bchemicals','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910046523&hterms=high+reaction+chemicals&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dhigh%2Breaction%2Bchemicals"><span><span class="hlt">Earth</span>'s core-<span class="hlt">mantle</span> boundary - Results of experiments at high pressures and temperatures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Knittle, Elise; Jeanloz, Raymond</p> <p>1991-01-01</p> <p>Laboratory experiments document that liquid iron reacts chemically with silicates at high pressures (above 2.4 x 10 to the 10th Pa) and temperatures. In particular, (Mg,Fe)SiO3 perovskite, the most abundant mineral of <span class="hlt">earth</span>'s lower <span class="hlt">mantle</span>, is expected to react with liquid iron to produce metallic alloys (FeO and FeSi) and nonmetallic silicates (SiO2 stishovite and MgSiO3 perovskite) at the pressures of the core-<span class="hlt">mantle</span> boundary, 14 x 10 to the 10th Pa. The experimental observations, in conjunction with seismological data, suggest that the lowermost 200 to 300 km of <span class="hlt">earth</span>'s <span class="hlt">mantle</span>, the D-double-prime layer, may be an extremely heterogeneous region as a result of chemical reactions between the silicate <span class="hlt">mantle</span> and the liquid iron alloy of <span class="hlt">earth</span>'s core. The combined thermal-chemical-electrical boundary layer resulting from such reactions offers a plausible explanation for the complex behavior of seismic waves near the core-<span class="hlt">mantle</span> boundary and could influence <span class="hlt">earth</span>'s magnetic field observed at the surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150003798','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150003798"><span>Water Content of <span class="hlt">Earth</span>'s Continental <span class="hlt">Mantle</span> Is Controlled by the Circulation of Fluids or Melts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Peslier, Anne; Woodland, Alan B.; Bell, David R.; Lazarov, Marina; Lapen, Thomas J.</p> <p>2014-01-01</p> <p>A key mission of the ARES Directorate at JSC is to constrain models of the formation and geological history of terrestrial planets. Water is a crucial parameter to be measured with the aim to determine its amount and distribution in the interior of <span class="hlt">Earth</span>, Mars, and the Moon. Most of that "water" is not liquid water per se, but rather hydrogen dissolved as a trace element in the minerals of the rocks at depth. Even so, the middle layer of differentiated planets, the <span class="hlt">mantle</span>, occupies such a large volume and mass of each planet that when it is added at the planetary scale, oceans worth of water could be stored in its interior. The <span class="hlt">mantle</span> is where magmas originate. Moreover, on <span class="hlt">Earth</span>, the <span class="hlt">mantle</span> is where the boundary between tectonic plates and the underlying asthenosphere is located. Even if <span class="hlt">mantle</span> rocks in <span class="hlt">Earth</span> typically contain less than 200 ppm H2O, such small quantities have tremendous influence on how easily they melt (i.e., the more water there is, the more magma is produced) and deform (the more water there is, the less viscous they are). These two properties alone emphasize that to understand the distribution of volcanism and the mechanism of plate tectonics, the water content of the <span class="hlt">mantle</span> must be determined - <span class="hlt">Earth</span> being a template to which all other terrestrial planets can be compared.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2242691','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2242691"><span>Rethinking <span class="hlt">early</span> <span class="hlt">Earth</span> phosphorus geochemistry</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Pasek, Matthew A.</p> <p>2008-01-01</p> <p>Phosphorus is a key biologic element, and a prebiotic pathway leading to its incorporation into biomolecules has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochemistry of phosphorus on the <span class="hlt">early</span> <span class="hlt">Earth</span> was instead controlled by reduced oxidation state phosphorus compounds such as phosphite (HPO32−), which are more soluble and reactive than orthophosphates. This reduced oxidation state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atmosphere. This alternate view of <span class="hlt">early</span> <span class="hlt">Earth</span> phosphorus geochemistry provides an unexplored route to the formation of pertinent prebiotic phosphorus compounds, suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochemical usage of reduced oxidation state phosphorus compounds in life today. Possible studies are suggested that may detect reduced oxidation state phosphorus compounds in ancient Archean rocks. PMID:18195373</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18195373','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18195373"><span>Rethinking <span class="hlt">early</span> <span class="hlt">Earth</span> phosphorus geochemistry.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pasek, Matthew A</p> <p>2008-01-22</p> <p>Phosphorus is a key biologic element, and a prebiotic pathway leading to its incorporation into biomolecules has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochemistry of phosphorus on the <span class="hlt">early</span> <span class="hlt">Earth</span> was instead controlled by reduced oxidation state phosphorus compounds such as phosphite (HPO(3)(2-)), which are more soluble and reactive than orthophosphates. This reduced oxidation state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atmosphere. This alternate view of <span class="hlt">early</span> <span class="hlt">Earth</span> phosphorus geochemistry provides an unexplored route to the formation of pertinent prebiotic phosphorus compounds, suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochemical usage of reduced oxidation state phosphorus compounds in life today. Possible studies are suggested that may detect reduced oxidation state phosphorus compounds in ancient Archean rocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1393536-disproportionation-mg-fe-sio3-perovskite-earth-deep-lower-mantle','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1393536-disproportionation-mg-fe-sio3-perovskite-earth-deep-lower-mantle"><span>Disproportionation of (Mg,Fe)SiO 3 perovskite in <span class="hlt">Earth</span>'s deep lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Zhang, L.; Meng, Y.; Yang, W.</p> <p>2014-05-22</p> <p>The mineralogical constitution of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> dictates the geophysical and geochemical properties of this region. Previous models of a perovskite-dominant lower <span class="hlt">mantle</span> have been built on the assumption that the entire lower <span class="hlt">mantle</span> down to the top of the D" layer contains ferromagnesian silicate [(Mg,Fe)SiO 3] with nominally 10 mole percent Fe. On the basis of experiments in laser-heated diamond anvil cells, at pressures of 95 to 101 gigapascals and temperatures of 2200 to 2400 kelvin, we found that such perovskite is unstable; it loses its Fe and disproportionates to a nearly Fe-free MgSiO 3 perovskite phase and anmore » Fe-rich phase with a hexagonal structure. This observation has implications for enigmatic seismic features beyond ~2000 kilometers depth and suggests that the lower <span class="hlt">mantle</span> may contain previously unidentified major phases.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24926016','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24926016"><span><span class="hlt">Earth</span>'s interior. Dehydration melting at the top of the lower <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schmandt, Brandon; Jacobsen, Steven D; Becker, Thorsten W; Liu, Zhenxian; Dueker, Kenneth G</p> <p>2014-06-13</p> <p>The high water storage capacity of minerals in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing <span class="hlt">mantle</span>. We examined the effects of downwelling from the transition zone into the lower <span class="hlt">mantle</span> with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling <span class="hlt">mantle</span> is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone. Copyright © 2014, American Association for the Advancement of Science.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.458..252F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.458..252F"><span>Sensitivities of <span class="hlt">Earth</span>'s core and <span class="hlt">mantle</span> compositions to accretion and differentiation processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, Rebecca A.; Campbell, Andrew J.; Ciesla, Fred J.</p> <p>2017-01-01</p> <p>The <span class="hlt">Earth</span> and other terrestrial planets formed through the accretion of smaller bodies, with their core and <span class="hlt">mantle</span> compositions primarily set by metal-silicate interactions during accretion. The conditions of these interactions are poorly understood, but could provide insight into the mechanisms of planetary core formation and the composition of <span class="hlt">Earth</span>'s core. Here we present modeling of <span class="hlt">Earth</span>'s core formation, combining results of 100 N-body accretion simulations with high pressure-temperature metal-silicate partitioning experiments. We explored how various aspects of accretion and core formation influence the resulting core and <span class="hlt">mantle</span> chemistry: depth of equilibration, amounts of metal and silicate that equilibrate, initial distribution of oxidation states in the disk, temperature distribution in the planet, and target:impactor ratio of equilibrating silicate. Virtually all sets of model parameters that are able to reproduce the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> composition result in at least several weight percent of both silicon and oxygen in the core, with more silicon than oxygen. This implies that the core's light element budget may be dominated by these elements, and is consistent with ≤1-2 wt% of other light elements. Reproducing geochemical and geophysical constraints requires that <span class="hlt">Earth</span> formed from reduced materials that equilibrated at temperatures near or slightly above the <span class="hlt">mantle</span> liquidus during accretion. The results indicate a strong tradeoff between the compositional effects of the depth of equilibration and the amounts of metal and silicate that equilibrate, so these aspects should be targeted in future studies aiming to better understand core formation conditions. Over the range of allowed parameter space, core and <span class="hlt">mantle</span> compositions are most sensitive to these factors as well as stochastic variations in what the planet accreted as a function of time, so tighter constraints on these parameters will lead to an improved understanding of <span class="hlt">Earth</span>'s core composition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24889632','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24889632"><span>Deep <span class="hlt">mantle</span> structure as a reference frame for movements in and on the <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Torsvik, Trond H; van der Voo, Rob; Doubrovine, Pavel V; Burke, Kevin; Steinberger, Bernhard; Ashwal, Lewis D; Trønnes, Reidar G; Webb, Susan J; Bull, Abigail L</p> <p>2014-06-17</p> <p><span class="hlt">Earth</span>'s residual geoid is dominated by a degree-2 mode, with elevated regions above large low shear-wave velocity provinces on the core-<span class="hlt">mantle</span> boundary beneath Africa and the Pacific. The edges of these deep <span class="hlt">mantle</span> bodies, when projected radially to the <span class="hlt">Earth</span>'s surface, correlate with the reconstructed positions of large igneous provinces and kimberlites since Pangea formed about 320 million years ago. Using this surface-to-core-<span class="hlt">mantle</span> boundary correlation to locate continents in longitude and a novel iterative approach for defining a paleomagnetic reference frame corrected for true polar wander, we have developed a model for absolute plate motion back to earliest Paleozoic time (540 Ma). For the Paleozoic, we have identified six phases of slow, oscillatory true polar wander during which the <span class="hlt">Earth</span>'s axis of minimum moment of inertia was similar to that of Mesozoic times. The rates of Paleozoic true polar wander (<1°/My) are compatible with those in the Mesozoic, but absolute plate velocities are, on average, twice as high. Our reconstructions generate geologically plausible scenarios, with large igneous provinces and kimberlites sourced from the margins of the large low shear-wave velocity provinces, as in Mesozoic and Cenozoic times. This absolute kinematic model suggests that a degree-2 convection mode within the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> may have operated throughout the entire Phanerozoic.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1915602S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1915602S"><span>Using geoneutrinos to constrain the radiogenic power in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Šrámek, Ondřej; Roskovec, Bedřich; Wipperfurth, Scott A.; Xi, Yufei; McDonough, William F.</p> <p>2017-04-01</p> <p>The <span class="hlt">Earth</span>'s engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of <span class="hlt">Earth</span>'s composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving <span class="hlt">mantle</span> dynamics. Together with established geoscientific disciplines (seismology, geodynamics, petrology, mineral physics), experimental particle physics now brings additional constraints to our understanding of <span class="hlt">mantle</span> energetics. Measurements of the <span class="hlt">Earth</span>'s flux of geoneutrinos, electron antineutrinos emitted in β- decays of naturally occurring radionuclides, reveal the amount of uranium and thorium in the <span class="hlt">Earth</span> and set limits on the amount of radiogenic power in the planet. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the <span class="hlt">mantle</span>'s radiogenic power. Measuring geoneutrinos at oceanic locations, distant from nuclear reactors and continental crust, would best reveal the <span class="hlt">mantle</span> flux and by performing a coarse scale geoneutrino tomography could even test the hypothesis of large heterogeneous structures in deep <span class="hlt">mantle</span> enriched in heat-producing elements. The current geoneutrino detecting experiments, KamLAND in Japan and Borexino in Italy, will by year ˜ 2020 be supplemented with three more experiments: SNO+ in Canada, and JUNO and Jinping in China. We predict the geoneutrino flux at all experimental sites. Within ˜ 8 years from today, the combination of data from all experiments will exclude end-member compositional models of the silicate <span class="hlt">Earth</span> at the 1σ level, reveal the radiogenic contribution to the global surface heat loss, and provide tight limits on radiogenic power in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Additionally, we discuss how the geoneutrino measurements at the three relatively near-lying (≤ 3000 km) detectors KamLAND, JUNO, and Jinping may be harnessed to improve the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004Natur.427..234S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004Natur.427..234S"><span>Tungsten isotope evidence that <span class="hlt">mantle</span> plumes contain no contribution from the <span class="hlt">Earth</span>'s core</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scherstén, Anders; Elliott, Tim; Hawkesworth, Chris; Norman, Marc</p> <p>2004-01-01</p> <p>Osmium isotope ratios provide important constraints on the sources of ocean-island basalts, but two very different models have been put forward to explain such data. One model interprets 187Os-enrichments in terms of a component of recycled oceanic crust within the source material. The other model infers that interaction of the <span class="hlt">mantle</span> with the <span class="hlt">Earth</span>'s outer core produces the isotope anomalies and, as a result of coupled 186Os-187Os anomalies, put time constraints on inner-core formation. Like osmium, tungsten is a siderophile (`iron-loving') element that preferentially partitioned into the <span class="hlt">Earth</span>'s core during core formation but is also `incompatible' during <span class="hlt">mantle</span> melting (it preferentially enters the melt phase), which makes it further depleted in the <span class="hlt">mantle</span>. Tungsten should therefore be a sensitive tracer of core contributions in the source of <span class="hlt">mantle</span> melts. Here we present high-precision tungsten isotope data from the same set of Hawaiian rocks used to establish the previously interpreted 186Os-187Os anomalies and on selected South African rocks, which have also been proposed to contain a core contribution. None of the samples that we have analysed have a negative tungsten isotope value, as predicted from the core-contribution model. This rules out a simple core-<span class="hlt">mantle</span> mixing scenario and suggests that the radiogenic osmium in ocean-island basalts can better be explained by the source of such basalts containing a component of recycled crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26542683','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26542683"><span>Atmospheric Ar and Ne returned from <span class="hlt">mantle</span> depths to the <span class="hlt">Earth</span>'s surface by forearc recycling.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Baldwin, Suzanne L; Das, J P</p> <p>2015-11-17</p> <p>In subduction zones, sediments, hydrothermally altered lithosphere, fluids, and atmospheric gases are transported into the <span class="hlt">mantle</span>, where ultrahigh-pressure (UHP) metamorphism takes place. However, the extent to which atmospheric noble gases are trapped in minerals crystallized during UHP metamorphism is unknown. We measured Ar and Ne trapped in phengite and omphacite from the youngest known UHP terrane on <span class="hlt">Earth</span> to determine the composition of Ar and Ne returned from <span class="hlt">mantle</span> depths to the surface by forearc recycling. An (40)Ar/(39)Ar age [7.93 ± 0.10 My (1σ)] for phengite is interpreted as the timing of crystallization at <span class="hlt">mantle</span> depths and indicates that (40)Ar/(39)Ar phengite ages reliably record the timing of UHP metamorphism. Both phengite and omphacite yielded atmospheric (38)Ar/(36)Ar and (20)Ne/(22)Ne. Our study provides the first documentation, to our knowledge, of entrapment of atmospheric Ar and Ne in phengite and omphacite. Results indicate that a subduction barrier for atmospheric-derived noble gases does not exist at <span class="hlt">mantle</span> depths associated with UHP metamorphism. We show that the crystallization age together with the isotopic composition of nonradiogenic noble gases trapped in minerals formed during subsolidus crystallization at <span class="hlt">mantle</span> depths can be used to unambiguously assess forearc recycling of atmospheric noble gases. The flux of atmospheric noble gas entering the deep <span class="hlt">Earth</span> through subduction and returning to the surface cannot be fully realized until the abundances of atmospheric noble gases trapped in exhumed UHP rocks are known.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910044073&hterms=earth+magnetic+field&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dearth%2Bmagnetic%2Bfield','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910044073&hterms=earth+magnetic+field&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dearth%2Bmagnetic%2Bfield"><span>Steady state toroidal magnetic field at <span class="hlt">earth</span>'s core-<span class="hlt">mantle</span> boundary</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Levy, Eugene H.; Pearce, Steven J.</p> <p>1991-01-01</p> <p>Measurements of the dc electrical potential near the top of <span class="hlt">earth</span>'s <span class="hlt">mantle</span> have been extrapolated into the deep <span class="hlt">mantle</span> in order to estimate the strength of the toroidal magnetic field component at the core-<span class="hlt">mantle</span> interface. Recent measurements have been interpreted as indicating that at the core-<span class="hlt">mantle</span> interface, the magnetic toroidal and poloidal field components are approximately equal in magnitude. A motivation for such measurements is to obtain an estimate of the strength of the toroidal magnetic field in the core, a quantity important to our understanding of the geomagnetic field's dynamo generation. Through the use of several simple and idealized calculation, this paper discusses the theoretical relationship between the amplitude of the toroidal magnetic field at the core-<span class="hlt">mantle</span> boundary and the actual amplitude within the core. Even with a very low inferred value of the toroidal field amplitude at the core-<span class="hlt">mantle</span> boundary, (a few gauss), the toroidal field amplitude within the core could be consistent with a magnetohydrodynamic dynamo dominated by nonuniform rotation and having a strong toroidal magnetic field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR31A0425H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR31A0425H"><span>Reduced Lattice Thermal Conductivity of Fe-bearing Bridgmanite in <span class="hlt">Earth</span>'s Deep <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsieh, W. P.; Deschamps, F.; Okuchi, T.; Lin, J. F.</p> <p>2017-12-01</p> <p>Complex seismic and thermo-chemical features have been revealed in <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span>. Particularly, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, which, in turn, may alter the lower <span class="hlt">mantle</span> dynamics and heat flux across core-<span class="hlt">mantle</span> boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. Importantly, the pressure-induced lattice distortion in bridgmanite could affect its lattice thermal conductivity, but this effect remains largely unknown. Here we report our measurements of the lattice thermal conductivity of Fe-bearing and (Fe,Al)-bearing bridgmanites to 120 GPa using optical pump-probe spectroscopy. The thermal conductivity of Fe-bearing bridgmanite increases monotonically with pressure, but drops significantly around 45 GPa presumably due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost <span class="hlt">mantle</span> conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower <span class="hlt">mantle</span> and below would promote <span class="hlt">mantle</span> flow against a potential viscosity barrier, facilitating slabs crossing over the 1000-km depth. Modeling of our results applied to the LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that, while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013Icar..225...50T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013Icar..225...50T"><span><span class="hlt">Mantle</span> dynamics in super-<span class="hlt">Earths</span>: Post-perovskite rheology and self-regulation of viscosity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tackley, P. J.; Ammann, M.; Brodholt, J. P.; Dobson, D. P.; Valencia, D.</p> <p>2013-07-01</p> <p>The discovery of extra-solar "super-<span class="hlt">Earth</span>" planets with sizes up to twice that of <span class="hlt">Earth</span> has prompted interest in their possible lithosphere and <span class="hlt">mantle</span> dynamics and evolution. Simple scalings suggest that super-<span class="hlt">Earths</span> are more likely than an equivalent <span class="hlt">Earth</span>-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigour in the deep <span class="hlt">mantle</span>, which, if extralopated to the largest super-<span class="hlt">Earths</span> might, according to conventional thinking, result in no convection in their deep <span class="hlt">mantles</span> due to the very low effective Rayleigh number. Here we evaluate this. First, as the <span class="hlt">mantle</span> of a super-<span class="hlt">Earth</span> is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1 TPa, for both slowest diffusion (upper-bound rheology) and fastest diffusion (lower-bound rheology) directions. Along a 1600 K adiabat the upper-bound rheology would lead to a post-perovskite layer of a very high (˜1030 Pa s) but relatively uniform viscosity, whereas the lower-bound rheology leads to a post-perovskite viscosity increase of ˜7 orders of magnitude with depth; in both cases the deep <span class="hlt">mantle</span> viscosity would be too high for convection. Second, we use these DFT-calculated values in statistically steady-state numerical simulations of <span class="hlt">mantle</span> convection and lithosphere dynamics of planets with up to ten <span class="hlt">Earth</span> masses. The models assume a compressible <span class="hlt">mantle</span> including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behaviour. Results confirm the likelihood of plate tectonics for planets with <span class="hlt">Earth</span>-like surface conditions (temperature and water) and show a self-regulation of deep <span class="hlt">mantle</span> temperature. The deep <span class="hlt">mantle</span> is not adiabatic; instead feedback between internal heating, temperature and viscosity regulates the temperature such that the viscosity has the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhRvB..84r4102S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhRvB..84r4102S"><span>Effects of spin transition on diffusion of Fe2+ in ferropericlase in <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Saha, Saumitra; Bengtson, Amelia; Crispin, Katherine L.; van Orman, James A.; Morgan, Dane</p> <p>2011-11-01</p> <p>Knowledge of Fe composition in lower-<span class="hlt">mantle</span> minerals (primarily perovskite and ferropericlase) is essential to a complete understanding of the <span class="hlt">Earth</span>'s interior. Fe cation diffusion potentially controls many aspects of the distribution of Fe in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>, including mixing of chemical heterogeneities, element partitioning, and the extent of core-<span class="hlt">mantle</span> communications. Fe in ferropericlase has been shown to undergo a spin transition starting at about 40 GPa and exists in a mixture of high-spin and low-spin states over a wide range of pressures. Present experimental data on Fe transport in ferropericlase is limited to pressures below 35 GPa and provides little information on the pressure dependence of the activation volume and none on the impact of the spin transition on diffusion. Therefore, known experimental data on Fe diffusion cannot be reliably extrapolated to predict diffusion throughout the lower <span class="hlt">mantle</span>. Here, first-principles and statistical modeling are combined to predict diffusion of Fe in ferropericlase over the entire lower <span class="hlt">mantle</span>, including the effects of the Fe spin transition. A thorough statistical thermodynamic treatment is given to fully incorporate the coexistence of high- and low-spin Fe in the model of overall Fe diffusion in the lower <span class="hlt">mantle</span>. Pure low-spin Fe diffuses approximately 104 times slower than high-spin Fe in ferropericlase but Fe diffusion of the mixed-spin state is only about 10 times slower than that of high-spin Fe. The predicted Fe diffusivities demonstrate that ferropericlase is unlikely to be rate limiting in transporting Fe in deep <span class="hlt">earth</span> since much slower Fe diffusion in perovskite is predicted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR43A0460P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR43A0460P"><span>Stability and Solid Solutions of Hydrous Alumino-Silicates in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Panero, W. R.; Caracas, R.</p> <p>2017-12-01</p> <p>The degree to which the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> stores and cycles water in excess of the storage capacity of nominally anhydrous minerals is dependent upon the stability of hydrous phases under <span class="hlt">mantle</span>-relevant pressures, temperatures, and compositions. Two hydrous phases, phase D and phase H are stable to the pressures and temperatures of the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>, suggesting that the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> may participate in the cycling of water. Each phase has a wide solid solution series between MgSi2O6H2-Al2SiO6H2 and MgSiO4H2-2δAlOOH-SiO2, respectively, yet most work addresses end-member compositions for analysis of stability and elastic properties. We present the results of density functional theory calculations on the stability, structure, bonding, partitioning, and elasticity of hydrous phases D and H in the Al2O3-SiO2-MgO-H2O system, addressing the solid solution series through a statistical sampling of site occupancy and calculation of the partition function from the grand canonical ensemble. We find that the addition of Al to the endmember compositions stabilizes each phase to higher temperatures through additional configurational entropy. We further find that solid solutions tend not to undergo hydrogen-bond symmetrization as is found in the end member compositions as a result of non-symmetric bonding environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T44D..01B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T44D..01B"><span>Visualising <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> based on Global Adjoint Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bozdag, E.; Pugmire, D.; Lefebvre, M. P.; Hill, J.; Komatitsch, D.; Peter, D. B.; Podhorszki, N.; Tromp, J.</p> <p>2017-12-01</p> <p>Recent advances in 3D wave propagation solvers and high-performance computing have enabled regional and global full-waveform inversions. Interpretation of tomographic models is often done on visually. Robust and efficient visualization tools are necessary to thoroughly investigate large model files, particularly at the global scale. In collaboration with Oak Ridge National Laboratory (ORNL), we have developed effective visualization tools and used for visualization of our first-generation global model, GLAD-M15 (Bozdag et al. 2016). VisIt (https://wci.llnl.gov/simulation/computer-codes/visit/) is used for initial exploration of the models and for extraction of seismological features. The broad capability of VisIt, and its demonstrated scalability proved valuable for experimenting with different visualization techniques, and in the creation of timely results. Utilizing VisIt's plugin-architecture, a data reader plugin was developed, which reads the ADIOS (https://www.olcf.ornl.gov/center-projects/adios/) format of our model files. Blender (https://www.blender.org) is used for the setup of lighting, materials, camera paths and rendering of geometry. Python scripting was used to control the orchestration of different geometries, as well as camera animation for 3D movies. While we continue producing 3D contour plots and movies for various seismic parameters to better visualize plume- and slab-like features as well as anisotropy throughout the <span class="hlt">mantle</span>, our aim is to make visualization an integral part of our global adjoint tomography workflow to routinely produce various 2D cross-sections to facilitate examination of our models after each iteration. This will ultimately form the basis for use of pattern recognition techniques in our investigations. Simulations for global adjoint tomography are performed on ORNL's Titan system and visualization is done in parallel on ORNL's post-processing cluster Rhea.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoRL..42.3338C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoRL..42.3338C"><span>Electrical conductivity of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> from the first Swarm magnetic field measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Civet, F.; Thébault, E.; Verhoeven, O.; Langlais, B.; Saturnino, D.</p> <p>2015-05-01</p> <p>We present a 1-D electrical conductivity profile of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> down to 2000 km derived from L1b Swarm satellite magnetic field measurements from November 2013 to September 2014. We first derive a model for the main magnetic field, correct the data for a lithospheric field model, and additionally select the data to reduce the contributions of the ionospheric field. We then model the primary and induced magnetospheric fields for periods between 2 and 256 days and perform a Bayesian inversion to obtain the probability density function for the electrical conductivity as function of depth. The conductivity increases by 3 orders of magnitude in the 400-900 km depth range. Assuming a pyrolitic <span class="hlt">mantle</span> composition, this profile is interpreted in terms of temperature variations leading to a temperature gradient in the lower <span class="hlt">mantle</span> that is close to adiabatic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUSM.V34A..01D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUSM.V34A..01D"><span><span class="hlt">Earth</span>'s Deep Carbon Cycle Constrained by Partial Melting of <span class="hlt">Mantle</span> Peridotite and Eclogite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dasgupta, R.; Hirschmann, M. M.; Withers, A. C.</p> <p>2006-05-01</p> <p>The mass of carbon in the <span class="hlt">mantle</span> is thought to exceed that in all <span class="hlt">Earth</span>'s other reservoirs combined1 and large fluxes of carbon are cycled into and out of the <span class="hlt">mantle</span> via subduction and volcanic emission. Devolatilization is known to release water in the <span class="hlt">mantle</span> wedge, but release of carbon could be delayed if the relevant decarbonation reactions or solidi of oceanic crust are not encountered along P-T path of subduction. Outgassing of CO2 from the <span class="hlt">mantle</span> also has a critical influence on <span class="hlt">Earth</span>'s climate for time scales of 108-109 yr1. The residence time for carbon in the <span class="hlt">mantle</span> is thought to exceed the age of the <span class="hlt">Earth</span>1,2, but it could be significantly shorter owing to pervasive deep melting beneath oceanic ridges. The dominant influx of carbon is via carbonate in altered ocean-floor basalts, which survives decarbonation during subduction. Our experiments demonstrate that solidi of carbonated eclogite remain hotter than average subduction geotherms at least as deep as transition zone3, and thus significant subducted C is delivered to the deep <span class="hlt">Earth</span>, rather than liberated in the shallow <span class="hlt">mantle</span> by melting. Flux of CO2 into the <span class="hlt">mantle</span>, assuming average estimate of carbon in altered ocean crust of 0.21 wt. % CO24, can amount to 0.15 × 1015 g/yr. In upwelling <span class="hlt">mantle</span>, however, partial melting of carbonated eclogite releases calcio-dolomitic carbonatite melt at depths near ~400 km and metasomatically implants carbonate to surrounding peridotite. Thus, volcanic release of CO2 to basalt source regions is likely controlled by the solidus of carbonated peridotite. Our recent experiments with nominally anhydrous, carbonate-bearing garnet lherzolite indicate that the solidus of peridotite with a trace amount of CO2 is ~500 °C lower than that of volatile-free peridotite at 10 GPa5. In upwelling <span class="hlt">mantle</span> the solidus of carbonated lherzolite is ~100-200 km shallower than that of eclogite+CO2, but beneath oceanic ridges, initial melting occurs as deep as 300-330 km. For peridotite</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19820038730&hterms=earths+outer+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dearths%2Bouter%2Bcore','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19820038730&hterms=earths+outer+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dearths%2Bouter%2Bcore"><span>Composition of the <span class="hlt">earth</span>'s upper <span class="hlt">mantle</span>. II - Volatile trace elements in ultramafic xenoliths</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Morgan, J. W.; Wandless, G. A.; Petrie, R. K.; Irving, A. J.</p> <p>1980-01-01</p> <p>Radiochemical neutron activation analysis was used to determine the nine volatile elements Ag, Bi, Cd, In, Sb, Se, Te, Tl, and Zn in 19 ultramafic rocks, consisting mainly of spinel and garnet lherzolites. A sheared garnet lherzolite, PHN 1611, may approximate undepleted <span class="hlt">mantle</span> material and tends to have a higher volatile element content than the depleted <span class="hlt">mantle</span> material represented by spinel lherzolites. Comparisons of continental basalts with PHN 1611 and of oceanic ridge basalts with spinel lherzolites show similar basalt: source material partition factors for eight of the nine volatile elements, Sb being the exception. The strong depletion of Te and Se in the <span class="hlt">mantle</span>, relative to lithophile elements of similar volatility, suggests that 97% of the <span class="hlt">earth</span>'s S, Se and Te may be in the outer core.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12460482','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12460482"><span>The thermochemical structure and evolution of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>: constraints and numerical models.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tackley, Paul J; Xie, Shunxing</p> <p>2002-11-15</p> <p>Geochemical observations place several constraints on geophysical processes in the <span class="hlt">mantle</span>, including a requirement to maintain several distinct reservoirs. Geophysical constraints limit plausible physical locations of these reservoirs to a thin basal layer, isolated deep 'piles' of material under large-scale <span class="hlt">mantle</span> upwellings, high-viscosity blobs/plums or thin strips throughout the <span class="hlt">mantle</span>, or some combination of these. A numerical model capable of simulating the thermochemical evolution of the <span class="hlt">mantle</span> is introduced. Preliminary simulations are more differentiated than <span class="hlt">Earth</span> but display some of the proposed thermochemical processes, including the generation of a high-mu <span class="hlt">mantle</span> reservoir by recycling of crust, and the generation of a high-(3)He/(4)He reservoir by recycling of residuum, although the resulting high-(3)He/(4)He material tends to aggregate near the top, where mid-ocean-ridge melting should sample it. If primitive material exists as a dense basal layer, it must be much denser than subducted crust in order to retain its primitive (e.g. high-(3)He) signature. Much progress is expected in the near future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28706289','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28706289"><span>Hydrogen self-diffusion in single crystal olivine and electrical conductivity of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Novella, Davide; Jacobsen, Benjamin; Weber, Peter K; Tyburczy, James A; Ryerson, Frederick J; Du Frane, Wyatt L</p> <p>2017-07-13</p> <p>Nominally anhydrous minerals formed deep in the <span class="hlt">mantle</span> and transported to the <span class="hlt">Earth</span>'s surface contain tens to hundreds of ppm wt H 2 O, providing evidence for the presence of dissolved water in the <span class="hlt">Earth</span>'s interior. Even at these low concentrations, H 2 O greatly affects the physico-chemical properties of <span class="hlt">mantle</span> materials, governing planetary dynamics and evolution. The diffusion of hydrogen (H) controls the transport of H 2 O in the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>, but is not fully understood for olivine ((Mg, Fe) 2 SiO 4 ) the most abundant mineral in this region. Here we present new hydrogen self-diffusion coefficients in natural olivine single crystals that were determined at upper <span class="hlt">mantle</span> conditions (2 GPa and 750-900 °C). Hydrogen self-diffusion is highly anisotropic, with values at 900 °C of 10 -10.9 , 10 -12.8 and 10 -11.9 m 2 /s along [100], [010] and [001] directions, respectively. Combined with the Nernst-Einstein relation, these diffusion results constrain the contribution of H to the electrical conductivity of olivine to be σ H  = 10 2.12 S/m·C H2O ·exp -187kJ/mol/(RT) . Comparisons between the model presented in this study and magnetotelluric measurements suggest that plausible H 2 O concentrations in the upper <span class="hlt">mantle</span> (≤250 ppm wt) can account for high electrical conductivity values (10 -2 -10 -1  S/m) observed in the asthenosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940007738&hterms=Earths+last+life&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DEarths%2Blast%2Blife','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940007738&hterms=Earths+last+life&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DEarths%2Blast%2Blife"><span>Oxidation state of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> during the last 3800 million years: Implications for the origin of life</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Delano, J. W.</p> <p>1993-01-01</p> <p>A popular, as well as scientifically rigorous, scenario for the origin of life on <span class="hlt">Earth</span> involves the production of organic molecules by interaction of lightning (or other forms of energy) with a chemically reducing atmosphere in the <span class="hlt">early</span> history of <span class="hlt">Earth</span>. Experiments since the 1950's have convincingly demonstrated that the yield of organic molecules is high when the atmosphere contains molecular hydrogen, methane, ammonia, and water vapor. Additional work has also shown that such a highly reducing atmosphere might not, however, have been sufficiently long-lived in the presence of intense solar ultraviolet radiation for life to have formed from it. One way of maintaining such an atmosphere would be to have a continual replenishment of the reduced gases by prolonged volcanic outgassing from a reducing of <span class="hlt">Earth</span>'s interior. The length of time that this replenishment might need to continue is in part constrained by the flux of asteroids onto the <span class="hlt">Earth</span>'s surface containing sufficient energy to destroy most, if not all, life that had developed up to that point in time. If a reducing atmosphere is a key ingredient for the origin of life on <span class="hlt">Earth</span>, the time of the last environmental sterilization due to large impacts would be an important constraint. In a deep marine setting (e.g., hydrothermal vent), the last global sterilization might have occurred at 4200-4000 Ma. On the <span class="hlt">Earth</span>'s surface, the last global sterilization event might have occurred at 4000-3700 Ma. If these are meaningful constraints, how likely is it that a reducing atmosphere could have survived on the <span class="hlt">Earth</span> until about 3800 Ma ago? Due to the importance of replenishing this atmosphere with reducing components by volcanic outgassing from the <span class="hlt">mantle</span>, geochemical information on the history of the <span class="hlt">mantle</span>'s oxidation state would be useful for addressing this question. Geochemical and experimental data discussed in this abstract suggest that extrusive mafic volcanics derived from the upper <span class="hlt">mantle</span> have had</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V42A..01C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V42A..01C"><span>A Geochemical View on the Interplay Between <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> and Crust</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chauvel, C.</p> <p>2017-12-01</p> <p>Over most of <span class="hlt">Earth</span> history, oceanic and continental crust was created and destroyed. The formation of both types of crust involves the crystallization and differentiation of magmas producing by <span class="hlt">mantle</span> melting. Their destruction proceeds by mechanical erosion and weathering above sea level, chemical alteration on the seafloor, and bulk recycling in subduction zones. All these processes enrich of some chemical element and deplete others but each process has its own effect on chemical elements. While the flux of material from <span class="hlt">mantle</span> to crust is well understood, the return flux is much more complex. In contrast to <span class="hlt">mantle</span> processes, erosion, weathering, chemical alteration and sedimentary processes strongly decouple elements such as the rare <span class="hlt">earths</span> and high-field strength elements due to their different solubilities in surface fluids and mineralogical sorting during transport. Soluble elements such as strontium or uranium are quantitatively transported to the ocean by rivers and decoupled from less soluble elements. Over geological time, such decoupling significantly influences the extent to which chemical elements remain at the <span class="hlt">Earth</span>'s surface or find their way back to the <span class="hlt">mantle</span> through subduction zones. For example, elements like Hf or Nd are retained in heavy minerals on continents whereas U and Sr are transported to the oceans and then in subduction zones to the <span class="hlt">mantle</span>. The consequence is that different radiogenic isotopic systems give disparate age estimates for the continental crust; e.g, Hf ages could be too old. In subduction zones, chemical elements are also decoupled, due to contrasting behavior during dehydration or melting in subducting slabs. The material sent back into the <span class="hlt">mantle</span> is generally enriched in non-soluble elements while most fluid-mobile elements return to the crust. This, in turn, affects the relationship between the Rb-Sr, Sm-Nd, Lu-Hf and U-Th-Pb isotopic systems and creates correlations unlike those based on magmatic processes. By</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17757971','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17757971"><span>Helium Flux from the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> as Estimated from Hawaiian Fumarolic Degassing.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Naughton, J J; Lee, J H; Keeling, D; Finlayson, J B; Dority, G</p> <p>1973-04-06</p> <p>Averaged helium to carbon dioxide ratios measured from systematic collections of gases from Sulphur Bank fumarole. Kilauea, Hawaii, when coupled with estimates of carbon in the <span class="hlt">earth</span>'s crust, give a helium flux of 1 x 105 atoms per square centimeter per second. This is within the lower range of other estimates, and may represent the flux from deep-seated sources in the upper <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhRvB..90s5205H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhRvB..90s5205H"><span>First-principles study of intermediate-spin ferrous iron in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsu, Han; Wentzcovitch, Renata M.</p> <p>2014-11-01</p> <p>Spin crossover of iron is of central importance in solid <span class="hlt">Earth</span> geophysics. It impacts all physical properties of minerals that altogether constitute ˜95 vol% of the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>: ferropericlase [(Mg,Fe)O] and Fe-bearing magnesium silicate (MgSiO3) perovskite. Despite great strides made in the past decade, the existence of an intermediate-spin (IS) state in ferrous iron (Fe2 +) (with total electron spin S =1 ) and its possible role in the pressure-induced spin crossover in these lower-<span class="hlt">mantle</span> minerals still remain controversial. Using density functional theory + self-consistent Hubbard U (DFT+Usc ) calculations, we investigate all possible types of IS states of Fe2 + in (Mg,Fe)O and (Mg,Fe)SiO3 perovskite. Among the possible IS states in these minerals, the most probable IS state has an electronic configuration that significantly reduces the electron overlap and the iron nuclear quadrupole splitting (QS). These most probable IS states, however, are still energetically disfavored, and their QSs are inconsistent with Mössbauer spectra. We therefore conclude that IS Fe2 + is highly unlikely in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22348175-water-cycling-between-ocean-mantle-super-earths-need-waterworlds','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22348175-water-cycling-between-ocean-mantle-super-earths-need-waterworlds"><span>Water cycling between ocean and <span class="hlt">mantle</span>: Super-<span class="hlt">earths</span> need not be waterworlds</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Cowan, Nicolas B.; Abbot, Dorian S., E-mail: n-cowan@northwestern.edu</p> <p>2014-01-20</p> <p>Large terrestrial planets are expected to have muted topography and deep oceans, implying that most super-<span class="hlt">Earths</span> should be entirely covered in water, so-called waterworlds. This is important because waterworlds lack a silicate weathering thermostat so their climate is predicted to be less stable than that of planets with exposed continents. In other words, the continuously habitable zone for waterworlds is much narrower than for <span class="hlt">Earth</span>-like planets. A planet's water is partitioned, however, between a surface reservoir, the ocean, and an interior reservoir, the <span class="hlt">mantle</span>. Plate tectonics transports water between these reservoirs on geological timescales. Degassing of melt at mid-ocean ridgesmore » and serpentinization of oceanic crust depend negatively and positively on seafloor pressure, respectively, providing a stabilizing feedback on long-term ocean volume. Motivated by <span class="hlt">Earth</span>'s approximately steady-state deep water cycle, we develop a two-box model of the hydrosphere and derive steady-state solutions to the water partitioning on terrestrial planets. Critically, hydrostatic seafloor pressure is proportional to surface gravity, so super-<span class="hlt">Earths</span> with a deep water cycle will tend to store more water in the <span class="hlt">mantle</span>. We conclude that a tectonically active terrestrial planet of any mass can maintain exposed continents if its water mass fraction is less than ∼0.2%, dramatically increasing the odds that super-<span class="hlt">Earths</span> are habitable. The greatest source of uncertainty in our study is <span class="hlt">Earth</span>'s current <span class="hlt">mantle</span> water inventory: the greater its value, the more robust planets are to inundation. Lastly, we discuss how future missions can test our hypothesis by mapping the oceans and continents of massive terrestrial planets.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.P32A..06B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.P32A..06B"><span>On the Modes of <span class="hlt">Mantle</span> Convection in Super-<span class="hlt">Earths</span> (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bercovici, D.</p> <p>2010-12-01</p> <p>The relatively recent discovery of larger-than-<span class="hlt">Earth</span> extra-solar terrestrial planets has opened up many possibilities for different modes of interior dynamics, including <span class="hlt">mantle</span> convection. A great deal of basic mineral physics is still needed to understand the state of matter and rheology of these super terrestrials, even assuming similar compositions to <span class="hlt">Earth</span> (which is itself unlikely given the effect of singular events such as giant impacts and lunar formation). There has been speculation and debate as to whether the larger Rayleigh numbers of super-<span class="hlt">Earth</span>'s would promote plate tectonic style recycling, which is considered a crucial negative feedback for buffering atmospheric CO2 and stabilizing climate through weathering and mineral carbonation. However, models of plate generation through grainsize-reducing damage (see Foley & Bercovici this session) show that the effect of larger Rayleigh numbers is offset by an increase in the lithosphere-<span class="hlt">mantle</span> viscosity contrast (due to a hotter <span class="hlt">mantle</span>). Super-<span class="hlt">Earth</span>'s are therefore probably no more (or less) prone to plate tectonics than "normal" <span class="hlt">Earths</span>; other conditions like surface temperature (and thus orbital position) are more important than size for facilitating plate tectonic cycling, which is of course more in keeping with observations in our own solar system (i.e., the disparity between <span class="hlt">Earth</span> and Venus). Regardless, two major questions remain. First, what are the other modes of convective recycling that would possibly buffer CO2 and allow for a negative feedback that stabilizes climate? For example, subarial basaltic volcanism associated with plume or diapiric convection could potentially draw down CO2 because of the reactibility of mafic minerals; this mechanism possibly helped trigger Snow Ball events in the Proterozoic <span class="hlt">Earth</span> during break-up of near-equatorial super-continents. Second, what observations of exo-planets provide tests for theories of tectonics or convective cycling? Spectroscopic techniques are most</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23282365','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23282365"><span>The oxidation state of the <span class="hlt">mantle</span> and the extraction of carbon from <span class="hlt">Earth</span>'s interior.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stagno, Vincenzo; Ojwang, Dickson O; McCammon, Catherine A; Frost, Daniel J</p> <p>2013-01-03</p> <p>Determining the oxygen fugacity of <span class="hlt">Earth</span>'s silicate <span class="hlt">mantle</span> is of prime importance because it affects the speciation and mobility of volatile elements in the interior and has controlled the character of degassing species from the <span class="hlt">Earth</span> since the planet's formation. Oxygen fugacities recorded by garnet-bearing peridotite xenoliths from Archaean lithosphere are of particular interest, because they provide constraints on the nature of volatile-bearing metasomatic fluids and melts active in the oldest <span class="hlt">mantle</span> samples, including those in which diamonds are found. Here we report the results of experiments to test garnet oxythermobarometry equilibria under high-pressure conditions relevant to the deepest <span class="hlt">mantle</span> xenoliths. We present a formulation for the most successful equilibrium and use it to determine an accurate picture of the oxygen fugacity through cratonic lithosphere. The oxygen fugacity of the deepest rocks is found to be at least one order of magnitude more oxidized than previously estimated. At depths where diamonds can form, the oxygen fugacity is not compatible with the stability of either carbonate- or methane-rich liquid but is instead compatible with a metasomatic liquid poor in carbonate and dominated by either water or silicate melt. The equilibrium also indicates that the relative oxygen fugacity of garnet-bearing rocks will increase with decreasing depth during adiabatic decompression. This implies that carbon in the asthenospheric <span class="hlt">mantle</span> will be hosted as graphite or diamond but will be oxidized to produce carbonate melt through the reduction of Fe(3+) in silicate minerals during upwelling. The depth of carbonate melt formation will depend on the ratio of Fe(3+) to total iron in the bulk rock. This 'redox melting' relationship has important implications for the onset of geophysically detectable incipient melting and for the extraction of carbon dioxide from the <span class="hlt">mantle</span> through decompressive melting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28377520','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28377520"><span>Hydration-reduced lattice thermal conductivity of olivine in <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chang, Yun-Yuan; Hsieh, Wen-Pin; Tan, Eh; Chen, Jiuhua</p> <p>2017-04-18</p> <p><span class="hlt">Earth</span>'s water cycle enables the incorporation of water (hydration) in <span class="hlt">mantle</span> minerals that can influence the physical properties of the <span class="hlt">mantle</span>. Lattice thermal conductivity of <span class="hlt">mantle</span> minerals is critical for controlling the temperature profile and dynamics of the <span class="hlt">mantle</span> and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg 0.9 Fe 0.1 ) 2 SiO 4 (Fo90) up to 15 gigapascals using an ultrafast optical pump-probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at <span class="hlt">mantle</span> transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine-wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper <span class="hlt">mantle</span> and enhance water transportation to the transition zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998PhDT.......273C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998PhDT.......273C"><span>Silicate garnet studies at high pressures: A view into the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Conrad, Pamela Gales</p> <p></p> <p>Silicate garnets are an abundant component in the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> and transition zone. Therefore, an understanding of garnet behavior under the pressure and temperature conditions of the <span class="hlt">mantle</span> is critical to the development of models for <span class="hlt">mantle</span> mineralogy and dynamics. Work from three projects is presented in this report. Each investigation explores an aspect of silicate garnet behavior under high pressures. Moreover, each investigation was made possible by state-of-the-art methods that have previously been unavailable. Brillouin scattering was used to determine the elastic constants and aggregate elastic moduli of three end-member garnets at high pressures in a diamond anvil cell. These are the first high-pressure measurements of the elastic constants of end-member silicate garnets by direct measurement of acoustic velocities. The results indicate that the pressure dependence of silicate garnet elastic constants varies with composition. Therefore, extrapolation from measurements on mixed composition garnets is not possible. A new method of laser heating minerals in a diamond anvil cell has made possible the determination of the high-pressure and high-temperature stability of almandine garnet. This garnet does not transform to a silicate perovskite phase as does pyrope garnet, but it decomposes to its constituent oxides: FeO, Alsb2Osb3, and SiOsb2. These results disprove an earlier prediction that ferrous iron may expand the stability field of garnet to the lower <span class="hlt">mantle</span>. The present results demonstrate that this is not the case. The third topic is a presentation of the results of a new technique for studying inclusions in <span class="hlt">mantle</span> xenoliths with synchrotron X-ray microdiffraction. The results demonstrate the importance of obtaining structural as well as chemical information on inclusions within diamonds and other high-pressure minerals. An unusual phase with garnet composition is investigated and several other phases are identified from a suite of natural</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20070020208&hterms=earths+outer+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dearths%2Bouter%2Bcore','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20070020208&hterms=earths+outer+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dearths%2Bouter%2Bcore"><span>Motion of the <span class="hlt">Mantle</span> in the Translational Modes of the <span class="hlt">Earth</span> and Mercury</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grinfeld, Pavel; Wisdom, Jack</p> <p>2005-01-01</p> <p>Slichter modes refer to the translational motion of the inner core with respect to the outer core and the <span class="hlt">mantle</span>. The polar Slichter mode is the motion of the inner core along the axis of rotation. Busse presented an analysis of the polar mode which yielded an expression for its period. Busse's analysis included the assumption that the <span class="hlt">mantle</span> was stationary. This approximation is valid for planets with small inner cores, such as the <span class="hlt">Earth</span> whose inner core is about 1/60 of the total planet mass. On the other hand, many believe that Mercury's core may be enormous. If so, the motion of the <span class="hlt">mantle</span> should be expected to produce a significant effect. We present a formal framework for including the motion of the <span class="hlt">mantle</span> in the analysis of the translational motion of the inner core. We analyze the effect of the motion of the <span class="hlt">mantle</span> on the Slichter modes for a non-rotating planet with an inner core of arbitrary size. We omit the effects of viscosity in the outer core, magnetic effects, and solid tides. Our approach is perturbative and is based on a linearization of Euler's equations for the motion of the fluid and Newton's second law for the motion of the inner core. We find an analytical expression for the period of the Slichter mode. Our result agrees with Busse's in the limiting case of small inner core. We present the unexpected result that even for Mercury the motion of the <span class="hlt">mantle</span> does not significantly change the period of oscillation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920060793&hterms=history+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dhistory%2BEarth','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920060793&hterms=history+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dhistory%2BEarth"><span>Internally heated <span class="hlt">mantle</span> convection and the thermal and degassing history of the <span class="hlt">earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Williams, David R.; Pan, Vivian</p> <p>1992-01-01</p> <p>An internally heated model of parameterized whole <span class="hlt">mantle</span> convection with viscosity dependent on temperature and volatile content is examined. The model is run for 4l6 Gyr, and temperature, heat flow, degassing and regassing rates, stress, and viscosity are calculated. A nominal case is established which shows good agreement with accepted <span class="hlt">mantle</span> values. The effects of changing various parameters are also tested. All cases show rapid cooling <span class="hlt">early</span> in the planet's history and strong self-regulation of viscosity due to the temperature and volatile-content dependence. The effects of weakly stress-dependent viscosity are examined within the bounds of this model and are found to be small. <span class="hlt">Mantle</span> water is typically outgassed rapidly to reach an equilibrium concentration on a time scale of less than 200 Myr for almost all models, the main exception being for models which start out with temperatures well below the melting temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2897N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2897N"><span>Self-consistent formation of continents on <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Noack, Lena; Van Hoolst, Tim; Breuer, Doris; Dehant, Véronique</p> <p>2013-04-01</p> <p>In our study we want to understand how <span class="hlt">Earth</span> evolved with time and examine the initiation of plate tectonics and the possible formation of continents on <span class="hlt">Earth</span>. Plate tectonics and continents seem to influence the likelihood of a planet to harbour life [1], and both are strongly influenced by the planetary interior (e.g. <span class="hlt">mantle</span> temperature and rheology) and surface conditions (e.g. stabilizing effect of continents, atmospheric temperature), and may also depend on the biosphere. <span class="hlt">Earth</span> is the only terrestrial planet (i.e. with a rocky <span class="hlt">mantle</span> and iron core) in the solar system where long-term plate tectonics evolved. Knowing the factors that have a strong influence on the occurrence of plate tectonics allows for prognoses about plate tectonics on terrestrial exoplanets that have been detected in the past decade, and about the likelihood of these planets to harbour <span class="hlt">Earth</span>-like life. For this purpose, planetary interior and surface processes are coupled via 'particles' as computational tracers in the 3D code GAIA [2,3]. These particles are dispersed in the <span class="hlt">mantle</span> and crust of the modelled planet and can track the relevant rock properties (e.g. density or water content) over time. During the thermal evolution of the planet, the particles are advected due to <span class="hlt">mantle</span> convection and along melt paths towards the surface and help to gain information about the thermo-chemical system. This way basaltic crust that is subducted into the silicate <span class="hlt">mantle</span> is traced in our model. It is treated differently than <span class="hlt">mantle</span> silicates when re-molten, such that granitic (felsic) crust is produced (similar to the evolution of continental crust on <span class="hlt">early</span> <span class="hlt">Earth</span> [4]), which is stored in the particle properties. We apply a pseudo-plastic rheology and use small friction coefficients (since an increased reference viscosity is used in our model). We obtain initiation of plate tectonics and self-consistent formation of pre-continents after a few Myr up to several Gyr - depending on the initial conditions</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21901010','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21901010"><span>The tungsten isotopic composition of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> before the terminal bombardment.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Willbold, Matthias; Elliott, Tim; Moorbath, Stephen</p> <p>2011-09-07</p> <p>Many precious, 'iron-loving' metals, such as gold, are surprisingly abundant in the accessible parts of the <span class="hlt">Earth</span>, given the efficiency with which core formation should have removed them to the planet's deep interior. One explanation of their over-abundance is a 'late veneer'--a flux of meteorites added to the <span class="hlt">Earth</span> after core formation as a 'terminal' bombardment that culminated in the cratering of the Moon. Some 3.8 billion-year-old rocks from Isua, Greenland, are derived from sources that retain an isotopic memory of events pre-dating this cataclysmic meteorite shower. These Isua samples thus provide a window on the composition of the <span class="hlt">Earth</span> before such a late veneer and allow a direct test of its importance in modifying the composition of the planet. Using high-precision (less than 6 parts per million, 2 standard deviations) tungsten isotope analyses of these rocks, here we show that they have a isotopic tungsten ratio (182)W/(184)W that is significantly higher (about 13 parts per million) than modern terrestrial samples. This finding is in good agreement with the expected influence of a late veneer. We also show that alternative interpretations, such as partial remixing of a deep-<span class="hlt">mantle</span> reservoir formed in the Hadean eon (more than four billion years ago) or core-<span class="hlt">mantle</span> interaction, do not explain the W isotope data well. The decrease in <span class="hlt">mantle</span> (182)W/(184)W occurs during the Archean eon (about four to three billion years ago), potentially on the same timescale as a notable decrease in (142)Nd/(144)Nd (refs 3 and 6). We speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of <span class="hlt">mantle</span> convection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P51A2121W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P51A2121W"><span>Source of Volatiles in <span class="hlt">Earth</span>'s Deep <span class="hlt">Mantle</span> from Neon Isotope Systematics in the South Atlantic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Williams, C. D.; Mukhopadhyay, S.</p> <p>2016-12-01</p> <p>The noble gases play an important role in understanding <span class="hlt">Earth</span>'s accretion and subsequent evolution. Neon isotopes in particular have the potential to distinguish between distinct sources of <span class="hlt">Earth</span>'s volatiles e.g., acquisition of nebular gas, solar wind implanted materials or chondritic meteorites and their components. The neon isotopic composition of the deep <span class="hlt">mantle</span> remains subject to debate with the majority of <span class="hlt">mantle</span>-derived basalts displaying maximum 20Ne/22Ne ratios less than 12.5, similar to values determined for the convective <span class="hlt">mantle</span> (20Ne/22Ne = 12.49 +/- 0.04; [1]). These values are also much lower than those of solar wind (20Ne/22Ne = 13.8; [2,3]) and estimates of the nebular gas (20Ne/22Ne = 13.4; [4]) but comparable to solar wind implanted meteoritic materials (20Ne/22Ne = 12.5-12.7; [5]). Here we determine the neon isotopic composition of <span class="hlt">mantle</span>-derived materials from the south Atlantic. These samples display strong linear correlations in 20Ne/22Ne-21Ne/22Ne space with maximum 20Ne/22Ne ratios that are resolvable from and higher than materials derived from the convecting <span class="hlt">mantle</span> as well as models of solar wind implantation. These results supplement a growing database of <span class="hlt">mantle</span> materials characterized by 20Ne/22Ne ratios greater than 12.5, challenging the notion that the entire <span class="hlt">mantle</span> acquired volatiles from solar wind implanted meteoritic materials. In this presentation we will explore alternative origins for these volatiles and provide testable predictions for each scenario. [1] G. Holland, C.J. Ballentine.. Nature 441 (2006), 186-191. [2] A. Gimberg et al. GCA 72 (2008), 626-645. [3] V.S. Heber et al. GCA 73 (2009), 7414-7432. [4] V. S. Heber et al. ApJ 759 (2012), 121. [5] R. Wieler in: D. Porcelli, C.J. Ballentine, R. Wieler (Eds.), Reviews in Mineralogy and Geochemistry 47 (2002), 21-70.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1812995P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1812995P"><span>Effects of differentiation on the geodynamics of the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Piccolo, Andrea; Kaus, Boris; White, Richard; Johnson, Tim</p> <p>2016-04-01</p> <p>Archean geodynamic processes are not well understood, but there is general agreement that the <span class="hlt">mantle</span> potential temperature was higher than present, and that as a consequence significant amounts of melt were produced both in the <span class="hlt">mantle</span> and any overlying crust. This has likely resulted in crustal differentiation. An <span class="hlt">early</span> attempt to model the geodynamic effects of differentiation was made by Johnson et al. (2014), who used numerical modeling to investigate the crust production and recycling in conjunction with representative phase diagrams (based on the inferred chemical composition of the primary melt in accordance with the Archean temperature field). The results of the simulations show that the base of the over-thickened primary basaltic crust becomes gravitational unstable due to the mineral assemblage changes. This instability leads to the dripping of dense material into the <span class="hlt">mantle</span>, which causes an asthenospheric return flow, local partial melting and new primary crust generation that is rapidly recycled in to <span class="hlt">mantle</span>. Whereas they gave important insights, the previous simulations were simplified in a number of aspects: 1) the rheology employed was viscous, and both elasticity and pressure-dependent plasticity were not considered; 2) extracted <span class="hlt">mantle</span> melts were 100% transformed into volcanic rocks, whereas on the present day <span class="hlt">Earth</span> only about 20-30% are volcanic and the remainder is plutonic; 3) the effect of a free surface was not studied in a systematic manner. In order to better understand how these simplifications affect the geodynamic models, we here present additional simulations to study the effects of each of these parameters. Johnson, T.E., Brown, M., Kaus, B., and VanTongeren, J.A., 2014, Delamination and recycling of Archaean crust caused by gravitational instabilities: Nature Geoscience, v. 7, no. 1, p. 47-52, doi: 10.1038/NGEO2019.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.2643W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.2643W"><span><span class="hlt">Mantle</span> convection and the distribution of geochemical reservoirs in the silicate shell of the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walzer, Uwe; Hendel, Roland</p> <p>2010-05-01</p> <p>We present a dynamic 3-D spherical-shell model of <span class="hlt">mantle</span> convection and the evolution of the chemical reservoirs of the <span class="hlt">Earth`s</span> silicate shell. Chemical differentiation, convection, stirring and thermal evolution constitute an inseparable dynamic system. Our model is based on the solution of the balance equations of mass, momentum, energy, angular momentum, and four sums of the number of atoms of the pairs 238U-206Pb, 235U-207Pb, 232Th-208Pb, and 40K-40Ar. Similar to the present model, the continental crust of the real <span class="hlt">Earth</span> was not produced entirely at the start of the evolution but developed episodically in batches [1-7]. The details of the continental distribution of the model are largely stochastic, but the spectral properties are quite similar to the present real <span class="hlt">Earth</span>. The calculated Figures reveal that the modeled present-day <span class="hlt">mantle</span> has no chemical stratification but we find a marble-cake structure. If we compare the observational results of the present-day proportion of depleted MORB <span class="hlt">mantle</span> with the model then we find a similar order of magnitude. The MORB source dominates under the lithosphere. In our model, there are nowhere pure unblended reservoirs in the <span class="hlt">mantle</span>. It is, however, remarkable that, in spite of 4500 Ma of solid-state <span class="hlt">mantle</span> convection, certain strong concentrations of distributed chemical reservoirs continue to persist in certain volumes, although without sharp abundance boundaries. We deal with the question of predictable and stochastic portions of the phenomena. Although the convective flow patterns and the chemical differentiation of oceanic plateaus are coupled, the evolution of time-dependent Rayleigh number, Rat , is relatively well predictable and the stochastic parts of the Rat(t)-curves are small. Regarding the juvenile growth rates of the total mass of the continents, predictions are possible only in the first epoch of the evolution. Later on, the distribution of the continental-growth episodes is increasingly stochastic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Natur.553..491J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Natur.553..491J"><span><span class="hlt">Early</span> episodes of high-pressure core formation preserved in plume <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jackson, Colin R. M.; Bennett, Neil R.; Du, Zhixue; Cottrell, Elizabeth; Fei, Yingwei</p> <p>2018-01-01</p> <p>The decay of short-lived iodine (I) and plutonium (Pu) results in xenon (Xe) isotopic anomalies in the <span class="hlt">mantle</span> that record Earth’s earliest stages of formation. Xe isotopic anomalies have been linked to degassing during accretion, but degassing alone cannot account for the co-occurrence of Xe and tungsten (W) isotopic heterogeneity in plume-derived basalts and their long-term preservation in the <span class="hlt">mantle</span>. Here we describe measurements of I partitioning between liquid Fe alloys and liquid silicates at high pressure and temperature and propose that Xe isotopic anomalies found in modern plume rocks (that is, rocks with elevated 3He/4He ratios) result from I/Pu fractionations during <span class="hlt">early</span>, high-pressure episodes of core formation. Our measurements demonstrate that I becomes progressively more siderophile as pressure increases, so that portions of <span class="hlt">mantle</span> that experienced high-pressure core formation will have large I/Pu depletions not related to volatility. These portions of <span class="hlt">mantle</span> could be the source of Xe and W anomalies observed in modern plume-derived basalts. Portions of <span class="hlt">mantle</span> involved in <span class="hlt">early</span> high-pressure core formation would also be rich in FeO, and hence denser than ambient <span class="hlt">mantle</span>. This would aid the long-term preservation of these <span class="hlt">mantle</span> portions, and potentially points to their modern manifestation within seismically slow, deep <span class="hlt">mantle</span> reservoirs with high 3He/4He ratios.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910004786','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910004786"><span>Abstracts for the International Workshop on Meteorite Impact on the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1990-01-01</p> <p>This volume contains abstracts that were accepted for presentation at the International Workshop on Meteorite Impact on the <span class="hlt">Early</span> <span class="hlt">Earth</span>, September 21-22, 1990, in Perth, Western Australia. The effects these impacts had on the young <span class="hlt">Earth</span> are emphasized and a few of the topics covered are as follows: impact induced hot atmosphere, crater size and distribution, late heavy bombardment, terrestrial <span class="hlt">mantle</span> and crust, impact damage, continental growth, volcanism, climate catastrophes, shocked quartz, and others.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMDI31B2185B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMDI31B2185B"><span>Global Transition Zone Anisotropy and Consequences for <span class="hlt">Mantle</span> Flow and <span class="hlt">Earth</span>'s Deep Water Cycle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Beghein, C.; Yuan, K.</p> <p>2011-12-01</p> <p>The transition zone has long been at the center of the debate between multi- and single-layered convection models that directly relate to heat transport and chemical mixing throughout the <span class="hlt">mantle</span>. It has also been suggested that the transition zone is a reservoir that collects water transported by subduction of the lithosphere into the <span class="hlt">mantle</span>. Since water lowers <span class="hlt">mantle</span> minerals density and viscosity, thereby modifying their rheology and melting behavior, it likely affects global <span class="hlt">mantle</span> dynamics and the history of plate tectonics. Constraining <span class="hlt">mantle</span> flow is therefore important for our understanding of <span class="hlt">Earth</span>'s thermochemical evolution and deep water cycle. Because it can result from deformation by dislocation creep during convection, seismic anisotropy can help us model <span class="hlt">mantle</span> flow. It is relatively well constrained in the uppermost <span class="hlt">mantle</span>, but its presence in the transition zone is still debated. Its detection below 250 km depth has been challenging to date because of the poor vertical resolution of commonly used datasets. In this study, we used global Love wave overtone phase velocity maps, which are sensitive to structure down to much larger depths than fundamental modes alone, and have greater depth resolution than shear wave-splitting data. This enabled us to obtain a first 3-D model of azimuthal anisotropy for the upper 800km of the <span class="hlt">mantle</span>. We inverted the 2Ψ terms of anisotropic phase velocity maps [Visser, et al., 2008] for the first five Love wave overtones between 35s and 174s period. The resulting model shows that the average anisotropy amplitude for vertically polarized shear waves displays two main stable peaks: one in the uppermost <span class="hlt">mantle</span> and, most remarkably, one in the lower transition zone. F-tests showed that the presence of 2Ψ anisotropy in the transition zone is required to improve the third, fourth, and fifth overtones fit. Because of parameter trade-offs, however, we cannot exclude that the anisotropy is located in the upper transition zone as</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1368245-situ-determination-crystal-structure-chemistry-minerals-earth-deep-lower-mantle-conditions','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1368245-situ-determination-crystal-structure-chemistry-minerals-earth-deep-lower-mantle-conditions"><span>In situ determination of crystal structure and chemistry of minerals at <span class="hlt">Earth</span>'s deep lower <span class="hlt">mantle</span> conditions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Yuan, Hongsheng; Zhang, Li</p> <p></p> <p>Recent advances in experimental techniques and data processing allow in situ determination of mineral crystal structure and chemistry up to Mbar pressures in a laser-heated diamond anvil cell (DAC), providing the fundamental information of the mineralogical constitution of our <span class="hlt">Earth</span>'s interior. This work highlights several recent breakthroughs in the field of high-pressure mineral crystallography, including the stability of bridgmanite, the single-crystal structure studies of post-perovskite and H-phase as well as the identification of hydrous minerals and iron oxides in the deep lower <span class="hlt">mantle</span>. The future development of high-pressure crystallography is also discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910048275&hterms=recycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Drecycling','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910048275&hterms=recycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Drecycling"><span>Deep-focus earthquakes and recycling of water into the <span class="hlt">earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meade, Charles; Jeanloz, Raymond</p> <p>1991-01-01</p> <p>For more than 50 years, observations of earthquakes to depths of 100 to 650 kilometers inside <span class="hlt">earth</span> have been enigmatic: at these depths, rocks are expected to deform by ductile flow rather than brittle fracturing or frictional sliding on fault surfaces. Laboratory experiments and detailed calculations of the pressures and temperatures in seismically active subduction zones indicate that this deep-focus seismicity could originate from dehydration and high-pressure structural instabilities occurring in the hydrated part of the lithosphere that sinks into the upper <span class="hlt">mantle</span>. Thus, seismologists may be mapping the recirculation of water from the oceans back into the deep interior of the planet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040081228&hterms=niches+riches&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dniches%2Briches','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040081228&hterms=niches+riches&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dniches%2Briches"><span>Autotrophic Ecosystems on the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schulte, M.</p> <p>2003-01-01</p> <p>Ophiolite sequences, sections of lower oceanic crust and upper <span class="hlt">mantle</span> that have been thrust onto continental craton, are located in northern and central California and provide easily accessible areas that serve as good analogs for similar, more extensive areas of the <span class="hlt">early</span> <span class="hlt">Earth</span>. We have begun investigating and characterizing these sites in order to understand better the processes that may be responsible for the water chemistry, mineralogy and biology of similar environments on the <span class="hlt">early</span> <span class="hlt">Earth</span>. The geophysical and geochemical processes in these terranes provide niches for unique communities of extremeophiles and likely provide a good analog to the location that first gave rise to life on <span class="hlt">Earth</span>. The ophiolites found in northern and central California include the Trinity, Josephine, Coast Range and Point Sal, all of which are approximately 160 million years old. Fluids from serpentinizing springs are generally alkaline with high pH and H2 contents, indicating that the mafic rock compositions control the fluid composition through water-rock reactions during relatively low-grade hydrothermal processes. There are significant amounts of primary mineralogy remaining in the rocks, meaning that substantial alteration processes are still occurring in these terranes. The general reaction for serpentinization of olivine is given by one of the authors. olivine + H2O = serpentine + brucite + magnetite + H2. We have analyzed the mineralogical composition of several rock samples collected from the Coast Range Ophiolite near Clear Lake, CA by electron microprobe. The remnant primary mineralogy is fairly urnform in composition, with an olivine composition of Fo(sub 90), and with pyroxene compositions of En(sub 90) for orthopyroxene and En(sub 49)Wo(sub 48)Fs(sub 03) for the clinopyroxene. Other primary phases observed include chromites and other spinels. Examination of petrographic thin sections reveals that serpentinization reactions have occurred in these locations. The serpentine</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/21562523-mantle-convection-plate-tectonics-volcanism-hot-exo-earths','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/21562523-mantle-convection-plate-tectonics-volcanism-hot-exo-earths"><span><span class="hlt">MANTLE</span> CONVECTION, PLATE TECTONICS, AND VOLCANISM ON HOT EXO-<span class="hlt">EARTHS</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Van Summeren, Joost; Conrad, Clinton P.; Gaidos, Eric, E-mail: summeren@hawaii.edu</p> <p></p> <p>Recently discovered exoplanets on close-in orbits should have surface temperatures of hundreds to thousands of Kelvin. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many hundreds to thousands of Kelvin between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for <span class="hlt">Earth</span>-mass planets on the (1) pattern of <span class="hlt">mantle</span> convection, (2) tectonic regime, and (3) rate and distribution of partial melting, using numerical simulations of <span class="hlt">mantle</span> convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate thatmore » if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a {approx}>400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of <span class="hlt">mantle</span> convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dichotomy, with plate-like tectonics on the night side and a continuously evolving mobile lid on the day side with diffuse surface deformation and vigorous volcanism. If volcanic outgassing establishes an atmosphere and redistributes heat, plate tectonics is globally replaced by diffuse surface deformation and volcanism accelerates and becomes distributed more uniformly across the planetary surface.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994E%26PSL.121....1V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994E%26PSL.121....1V"><span>Cooling of the <span class="hlt">Earth</span> in the Archaean: Consequences of pressure-release melting in a hotter <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vlaar, N. J.; van Keken, P. E.; van den Berg, A. P.</p> <p>1994-01-01</p> <p>A model is presented to describe the cooling of the <span class="hlt">Earth</span> in the Archaean. At the higher Archaean <span class="hlt">mantle</span> temperatures pressure-release melting starts deeper and generates a thicker basaltic or komatiitic crust and depleted harzburgite layer compared with the present-day situation. Intrinsic compositional stability and lack of mechanical coherency renders the mechanism of plate tectonics ineffective. It is proposed that the Archaean continents stabilised <span class="hlt">early</span> on top of a compositionally stratified root. In the Archaean oceanic lithosphere, hydrated upper crust can founder and recycle through its high-pressure phase eclogite. Eclogite remelting and new pressure-release melting generates new crustal material. Migration of magma and latent heat release by solidification at the surface provides an efficient mechanism to cool the <span class="hlt">mantle</span> by several hundreds of degrees during the Archaean. This can satisfactorily explain the occurrence of high extrusion temperature komatiites and lower extrusion temperature basalts in greenstone belts as being derived from the same source by different mechanisms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V23F..07B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V23F..07B"><span>Discovery Of Low Oxygen Fugacity (fo2) Mineral And Fluid Phases In Lower <span class="hlt">Mantle</span> -Derived <span class="hlt">Early</span> Pulse Of The Deccan Flood Basalts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Basu, A. R.; Das, S.</p> <p>2017-12-01</p> <p>Estimation of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> mineralogy and oxygen fugacity are principally based on indirect geophysical and experimental studies. According to these studies, the <span class="hlt">mantle</span> becomes increasingly reducing from upper to lower <span class="hlt">mantle</span> due to the distribution of ferric (Fe3+) and ferrous (Fe2+) iron in perovskite, the dominant mineral phase in the lower <span class="hlt">mantle</span>. However, the natural occurrence of low oxygen fugacity (fO2), lower <span class="hlt">mantle</span> mineral and fluid phases are rare, except some for discrete inclusions in superdeep diamonds. In this study, we document that some rocks associated with plume volcanism, such as the Deccan flood basalt volcanic province, preserve the lower <span class="hlt">mantle</span> mineral phases. We document here unusual primary texture - bearing minerals in olivine-clinopyroxene bearing picrite intrusives associated with the Deccan Traps. The olivine and clinopyroxene of these rocks have high 3He/4He ratio (R/RA 14) as well as Nd, Sr and Pb isotopes identical to those of the Réunion plume, clearly indicating their lower <span class="hlt">mantle</span> - derivation. These rocks are the initial pulse at 68Ma of the Deccan Trap eruption [1]. Presence of unusual exsolved lamella and rectangular, vermicular intergrowths of diopside and magnetite in olivine indicate a precursory phase with higher Fe3+. The diopside part in rectangular intergrowth show presence of hydrocarbon. Trails of small graphitic carbon crystals are also present both in the cores of these olivine and diopside. We suggest that the hydrocarbons are derived from the lower <span class="hlt">mantle</span> having much lesser fO2 than the upper <span class="hlt">mantle</span>. This study unequivocally indicates that direct lower <span class="hlt">mantle</span> mineralogical signature, including their fo2 can be obtained from <span class="hlt">early</span> pulse of plume volcanism. References: [1] Basu A R, Renne P R, Dasgupta D K, Teichmann F, Poreda R J, Science 261, 902 - 906; 1993.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22392985','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22392985"><span>Isotope composition and volume of <span class="hlt">Earth</span>'s <span class="hlt">early</span> oceans.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pope, Emily C; Bird, Dennis K; Rosing, Minik T</p> <p>2012-03-20</p> <p>Oxygen and hydrogen isotope compositions of <span class="hlt">Earth</span>'s seawater are controlled by volatile fluxes among <span class="hlt">mantle</span>, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these <span class="hlt">Earth</span> system reservoirs, but hydrogen's was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in <span class="hlt">Earth</span>'s oceans. Our calculations predict that the oceans of <span class="hlt">early</span> <span class="hlt">Earth</span> were up to 26% more voluminous, and atmospheric CH(4) and CO(2) concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean <span class="hlt">Earth</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA....10928V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....10928V"><span>Crustal formation and recycling in an oceanic environment in the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.</p> <p>2003-04-01</p> <p>Several lines of evidence indicate higher <span class="hlt">mantle</span> temperatures (by some hundreds of degrees) during the <span class="hlt">early</span> history of the <span class="hlt">Earth</span>. Due to the strong effect of temperature on viscosity as well as on the degree of melting, this enforces a geodynamic regime which is different from the present plate tectonics, and in which smaller scale processes play a more important role. Upwelling of a hotter <span class="hlt">mantle</span> produces a thicker oceanic crust, of which the lower part may reside in the eclogite stability field. This facilitates delamination, making room for fresh <span class="hlt">mantle</span> material which may partly melt and add new material to the crust (Vlaar et al., 1994). We present results of numerical thermo-chemical convection models including a simple approximate melt segregation mechanism in which we investigate this alternative geodynamic regime, and its effect on the cooling history and chemical evolution of the <span class="hlt">mantle</span>. Our results show that the mechanism is capable of working on two scales. On a small scale, involving the lower boundary of the crust, delaminations and downward transport of eclogite into the upper <span class="hlt">mantle</span> takes place. On a larger scale, involving the entire crustal column, (parts of) the crust may episodically sink into the <span class="hlt">mantle</span> and be replaced by a fresh crust. Both are capable of significantly and rapidly cooling a hot upper <span class="hlt">mantle</span> by driving partial melting and thus the generation of new crust. After some hundreds of millions of years, as the temperature drops, the mechanism shuts itself off, and the cooling rate significantly decreases. Vlaar, N.J., P.E. van Keken and A.P. van den Berg (1994), Cooling of the <span class="hlt">Earth</span> in the Archaean: consequences of pressure-release melting in a hotter <span class="hlt">mantle</span>, <span class="hlt">Earth</span> and Planetary Science Letters, vol 121, pp. 1-18</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.488..134Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.488..134Y"><span>Nitrogen solubility in the deep <span class="hlt">mantle</span> and the origin of <span class="hlt">Earth</span>'s primordial nitrogen budget</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yoshioka, Takahiro; Wiedenbeck, Michael; Shcheka, Svyatoslav; Keppler, Hans</p> <p>2018-04-01</p> <p>The solubility of nitrogen in the major minerals of the <span class="hlt">Earth</span>'s transition zone and lower <span class="hlt">mantle</span> (wadsleyite, ringwoodite, bridgmanite, and Ca-silicate perovskite) coexisting with a reduced, nitrogen-rich fluid phase was measured. Experiments were carried out in multi-anvil presses at 14 to 24 GPa and 1100 to 1800 °C close to the Fe-FeO buffer. Starting materials were enriched in 15N and the nitrogen concentrations in run products were measured by secondary ion mass spectrometry. Observed nitrogen (15N) solubilities in wadsleyite and ringwoodite typically range from 10 to 250 μg/g and strongly increase with temperature. Nitrogen solubility in bridgmanite is about 20 μg/g, while Ca-silicate perovskite incorporates about 30 μg/g under comparable conditions. Partition coefficients of nitrogen derived from coexisting phases are DNwadsleyite/olivine = 5.1 ± 2.1, DNringwoodite/wadsleyite = 0.49 ± 0.29, and DNbridgmanite/ringwoodite = 0.24 (+ 0.30 / - 0.19). Nitrogen solubility in the solid, iron-rich metal phase coexisting with the silicates was also measured and reached a maximum of nearly 1 wt.% 15N at 23 GPa and 1400 °C. These data yield a partition coefficient of nitrogen between iron metal and bridgmanite of DNmetal/bridgmanite ∼ 98, implying that in a lower <span class="hlt">mantle</span> containing about 1% of iron metal, about half of the nitrogen still resides in the silicates. The high nitrogen solubility in wadsleyite and ringwoodite may be responsible for the low nitrogen concentrations often observed in ultradeep diamonds from the transition zone. Overall, the solubility data suggest that the transition zone and the lower <span class="hlt">mantle</span> have the capacity to store at least 33 times the mass of nitrogen presently residing in the atmosphere. By combining the nitrogen solubility data in minerals with data on nitrogen solubility in silicate melts, mineral/melt partition coefficients of nitrogen can be estimated, from which the behavior of nitrogen during magma ocean crystallization can</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IJAsB..14..233C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IJAsB..14..233C"><span>Spin evolution of <span class="hlt">Earth</span>-sized exoplanets, including atmospheric tides and core-<span class="hlt">mantle</span> friction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cunha, Diana; Correia, Alexandre C. M.; Laskar, Jacques</p> <p>2015-04-01</p> <p>Planets with masses between 0.1 and 10 M ⊕ are believed to host dense atmospheres. These atmospheres can play an important role on the planet's spin evolution, since thermal atmospheric tides, driven by the host star, may counterbalance gravitational tides. In this work, we study the long-term spin evolution of <span class="hlt">Earth</span>-sized exoplanets. We generalize previous works by including the effect of eccentric orbits and obliquity. We show that under the effect of tides and core-<span class="hlt">mantle</span> friction, the obliquity of the planets evolves either to 0° or 180°. The rotation of these planets is also expected to evolve into a very restricted number of equilibrium configurations. In general, none of these equilibria is synchronous with the orbital mean motion. The role of thermal atmospheric tides becomes more important for <span class="hlt">Earth</span>-sized planets in the habitable zones of their systems; so they cannot be neglected when we search for their potential habitability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.489..251I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.489..251I"><span>Evidence for {100}<011> slip in ferropericlase in <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> from high-pressure/high-temperature experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Immoor, J.; Marquardt, H.; Miyagi, L.; Lin, F.; Speziale, S.; Merkel, S.; Buchen, J.; Kurnosov, A.; Liermann, H.-P.</p> <p>2018-05-01</p> <p>Seismic anisotropy in <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span>, resulting from Crystallographic Preferred Orientation (CPO) of elastically anisotropic minerals, is among the most promising observables to map <span class="hlt">mantle</span> flow patterns. A quantitative interpretation, however, is hampered by the limited understanding of CPO development in lower <span class="hlt">mantle</span> minerals at simultaneously high pressures and temperatures. Here, we experimentally determine CPO formation in ferropericlase, one of the elastically most anisotropic deep <span class="hlt">mantle</span> phases, at pressures of the lower <span class="hlt">mantle</span> and temperatures of up to 1400 K using a novel experimental setup. Our data reveal a significant contribution of slip on {100} to ferropericlase CPO in the deep lower <span class="hlt">mantle</span>, contradicting previous inferences based on experimental work at lower <span class="hlt">mantle</span> pressures but room temperature. We use our results along with a geodynamic model to show that deformed ferropericlase produces strong shear wave anisotropy in the lowermost <span class="hlt">mantle</span>, where horizontally polarized shear waves are faster than vertically polarized shear waves, consistent with seismic observations. We find that ferropericlase alone can produce the observed seismic shear wave splitting in D″ in regions of downwelling, which may be further enhanced by post-perovskite. Our model further shows that the interplay between ferropericlase (causing VSH > VSV) and bridgmanite (causing VSV > VSH) CPO can produce a more complex anisotropy patterns as observed in regions of upwelling at the margin of the African Large Low Shear Velocity Province.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.V11B..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.V11B..01M"><span>Helium and neon isotopes in the <span class="hlt">mantle</span>: constraints on the origin of volatiles on <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moreira, M. A.</p> <p>2005-12-01</p> <p>It is now obvious that the <span class="hlt">mantle</span> neon is solar-like. The possibility that the origin of this solar flavor is due to incorporation of irradiated parent bodies during accretion (e.g. gas rich meteorites) has been evoked by Trieloff and collaborators. The main argument is the fact there are no precise 20Ne/22Ne measured ratios above 13 in oceanic basalts, whereas the solar wind has a 20Ne/22Ne of 13.8 and the "neon B" neon shows a ratio of 12.6-12.8. The second argument for an irradiated origin is the air-like 38Ar/36Ar in <span class="hlt">mantle</span>-derived samples (the "neon B" argon is close to air), distinct from the solar argon. Here we present another argument for an irradiated origin of the rare gases in the <span class="hlt">Earth</span>. The global correlation in oceanic basalts (MORB and OIB) between 4He/3He and 21Ne/22Ne (corrected for air contamination) gives a mixing hyperbolae with a r parameter (r=(3He/22Ne)MORB/(3He/22Ne)PM) close to 10. It is now clear that 3He/22Ne ratio in the MORB source is around 7, giving for the primitive <span class="hlt">mantle</span> (PM) a 3He/22Ne of 0.7. The solar 3He/22Ne ratio is estimated at 5-6 whereas the gas rich meteorites show a ratio of 0.3. Therefore, the global correlation in oceanic basalts between the helium and neon isotopic ratios suggests that (some) parent bodies of the <span class="hlt">Earth</span> were gas rich meteorites, irradiated by an energetic solar wind during the planetary accretion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=plate+AND+tectonics&pg=5&id=EJ645992','ERIC'); return false;" href="https://eric.ed.gov/?q=plate+AND+tectonics&pg=5&id=EJ645992"><span>The <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> Is Solid: Teachers' Misconceptions About the <span class="hlt">Earth</span> and Plate Tectonics.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>King, Chris</p> <p>2000-01-01</p> <p>Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of <span class="hlt">Earth</span>. (Author/YDS)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T33J..05Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T33J..05Z"><span>A Model for <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> Dynamic History for The Last 500 Ma and Its Implications for Continental Vertical Motions and Geomagnetism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhong, S.; Olson, P.; Zhang, N.</p> <p>2012-12-01</p> <p>Seismic tomography studies indicate that the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., thermochemical piles) and circum Pacific seismically fast anomalies (i.e., degree 2) in the lower <span class="hlt">mantle</span>. <span class="hlt">Mantle</span> convection calculations including plate motion history for the last 120 Ma suggest that these degree 2 thermochemical structures result from plate subduction history (e.g., McNamara and Zhong, 2005). Given the important controls of <span class="hlt">mantle</span> structure and dynamics on surface tectonics and volcanism and geodynamo in the core, an important question is the long-term evolution of <span class="hlt">mantle</span> structures, for example, was the <span class="hlt">mantle</span> structure in the past similar to the present-day's degree 2 structure, or significantly different from the present day? To address this question, we constructed a proxy model of plate motions for the African hemisphere for the last 450 Ma using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations (e.g., Pangea assembly and breakup). Coupled with assumed oceanic plate motions for the Pacific hemisphere before 120 Ma, this proxy model for the plate motion history is used in three dimensional spherical models of <span class="hlt">mantle</span> convection to study the evolution of <span class="hlt">mantle</span> structure since the <span class="hlt">Early</span> Paleozoic. Our model calculations reproduce well the present day degree 2 <span class="hlt">mantle</span> structure including the African and Pacific thermochemical piles, and present-day surface heat flux, bathymetry and dynamic topography. Our results suggest that while the <span class="hlt">mantle</span> in the African hemisphere before the assembly of Pangea is dominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ˜230 Ma. Particularly, the last 120 Ma plate motion plays an important role in generating the African thermochemical pile. We reconstruct temporal</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Icar..305..350R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Icar..305..350R"><span>Vacancies in MgO at ultrahigh pressure: About <span class="hlt">mantle</span> rheology of super-<span class="hlt">Earths</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ritterbex, Sebastian; Harada, Takafumi; Tsuchiya, Taku</p> <p>2018-05-01</p> <p>First-principles calculations are performed to investigate vacancy formation and migration in the B2 phase of MgO. Defect energetics suggest the importance of intrinsic non-interacting vacancy pairs, even though the extrinsic vacancy concentration might govern atomic diffusion in the B2 phase of MgO. The enthalpies of ionic vacancy migration are generally found to decrease across the B1-B2 phase transition around a pressure of 500 GPa. It is shown that this enthalpy change induces a substantial increase in the rate of vacancy diffusion in MgO of almost four orders of magnitude (∼104) when the B1 phase transforms into the B2 phase with increasing pressure. If plastic deformation is controlled by vacancy diffusion, <span class="hlt">mantle</span> viscosity is expected to decrease in relation to this enhanced diffusion rate in MgO across the B1-B2 transition in the interior of <span class="hlt">Earth</span>-like large exoplanets. Our results of atomic relaxations near the defects suggest that diffusion controlled creep viscosity may generally decrease across high-pressure phase transitions with increasing coordination number. Plastic flow and resulting <span class="hlt">mantle</span> convection in the interior of these super-<span class="hlt">Earths</span> may be therefore less sluggish than previously thought.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29218058','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29218058"><span>Assessment of the effect of three-dimensional <span class="hlt">mantle</span> density heterogeneity on <span class="hlt">earth</span> rotation in tidal frequencies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Lanbo; Chao, Benjamin F; Sun, Wenke; Kuang, Weijia</p> <p>2016-11-01</p> <p>In this paper we report the assessment of the effect of the three-dimensional (3D) density heterogeneity in the <span class="hlt">mantle</span> on <span class="hlt">Earth</span> Orientation Parameters (EOP) (i.e., the polar motion, or PM, and the length of day, or LOD) in the tidal frequencies. The 3D <span class="hlt">mantle</span> density model is estimated based upon a global S-wave velocity tomography model (S16U6L8) and the mineralogical knowledge derived from laboratory experiment. The lateral density variation is referenced against the Preliminary Reference <span class="hlt">Earth</span> Model (PREM). Using this approach the effects of the heterogeneous <span class="hlt">mantle</span> density variation in all three tidal frequencies (zonal long periods, tesseral diurnal, and sectorial semidiurnal) are estimated in both PM and LOD. When compared with mass or density perturbations originated on the <span class="hlt">earth</span>'s surface such as the oceanic and barometric changes, the heterogeneous <span class="hlt">mantle</span> only contributes less than 10% of the total variation in PM and LOD in tidal frequencies. Nevertheless, including the 3D variation of the density in the <span class="hlt">mantle</span> into account explained a substantial portion of the discrepancy between the observed signals in PM and LOD extracted from the lump-sum values based on continuous space geodetic measurement campaigns (e.g., CONT94) and the computed contribution from ocean tides as predicted by tide models derived from satellite altimetry observations (e.g., TOPEX/Poseidon). In other word, the difference of the two, at all tidal frequencies (long-periods, diurnals, and semi-diurnals) contains contributions of the lateral density heterogeneity of the <span class="hlt">mantle</span>. Study of the effect of <span class="hlt">mantle</span> density heterogeneity effect on torque-free <span class="hlt">earth</span> rotation may provide useful constraints to construct the Reference <span class="hlt">Earth</span> Model (REM), which is the next major objective in global geophysics research beyond PREM.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940017201','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940017201"><span>Core formation, wet <span class="hlt">early</span> <span class="hlt">mantle</span>, and H2O degassing on <span class="hlt">early</span> Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kuramoto, K.; Matsui, T.</p> <p>1993-01-01</p> <p>Geophysical and geochemical observations strongly suggest a 'hot origin of Mars,' i.e., the <span class="hlt">early</span> formation of both the core and the crust-<span class="hlt">mantle</span> system either during or just after planetary accretion. To consider the behavior of H2O in the planetary interior it is specifically important to determine by what mechanism the planet is heated enough to cause melting. For Mars, the main heat source is probably accretional heating. Because Mars is small, the accretion energy needs to be effectively retained in its interior. Therefore, the three candidates of heat retention mechanism are discussed first: (1) the blanketing effect of the primordial H2-He atmosphere; (2) the blanketing effect of the impact-induced H2O-CO2 atmosphere; and (3) the higher deposition efficiency of impact energy due to larger impacts. It was concluded that (3) the is the most plausible mechanism for Mars. Then, its possible consequence on how wet the <span class="hlt">early</span> martian <span class="hlt">mantle</span> was is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Natur.545..332R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Natur.545..332R"><span>Continental crust formation on <span class="hlt">early</span> <span class="hlt">Earth</span> controlled by intrusive magmatism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rozel, A. B.; Golabek, G. J.; Jain, C.; Tackley, P. J.; Gerya, T.</p> <p>2017-05-01</p> <p>The global geodynamic regime of <span class="hlt">early</span> <span class="hlt">Earth</span>, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean <span class="hlt">mantle</span> temperature and more intense juvenile magmatism than in the present-day <span class="hlt">Earth</span>, two crust-<span class="hlt">mantle</span> interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism and the “Plutonic squishy lid” tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce <span class="hlt">Earth</span>-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean <span class="hlt">Earth</span> operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28482358','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28482358"><span>Continental crust formation on <span class="hlt">early</span> <span class="hlt">Earth</span> controlled by intrusive magmatism.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rozel, A B; Golabek, G J; Jain, C; Tackley, P J; Gerya, T</p> <p>2017-05-18</p> <p>The global geodynamic regime of <span class="hlt">early</span> <span class="hlt">Earth</span>, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean <span class="hlt">mantle</span> temperature and more intense juvenile magmatism than in the present-day <span class="hlt">Earth</span>, two crust-<span class="hlt">mantle</span> interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism and the "Plutonic squishy lid" tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce <span class="hlt">Earth</span>-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean <span class="hlt">Earth</span> operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4998958','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4998958"><span>An <span class="hlt">early</span> geodynamo driven by exsolution of <span class="hlt">mantle</span> components from Earth’s core</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Badro, James; Siebert, Julien; Nimmo, Francis</p> <p>2016-01-01</p> <p>Terrestrial core formation occurred in the <span class="hlt">early</span> molten <span class="hlt">Earth</span> by gravitational segregation of immiscible metal and silicate melts, stripping iron-loving elements from the silicate <span class="hlt">mantle</span> to the metallic core1–3, and leaving rock-loving components behind. Here we performed experiments showing that at high enough temperature, Earth’s major rock-loving component, magnesium oxide, can also dissolve in core-forming metallic melts. Our data clearly point to a dissolution reaction, and are in agreement with recent DFT calculations4. Using core formation models5, we further show that a high-temperature event during Earth’s accretion (such as the Moon-forming giant impact6) can contribute significant amounts of magnesium to the <span class="hlt">early</span> core. As it subsequently cools, the ensuing exsolution7 of buoyant magnesium oxide generates a substantial amount of gravitational energy. This energy is comparable to if not significantly higher than that produced by inner core solidification8 — the primary driver of the Earth’s current magnetic field9–11. Since the inner core is too young12 to explain the existence of an ancient field prior to ~1 billion years, our results solve the conundrum posed by the recent paleomagnetic observation13 of an ancient field at least 3.45 Gyr old. PMID:27437583</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.P21A1582S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.P21A1582S"><span>Thermodynamic properties, melting temperature and viscosity of the <span class="hlt">mantles</span> of Super <span class="hlt">Earths</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stamenkovic, V.; Spohn, T.; Breuer, D.</p> <p>2010-12-01</p> <p>The recent dicscovery of extrasolar planets with radii of about twice the <span class="hlt">Earth</span> radius and masses of several <span class="hlt">Earth</span> masses such as e.g., Corot-7b (approx 5Mearth and 1.6Rearth, Queloz et al. 2009) has increased the interest in the properties of rock at extremely high pressures. While the pressure at the Earth’s core-<span class="hlt">mantle</span> boundary is about 135GPa, pressures at the base of the <span class="hlt">mantles</span> of extraterrestrial rocky planets - if these are at all differentiated into <span class="hlt">mantles</span> and cores - may reach Tera Pascals. Although the properties and the mineralogy of rock at extremely high pressure is little known there have been speculations about <span class="hlt">mantle</span> convection, plate tectonics and dynamo action in these “Super-Earths”. We assume that the <span class="hlt">mantles</span> of these planets can be thought of as consisting of perovskite but we discuss the effects of the post-perovskite transition and of MgO. We use the Keane equation of state and the Slater relation (see e.g., Stacey and Davies 2004) to derive an infinite pressure value for the Grüneisen parameter of 1.035. To derive this value we adopted the infinite pressure limit for K’ (pressure derivative of the bulk modulus) of 2.41 as derived by Stacey and Davies (2004) by fitting PREM. We further use the Lindeman law to calculate the melting curve. We gauge the melting curve using the available experimental data for pressures up to 120GPa. The melting temperature profile reaches 6000K at 135GPa and increases to temperatures between 12,000K and 24,000K at 1.1TPa with a preferred value of 21,000K. We find the adiabatic temperature increase to reach 2,500K at 135GPa and 5,400K at 1.1TPa. To calculate the pressure dependence of the viscosity we assume that the rheology is diffusion controlled and calculate the partial derivative with respect to pressure of the activation enthalpy. We cast the partial derivative in terms of an activation volume and use the semi-empirical homologous temperature scaling (e.g., Karato 2008). We find that the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMDI21B1960Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMDI21B1960Z"><span>The Evolution of the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> Structure and Surface and Core-<span class="hlt">mantle</span> Boundary Heat Flux since the Paleozoic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, N.; Zhong, S.</p> <p>2010-12-01</p> <p>The cause for and time evolution of the seismically observed African and Pacific slow anomalies (i.e., superplumes) are still unclear with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Ma and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma ago) and the <span class="hlt">mantle</span> in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree-1 structure before the Pangea formation). Here, we construct a plate motion history back to 450 Ma and use it as time-dependent surface boundary conditions in 3-dimensional spherical models of thermochemical <span class="hlt">mantle</span> convection to study the evolution of <span class="hlt">mantle</span> structure as well as the surface and core-<span class="hlt">mantle</span> boundary heat flux. Our results for the <span class="hlt">mantle</span> structures suggest that while the <span class="hlt">mantle</span> in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ~240 Ma (i.e., ~100 Ma after the assembly of Pangea). The evolution of <span class="hlt">mantle</span> structure has implications for heat flux at the surface and core-<span class="hlt">mantle</span> boundary (CMB). Our results show that while the plate motion controls the surface heat flux, the major cold downwellings control the core-<span class="hlt">mantle</span> boundary heat flux. A notable feature in surface heat flux from our models is that the surface heat flux peaks at ~100 Ma ago but decreases for the last 100 Ma due to the breakup of Pangea and its subsequent plate evolution. The CMB heat flux in the equatorial regions shows two minima during period 320-250 Ma and period 120-84 Ma. The first minimum clearly results from the disappearance of a major cold downwelling</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910013674','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910013674"><span>Obliquity histories of <span class="hlt">Earth</span> and Mars: Influence of inertial and dissipative core-<span class="hlt">mantle</span> coupling</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bills, Bruce G.</p> <p>1990-01-01</p> <p>For both the <span class="hlt">Earth</span> and Mars, secular variations in the angular separation of the spin axis from the orbit normal are suspected of driving major climatic changes. There is considerable interest in determining the amplitude and timing of these obliquity variations. If the orientation of the orbital plane were inertially fixed, and the planet were to act as a rigid body in it response to precessional torques, the spin axis would simply precess around the orbit at a fixed obliquity and at a uniform angular rate. The precession rate parameter depends on the principal moments of inertia and rotation rate of the perturbed body, and on the gravitational masses and semiminor axes of the perturbing bodies. For Mars, the precession rate is not well known, but probably lies in the interval 8 to 10 arcsec/year. Gravitational interactions between the planets lead to secular motions of the orbit planes. In the rigid body case, the spin axis still attempts to precess about the instantaneous orbit normal, but now the obliquity varies. The hydrostatic figure of a planet represents a compromise between gravitation, which attempts to attain spherical symmetry, and rotation, which prefers cylindrical symmetry. Due to their higher mean densities the cores of the <span class="hlt">Earth</span> and Mars will be more nearly spherical than the outer layers of these planets. On short time scales it is appropriate to consider the core to be an inviscid fluid constrained to move with the ellipsoidal region bounded by the rigid <span class="hlt">mantle</span>. The inertial coupling provided by this mechanism is effective whenever the ellipticicy of the container exceeds the ratio of precessional to rotational rates. If the <span class="hlt">mantle</span> were actually rigid, this would be an extremely effective type of coupling. However, on sufficiently long time scales, the <span class="hlt">mantle</span> will deform viscously and can accommodate the motions of the core fluid. A fundamentally different type of coupling is provided by electromagnetic or viscous torques. This type of coupling</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFMMR11A..01A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFMMR11A..01A"><span>Birch's <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anderson, D. L.</p> <p>2002-12-01</p> <p>Francis Birch's 1952 paper started the sciences of mineral physics and physics of the <span class="hlt">Earth</span>'s interior. Birch stressed the importance of pressure, compressive strain and volume in <span class="hlt">mantle</span> physics. Although this may seem to be an obvious lesson many modern paradoxes in the internal constitution of the <span class="hlt">Earth</span> and <span class="hlt">mantle</span> dynamics can be traced to a lack of appreciation for the role of compression. The effect of pressure on thermal properties such as expansivity can gravitational stratify the <span class="hlt">Earth</span> irreversibly during accretion and can keep it chemically stratified. The widespread use of the Boussinesq approximation in <span class="hlt">mantle</span> geodynamics is the antithesis of Birchian physics. Birch pointed out that eclogite was likely to be an important component of the upper <span class="hlt">mantle</span>. Plate tectonic recycling and the bouyancy of oceanic crust at midmantle depths gives credence to this suggestion. Although peridotite dominates the upper <span class="hlt">mantle</span>, variations in eclogite-content may be responsible for melting- or fertility-spots. Birch called attention to the Repetti Discontinuity near 900 km depth as an important geodynamic boundary. This may be the chemical interface between the upper and lower <span class="hlt">mantles</span>. Recent work in geodynamics and seismology has confirmed the importance of this region of the <span class="hlt">mantle</span> as a possible barrier. Birch regarded the transition region (TR ; 400 to 1000 km ) as the key to many problems in <span class="hlt">Earth</span> sciences. The TR contains two major discontinuities ( near 410 and 650 km ) and their depths are a good <span class="hlt">mantle</span> thermometer which is now being exploited to suggest that much of plate tectonics is confined to the upper <span class="hlt">mantle</span> ( in Birch's terminology, the <span class="hlt">mantle</span> above 1000 km depth ). The lower <span class="hlt">mantle</span> is homogeneous and different from the upper <span class="hlt">mantle</span>. Density and seismic velocity are very insensitive to temperature there, consistent with tomography. A final key to the operation of the <span class="hlt">mantle</span> is Birch's suggestion that radioactivities were stripped out of the deeper parts of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGeo..100..198F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGeo..100..198F"><span><span class="hlt">Early</span> <span class="hlt">Earth</span> plume-lid tectonics: A high-resolution 3D numerical modelling approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fischer, R.; Gerya, T.</p> <p>2016-10-01</p> <p>Geological-geochemical evidence point towards higher <span class="hlt">mantle</span> potential temperature and a different type of tectonics (global plume-lid tectonics) in the <span class="hlt">early</span> <span class="hlt">Earth</span> (>3.2 Ga) compared to the present day (global plate tectonics). In order to investigate tectono-magmatic processes associated with plume-lid tectonics and crustal growth under hotter <span class="hlt">mantle</span> temperature conditions, we conduct a series of 3D high-resolution magmatic-thermomechanical models with the finite-difference code I3ELVIS. No external plate tectonic forces are applied to isolate 3D effects of various plume-lithosphere and crust-<span class="hlt">mantle</span> interactions. Results of the numerical experiments show two distinct phases in coupled crust-<span class="hlt">mantle</span> evolution: (1) a longer (80-100 Myr) and relatively quiet 'growth phase' which is marked by growth of crust and lithosphere, followed by (2) a short (∼20 Myr) and catastrophic 'removal phase', where unstable parts of the crust and <span class="hlt">mantle</span> lithosphere are removed by eclogitic dripping and later delamination. This modelling suggests that the <span class="hlt">early</span> <span class="hlt">Earth</span> plume-lid tectonic regime followed a pattern of episodic growth and removal also called episodic overturn with a periodicity of ∼100 Myr.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V41F..07V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V41F..07V"><span>Archean Pb Isotope Evolution: Implications for the <span class="hlt">Early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vervoort, J. D.; Thorpe, R.; Albarede, F.; Blichert-Toft, J.</p> <p>2008-12-01</p> <p>.728 Ga (Normetal) to 2.70 Ga (Noranda). The Pb isotopic compositions from these galenas, when normalized to a common age of 2.7 Ga, define a highly linear array in 207Pb/204Pb vs. 206Pb/204Pb. This array is nearly coincident with the 2.7 Ga geochron with a slope that corresponds to an age of ~4.4 Ga and with an extraordinary large range of 207Pb/204Pb, about the same magnitude as modern MORB. These data have important implications for the evolution of the Archean <span class="hlt">mantle</span>. First, the slope of the Abitibi Pb-Pb array and its coincidence with the 2.7 Ga geochron suggests widespread U-Pb differentiation within the first hundred million years of <span class="hlt">Earth</span>'s history. This may have been due to either core formation or silicate/melt differentiation due to widespread melting of the <span class="hlt">mantle</span> (e.g., formation of a magma ocean). Second, variations in μ in the Abitibi <span class="hlt">mantle</span> and the subsequent Pb isotopic heterogeneities, whatever their cause, have not been significantly changed from 4.4 until 2.7 Ga. This implies that changes in μ in the Abitibi <span class="hlt">mantle</span> source between 4.4 and 2.7 Ga, such as would be caused by crust extraction or recycling of older crust into this region of the <span class="hlt">mantle</span>, were insufficient to destroy the original μ variations created at 4.4 Ga. Therefore, it appears that this portion of the <span class="hlt">mantle</span> had essentially remained isolated and undisturbed from the <span class="hlt">early</span> Hadean until the late Archean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23739427','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23739427"><span>Argon isotopic composition of Archaean atmosphere probes <span class="hlt">early</span> <span class="hlt">Earth</span> geodynamics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pujol, Magali; Marty, Bernard; Burgess, Ray; Turner, Grenville; Philippot, Pascal</p> <p>2013-06-06</p> <p>Understanding the growth rate of the continental crust through time is a fundamental issue in <span class="hlt">Earth</span> sciences. The isotopic signatures of noble gases in the silicate <span class="hlt">Earth</span> (<span class="hlt">mantle</span>, crust) and in the atmosphere afford exceptional insight into the evolution through time of these geochemical reservoirs. However, no data for the compositions of these reservoirs exists for the distant past, and temporal exchange rates between <span class="hlt">Earth</span>'s interior and its surface are severely under-constrained owing to a lack of samples preserving the original signature of the atmosphere at the time of their formation. Here, we report the analysis of argon in Archaean (3.5-billion-year-old) hydrothermal quartz. Noble gases are hosted in primary fluid inclusions containing a mixture of Archaean freshwater and hydrothermal fluid. Our analysis reveals Archaean atmospheric argon with a (40)Ar/(36)Ar value of 143 ± 24, lower than the present-day value of 298.6 (for which (40)Ar has been produced by the radioactive decay of the potassium isotope (40)K, with a half-life of 1.25 billion years; (36)Ar is primordial in origin). This ratio is consistent with an <span class="hlt">early</span> development of the felsic crust, which might have had an important role in climate variability during the first half of <span class="hlt">Earth</span>'s history.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001RvGeo..39..507K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001RvGeo..39..507K"><span>High-pressure elastic properties of major materials of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> from first principles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karki, Bijaya B.; Stixrude, Lars; Wentzcovitch, Renata M.</p> <p>2001-11-01</p> <p>The elasticity of materials is important for our understanding of processes ranging from brittle failure, to flexure, to the propagation of elastic waves. Seismologically revealed structure of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>, including the radial (one-dimensional) profile, lateral heterogeneity, and anisotropy are determined largely by the elasticity of the materials that make up this region. Despite its importance to geophysics, our knowledge of the elasticity of potentially relevant mineral phases at conditions typical of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> is still limited: Measuring the elastic constants at elevated pressure-temperature conditions in the laboratory remains a major challenge. Over the past several years, another approach has been developed based on first-principles quantum mechanical theory. First-principles calculations provide the ideal complement to the laboratory approach because they require no input from experiment; that is, there are no free parameters in the theory. Such calculations have true predictive power and can supply critical information including that which is difficult to measure experimentally. A review of high-pressure theoretical studies of major <span class="hlt">mantle</span> phases shows a wide diversity of elastic behavior among important tetrahedrally and octahedrally coordinated Mg and Ca silicates and Mg, Ca, Al, and Si oxides. This is particularly apparent in the acoustic anisotropy, which is essential for understanding the relationship between seismically observed anisotropy and <span class="hlt">mantle</span> flow. The acoustic anisotropy of the phases studied varies from zero to more than 50% and is found to depend on pressure strongly, and in some cases nonmonotonically. For example, the anisotropy in MgO decreases with pressure up to 15 GPa before increasing upon further compression, reaching 50% at a pressure of 130 GPa. Compression also has a strong effect on the elasticity through pressure-induced phase transitions in several systems. For example, the transition from stishovite to CaCl2</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....1377H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....1377H"><span>A petrological view of <span class="hlt">early</span> <span class="hlt">Earth</span> geodynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Herzberg, C.</p> <p>2003-04-01</p> <p> primary magmas contained 14 to 22% MgO, similar to Reykjanes MORB, Gorgona, Hawaii, and the <span class="hlt">early</span> Icelandic plume in the model of Herzberg & O'Hara (2002). However, a few xenoliths record T_P as low as 1300oC. Two geodynamic interpretations follow: 1) Archean cratonic <span class="hlt">mantle</span> formed as residues below ridges and hotspots similar to those of today, except the lithosphere was somewhat thinner in some cases, 2) Archean cratonic <span class="hlt">mantle</span> formed as residues below hot ridges in most cases. <span class="hlt">Early</span> Proterozoic sheeted dikes and eruptives from the Cape Smith Belt in Canada are consistent with the hot ridge interpretation. Ridge potential temperatures could have been 1520-1570oC, higher than modern ridges (1300-1450oC) but similar to those for the Gorgona and <span class="hlt">early</span> Tertiary Icelandic plumes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFM.U41A0728K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFM.U41A0728K"><span>A Comparison of Methods for Modeling Geochemical Variability in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kellogg, J. B.; Tackley, P. J.</p> <p>2004-12-01</p> <p>Numerial models of isotopic and chemical heterogeneity of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> fall into three categories, in decreasing order of computational demand. First, several authors have used chemical tracers within a full thermo-chemical convection calculation (e.g., Christensen and Hofmann, 1994, van Keken and Ballentine, 1999; Xie and Tackley, 2004). Second, Kellogg et al. (2002) proposed an extension of the traditional geochemical box model calculations in which numerous subreservoirs were tracked within the bulk depleted <span class="hlt">mantle</span> reservoir. Third, Allègre and Lewin (1995) described a framework in which the variance in chemical and isotopic ratios were treated as quantities intrinsic to the bulk reservoirs, complete with sources and sinks. Results from these three methods vary, particularly with respect to conclusions drawn about the meaning of the Pb-Pb pseudo-isochron. We revisit these methods in an attempt to arrive at a common understanding. By considering all three we better identify the strengths and weaknesses of each approach and allow each to inform the other. Finally, we present results from a new hybrid model that combines the complexity and regional-scale variability of the thermochemical convection models with the short length-scale sensitivity of the Kellogg et al. approach.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140007370','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140007370"><span>Core-<span class="hlt">Mantle</span> Partitioning of Volatile Elements and the Origin of Volatile Elements in <span class="hlt">Earth</span> and Moon</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Righter, K.; Pando, K.; Danielson, L.; Nickodem, K.</p> <p>2014-01-01</p> <p>Depletions of siderophile elements in <span class="hlt">mantles</span> have placed constraints on the conditions on core segregation and differentiation in bodies such as <span class="hlt">Earth</span>, <span class="hlt">Earth</span>'s Moon, Mars, and asteroid 4 Vesta. Among the siderophile elements there are a sub-set that are also volatile (volatile siderophile elements or VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd), and thus can help to constrain the origin of volatile elements in these bodies, and in particular the <span class="hlt">Earth</span> and Moon. One of the fundamental observations of the geochemistry of the Moon is the overall depletion of volatile elements relative to the <span class="hlt">Earth</span>, but a satisfactory explanation has remained elusive. Hypotheses for <span class="hlt">Earth</span> include addition during accretion and core formation and mobilized into the metallic core, multiple stage origin, or addition after the core formed. Any explanation for volatile elements in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> must also be linked to an explanation of these elements in the lunar <span class="hlt">mantle</span>. New metal-silicate partitioning data will be applied to the origin of volatile elements in both the <span class="hlt">Earth</span> and Moon, and will evaluate theories for exogenous versus endogenous origin of volatile elements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.3792V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.3792V"><span>EAG Eminent Speaker: Two types of Archean continental crust: plume and plate tectonics on <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Van Kranendonk, M. J.</p> <p>2012-04-01</p> <p>Over 4.5 billion years, <span class="hlt">Earth</span> has evolved from a molten ball to a cooler planet with large continental plates, but how and when continents grew and plate tectonics started remain poorly understood. In this paper, I review the evidence that 3.5-3.2 Ga continental nuclei of the Pilbara (Australia) and Kaapvaal (southern Africa) cratons formed as thick volcanic plateaux over hot, upwelling <span class="hlt">mantle</span> and survived due to contemporaneous development of highly depleted, buoyant, unsubductable <span class="hlt">mantle</span> roots. This type of crust is distinct from, but complimentary to, high-grade gneiss terranes, as exemplified by the North Atlantic Craton of West Greenland, which formed through subduction-accretion tectonics on what is envisaged as a vigorously convecting <span class="hlt">early</span> <span class="hlt">Earth</span> with small plates. Thus, it is proposed that two types of crust formed on <span class="hlt">early</span> <span class="hlt">Earth</span>, in much the same way as in modern <span class="hlt">Earth</span>, but with distinct differences resulting from a hotter Archean <span class="hlt">mantle</span>. Volcanic plateaux provided a variety of stable habitats for <span class="hlt">early</span> life, including chemical nutrient rich, shallow-water hydrothermal systems and shallow marine carbonate platforms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70013226','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70013226"><span>Upper <span class="hlt">mantle</span> electrical conductivity for seven subcontinental regions of the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href=""></a></p> <p>Campbell, W.H.; Schiffmacher, E.R.</p> <p>1988-01-01</p> <p>Spherical harmonic analysis coefficients of the external and internal parts of the quiet-day geomagnetic field variations (Sq) separated for the 7 continental regions of the observatories have been used to determine conductivity profiles to depths of about 600 km by the Schmucker equivalent substitute conductor method. The profiles give evidence of increases in conductivity between about 150 and 350 km depth, then a general increase in conductivity thereafter. For South America we found a high conductivity at shallow depths. The European profile showed a highly conducting layer near 125 km. At the greater depths, Europe, Australia and South America had the lowest values of conductivity. North America and east Asia had intermediate values whereas the African and central Asian profiles both showed the conductivities rising rapidly beyond 450 km depth. The regional differences indicate that there may be considerable lateral heterogeneity of electrical conductivity in the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>. -Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29590042','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29590042"><span>Ice-VII inclusions in diamonds: Evidence for aqueous fluid in <span class="hlt">Earth</span>'s deep <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tschauner, O; Huang, S; Greenberg, E; Prakapenka, V B; Ma, C; Rossman, G R; Shen, A H; Zhang, D; Newville, M; Lanzirotti, A; Tait, K</p> <p>2018-03-09</p> <p>Water-rich regions in <span class="hlt">Earth</span>'s deeper <span class="hlt">mantle</span> are suspected to play a key role in the global water budget and the mobility of heat-generating elements. We show that ice-VII occurs as inclusions in natural diamond and serves as an indicator for such water-rich regions. Ice-VII, the residue of aqueous fluid present during growth of diamond, crystallizes upon ascent of the host diamonds but remains at pressures as high as 24 gigapascals; it is now recognized as a mineral by the International Mineralogical Association. In particular, ice-VII in diamonds points toward fluid-rich locations in the upper transition zone and around the 660-kilometer boundary. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMMR21A2318W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMMR21A2318W"><span>Deformation and seismic anisotropy of silicate post-perovskite in the <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>wu, X.; Lin, J.; Mao, Z.; Liu, J.; Kaercher, P. M.; Wenk, H.; Prakapenka, V.; Zhuravlev, K. K.</p> <p>2013-12-01</p> <p>The D' layer in the <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span> with an average thickness of 250 km right above the core-<span class="hlt">mantle</span> boundary plays a significant role in the geophysics, geochemistry, and geodynamics of the planet's interior. Seismic observations of the region have shown a number of enigmatic features including shear wave discontinuity and seismic wave anisotropy. The seismic anisotropy, in which the horizontally-polarized shear wave (VSH) travels faster than the vertically-polarized shear wave (VSV) by 1%~3% in areas below the circum Pacific, has been proposed to be a result of the lattice-preferred orientation of silicate post-perovskite (PPv) that is to be the most abundant phase in the D' layer [1]. Therefore, understanding the elasticity and deformation of the PPv phase is critical under relevant P-T conditions of the region. However, experimental results on the textures and the elastic anisotropy of PPv remain largely limited and controversial. Specifically, a number of slip systems of PPv, such as (010), (100), (110) and (001), have been proposed based on experimental and theoretical results [2-4]. Here we have studied the textures and deformation mechanism of iron-bearing PPv ((Mg0.75,Fe0.25)SiO3) at relevant P-T conditions of the lowermost <span class="hlt">mantle</span> using synchrotron radiation radial x-ray diffraction in a membrane-driven laser-heated diamond anvil cell. The diffraction patterns were recorded from the laser-heated PPv sample during further compression between 130 GPa and 150 GPa. Analyses of the diffraction patterns and simulation results from viscoplastic self-consistent polycrystal plasticity code (VPSC) show that the development of active slip systems can be strongly influenced by experimental pressure-temperature-time conditions. At relevant P-T conditions of the lowermost <span class="hlt">mantle</span>, our results demonstrate that the dominant slip systems of PPv should be (001)[100] and (001)[010]. Combined these results with the elasticity of PPv, we provide more constrains on the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815891T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815891T"><span>A thermodynamic recipe for baking the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> and core as a whole</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tirone, Max; Faak, Kathi</p> <p>2016-04-01</p> <p>A rigorous understanding of the thermal and dynamic evolution of the core and the interaction with the silicate <span class="hlt">mantle</span> cannot preclude a non-empirical petrological description of the problem which takes the form of a thermodynamic model. Because the <span class="hlt">Earth</span>'s core is predominantly made of iron such model may seem relatively straightforward, simply delivering a representation of the phase transformations in the P,T space. However due to well known geophysical considerations, a certain amount of light elements should be added. With the Occam's razor principle in mind, potential candidates could be the most abundant and easily accessible elements in the <span class="hlt">mantle</span>, O, Si and Mg. Given these premises, the challenging problems on developing this type of model are: - a thermodynamic formulation should not simply describe phase equilibrium relations at least in the Fe-Si-O system (a formidable task itself) but should be also consistently applicable to evaluate thermophysical properties of liquid components and solids phases at extreme conditions (P=500-2000 kbar, T=1000-5000 K). Presently these properties are unknown for certain mineral and liquid components or partially available from scattered sources. - experimental data on the phase relations for iron rich liquid are extremely difficult to obtain and could not cover the entire P,T,X spectrum. - interaction of the outer core with the silicate <span class="hlt">mantle</span> requires a melt model that is capable of describing a vast range of compositions ranging from metal-rich liquids to silicate liquids. The compound energy formalism for liquids with variable tendency to ionization developed by Hillert and coworkers is a sublattice model with varying stoichiometry that includes vacancies and neutral species in one site. It represents the ideal candidate for the task in hand. The thermodynamic model unfortunately is rather complex and a detailed description of the formulation for practical applications like chemical equilibrium calculations is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20000000540&hterms=dissolve&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Ddissolve','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20000000540&hterms=dissolve&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Ddissolve"><span>Acquisition and <span class="hlt">Early</span> Losses of Rare Gases from the Deep <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Porcelli, D.; Cassen, P.; Woolum, D.; Wasserburg, G. J.</p> <p>1998-01-01</p> <p>Direct observations show that the deep <span class="hlt">Earth</span> contains rare gases of solar composition distinct from those in the atmosphere. We examine the implications of <span class="hlt">mantle</span> rare gas characteristics on acquisition of rare gases from the solar nebula and subsequent losses due to a large impact. Deep <span class="hlt">mantle</span> rare gas concentrations and isotopic compositions can be obtained from a model of transport and distribution of <span class="hlt">mantle</span> rare gases. This model assumes the lower <span class="hlt">mantle</span> closed <span class="hlt">early</span>, while the upper <span class="hlt">mantle</span> is open to subduction from the atmosphere and mass transfer from the lower <span class="hlt">mantle</span>. Constraints are derived that can be incorporated into models for terrestrial volatile acquisition: (1) Calculated lower-<span class="hlt">mantle</span> Xe-isotopic ratios indicate that the fraction of radiogenic Xe produced by I-129 and Pu-244 during the first about 10(exp 8) yr was lost, a conclusion also drawn for atmospheric Xe. Thus, either the <span class="hlt">Earth</span> was made from materials that had lost >99% of rare gases about (0.7-2) x 10(exp 8) yr after the solar system formed, or gases were then lost from the fully formed <span class="hlt">Earth</span>. (2) Concentrations of 3He and 20Ne in the lower <span class="hlt">mantle</span> were established after these losses. (3) Neon-isotopic data indicates that <span class="hlt">mantle</span> Ne has solar composition. The model allows for solar Ar/Ne and Xe/Ne in the lower <span class="hlt">mantle</span> if a dominant fraction of upper <span class="hlt">mantle</span> Ar and Xe are subduction-derived. If <span class="hlt">Earth</span> formed in the presence of the solar nebula, it could have been melted by accretional energy and the blanketing effect of a massive, nebula-derived atmosphere. Gases from this atmosphere would have been sequestered within the molten <span class="hlt">Earth</span> by dissolution at the surface and downward mixing. It was found that too much Ne would be dissolved in the <span class="hlt">Earth</span> unless the atmosphere began to escape when the <span class="hlt">Earth</span> was only partially assembled. Here we consider conditions required to initially dissolve sufficient rare gases to account for the present lower <span class="hlt">mantle</span> concentrations after subsequent losses at 10(exp 8</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IJEaS.107.1033G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IJEaS.107.1033G"><span><span class="hlt">Mantle</span> source heterogeneity of the <span class="hlt">Early</span> Jurassic basalt of eastern North America</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gregory Shellnutt, J.; Dostal, Jaroslav; Yeh, Meng-Wan</p> <p>2018-04-01</p> <p>One of the defining characteristics of the basaltic rocks from the <span class="hlt">Early</span> Jurassic Eastern North America (ENA) sub-province of the Central Atlantic Magmatic Province (CAMP) is the systematic compositional variation from South to North. Moreover, the tectono-thermal regime of the CAMP is debated as it demonstrates geological and structural characteristics (size, radial dyke pattern) that are commonly associated with <span class="hlt">mantle</span> plume-derived mafic continental large igneous provinces but is considered to be unrelated to a plume. <span class="hlt">Mantle</span> potential temperature ( T P) estimates of the northern-most CAMP flood basalts (North Mountain basalt, Fundy Basin) indicate that they were likely produced under a thermal regime ( T P ≈ 1450 °C) that is closer to ambient <span class="hlt">mantle</span> ( T P ≈ 1400 °C) conditions and are indistinguishable from other regions of the ENA sub-province ( T Psouth = 1320-1490 °C, T Pnorth = 1390-1480 °C). The regional <span class="hlt">mantle</span> potential temperatures are consistent along the 3000-km-long ENA sub-province suggesting that the CAMP was unlikely to be generated by a <span class="hlt">mantle</span> plume. Furthermore, the <span class="hlt">mantle</span> potential temperature calculation using the rocks from the Northern Appalachians favors an Fe-rich <span class="hlt">mantle</span> (FeOt = 8.6 wt %) source, whereas the rocks from the South Appalachians favor a less Fe-rich (FeOt = 8.3 wt %) source. The results indicate that the spatial-compositional variation of the ENA basaltic rocks is likely related to differing amounts of melting of <span class="hlt">mantle</span> sources that reflect the uniqueness of their regional accreted terranes (Carolinia and West Avalonia) and their post-accretion, pre-rift structural histories.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15817816','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15817816"><span>A hydrogen-rich <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tian, Feng; Toon, Owen B; Pavlov, Alexander A; De Sterck, H</p> <p>2005-05-13</p> <p>We show that the escape of hydrogen from <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have been more efficient than either exogenous delivery or synthesis in hydrothermal systems. The organic soup in the oceans and ponds on <span class="hlt">early</span> <span class="hlt">Earth</span> would have been a more favorable place for the origin of life than previously thought.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11315711','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11315711"><span><span class="hlt">Early</span> onset of bilateral brachial plexopathy during <span class="hlt">mantle</span> radiotherapy for Hodgkin's disease.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Churn, M; Clough, V; Slater, A</p> <p>2000-01-01</p> <p>We report a case of brachial plexus neuropathy occurring in a 50-year-old man treated with standard <span class="hlt">mantle</span> radiotherapy for <span class="hlt">early</span>-stage Hodgkin's disease. A dose of 35 Gy in 20 fractions was given to the <span class="hlt">mantle</span> field, following by a boost to the right side of the neck (8 Gy in four fractions). The onset of symptoms was <span class="hlt">early</span> in the course of treatment and a gradual and almost full recovery was observed over 3 years after completion ofradiotherapy. The diagnosis was supported by electromyography. The temporal relationship of the radiotherapy and the onset of the brachial plexus neuropathy suggests a cause and effect, but this association is rarely reported after <span class="hlt">mantle</span> radiotherapy. We review the aetiology of this condition and postulate possible mechanisms in this patient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.2390F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.2390F"><span>Comparison of the <span class="hlt">Mantle</span> Potential Temperature of Ancient Mars and the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Filiberto, Justin; Dasgupta, Rajdeep</p> <p>2016-04-01</p> <p>Basaltic igneous rocks shed light onto the chemistry, tectonic, and thermal state of planetary interiors. For the purpose of comparative planetology, therefore, it is critical to fully utilize the compositional diversity of basaltic rocks for different terrestrial planets. For Mars, basaltic compositions have been analyzed in situ on the surface at three different landing sites, from orbit providing global geochemistry, and in the laboratory for specific Martian meteorites [1-4]. This provides a range in chemistry and age of Martian rocks. Terrestrial mafic to ultramafic igneous rocks have a range in chemistry across different tectonic regimes and different ages [5-8]. These differences in chemistry and age of planetary basalts may reflect changes in the conditions of partial melting in the planetary interiors. Therefore, here we compare estimates of basalt genesis conditions for Mars with rocks from the Noachian (Gusev Crater, Meridiani Planum, Gale Crater, and a clast in the NWA 7034 meteorite [9, 10]), Hesperian (surface volcanics [11]), and Amazonian (surface volcanics and shergottites [11-14]), to calculate an average <span class="hlt">mantle</span> potential temperature for different Martian epochs and investigate how the interior of Mars has changed through time. We also calculate formation conditions for terrestrial komatiites and Archean basalts to calculate an average <span class="hlt">mantle</span> potential temperature during the Archean. Finally, we compare Martian <span class="hlt">mantle</span> potential temperatures with petrologic estimate of cooling for the <span class="hlt">Earth</span> to compare the cooling history for Mars and the <span class="hlt">Earth</span>. References: [1] Squyres S.W. et al. (2006) JGR. doi:10.1029/2005je002562. [2] Schmidt M.E., et al. (2014) JGRP. doi:2013JE004481. [3] Zipfel J. et al. (2011) MaPS. 46(1): 1-20. [4] Treiman A.H. and Filiberto J. (2015) MaPS. DOI:10.1111/maps.12363. [5] Putirka K.D.(2005) G-cubed. DOI:10.1029/2005gc000915. [6] Putirka K.D. et al. (2007) ChemGeo. 241(3-4): 177-206. [7] Courtier A.M. et al. (2007) EPSL. 264</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMDI51B..06O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMDI51B..06O"><span>Stability of iron-rich magnesiowüstite in <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ohta, K.; Fujino, K.; Kuwayama, Y.; Kondo, T.; Shimizu, K.; Ohishi, Y.</p> <p>2012-12-01</p> <p>At ambient conditions, MgO periclase and FeO wüstite form a solid solution (Mg1-xFex)O, named ferropericlase (x ≤ 0.5) and magnesiowüstite (x > 0.5). (Mg1-xFex)O ferropericlase is considered to be a major component of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>, and may play an important role for its structure and dynamics. Iron-rich magnesiowüstite also needs to be considered because of possible iron enrichment at the core-<span class="hlt">mantle</span> boundary region [e.g., Nomura et al., 2011]. Recent laser-heated diamond anvil cell experiments on FeO revealed that NaCl-type (B1) structured FeO underwent an insulator-metal transition at about 70 GPa and 1800 K without any structural transformation [Fischer et al., 2011; Ohta et al., 2012]. These results imply that the metallic B1 FeO would require a two-phase field for the MgO-FeO binary system due to different chemical bonding between insulating MgO and metallic FeO. We performed simultaneous electrical conductivity and x-ray diffraction measurements on (Mg0.20Fe0.80)O and (Mg0.05Fe0.95)O magnesiowüstite up to 140 GPa and 2100 K, and then examined recovered samples by using analytical transmission electron microprobe. We obtained some evidences for the dissociation of (Mg0.05Fe0.95)O into lighter and heavier phases than starting material occurring above 70 GPa and 1900 K, which is most likely due to the metallization of FeO component. On the other hand, we did not observe such dissociation and metallization in (Mg0.20Fe0.80)O. Observed dissociation in (Mg0.05Fe0.95)O might contribute to the heterogeneity in seismic wave and electrical conductivity at the <span class="hlt">Earth</span>'s core-<span class="hlt">mantle</span> boundary region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.449...96M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.449...96M"><span>Massive impact-induced release of carbon and sulfur gases in the <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marchi, S.; Black, B. A.; Elkins-Tanton, L. T.; Bottke, W. F.</p> <p>2016-09-01</p> <p>Recent revisions to our understanding of the collisional history of the Hadean and <span class="hlt">early</span>-Archean <span class="hlt">Earth</span> indicate that large collisions may have been an important geophysical process. In this work we show that the <span class="hlt">early</span> bombardment flux of large impactors (>100 km) facilitated the atmospheric release of greenhouse gases (particularly CO2) from <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Depending on the timescale for the drawdown of atmospheric CO2, the <span class="hlt">Earth</span>'s surface could have been subject to prolonged clement surface conditions or multiple freeze-thaw cycles. The bombardment also delivered and redistributed to the surface large quantities of sulfur, one of the most important elements for life. The stochastic occurrence of large collisions could provide insights on why the <span class="hlt">Earth</span> and Venus, considered <span class="hlt">Earth</span>'s twin planet, exhibit radically different atmospheres.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1376239-reduced-lattice-thermal-conductivity-fe-bearing-bridgmanite-earth-deep-mantle-reduced-conductivity-fe-bridgmanite','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1376239-reduced-lattice-thermal-conductivity-fe-bearing-bridgmanite-earth-deep-mantle-reduced-conductivity-fe-bridgmanite"><span>Reduced lattice thermal conductivity of Fe-bearing bridgmanite in <span class="hlt">Earth</span>'s deep <span class="hlt">mantle</span>: Reduced Conductivity of Fe-Bridgmanite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo</p> <p></p> <p>Complex seismic, thermal, and chemical features have been reported in <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span>. In particular, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower <span class="hlt">mantle</span> dynamics and heat flux across core-<span class="hlt">mantle</span> boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. Importantly, the pressure-induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermalmore » conductivity of Fe-bearing bridgmanite to 120 GPa using optical pump-probe spectroscopy. The conductivity of Fe-bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost <span class="hlt">mantle</span> conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower <span class="hlt">mantle</span> and below would promote <span class="hlt">mantle</span> flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18..675M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18..675M"><span>Duration of the hydrocarbon fluid formation under thermobaric conditions of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukhina, Elena; Kolesnikov, Anton; Kutcherov, Vladimir</p> <p>2016-04-01</p> <p>Deep abiogenic formation of hydrocarbons is an inherent part of the <span class="hlt">Earth</span>'s global carbon cycle. It was experimentally confirmed that natural gas could be formed from inorganic carbon and hydrogen containing minerals at pressure and temperature corresponding to the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> conditions. Reaction between calcite, wustite and water in the large volume device was studied in several works. It was previously proposed that reaction is possible only after 40 minutes of exposure at high pressure and temperature. In this work similar experiment at P = 60 kbar and T = 1200 K were carried out in "Toroid" type chamber with the 5 seconds duration of thermobaric exposure. Gas chromatographic analysis of the reaction products has shown the presence of hydrocarbon mixture comparable to 5 minutes and 6 hours exposure experiments. Based on this fact it is possible to conclude that the reaction of natural gas formation is instant at least at given thermobaric conditions. This experiment will help to better understand the process of deep hydrocarbon generation, particularly its kinetics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993Litho..30..223A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993Litho..30..223A"><span>Physical state of the very <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abe, Yutaka</p> <p>1993-09-01</p> <p>The earliest surface environment of the <span class="hlt">Earth</span> is reconstructed in accordance with the planetary formation theory. Formation of an atmosphere is an inevitable consequence of <span class="hlt">Earth</span>'s formation. The atmosphere near the close of accretion is composed of 200 ˜ 300 bars of H 2 and H 2O, and several tens of bars of CO and CO 2. Either by the blanketing effect of the proto-atmosphere or heating by large planetesimal impacts a magma ocean is formed during accretion. We can distinguish three stages for the thermal evolution of the magma ocean and proto-crust. Stage 0 is characterized by a super-liquidus (or completely molten) regime near the surface. At this stage the surface of the <span class="hlt">Earth</span> is covered by a super-liquidus magma ocean. No chemical differentiation is expected during this stage. Once the energy flux released by planet formation decreases to the 200 W/m 2 level the super-liquidus magma ocean then disappears within a time interval of 1 m.y. This is the transition from stage 0 to 1. Stage 1 is characterized by a partially molten magma ocean. In the magma ocean consisting of 20 ˜ 30% partial melt, heat transport is controlled by melt-solid separation (a type of compositional convection) rather than thermal convection. Chemical differentiation of the <span class="hlt">mantle</span> mainly occurs in this stage. Once the energy flux drops to the 160 W/m 2 level, more than 90% of water vapor in the proto-atmosphere condense to form the proto-oceans. Several tens of bars of CO and CO 2 remain in the atmosphere just after formation of the oceans. Water oceans are occasionally evaporated by large impacts. After each such event, recondensation of the ocean takes several hundred years. Although the surface is covered by a chilled proto-crust, it is short-lived because of extensive volcanic resurfacing activity as well as meteorite impacts resurfacing. This stage ends when the energy flux drops to 0.1 ˜ 1 W/m 2 level. The duration time of stage 1 is estimated to be several hundred million years (the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.6685G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.6685G"><span>Linking the <span class="hlt">Earth</span>'s surface with the deep-<span class="hlt">mantle</span> plume beneath a region from Iceland to the city of Perm</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glišović, Petar; Forte, Alessandro; Simmons, Nathan; Grand, Stephen</p> <p>2014-05-01</p> <p>Current tomography models consistently reveal three large-scale regions of strongly reduced seismic velocity in the lowermost <span class="hlt">mantle</span> under the Pacific, Africa and a region that extends from below Iceland to the city of Perm (the Perm Anomaly). We have carried out <span class="hlt">mantle</span> dynamic simulations (Glišović et al., GJI 2012; Glišović & Forte, EPSL 2014) of the evolution of these large-scale structures that directly incorporate: 1) robust constraints provided by joint seismic-geodynamic inversions of <span class="hlt">mantle</span> density structure with constraints provided by mineral physics data (Simmons et al., GJI 2009); and 2) constraints on <span class="hlt">mantle</span> viscosity inferred by inversion of a suite of convection-related and glacial isostatic adjustment data sets (Mitrovica & Forte, EPSL 2004) characterised by <span class="hlt">Earth</span>-like Rayleigh numbers. The convection simulations provide a detailed insight into the very-long-time evolution of the buoyancy of these lower-<span class="hlt">mantle</span> anomalies. We find, in particular, that the buoyancy associated with the Perm Anomaly generates a very long-lived superplume that is connected to the paleomagnetic location of the Siberian Traps at the time of their eruption (Smirnov & Tarduno, EPSL 2010) and also to location of North Atlantic Igneous Provinces (i.e., the opening of North Atlantic Ocean).</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26601281','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26601281"><span>Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-Ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo</p> <p>2015-10-01</p> <p>Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper <span class="hlt">mantle</span> conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper <span class="hlt">mantle</span>. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 10(19.6) to 10(20.7) Pa·s throughout the asthenospheric upper <span class="hlt">mantle</span> with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size-sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.V32B..06L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.V32B..06L"><span>Constraints on The Coupled Thermal Evolution of the <span class="hlt">Earth</span>'s Core and <span class="hlt">Mantle</span>, The Age of The Inner Core, And The Origin of the 186Os/188Os Core(?) Signal in Plume-Derived Lavas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lassiter, J. C.</p> <p>2005-12-01</p> <p>Thermal and chemical interaction between the core and <span class="hlt">mantle</span> has played a critical role in the thermal and chemical evolution of the <span class="hlt">Earth</span>'s interior. Outer core convection is driven by core cooling and inner core crystallization. Core/<span class="hlt">mantle</span> heat transfer also buffers <span class="hlt">mantle</span> potential temperature, resulting in slower rates of <span class="hlt">mantle</span> cooling (~50-100 K/Ga) than would be predicted from the discrepancy between current rates of surface heat loss (~44 TW) and internal radioactive heat production (~20 TW). Core/<span class="hlt">mantle</span> heat transfer may also generate thermal <span class="hlt">mantle</span> plumes responsible for ocean island volcanic chains such as the Hawaiian Islands. Several studies suggest that <span class="hlt">mantle</span> plumes, in addition to transporting heat from the core/<span class="hlt">mantle</span> boundary, also carry a chemical signature of core/<span class="hlt">mantle</span> interaction. Elevated 186Os/188Os ratios in lavas from Hawaii, Gorgona, and in the 2.8 Ga Kostomuksha komatiites have been interpreted as reflecting incorporation of an outer core component with high time-integrated Pt/Os and Re/Os ( Brandon et al., 1999, 2003; Puchtel et al., 2005). Preferential partitioning of Os relative to Re and Pt into the inner core during inner core growth may generate elevated Re/Os and Pt/Os ratios in the residual outer core. Because of the long half-life of 190Pt (the parent of 186Os, t1/2 = 489 Ga), an elevated 186Os/188Os outer core signature in plume lavas requires that inner core crystallization began <span class="hlt">early</span> in <span class="hlt">Earth</span> history, most likely prior to 3.5 Ga. This in turn requires low time-averaged core/<span class="hlt">mantle</span> heat flow (<~2.5 TW) or large quantities of heat-producing elements in the core. Core/<span class="hlt">mantle</span> heat flow may be estimated using boundary-layer theory, by measuring the heat transported in <span class="hlt">mantle</span> plumes, by estimating the heat transported along the outer core adiabat, or by comparing the rates of heat production, surface heat loss, and secular cooling of the <span class="hlt">mantle</span>. All of these independent methods suggest time-averaged core/<span class="hlt">mantle</span> heat flow of ~5</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.7508M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.7508M"><span>Effects of <span class="hlt">Earth</span>'s rotation on the <span class="hlt">early</span> differentiation of a terrestrial magma ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maas, Christian; Hansen, Ulrich</p> <p>2015-11-01</p> <p>Similar to other terrestrial planets like Moon and Mars, <span class="hlt">Earth</span> experienced a magma ocean period about 4.5 billion years ago. On <span class="hlt">Earth</span> differentiation processes in the magma ocean set the initial conditions for core formation and <span class="hlt">mantle</span> evolution. During the magma ocean period <span class="hlt">Earth</span> was rotating significantly faster than today. Further, the viscosity of the magma was low, thus that planetary rotation potentially played an important role for differentiation. However, nearly all previous studies neglect rotational effects. All in all, our results suggest that planetary rotation plays an important role for magma ocean crystallization. We employ a 3-D numerical model to study crystal settling in a rotating and vigorously convecting <span class="hlt">early</span> magma ocean. We show that crystal settling in a terrestrial magma ocean is crucially affected by latitude as well as by rotational strength and crystal density. Due to rotation an inhomogeneous accumulation of crystals during magma ocean solidification with a distinct crystal settling between pole and equator could occur. One could speculate that this may have potentially strong effects on the magma ocean solidification time and the <span class="hlt">early</span> <span class="hlt">mantle</span> composition. It could support the development of a basal magma ocean and the formation of anomalies at the core-<span class="hlt">mantle</span> boundary in the equatorial region, reaching back to the time of magma ocean solidification.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvL.118c6402F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvL.118c6402F"><span>Abnormal Elasticity of Single-Crystal Magnesiosiderite across the Spin Transition in <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fu, Suyu; Yang, Jing; Lin, Jung-Fu</p> <p>2017-01-01</p> <p>Brillouin light scattering and impulsive stimulated light scattering have been used to determine the full elastic constants of magnesiosiderite [(Mg0.35Fe0.65)CO3 ] up to 70 GPa at room temperature in a diamond-anvil cell. Drastic softening in C11 , C33 , C12 , and C13 elastic moduli associated with the compressive stress component and stiffening in C44 and C14 moduli associated with the shear stress component are observed to occur within the spin transition between ˜42.4 and ˜46.5 GPa . Negative values of C12 and C13 are also observed within the spin transition region. The Born criteria constants for the crystal remain positive within the spin transition, indicating that the mixed-spin state remains mechanically stable. Significant auxeticity can be related to the electronic spin transition-induced elastic anomalies based on the analysis of Poisson's ratio. These elastic anomalies are explained using a thermoelastic model for the rhombohedral system. Finally, we conclude that mixed-spin state ferromagnesite, which is potentially a major deep-carbon carrier, is expected to exhibit abnormal elasticity, including a negative Poisson's ratio of -0.6 and drastically reduced VP by 10%, in <span class="hlt">Earth</span>'s midlower <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JPhCS.653a2095O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JPhCS.653a2095O"><span>Spin crossover and Mott—Hubbard transition under high pressure and high temperature in the low <span class="hlt">mantle</span> of the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ovchinnikov, S. G.; Ovchinnikova, T. M.; Plotkin, V. V.; Dyad'kov, P. G.</p> <p>2015-11-01</p> <p>Effect of high pressure induced spin crossover on the magnetic, electronic and structural properties of the minerals forming the <span class="hlt">Earth</span>'s low <span class="hlt">mantle</span> is discussed. The low temperature P, T phase diagram of ferropericlase has the quantum phase transition point Pc = 56 GPa at T = 0 confirmed recently by the synchrotron Mössbauer spectroscopy. The LDA+GTB calculated phase diagram describes the experimental data. Its extension to the high temperature resulted earlier in prediction of the metallic properties of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> at the depth 1400 km < h < 1800 km. Estimation of the electrical conductivity based on the percolation theory is given. We discuss also the thermodynamic properties and structural anomalies resulting from the spin crossover and metal-insulator transition and compare them with the experimental seismic and geomagnetic field data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2413174','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2413174"><span>X-ray Raman scattering study of MgSiO3 glass at high pressure: Implication for triclustered MgSiO3 melt in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Lee, Sung Keun; Lin, Jung-Fu; Cai, Yong Q.; Hiraoka, Nozomu; Eng, Peter J.; Okuchi, Takuo; Mao, Ho-kwang; Meng, Yue; Hu, Michael Y.; Chow, Paul; Shu, Jinfu; Li, Baosheng; Fukui, Hiroshi; Lee, Bum Han; Kim, Hyun Na; Yoo, Choong-Shik</p> <p>2008-01-01</p> <p>Silicate melts at the top of the transition zone and the core-<span class="hlt">mantle</span> boundary have significant influences on the dynamics and properties of <span class="hlt">Earth</span>'s interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the <span class="hlt">early</span> <span class="hlt">Earth</span>. Diverse macroscopic properties of silicate melts in <span class="hlt">Earth</span>'s interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of <span class="hlt">Earth</span>'s interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; [3]O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. PMID:18535140</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70012107','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70012107"><span>Composition of the <span class="hlt">earth</span>'s upper <span class="hlt">mantle</span>-I. Siderophile trace elements in ultramafic nodules</span></a></p> <p><a target="_blank" href=""></a></p> <p>Morgan, J.W.; Wandless, G.A.; Petrie, R.K.; Irving, A.J.</p> <p>1981-01-01</p> <p>Seven siderophile elements (Au, Ge, Ir, Ni, Pd, Os, Re) were determined by radiochemical neutron activation analysis in 19 ultramafic rocks, which are spinel lherzollites-xenoliths from North and Central America, Hawaii and Australia, and garnet Iherzolitexenoliths from Lesotho. Abundances of the platinum metals are very uniform in spinel lherzolites averaging 3.4 ?? 1.2 ppb Os, 3.7 ?? 1.1 ppb Ir, and 4.6 ?? 2.0 ppb Pd. Sheared garnet lherzolite PHN 1611 has similar abundances of these elements, but in 4 granulated garnet lherzolites, abundances are more variable. In all samples, the Pt metals retain cosmic ( Cl-chondrite) ratios. Abundances of Au and Re vary more than those of Pt metals, but the Au/Re ratio remains close to the cosmic value. The fact that higher values of Au and Re approach cosmic proportions with respect to the Pt metals, suggests that Au and Re have been depleted in some ultramafic rocks from an initially chondrite-like pattern equivalent to about 0.01 of Cl chondrite abundances. The relative enrichment of Au and Re in crustal rocks is apparently the result of crust-<span class="hlt">mantle</span> fractionation and does not require a special circumstance of core-<span class="hlt">mantle</span> partitioning. Abundances of moderately volatile elements Ni, Co and Ge are very uniform in all rocks, and are much higher than those of the highly siderophile elements Au, Ir, Pd, Os and Re. When normalized to Cl chondrites, abundances of Ni and Co are nearly identical, averaging 0.20 ?? 0.02 and 0.22 ?? 0.02, respectively; but Ge is only 0.027 ?? 0.004. The low abundance of Ge relative to Ni and Co is apparently a reflection of the general depletion of volatile elements in the <span class="hlt">Earth</span>. The moderately siderophile elements cannot be derived from the same source as the highly siderophile elements because of the marked difference in Cl chondrite-normalized abundances and patterns. We suggest that most of the Ni, Co and Ge were enriched in the silicate by the partial oxidation of pre-existing volatile-poor Fe</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V33A2720K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V33A2720K"><span>Secondary overprinting of S-Se-Te signatures in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>: Implications for the Late Veneer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koenig, S.; Luguet, A.; Lorand, J.; Pearson, D.</p> <p>2013-12-01</p> <p>Sulphur, Selenium and Tellurium are both chalcophile and highly siderophile elements (HSE) with near-chondritic ratios and absolute abundances in the terrestrial <span class="hlt">mantle</span> that exceed those predicted by core-<span class="hlt">mantle</span> differentiation[1]. These 'excess' HSE abundances have been attributed to addition of ca. 0.5% of chondrite-like material that hit the <span class="hlt">Earth</span> in its accretionary stage between 4 to 3.8 billion years ago after core-<span class="hlt">mantle</span> differentiation (Late Veneer[2]). Therefore, like other HSE, S, Se and Te are considered potential tracers for the composition of the Late Veneer, provided that their bulk silicate <span class="hlt">Earth</span> abundances are properly constrained. In contrast to ca. 250 ppm S, Se and Te are ultra-trace elements in the terrestrial <span class="hlt">mantle</span>. Like all HSE, they are furthermore controlled by base metal sulphides (BMS) and micrometric platinum group minerals (PGMs)[3]. This strong control exerted by the host mineralogy and petrology on the S-Se-Te systematics at both the micro-scale and the whole-rock scale makes detailed mineralogical and petrological studies of BMS and PGM a pre-requisite to fully understand and accurately interpret the whole-rock signatures. Here we combine in-situ sulphide data and detailed mineralogical observations with whole-rock S-Se-Te-HSE signatures of both lherzolites and harburgites from different geodynamic settings. We demonstrate that the near-chondritic Se and Te signature of 'fertile' <span class="hlt">mantle</span> rocks (Se/Te ≈9×5) is not a primitive signature of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>, but rather reflects strong enrichment in metasomatic HSE host phases, which erased previous pristine signatures. Consequently, current attempts to identify a potential Late Veneer composition are seriously flawed because, neither refertilisation/metasomatism nor true melt depletion (e.g. harzburgitic residues) have been taken into account for the Primitive Upper <span class="hlt">Mantle</span> composition estimate[4]. Our combined whole rock and in-situ sulphide data indicate a refertilisation trend</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/5023807-early-earth-perspective-archean','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/5023807-early-earth-perspective-archean"><span>The <span class="hlt">early</span> <span class="hlt">Earth</span> -- A perspective on the Archean</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Hamilton, W.B.</p> <p>1993-04-01</p> <p>Dominant models of Archean tectonics and magmatism involve plate-tectonic mechanisms. Common tenets of geochemistry (e.g., model ages) and petrology visualize a cold-accreted <span class="hlt">Earth</span> in which primitive <span class="hlt">mantle</span> gradually fractionated to produce crust during and since Archean time. These popular assumptions appear to be incompatible with cosmologic and planetologic evidence and with Archean geology. All current quantitative and semiquantitative theories agree that the <span class="hlt">Earth</span> was largely or entirely melted (likely superheated) by giant impacts, including the Mars-size impact which splashed out the Moon, and by separation of the core. The <span class="hlt">Earth</span> at [approximately]4.5 Ga was a violently convecting anhydrous molten ball.more » Both this history and solar-system position indicate the bulk <span class="hlt">Earth</span> to be more refractory than chondrite. The outer part of whatever sold shell developed was repeatedly recycled by impacts before 3.9 Ga. Water and CO[sub 2] were added by impactors after the Moon-forming event; the <span class="hlt">mantle</span> is not a source of primordial volatiles, but rather is a sink that has depleted the hydrosphere. Voluminous liquidus ultramafic lava (komatiite) indicates that much Archean upper <span class="hlt">mantle</span> was above its solidus. Only komatiitic and basaltic magma entered Archean crust from the <span class="hlt">mantle</span>. Variably hydrous contamination, secondary melting, and fractionation in the crust produced intermediate and felsic melts. Magmatism was concurrent over vast tracts. Within at least the small sample of Archean crust that has not been recycled into the <span class="hlt">mantle</span>, heat loss was primarily by voluminous, dispersed magmatism, not, as in the modern <span class="hlt">Earth</span>, primarily through spreading windows through the crust. Only in Proterozoic time did plate-tectonic mechanisms become prevalent.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850024768&hterms=history+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dhistory%2BEarth','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850024768&hterms=history+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dhistory%2BEarth"><span>A review of noble gas geochemistry in relation to <span class="hlt">early</span> <span class="hlt">Earth</span> history</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kurz, M. D.</p> <p>1985-01-01</p> <p>One of the most fundamental noble gas constraints on <span class="hlt">early</span> <span class="hlt">Earth</span> history is derived from isotopic differences in (129)Xe/(130)Xe between various terrestrial materials. The short half life (17 m.y.) of extinct (129I, parent of (129)Xe, means that these differences must have been produced within the first 100 m.y. after terrestrial accretion. The identification of large anomalies in (129)Xe/(130)Xe in mid ocean ridge basalts (MORB), with respect to atmospheric xenon, suggests that the atmosphere and upper <span class="hlt">mantle</span> have remained separate since that time. This alone is a very strong argument for <span class="hlt">early</span> catastrophic degassing, which would be consistent with an <span class="hlt">early</span> fractionation resulting in core formation. However, noble gas isotopic systematics of oceanic basalts show that the <span class="hlt">mantle</span> cannot necessarily be regarded as a homogeneous system, since there are significant variations in (3)He/(4)He, (40)Ar/(36)Ar, and (129)Xe/(130)Xe. Therefore, the <span class="hlt">early</span> degassing cannot be considered to have acted on the whole <span class="hlt">mantle</span>. The specific mechanisms of degassing, in particular the thickness and growth of the <span class="hlt">early</span> crust, is an important variable in understanding present day noble gas inventories. Another constraint can be obtained from rocks that are thought to be derived from near the lithosphere asthenosphere boundary: ultramafic xenoliths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140003556','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140003556"><span>Core-<span class="hlt">Mantle</span> Partitioning of Volatile Elements and the Origin of Volatile Elements in <span class="hlt">Earth</span> and Moon</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Righter, Kevin; Pando, K.; Danielson, L.; Nickodem, K.</p> <p>2014-01-01</p> <p>Depletions of volatile siderophile elements (VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd) in <span class="hlt">mantles</span> of <span class="hlt">Earth</span> and Moon, constrain the origin of volatile elements in these bodies, and the overall depletion of volatile elements in Moon relative to <span class="hlt">Earth</span>. A satisfactory explanation has remained elusive [1,2]. We examine the depletions of VSE in <span class="hlt">Earth</span> and Moon and quantify the amount of depletion due to core formation and volatility of potential building blocks. We calculate the composition of the <span class="hlt">Earth</span>'s PUM during continuous accretion scenarios with constant and variable fO2. Results suggest that the VSE can be explained by a rather simple scenario of continuous accretion leading to a high PT metal-silicate equilibrium scenario that establishes the siderophile element content of <span class="hlt">Earth</span>'s PUM near the end of accretion [3]. Core formation models for the Moon explain most VSE, but calculated contents of In, Sn, and Zn (all with Tc < 750 K) are all still too high after core formation, and must therefore require an additional process to explain the depletions in the lunar <span class="hlt">mantle</span>. We discuss possible processes including magmatic degassing, evaporation, condensation, and vapor-liquid fractionation in the lunar disk.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040191783&hterms=Earths+last+life&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DEarths%2Blast%2Blife','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040191783&hterms=Earths+last+life&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DEarths%2Blast%2Blife"><span>Life Detection on the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Runnegar, B.</p> <p>2004-01-01</p> <p>Finding evidence for first the existence, and then the nature of life on the <span class="hlt">early</span> <span class="hlt">Earth</span> or <span class="hlt">early</span> Mars requires both the recognition of subtle biosignatures and the elimination of false positives. The history of the search for fossils in increasingly older Precambrian strata illustrates these difficulties very clearly, and new observational and theoretical approaches are both needed and being developed. At the microscopic level of investigation, three-dimensional morphological characterization coupled with in situ chemical (isotopic, elemental, structural) analysis is the desirable first step. Geological context is paramount, as has been demonstrated by the controversies over AH84001, the Greenland graphites, and the Apex chert microfossils . At larger scales, the nature of sedimentary bedforms and the structures they display becomes crucial, and here the methods of condensed matter physics prove most useful in discriminating between biological and non-biological constructions. Ultimately, a combination of geochemical, morphological, and contextural evidence may be required for certain life detection on the <span class="hlt">early</span> <span class="hlt">Earth</span> or elsewhere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.U13B..16H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.U13B..16H"><span>Ultra-high precision 142Nd/144Nd measurements of the Proterozoic and implications for mixing in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> through time</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hyung, E.; Jacobsen, S. B.</p> <p>2017-12-01</p> <p>The decay of 146Sm to 142Nd is an excellent a tracer for <span class="hlt">early</span> silicate differentiation events in the terrestrial planets, as the Sm/Nd ratio is usually fractionated during <span class="hlt">mantle</span> partial melting and magma ocean crystallization. The short half-life (103 or 68 Ma) renders the system extinct within the first 500 Ma of Solar System formation. Samples with 142Nd/144Nd ratios that are substantially different from the bulk silicate <span class="hlt">Earth</span> value of 142Nd/144Nd provide clear evidence for <span class="hlt">mantle</span> differentiation in the Hadean. Published data for the 3.4 to 3.8 Ga old Isua supracrustal rocks and dykes have demonstrated both positive and negative 142Nd/144Nd anomalies (30 ppm range) providing clear evidence for Hadean enriched and depleted <span class="hlt">mantle</span> reservoirs. In contrast, no 142Nd/144Nd anomalies have been found in modern day terrestrial samples with data that have 2σ uncertainties of about 5 ppm or more. Last year we reported improvements in 142Nd/144Nd measurements, using our IsotopX thermal ionization mass spectrometer, and obtained reproducibility of 142Nd/144Nd ratios to better than 2 ppm at the 2σ level. With this external reproducibility we found that all except one modern <span class="hlt">mantle</span>-derived basalt had within error identical 142Nd/144Nd ratios. One sample is about 3.4 ppm lower than the rest of the modern basalt samples, providing evidence for some limited Hadean <span class="hlt">mantle</span> differentiation signatures preserved up to present. We have also measured 142Nd/144Nd ratios for Proterozoic and Phanerozoic samples, whose ages range from 300 Ma to 2 Ga, to better than 2 ppm external reproducibility (2σ). Most of these samples also have 142Nd/144Nd ratios that cluster around the modern day value, but there are some samples that are either marginally high by 2 ppm or low by 2 ppm. Thus, while a 20 to 30 ppm range in 142Nd/144Nd is well resolved in the Archean, such large variability is not present in the Proterozoic and Phanerozoic. The relatively rapid changeover at the end of the Archean</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMMR11A4303M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMMR11A4303M"><span>Novel Techniques for High Pressure Falling Sphere Viscosimetry under Simulated <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> Conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mueller, H. J.; Beckmann, F.; Dobson, D. P.; Hunt, S. A.; Secco, R.; Lauterjung, J.; Lathe, C.</p> <p>2014-12-01</p> <p>Viscosity data of melts measured under in situ high pressure conditions are crucial for the understanding of <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> and the interior of terrestrial and extrasolar Super-<span class="hlt">Earth</span> planets. We report recent technical advances and techniques enabling falling sphere viscosity measurements in single- and double-stage DIA-type multi-anvil apparatus. For the experiments we used presses with a maximum load of 250 tons and 1750 tons. We anticipate that our system will enable viscosity measurements up to the maximum pressure for non-diamond anvils, i.e. pressures up to some 30 GPa. For the development of the new set ups the deformation of the cell assemblies were analyzed by X-ray absorption tomography at beamline W II at DESY/HASYLAB after the high pressure runs. These analysis gave considerable insights into strategies for improving the cell assembly with the result that the optimized assemblies could be used at much higher pressures without blow-outs. We think this approach is much faster and more beneficial than the classical way of trial and error. Additionally to prevent high pressure blow outs the task was to make the whole melting chamber accessible for the high pressure X-radiography system up to the maximum pressures. This way the accuracy and reliability of the measurements can be improved. For this goal we used X-ray transparent cBN-anvils at the single-stage DIA large volume press. Because this material is recently not available for the cube size of 32 mm this aproach did not work for the double-stage DIA. As a very useful and economical alternative we used slotted carbide anvils filled with fired pyrophyllite bars. To improve the frame quality of the platinum spheres taken by the CCD-camera the energy of the monochromatic X-rays had to be increased to 100 keV. The resulting ascent of scattered radiation required a new design of the X-radiography unit. Our results are demonstrated with viscosity measurements following Stokes law by evaluation of X</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10227199','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10227199"><span>Flash heating on the <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lyons, J R; Vasavada, A R</p> <p>1999-03-01</p> <p>It has been suggested that very large impact events (approximately 500 km diameter impactors) sterilized the surface of the young <span class="hlt">Earth</span> by producing enough rock vapor to boil the oceans. Here, we consider surface heating due to smaller impactors, and demonstrate that surface temperatures conductive to organic synthesis resulted. In particular, we focus on the synthesis of thermal peptides. Previously, laboratory experiments have demonstrated that dry heating a mixture of amino acids containing excess Asp, Glu, or Lys to temperatures approximately 170 degrees C for approximately 2 hours yields polypeptides. It has been argued that such temperature conditions would not have been available on the <span class="hlt">early</span> <span class="hlt">Earth</span>. Here we demonstrate, by analogy with the K/T impact, that the requisite temperatures are achieved on sand surfaces during the atmospheric reentry of fine ejecta particles produced by impacts of bolides approximately 10-20 km in diameter, assuming approximately 1-100 PAL CO2. Impactors of this size struck the <span class="hlt">Earth</span> with a frequency of approximately 1 per 10(4)-10(5) y at 4.2 Ga. Smaller bolides produced negligible global surface heating, whereas bolides > 30 km in diameter yielded solid surface temperatures > 1000 K, high enough to pyrolyze amino acids and other organic compounds. Thus, peptide formation would have occurred globally for a relatively narrow range of bolide sizes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1385861-disproportionation-mg-fe-sio3-perovskite-earth-deep-lower-mantle','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1385861-disproportionation-mg-fe-sio3-perovskite-earth-deep-lower-mantle"><span>Disproportionation of (Mg,Fe)SiO3 perovskite in <span class="hlt">Earth</span>'s deep lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Zhang, L.; Meng, Y.; Yang, W.</p> <p>2014-05-22</p> <p>The mineralogical constitution of the Earth’s <span class="hlt">mantle</span> dictates the geophysical and geochemical properties of this region. Previous models of a perovskite-dominant lower <span class="hlt">mantle</span> have been built on the assumption that the entire lower <span class="hlt">mantle</span> down to the top of the D'' layer contains ferromagnesian silicate [(Mg,Fe)SiO3] with nominally 10 mole percent Fe. On the basis of experiments in laser-heated diamond anvil cells, at pressures of 95 to 101 gigapascals and temperatures of 2200 to 2400 kelvin, we found that such perovskite is unstable; it loses its Fe and disproportionates to a nearly Fe-free MgSiO3 perovskite phase and an Fe-rich phasemore » with a hexagonal structure. This observation has implications for enigmatic seismic features beyond ~2000 kilometers depth and suggests that the lower <span class="hlt">mantle</span> may contain previously unidentified major phases.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011E%26PSL.304..251A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011E%26PSL.304..251A"><span>Solidus and liquidus profiles of chondritic <span class="hlt">mantle</span>: Implication for melting of the <span class="hlt">Earth</span> across its history</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andrault, Denis; Bolfan-Casanova, Nathalie; Nigro, Giacomo Lo; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed</p> <p>2011-04-01</p> <p>We investigated the melting properties of a synthetic chondritic primitive <span class="hlt">mantle</span> up to core-<span class="hlt">mantle</span> boundary (CMB) pressures, using laser-heated diamond anvil cell. Melting criteria are essentially based on the use of X-rays provided by synchrotron radiation. We report a solidus melting curve lower than previously determined using optical methods. The liquidus curve is found between 300 and 600 K higher than the solidus over the entire lower <span class="hlt">mantle</span>. At CMB pressures (135 GPa), the chondritic <span class="hlt">mantle</span> solidus and liquidus reach 4150 (± 150) K and 4725 (± 150) K, respectively. We discuss that the lower <span class="hlt">mantle</span> is unlikely to melt in the D″-layer, except if the highest estimate of the temperature profile at the base of the <span class="hlt">mantle</span>, which is associated with a very hot core, is confirmed. Therefore, recent suggestions of partial melting in the lowermost <span class="hlt">mantle</span> based on seismic observations of ultra-low velocity zones indicate either (1) a outer core exceeding 4150 K at the CMB or (2) the presence of chemical heterogeneities with high concentration of fusible elements. Our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion. Not only complete melting of the lower <span class="hlt">mantle</span> would require excessively high temperatures, but also, below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought. In addition, magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 GPa, as suggested by siderophile metal-silicate partitioning data. Such high surface temperature regime, where thermal blanketing is inefficient, points out to a transient character of the magma ocean, with a very fast cooling rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1343130-elasticity-ferropericlase-seismic-heterogeneity-earth-lower-mantle-ferropericlase-high-pressure-temperature-elasticity','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1343130-elasticity-ferropericlase-seismic-heterogeneity-earth-lower-mantle-ferropericlase-high-pressure-temperature-elasticity"><span>Elasticity of ferropericlase and seismic heterogeneity in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>: Ferropericlase High Pressure-Temperature Elasticity</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Yang, Jing; Lin, Jung-Fu; Jacobsen, Steven D.</p> <p>2016-12-16</p> <p>Deciphering the origin of seismic heterogeneity has been one of the major challenges in understanding the geochemistry and geodynamics of the deep <span class="hlt">mantle</span>. Fully anisotropic elastic properties of constituent minerals at relevant pressure-temperature conditions of the lower <span class="hlt">mantle</span> can be used to calculate seismic heterogeneity parameters in order to better understand chemically and thermally induced seismic heterogeneities. In this study, the single-crystal elastic properties of ferropericlase (Mg0.94Fe0.06)O were measured using Brillouin spectroscopy and X-ray diffraction at conditions up to 50 GPa and 900 K. The velocity-density results were modeled using third-order finite-strain theory and thermoelastic equations along a representative geothermmore » to investigate high pressure-temperature and compositional effects on the seismic heterogeneity parameters. Our results demonstrate that from 660 to 2000 km, compressional wave anisotropy of ferropericlase increased from 4% to 9.7%, while shear wave anisotropy increased from 9% to as high as 22.5%. The thermally induced lateral heterogeneity ratio (RS/P = ∂lnVS/∂lnVP) of ferropericlase was calculated to be 1.48 at ambient pressure but decreased to 1.43 at 40 GPa along a representative geotherm. The RS/P of a simplified pyrolite model consisting of 80% bridgmanite and 20% ferropericlase was approximately 1.5, consistent with seismic models at depths from 670 to 1500 km, but showed an increased mismatch at lower <span class="hlt">mantle</span> depths below ~1500 km. This discrepancy below mid-lower <span class="hlt">mantle</span> could be due to either a contribution from chemically induced heterogeneity or the effects of the Fe spin transition in the deeper parts of the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.V43D..03B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.V43D..03B"><span>Hf and Nd Isotope Evidence for Production of an Incompatible Trace Element Enriched Crustal Reservoir in <span class="hlt">Early</span> <span class="hlt">Earth</span> (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brandon, A. D.; Debaille, V.; Lapen, T. J.</p> <p>2010-12-01</p> <p>The final significant stage of accretion of the <span class="hlt">Earth</span> was likely a collision between proto-<span class="hlt">Earth</span> and a Mars sized impactor that formed the Moon. This event is thought to have produced enough thermal energy to melt all or most of the <span class="hlt">Earth</span>, with a consequent magma ocean (MO). During subsequent cooling, the <span class="hlt">Earth</span> would have formed its protocrust and corresponding <span class="hlt">mantle</span> lithosphere, consisting of solidified basalt-komatiitic melt, in combination with buoyant cumulates and late stage residual melts from the MO. Relative to the convecting <span class="hlt">mantle</span>, portions of this protolithosphere are likely to have been enriched in incompatible trace elements (ITE) in sufficient quantities to contain a significant amount of the bulk Earth’s budget for rare <span class="hlt">earth</span> elements, U, Th, and Hf. If the protolithosphere was negatively buoyant, it may have overturned at or near the final stages of MO crystallization and a significant portion of that material may have been transported into the deep <span class="hlt">mantle</span> where it resided and remixed into the convecting <span class="hlt">mantle</span> over <span class="hlt">Earth</span> history [1,2]. If the protolithosphere remained positively buoyant, its crust would have likely begun to erode from surface processes, and subsequently recycled back into the <span class="hlt">mantle</span> over time as sediment and altered crust, once a subduction mechanism arose. The Nd and Hf isotopic compositions of Earth’s earliest rocks support the idea that an <span class="hlt">early</span>-formed ITE-enriched reservoir was produced. The maxima in 142Nd/144Nd for 3.85 to 3.64 Ga rocks from Isua, Greenland decreases from +20 ppm to +12 ppm relative to the present day <span class="hlt">mantle</span> value, respectively [3]. This indicates mixing of an <span class="hlt">early</span>-formed ITE enriched reservoir back into the convecting <span class="hlt">mantle</span>. In addition, zircons from the 3.1 Ga Jack Hills conglomerate indicate that material with an enriched 176Lu/177Hf of ~0.02 and an age of 4.4 Ga or greater was present at the Earth’s surface over the first 2 Ga of <span class="hlt">Earth</span> history, supporting the scenario of a positively buoyant</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27279220','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27279220"><span>FeO2 and FeOOH under deep lower-<span class="hlt">mantle</span> conditions and <span class="hlt">Earth</span>'s oxygen-hydrogen cycles.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hu, Qingyang; Kim, Duck Young; Yang, Wenge; Yang, Liuxiang; Meng, Yue; Zhang, Li; Mao, Ho-Kwang</p> <p>2016-06-09</p> <p>The distribution, accumulation and circulation of oxygen and hydrogen in <span class="hlt">Earth</span>'s interior dictate the geochemical evolution of the hydrosphere, atmosphere and biosphere. The oxygen-rich atmosphere and iron-rich core represent two end-members of the oxygen-iron (O-Fe) system, overlapping with the entire pressure-temperature-composition range of the planet. The extreme pressure and temperature conditions of the deep interior alter the oxidation states, spin states and phase stabilities of iron oxides, creating new stoichiometries, such as Fe4O5 (ref. 5) and Fe5O6 (ref. 6). Such interactions between O and Fe dictate <span class="hlt">Earth</span>'s formation, the separation of the core and <span class="hlt">mantle</span>, and the evolution of the atmosphere. Iron, in its multiple oxidation states, controls the oxygen fugacity and oxygen budget, with hydrogen having a key role in the reaction of Fe and O (causing iron to rust in humid air). Here we use first-principles calculations and experiments to identify a highly stable, pyrite-structured iron oxide (FeO2) at 76 gigapascals and 1,800 kelvin that holds an excessive amount of oxygen. We show that the mineral goethite, FeOOH, which exists ubiquitously as 'rust' and is concentrated in bog iron ore, decomposes under the deep lower-<span class="hlt">mantle</span> conditions to form FeO2 and release H2. The reaction could cause accumulation of the heavy FeO2-bearing patches in the deep lower <span class="hlt">mantle</span>, upward migration of hydrogen, and separation of the oxygen and hydrogen cycles. This process provides an alternative interpretation for the origin of seismic and geochemical anomalies in the deep lower <span class="hlt">mantle</span>, as well as a sporadic O2 source for the Great Oxidation Event over two billion years ago that created the present oxygen-rich atmosphere.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20000031441&hterms=evolution+rock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Devolution%2Brock','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20000031441&hterms=evolution+rock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Devolution%2Brock"><span>Large-Scale Impact Cratering and <span class="hlt">Early</span> <span class="hlt">Earth</span> Evolution</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grieve, R. A. F.; Cintala, M. J.</p> <p>1997-01-01</p> <p> largest impacts, where the melt volume would have reached well into the <span class="hlt">mantle</span>. Any contribution from adiabatic melting or shock heating of the asthenosphere would have had similar mafic compositions. The depth of the melt sheets is unknown but would have been in the multilkilometer range. Bodies of basaltic melt > or = 300 m thick differentiate in the terrestrial environment, with the degree of differentiation being a function of the thickness of the body. We therefore expect that these thick, closed-system melt pools would have differentiated into an ultramafic-mafic base and felsic top. If only 10% of the impact melt produced in a single event creating a 400-km diameter transient cavity evolved into felsic differentiates, they would be comparable in volume to the Columbia River basalts. It has been estimated that at least 200 impact events of this size or larger occurred on the <span class="hlt">early</span> <span class="hlt">Earth</span> during a period of heavy bombardment. We speculate that these massive differentiated melt sheets may have had a role in the formation of the initial felsic component of the <span class="hlt">Earth</span>'s crust. Additional information is contained in the original.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790061863&hterms=bts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dbts','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790061863&hterms=bts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dbts"><span>The Moho as a magnetic boundary. [<span class="hlt">Earth</span> crust-<span class="hlt">mantle</span> boundary</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wasilewski, P. J.; Thomas, H. H.; Mayhew, M. A.</p> <p>1979-01-01</p> <p>Magnetism in the crust and the upper <span class="hlt">mantle</span> and magnetic results indicating that the seismic Moho is a magnetic boundary are considered. <span class="hlt">Mantle</span> derived rocks - peridotites from St. Pauls rocks, dunite xenoliths from the Kaupulehu flow, and peridotite, dunite, and eclogite xenoliths from Roberts Victor and San Carlos diatremes - are weakly magnetic with saturation magnetization values from 0.013 emu/gm to less than 0.001 emu/gm which is equivalent to 0.01 to 0.001 wt% Fe304. Literature on the minerals in <span class="hlt">mantle</span> xenoliths shows that metals and primary Fe304 are absent, and that complex Cr, Mg, Al, and Fe spinels are dominant. These spinels are non-magnetic at <span class="hlt">mantle</span> temperatures, and the crust/<span class="hlt">mantle</span> boundary can be specified as a magnetic mineralogy discontinuity. The new magnetic results indicate that the seismic Moho is a magnetic boundary, the source of magnetization is in the crust, and the maximum Curie isotherm depends on magnetic mineralogy and is located at depths which vary with the regional geothermal gradient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040089260&hterms=selective+attention&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dselective%2Battention','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040089260&hterms=selective+attention&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dselective%2Battention"><span>Carbon dioxide warming of the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Arrhenius, G.</p> <p>1997-01-01</p> <p>Svante Arrhenius' research in atmospheric physics extended beyond the recent past and the near future states of the <span class="hlt">Earth</span>, which today are at the center of sociopolitical attention. His plan encompassed all of the physical phenomena known at the time to relate to the formation and evolution of stars and planets. His two-volume textbook on cosmic physics is a comprehensive synopsis of the field. The inquiry into the possible cause of the ice ages and the theory of selective wavelength filter control led Arrhenius to consider the surface states of the other terrestrial planets, and of the ancient <span class="hlt">Earth</span> before it had been modified by the emergence of life. The rapid escape of hydrogen and the equilibration with igneous rocks required that carbon in the <span class="hlt">early</span> atmosphere prevailed mainly in oxidized form as carbon dioxide, together with other photoactive gases exerting a greenhouse effect orders of magnitude larger than in our present atmosphere. This effect, together with the ensuing chemical processes, would have set the conditions for life to evolve on our planet, seeded from spores spreading through an infinite Universe, and propelled, as Arrhenius thought, by stellar radiation pressure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11541253','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11541253"><span>Carbon dioxide warming of the <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Arrhenius, G</p> <p>1997-02-01</p> <p>Svante Arrhenius' research in atmospheric physics extended beyond the recent past and the near future states of the <span class="hlt">Earth</span>, which today are at the center of sociopolitical attention. His plan encompassed all of the physical phenomena known at the time to relate to the formation and evolution of stars and planets. His two-volume textbook on cosmic physics is a comprehensive synopsis of the field. The inquiry into the possible cause of the ice ages and the theory of selective wavelength filter control led Arrhenius to consider the surface states of the other terrestrial planets, and of the ancient <span class="hlt">Earth</span> before it had been modified by the emergence of life. The rapid escape of hydrogen and the equilibration with igneous rocks required that carbon in the <span class="hlt">early</span> atmosphere prevailed mainly in oxidized form as carbon dioxide, together with other photoactive gases exerting a greenhouse effect orders of magnitude larger than in our present atmosphere. This effect, together with the ensuing chemical processes, would have set the conditions for life to evolve on our planet, seeded from spores spreading through an infinite Universe, and propelled, as Arrhenius thought, by stellar radiation pressure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhDT.........9X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhDT.........9X"><span>Computational Studies of Thermodynamics and Kinetics of Metal Oxides in Li-Ion Batteries and <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span> Materials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Shenzhen</p> <p></p> <p>Metal oxide materials are ubiquitous in nature and in our daily lives. For example, the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> layer that makes up about 80% of our <span class="hlt">Earth</span>'s volume is composed of metal oxide materials, the cathode materials in the lithium-ion batteries that provide power for most of our mobile electronic devices are composed of metal oxides, the chemical components of the passivation layers on many kinds of metal materials that protect the metal from further corrosion are metal oxides. This thesis is composed of two major topics about the metal oxide materials in nature. The first topic is about our computational study of the iron chemistry in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> metal oxide materials, i.e. the bridgmanite (Fe-bearing MgSiO3 where iron is the substitution impurity element) and the ferropericlase (Fe-bearing MgO where iron is the substitution impurity element). The second topic is about our multiscale modeling works for understanding the nanoscale kinetic and thermodynamic properties of the metal oxide cathode interfaces in Li-ion batteries, including the intrinsic cathode interfaces (intergrowth of multiple types of cathode materials, compositional gradient cathode materials, etc.), the cathode/coating interface systems and the cathode/electrolyte interface systems. This thesis uses models based on density functional theory quantum mechanical calculations to explore the underlying physics behind several types of metal oxide materials existing in the interior of the <span class="hlt">Earth</span> or used in the applications of lithium-ion batteries. The exploration of this physics can help us better understand the geochemical and seismic properties of our <span class="hlt">Earth</span> and inspire us to engineer the next generation of electrochemical technologies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.474...25O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.474...25O"><span>The effect of iron and aluminum incorporation on lattice thermal conductivity of bridgmanite at the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Okuda, Yoshiyuki; Ohta, Kenji; Yagi, Takashi; Sinmyo, Ryosuke; Wakamatsu, Tatsuya; Hirose, Kei; Ohishi, Yasuo</p> <p>2017-09-01</p> <p>Bridgmanite (Bdg), iron (Fe)- and aluminum (Al)-bearing magnesium silicate perovskite is the most abundant mineral in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. Thus, its thermal conductivity governs the lower <span class="hlt">mantle</span> thermal conductivity that critically controls the thermo-chemical evolution of both the core and the lower <span class="hlt">mantle</span>. While there is extensive research for the lattice thermal conductivity of MgSiO3 Bdg, the effects of Fe and Al incorporation on its lattice thermal conduction are still controversial. Here we report the lattice thermal conductivity of Mg0.832Fe0.209Al0.060Si0.916O3 Bdg measured up to 142 GPa at 300 K using the pulsed light heating thermoreflectance technique in a diamond anvil cell. The results show that the lattice thermal conductivity of Bdg is 25.5 ± 2.2 W/m/K at 135 GPa and 300 K, which is 19% lower than that of Fe and Al-free Bdg at identical conditions. Considering the temperature effect on the lattice conductivity and the contribution of radiative thermal conductivity, the total thermal conductivity of Fe and Al-bearing Bdg does not change very much with temperature at 135 GPa, and could be higher than that of post-perovskite with identical chemical composition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100005360','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100005360"><span>Conditions of Core Formation in the <span class="hlt">Early</span> <span class="hlt">Earth</span>: Single Stage or Heterogeneous Accretion?</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Righter, Kevin</p> <p>2010-01-01</p> <p>Since approx.1990 high pressure and temperature (PT) experiments on metal-silicate systems have showed that partition coefficients [D(met/sil)] for siderophile (iron-loving) elements are much different than those measured at low PT conditions [1,2]. The high PT data have been used to argue for a magma ocean during growth of the <span class="hlt">early</span> <span class="hlt">Earth</span> [3,4]. In the ensuing decades there have been hundreds of new experiments carried out and published on a wide range of siderophile elements (> 80 experiments published for Ni, Co, Mo, W, P, Mn, V, Cr, Ga, Cu and Pd). At the same time several different models have been advanced to explain the siderophile elements in <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>: a) shallow depth magma ocean 25-30 GPa [3,5]; b) deep magma ocean; up to 50 GPa [6,7], and c) <span class="hlt">early</span> reduced and later oxidized magma ocean [8,9]. Some studies have drawn conclusions based on a small subset of siderophile elements, or a set of elements that provides little leverage on the big picture (like slightly siderophile elements), and no single study has attempted to quantitatively explain more than 5 elements at a time. The purpose of this abstract is to identify issues that have lead to a difference in interpretation, and to present updated predictive expressions based on new experimental data. The resulting expressions will be applied to the siderophile element depletions in <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.202..976N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.202..976N"><span>Viscosity structure of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> inferred from rotational variations due to GIA process and recent melting events</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakada, Masao; Okuno, Jun'ichi; Lambeck, Kurt; Purcell, Anthony</p> <p>2015-08-01</p> <p>We examine the geodetically derived rotational variations for the rate of change of degree-two harmonics of <span class="hlt">Earth</span>'s geopotential, skew5dot J_2, and true polar wander, combining a recent melting model of glaciers and the Greenland and Antarctic ice sheets taken from the IPCC 2013 Report (AR5) with two representative GIA ice models describing the last deglaciation, ICE5G and the ANU model developed at the Australian National University. Geodetically derived observations of skew4dot J_2 are characterized by temporal changes of -(3.7 ± 0.1) × 10-11 yr-1 for the period 1976-1990 and -(0.3 ± 0.1) × 10-11 yr-1 after ˜2000. The AR5 results make it possible to evaluate the recent melting of the major ice sheets and glaciers for three periods, 1900-1990, 1991-2001 and after 2002. The observed skew4dot J_2 and the component of skew4dot J_2 due to recent melting for different periods indicate a long-term change in skew4dot J_2-attributed to the <span class="hlt">Earth</span>'s response to the last glacial cycle-of -(6.0-6.5) × 10-11 yr-1, significantly different from the values adopted to infer the viscosity structure of the <span class="hlt">mantle</span> in most previous studies. This is a main conclusion of this study. We next compare this estimate with the values of skew4dot J_2 predicted by GIA ice models to infer the viscosity structure of the <span class="hlt">mantle</span>, and consequently obtain two permissible solutions for the lower <span class="hlt">mantle</span> viscosity (ηlm), ˜1022 and (5-10) × 1022 Pa s, for both adopted ice models. These two solutions are largely insensitive to the lithospheric thickness and upper <span class="hlt">mantle</span> viscosity as indicated by previous studies and relatively insensitive to the viscosity structure of the D″ layer. The ESL contributions from the Antarctic ice sheet since the last glacial maximum (LGM) for ICE5G and ANU are about 20 and 30 m, respectively, but glaciological reconstructions of the Antarctic LGM ice sheet have suggested that its ESL contribution may have been less than ˜10 m. The GIA-induced skew4dot J_2 for GIA</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PEPI..185....1T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PEPI..185....1T"><span>The effects of nickel and sulphur on the core-<span class="hlt">mantle</span> partitioning of oxygen in <span class="hlt">Earth</span> and Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tsuno, Kyusei; Frost, Daniel J.; Rubie, David C.</p> <p>2011-03-01</p> <p>Constraints on the partitioning of oxygen between silicates, oxides, and metallic liquids are important for determining the amount of oxygen that may have entered the cores of terrestrial planets and to identify likely reactions at the core-<span class="hlt">mantle</span> boundary. Several previous studies have examined oxygen partitioning between liquid Fe metal and ferropericlase, however, the cores of terrestrial planets also contain nickel and most likely sulphur. We have performed experiments to examine the effects of both nickel and sulphur on the partitioning of oxygen between ferropericlase and liquid Fe alloy up to pressures of 24.5 GPa in the temperature range 2430-2750 K using a multianvil press. The results show that at a fixed oxygen fugacity the proportion of oxygen that partitions into liquid metal will decrease by approximately 1-2 mol% on the addition of 10-20 mol% nickel to the liquid. The addition of around 30 mol% sulphur will, on the other hand, increase the metal oxygen content by approximately 10 mol%. Experiments to examine the combined effects of both nickel and sulphur, show a decrease in the effect of nickel on oxygen partitioning as the sulphur content of the metal increases. We expand an existing thermodynamic model for the partitioning of oxygen at high pressures and temperatures to include the effects of nickel and sulphur by fitting these experimental data, with further constraints provided by existing phase equilibria studies at similar conditions in the Fe-S and Fe-O-S systems. Plausible terrestrial core sulphur contents have little effect on oxygen partitioning. When our model is extrapolated to conditions of the present day terrestrial core-<span class="hlt">mantle</span> boundary, the presence of nickel is found to lower the oxygen content of the outer core that is in equilibrium with the expected <span class="hlt">mantle</span> ferropericlase FeO content, by approximately 1 weight %, in comparison to nickel free calculations. In agreement with nickel-free experiments, this implies that the <span class="hlt">Earth</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4066531','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4066531"><span>Deep <span class="hlt">mantle</span> structure as a reference frame for movements in and on the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Torsvik, Trond H.; van der Voo, Rob; Doubrovine, Pavel V.; Burke, Kevin; Steinberger, Bernhard; Ashwal, Lewis D.; Trønnes, Reidar G.; Webb, Susan J.; Bull, Abigail L.</p> <p>2014-01-01</p> <p>Earth’s residual geoid is dominated by a degree-2 mode, with elevated regions above large low shear-wave velocity provinces on the core–<span class="hlt">mantle</span> boundary beneath Africa and the Pacific. The edges of these deep <span class="hlt">mantle</span> bodies, when projected radially to the Earth’s surface, correlate with the reconstructed positions of large igneous provinces and kimberlites since Pangea formed about 320 million years ago. Using this surface-to-core–<span class="hlt">mantle</span> boundary correlation to locate continents in longitude and a novel iterative approach for defining a paleomagnetic reference frame corrected for true polar wander, we have developed a model for absolute plate motion back to earliest Paleozoic time (540 Ma). For the Paleozoic, we have identified six phases of slow, oscillatory true polar wander during which the Earth’s axis of minimum moment of inertia was similar to that of Mesozoic times. The rates of Paleozoic true polar wander (<1°/My) are compatible with those in the Mesozoic, but absolute plate velocities are, on average, twice as high. Our reconstructions generate geologically plausible scenarios, with large igneous provinces and kimberlites sourced from the margins of the large low shear-wave velocity provinces, as in Mesozoic and Cenozoic times. This absolute kinematic model suggests that a degree-2 convection mode within the Earth’s <span class="hlt">mantle</span> may have operated throughout the entire Phanerozoic. PMID:24889632</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMED41B0633G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMED41B0633G"><span>Development of a <span class="hlt">Mantle</span> Convection Physical Model to Assist with Teaching about <span class="hlt">Earth</span>'s Interior Processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glesener, G. B.; Aurnou, J. M.</p> <p>2010-12-01</p> <p>The Modeling and Educational Demonstrations Laboratory (MEDL) at UCLA is developing a <span class="hlt">mantle</span> convection physical model to assist educators with the pedagogy of Earth’s interior processes. Our design goal consists of two components to help the learner gain conceptual understanding by means of visual interactions without the burden of distracters, which may promote alternative conceptions. Distracters may be any feature of the conceptual model that causes the learner to use inadequate mental artifact to help him or her understand what the conceptual model is intended to convey. The first component, and most important, is a psychological component that links properties of “everyday things” (Norman, 1988) to the natural phenomenon, <span class="hlt">mantle</span> convection. Some examples of everyday things may be heat rising out from a freshly popped bag of popcorn, or cold humid air falling from an open freezer. The second component is the scientific accuracy of the conceptual model. We would like to simplify the concepts for the learner without sacrificing key information that is linked to other natural phenomena the learner will come across in future science lessons. By taking into account the learner’s mental artifacts in combination with a simplified, but accurate, representation of what scientists know of the Earth’s interior, we expect the learner to have the ability to create an adequate qualitative mental simulation of <span class="hlt">mantle</span> convection. We will be presenting some of our prototypes of this <span class="hlt">mantle</span> convection physical model at this year’s poster session and invite constructive input from our colleagues.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NPGeo..25...99B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NPGeo..25...99B"><span>Ensemble Kalman filter for the reconstruction of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> circulation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bocher, Marie; Fournier, Alexandre; Coltice, Nicolas</p> <p>2018-02-01</p> <p>Recent advances in <span class="hlt">mantle</span> convection modeling led to the release of a new generation of convection codes, able to self-consistently generate plate-like tectonics at their surface. Those models physically link <span class="hlt">mantle</span> dynamics to surface tectonics. Combined with plate tectonic reconstructions, they have the potential to produce a new generation of <span class="hlt">mantle</span> circulation models that use data assimilation methods and where uncertainties in plate tectonic reconstructions are taken into account. We provided a proof of this concept by applying a suboptimal Kalman filter to the reconstruction of <span class="hlt">mantle</span> circulation (Bocher et al., 2016). Here, we propose to go one step further and apply the ensemble Kalman filter (EnKF) to this problem. The EnKF is a sequential Monte Carlo method particularly adapted to solve high-dimensional data assimilation problems with nonlinear dynamics. We tested the EnKF using synthetic observations consisting of surface velocity and heat flow measurements on a 2-D-spherical annulus model and compared it with the method developed previously. The EnKF performs on average better and is more stable than the former method. Less than 300 ensemble members are sufficient to reconstruct an evolution. We use covariance adaptive inflation and localization to correct for sampling errors. We show that the EnKF results are robust over a wide range of covariance localization parameters. The reconstruction is associated with an estimation of the error, and provides valuable information on where the reconstruction is to be trusted or not.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70012153','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70012153"><span>Eastern Indian 3800-million-year-old crust and <span class="hlt">early</span> <span class="hlt">mantle</span> differentiation</span></a></p> <p><a target="_blank" href=""></a></p> <p>Basu, A.R.; Ray, S.L.; Saha, A.K.; Sarkar, S.N.</p> <p>1981-01-01</p> <p>Samarium-neodymium data for nine granitic and tonalite gneisses occurring as remnants within the Singhbhum granite batholith in eastern India define an isochron of age 3775 ?? 89 ?? 106 years with an initial 143Nd/144Nd ratio of 0.50798 ?? 0.00007. This age contrasts with the rubidium-strontium age of 3200 ?? 106 years for the same suite of rocks. On the basis of the new samarium-neodynium data, field data, and petrologic data, a scheme of evolution is proposed for the Archean crust in eastern India. The isotopic data provide evidence that parts of the <span class="hlt">earth</span>'s <span class="hlt">mantle</span> were already differentiated with respect to the chondritic samarium-neodymium ratio 3800 ?? 106 years ago.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFM.U72B0033B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFM.U72B0033B"><span>Two-Body Convection in the <span class="hlt">Mantle</span> of the <span class="hlt">Earth</span>: E/W Asymmetry, Under Astronomically Determined Tilt in g</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bostrom, R. C.</p> <p>2002-12-01</p> <p>Under purely geocentric gravity, over time displacement under <span class="hlt">mantle</span> convection is globally symmetrical, resulting in zero net lithosphere rotation. The effect is here explored of substituting the asymmetric <span class="hlt">Earth</span>-Moon field, gconv, prevalent in actuality. The gravity responsible for <span class="hlt">mantle</span> convection is defined as the vector sum of a vertical component and the day-averaged attraction of masses lagging tidal equilibrium. The increasingly accurately measured lunar recession may then be used to delimit the internal field in terms of the secular luni-tidal interval of the <span class="hlt">Earth</span> as a whole, some 600 seconds [1], without having to identify tidal components i.e. separate marine from body tides. In context the astronomic phase-lag may be viewed as a global isostatic anomaly, in which the longitude circles marking <span class="hlt">Earth</span>'s gravimetric figure are located east of those describing its perpetually unattained equilibrium figure by some 89 km at the Equator. Reference the hydrostatic ellipsoid gconv is tilted by the astronomically delimited amount, albeit that the phase lag is attributable in part to the convection itself. As with the convection, the tectonic significance of its asymmetry is determinable geodetically. Using present art-state a strategically located GPS grid [2] would provide continuously more precise separation of the asymmetric component of surface displacement. In developing plate-motion models including members of the Nuvel series, it would be logical to follow up rather than discard the set permitting minor asymmetrical convection sans net torque, such as an element of net-lithosphere-rotation relative to plumes. To conserve system angular-momentum, this may be the only valid set. Characteristics of the convection to be expected accord with 'paradoxical' features of plate tectonics under purely radial gravity, including: difficulty in closing plate-motion circuits; net-lithosphere-rotation refce. hot-spots, sans net torque; geotectonic maps ranging from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V33F0575D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V33F0575D"><span>A Model of Volcanic Outgassing for <span class="hlt">Earth</span>'s <span class="hlt">Early</span> Atmosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dhaliwal, J. K.; Kasting, J. F.; Zhang, Z.</p> <p>2017-12-01</p> <p>We build on historical paradigms of volcanic degassing [1] to account for non-linear relations among C-O-H-S volatiles, their speciation, solubility and concentrations in magmatic melts, and the resulting contribution to atmospheric volatile inventories. We focus on the build-up of greenhouse-relevant carbon species (CO2 and CH4) and molecular oxygen to better understand the environments of <span class="hlt">early</span> life and the Great Oxygenation Event [2,3,4]. The <span class="hlt">mantle</span> is an important reservoir of C-O-H-S volatiles [5], and melt concentrations depend on temperature, pressure and oxygen fugacity. We present a preliminary chemical model that simulates volatile concentrations released into the <span class="hlt">Earth</span>'s atmosphere at 1 bar, or pressures corresponding to the <span class="hlt">early</span> <span class="hlt">Earth</span> prior to 2.4 Ga. We maintain redox balance in the system using H+ [2, 6] because the melt oxidation state evolves with volatile melt concentrations [7] and affects the composition of degassed compounds. For example, low fO2 in the melt degasses CO, CH4, H2S and H2 while high fO2 yields CO2, SO2 and H2O [1,8,9]. Our calculations incorporate empirical relations from experimental petrology studies [e.g., 10, 11] to account for inter-dependencies among volatile element solubility trends. This model has implications for exploring planetary atmospheric evolution and potential greenhouse effects on Venus and Mars [12]­, and possibly exoplanets. A future direction of this work would be to link this chemical degassing model with different tectonic regimes [13] to account for degassing and ingassing, such as during subduction. References: [1] Holland, H. D. (1984) The chemical evolution of the atmosphere and oceans [2] Kasting, J. F. (2013) Chem. Geo. 362, 13-25 [3] Kasting, J.F. (1993) Sci. 259, 920-926 [4] Duncan, M.S. & Dasgupta, R. (2017) Nat. Geoscience 10, 387-392. [5] Hier-Majumder, S. & Hirschmann, M.M. (2017) G3, doi: 10.1002/2017GC006937 [6] Gaillard, F. et al. (2003) GCA 67, 2427- 2441 [7] Moussalam, Y. et al. (2014</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25416388','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25416388"><span>The <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere and <span class="hlt">early</span> life catalysts.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ramírez Jiménez, Sandra Ignacia</p> <p>2014-01-01</p> <p>Homochirality is a property of living systems on <span class="hlt">Earth</span>. The time, the place, and the way in which it appeared are uncertain. In a prebiotic scenario two situations are of interest: either an initial small bias for handedness of some biomolecules arouse and progressed with life, or an initial slight excess led to the actual complete dominance of the known chiral molecules. A definitive answer can probably never be given, neither from the fields of physics and chemistry nor biology. Some arguments can be advanced to understand if homochirality is necessary for the initiation of a prebiotic homochiral polymer chemistry, if this homochirality is suggesting a unique origin of life, or if a chiral template such as a mineral surface is always required to result in an enantiomeric excess. A general description of the <span class="hlt">early</span> <span class="hlt">Earth</span> scenario will be presented in this chapter, followed by a general description of some clays, and their role as substrates to allow the concentration and amplification of some of the building blocks of life.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035042','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035042"><span>Peptide synthesis in <span class="hlt">early</span> <span class="hlt">earth</span> hydrothermal systems</span></a></p> <p><a target="_blank" href=""></a></p> <p>Lemke, K.H.; Rosenbauer, R.J.; Bird, D.K.</p> <p>2009-01-01</p> <p>We report here results from experiments and thermodynamic calculations that demonstrate a rapid, temperature-enhanced synthesis of oligopeptides from the condensation of aqueous glycine. Experiments were conducted in custom-made hydrothermal reactors, and organic compounds were characterized with ultraviolet-visible procedures. A comparison of peptide yields at 260??C with those obtained at more moderate temperatures (160??C) gives evidence of a significant (13 kJ ?? mol-1) exergonic shift. In contrast to previous hydrothermal studies, we demonstrate that peptide synthesis is favored in hydrothermal fluids and that rates of peptide hydrolysis are controlled by the stability of the parent amino acid, with a critical dependence on reactor surface composition. From our study, we predict that rapid recycling of product peptides from cool into near-supercritical fluids in mid-ocean ridge hydrothermal systems will enhance peptide chain elongation. It is anticipated that the abundant hydrothermal systems on <span class="hlt">early</span> <span class="hlt">Earth</span> could have provided a substantial source of biomolecules required for the origin of life. Astrobiology 9, 141-146. ?? 2009 Mary Ann Liebert, Inc. 2009.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.9804H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.9804H"><span>Is <span class="hlt">Earth</span> coming out of the recent ice house age in the long-term? - constraints from probable <span class="hlt">mantle</span> CO2-degassing reconstructions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hartmann, Jens; Li, Gaojun; West, A. Joshua</p> <p>2017-04-01</p> <p>Enhanced partial melting of <span class="hlt">mantle</span> material probably started when the subduction motor started around 3.2 Ga ago as evidenced by the formation history of the continental crust. Carbon is degassing due partial melting as it is an incompatible element. Therefore, <span class="hlt">mantle</span> carbon degassing rates would change with time proportionally to the reservoir <span class="hlt">mantle</span> concentration evolution and the ocean crust production rate, causing a distinct CO2-degassing rate change with time. The evolution of the <span class="hlt">mantle</span> degassing rate has some implications for the reconstruction of the carbon cycle and therefore climate and <span class="hlt">Earth</span> surface processes rates, as CO2-degassing rates are used to constrain or to balance the atmosphere-ocean-crust carbon cycle system. It will be shown that compilations of CO2-degassing from relevant geological sources are probably exceeding the established CO2-sink terrestrial weathering, which is often used to constrain long-term <span class="hlt">mantle</span> degassing rates to close the carbon cycle on geological time scales. In addition, the scenarios for the degassing dynamics from the <span class="hlt">mantle</span> sources suggest that the <span class="hlt">mantle</span> is depleting its carbon content since 3 Ga. This has further implications for the long-term CO2-sink weathering. Results will be compared with geochemical proxies for weathering and weathering intensity dynamics, and will be set in context with snow ball <span class="hlt">Earth</span> events and long-term emplacement dynamics of mafic areas as Large Igneous Provinces. Decreasing <span class="hlt">mantle</span> degassing rates since about 2 Ga suggest a constraint for the evolution of the carbon cycle and recycling potential of the amount of subducted carbon. If the given scenarios hold further investigation, the contribution of <span class="hlt">mantle</span> degassing to climate forcing (directly and via recycling) will decrease further.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoRL..43.9611Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..43.9611Z"><span>Sound velocities of olivine at high pressures and temperatures and the composition of <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Jin S.; Bass, Jay D.</p> <p>2016-09-01</p> <p>We present the elastic properties of San Carlos olivine up to P = 12.8(8) GPa and T = 1300(200) K using Brillouin spectroscopy with CO2 laser heating. A comparison of our results with the global seismic model AK135 yields average olivine content near 410 km depth of about 37% and 43% in a dry and wet (1.9 wt % H2O) upper <span class="hlt">mantle</span>, respectively. These olivine contents are far less than in the pyrolite model. However, comparisons of our results with regional seismic models lead to very different conclusions. High olivine contents of up to 87% are implied by seismic models of the western U.S. and eastern Pacific regions. In contrast, we infer less than 35% olivine under the central Pacific. Strong variations of olivine content and upper <span class="hlt">mantle</span> lithologies near the 410 km discontinuity are suggested by regional seismic models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.G11A0697W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.G11A0697W"><span>The Effects of Core-<span class="hlt">Mantle</span> Interactions on <span class="hlt">Earth</span> Rotation, Surface Deformation, and Gravity Changes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watkins, A.; Gross, R. S.; Fu, Y.</p> <p>2017-12-01</p> <p>The length-of-day (LOD) contains a 6-year signal, the cause of which is currently unknown. The signal remains after removing tidal and surface fluid effects, thus the cause is generally believed to be angular momentum exchange between the <span class="hlt">mantle</span> and core. Previous work has established a theoretical relationship between pressure variations at the core-<span class="hlt">mantle</span> boundary (CMB) and resulting deformation of the overlying <span class="hlt">mantle</span> and crust. This study examines globally distributed GPS deformation data in search of this effect, and inverts the discovered global inter-annual component for the CMB pressure variations. The geostrophic assumption is then used to obtain fluid flow solutions at the edge of the core from the CMB pressure variations. Taylor's constraint is applied to obtain the flow deeper within the core, and the equivalent angular momentum and LOD changes are computed and compared to the known 6-year LOD signal. The amplitude of the modeled and measured LOD changes agree, but the degree of period and phase agreement is dependent upon the method of isolating the desired component in the GPS position data. Implications are discussed, and predictions are calculated for surface gravity field changes that would arise from the CMB pressure variations.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29259159','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29259159"><span>Experimental evidence supporting a global melt layer at the base of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Freitas, D; Manthilake, G; Schiavi, F; Chantel, J; Bolfan-Casanova, N; Bouhifd, M A; Andrault, D</p> <p>2017-12-19</p> <p>The low-velocity layer (LVL) atop the 410-km discontinuity has been widely attributed to dehydration melting. In this study, we experimentally reproduced the wadsleyite-to-olivine phase transformation in the upwelling <span class="hlt">mantle</span> across the 410-km discontinuity and investigated in situ the sound wave velocity during partial melting of hydrous peridotite. Our seismic velocity model indicates that the globally observed negative Vs anomaly (-4%) can be explained by a 0.7% melt fraction in peridotite at the base of the upper <span class="hlt">mantle</span>. The produced melt is richer in FeO (~33 wt.%) and H 2 O (~16.5 wt.%) and its density is determined to be 3.56-3.74 g cm -3 . The water content of this gravitationally stable melt in the LVL corresponds to a total water content in the <span class="hlt">mantle</span> transition zone of 0.22 ± 0.02 wt.%. Such values agree with estimations based on magneto-telluric observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDKP1082G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDKP1082G"><span>Origin of the <span class="hlt">Earth</span>'s Electromagnetic Field Based on the Pulsating <span class="hlt">Mantle</span> Hypothesis (PMH)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gholibeigian, Hassan</p> <p>2017-11-01</p> <p>In PMH, the <span class="hlt">Earth</span>'s Inner Core's Dislocation (ICD) and Outer Core's Bulge (OCB) phenomena are generated by unbalanced gravitational fields of the Sun and Moon on the <span class="hlt">Earth</span>. Distance between the <span class="hlt">Earth</span>'s center and inner core's center varies permanently in magnitude and direction inside two hemispheres. Geometrical loci of the inner core's center has the shape of back and force spiral cone in each hemisphere. In other words, the inner core is rotating fast in the outer core inverse of the <span class="hlt">Earth</span>'s rotation a round per day. This mechanism speed up the processes inside the core and generates a Large Scale Forced Convection System (LSFCS) inverse of the <span class="hlt">Earth</span>'s rotation in the core. The LSFCS is the origin of the <span class="hlt">Earth</span>'s electromagnetic field. The LSFCS generates huge mass transfer and momentum of inertia inside the <span class="hlt">Earth</span> too. The inner core's axis which is the <span class="hlt">Earth</span>'s electromagnetic axis doesn't cross the <span class="hlt">Earth</span>'s geophysical axis and rotates around it per day. The mechanism of this LSFCS has diurnal, monthly and yearly cycles. These cycles are sources of the <span class="hlt">Earth</span>'s electromagnetic field variability. Direction of the variable <span class="hlt">Earth</span>'s magnetic field lines from the South Pole (hemisphere) to the sky and 146 seconds/years apparent solar day length variations can be two observable factors for this mechanism. This dynamic system may occurred inside the other planets like the Sun and the Jupiter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013Natur.498..342T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013Natur.498..342T"><span>Volcanism on Mars controlled by <span class="hlt">early</span> oxidation of the upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tuff, J.; Wade, J.; Wood, B. J.</p> <p>2013-06-01</p> <p>Detailed information about the chemical composition and evolution of Mars has been derived principally from the SNC (shergottite-nakhlite-chassignite) meteorites, which are genetically related igneous rocks of Martian origin. They are chemically and texturally similar to terrestrial basalts and cumulates, except that they have higher concentrations of iron and volatile elements such as phosphorus and chlorine and lower concentrations of nickel and other chalcophile (sulphur-loving) elements. Most Martian meteorites have relatively young crystallization ages (1.4 billion years to 180 million years ago) and are considered to be derived from young, lightly cratered volcanic regions, such as the Tharsis plateau. Surface rocks from the Gusev crater analysed by the Spirit rover are much older (about 3.7 billion years old) and exhibit marked compositional differences from the meteorites. Although also basaltic in composition, the surface rocks are richer in nickel and sulphur and have lower manganese/iron ratios than the meteorites. This has led to doubts that Mars can be described adequately using the `SNC model'. Here we show, however, that the differences between the compositions of meteorites and surface rocks can be explained by differences in the oxygen fugacity during melting of the same sulphur-rich <span class="hlt">mantle</span>. This ties the sources of Martian meteorites to those of the surface rocks through an <span class="hlt">early</span> (>3.7 billion years ago) oxidation of the uppermost <span class="hlt">mantle</span> that had less influence on the deeper regions, which produce the more recent volcanic rocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EPSC...11..514G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EPSC...11..514G"><span>Refractive indices of <span class="hlt">Early</span> <span class="hlt">Earth</span> organic aerosol analogs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gavilan, L.; Carrasco, N.; Fleury, B.; Vettier, L.</p> <p>2017-09-01</p> <p>Organic hazes in the <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere are hypothesized to provide additional shielding to solar radiation. We simulate the conditions of this primitive atmosphere by adding CO2 to a N2:CH4 gas mixture feeding a plasma. In this plasma, solid organic films were produced simulating <span class="hlt">early</span> aerosols. We performed ellipsometry on these films from the visible to the near-ultraviolet range. Such measurements reveal how organic aerosols in the <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere preferentially absorb photons of shorter wavelengths than typical Titan tholins, suggesting a coolant role in the <span class="hlt">early</span> <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20060013506&hterms=chocolate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dchocolate','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20060013506&hterms=chocolate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dchocolate"><span>Siderophilic Cyanobacteria: Implications for <span class="hlt">Early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brown, I. I.; Mummey, D.; Sarkisova, S.; Shen, G.; Bryant, D. A.; Lindsay, J.; Garrison, D.; McKay, D. S.</p> <p>2006-01-01</p> <p>Of all extant environs, iron-depositing hot springs (IDHS) may exhibit the greatest similarity to late Precambrian shallow warm oceans in regards to temperature, O2 gradients and dissolved iron and H2S concentrations. Despite the insights into the ecology, evolutionary biology, paleogeobiochemistry, and astrobiology examination of IDHS could potentially provide, very few studies dedicated to the physiology and diversity of cyanobacteria (CB) inhabiting IDHS have been conducted. Results. Here we describe the phylogeny, physiology, ultrastructure and biogeochemical activity of several recent CB isolates from two different greater Yellowstone area IDHS, LaDuke and Chocolate Pots. Phylogenetic analysis of 16S rRNA genes indicated that 6 of 12 new isolates examined couldn't be placed within established CB genera. Some of the isolates exhibited pronounced requirements for elevated iron concentrations, with maximum growth rates observed when 0.4-1 mM Fe(3+) was present in the media. In light of "typical" CB iron requirements, our results indicate that elevated iron likely represents a salient factor selecting for "siderophilicM CB species in IDHS. A universal feature of our new isolates is their ability to produce thick EPS layers in which iron accumulates resulting in the generation of well preserved signatures. In parallel, siderophilic CB show enhanced ability to etch the analogs of iron-rich lunar regolith minerals and impact glasses. Despite that iron deposition by CB is not well understood mechanistically, we recently obtained evidence that the PS I:PS II ratio is higher in one of our isolates than for other CB. Although still preliminary, this finding is in direct support of the Y. Cohen hypothesis that PSI can directly oxidize Fe(2+). Conclusion. Our results may have implications for factors driving CB evolutionary relationships and biogeochemical processes on <span class="hlt">early</span> <span class="hlt">Earth</span> and probably Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMED41B0634C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMED41B0634C"><span>Hot Spots and <span class="hlt">Mantle</span> Plumes: A Window Into the Deep <span class="hlt">Earth</span> and a Lesson on How Science Really Works</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caplan-Auerbach, J.</p> <p>2010-12-01</p> <p> tomography to image deep plumes, the use of magnetic data to determine plume paleolatitude, and the search for heat flow anomalies near hot spots. On the final day of the class students revisit the three questions presented above and discuss whether their thoughts on the topic have changed as a result of studying the geophysics. Finally, the class discusses the issue in terms of Thomas Kuhn’s phases of scientific study, considering whether or not the <span class="hlt">mantle</span> plumes paradigm is in crisis. As evidenced by comments in student course evaluations, the project is very popular and students appreciate the opportunity to investigate a modern scientific controversy. The project not only helps students learn how geophysics may be used to study the deep <span class="hlt">earth</span>, it familiarizes them with current scientific literature, and perhaps most importantly, it allows them to learn about and engage in a critical scientific debate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR24B..01C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR24B..01C"><span>Unified Static and Dynamic Recrystallization Model for the Minerals of <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> Using Internal State Variable Model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cho, H. E.; Horstemeyer, M. F.; Baumgardner, J. R.</p> <p>2017-12-01</p> <p> <span class="hlt">mantle</span> dynamics can only be acquired once the various deformation regimes and mechanisms are comprehensively modeled. The results of this study demonstrate that this ISV model is a good modeling candidate to help reveal the realistic dynamics of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P44B..06L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P44B..06L"><span>Deep <span class="hlt">mantle</span> roots and continental hypsometry: implications for whole-<span class="hlt">Earth</span> elemental cycling, long-term climate, and the Cambrian explosion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, C. T.</p> <p>2016-12-01</p> <p>Most of <span class="hlt">Earth</span>'s continents today are above sea level, but the presence of thick packages of ancient sediments on top of the stable cores of continents indicates that continents must have been submerged at least once in their past. Elevations of continents are controlled by the interplay between crustal thickness, <span class="hlt">mantle</span> root thickness and the temperature of the ambient convecting <span class="hlt">mantle</span>. The history of a continent begins with mountain building through magmatic or tectonic crustal thickening, during which exhumation of deep-seated igneous and metamorphic rocks are highest. Mountain building is followed by a long interval of subsidence as a result of continued, but decreasing erosion and thermal relaxation, the latter in the form of a growing thermal boundary layer. Subsidence is manifest first as a boring interval in which no sedimentary record is preserved, followed by continent-scale submergence wherein sediments are deposited directly on deep-seated igneous/metamorphic basement, generating a major disconformity. The terminal resting elevation of a mature continent, however, is defined by the temperature of the ambient convecting <span class="hlt">mantle</span>: below sea level when the <span class="hlt">mantle</span> is hot and above sea level when the <span class="hlt">mantle</span> is cold. Using thermobarometric constraints on secular cooling of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>, our results suggest that <span class="hlt">Earth</span>, for most of its history, must have been a water world, with regions of land confined to narrow orogenic belts and oceans characterized by deep basins and shallow continental seas, the latter serving as repositories of sediments and key redox-sensitive biological nutrients, such as phosphorous. Cooling of the <span class="hlt">Earth</span> led to the gradual and irreversible rise of the continents, culminating in rapid emergence, through fits and starts and possible instabilities in climate, between 500-1000 Ma. Such emergence fundamentally altered marine biogeochemical cycling, continental weathering and the global hydrologic cycle, defining the backdrop for the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27389974','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27389974"><span>Long-term outcome for patients with <span class="hlt">early</span> stage marginal zone lymphoma and <span class="hlt">mantle</span> cell lymphoma.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Barzenje, Dlawer Abdulla; Holte, Harald; Fosså, Alexander; Ghanima, Waleed; Liestøl, Knut; Delabie, Jan; Kolstad, Arne</p> <p>2017-03-01</p> <p>In this study with prolonged follow up, we compared clinical outcome, including cause of death and incidence of second cancer, for patients with <span class="hlt">early</span> stage extranodal marginal zone lymphoma (EMZL, 49 patients), nodal marginal zone lymphoma (NMZL, nine patients) and <span class="hlt">mantle</span> cell lymphoma (MCL, 42 patients) with emphasis on potential benefit of radiotherapy. Radiotherapy was given to 40 patients with EMZL (nine had surgery only) and all NMZL patients. MCL patients received radiotherapy (17 patients), chemotherapy followed by radiotherapy (13 patients) or chemotherapy alone (12 patients). Compared to a matched control population no increased risk of second cancer or cardiovascular disease was observed. Radiotherapy alone was effective in EMZL and NMZL with low-relapse rates (20% and 33%) and a 10-year overall survival of 78% and 56%, respectively. High-relapse rate and inferior OS in MCL underline the need for extended staging with endoscopy and PET/CT and possibly for novel strategies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1335876-dry-mg-fe-sio3-perovskite-earth-lower-mantle','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1335876-dry-mg-fe-sio3-perovskite-earth-lower-mantle"><span>Dry (Mg,Fe)SiO 3 perovskite in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Panero, Wendy R.; Pigott, Jeffrey S.; Reaman, Daniel M.; ...</p> <p>2015-02-26</p> <p>Combined synthesis experiments and first-principles calculations show that MgSiO 3-perovskite with minor Al or Fe does not incorporate significant OH under lower <span class="hlt">mantle</span> conditions. Perovskite, stishovite, and residual melt were synthesized from natural Bamble enstatite samples (Mg/(Fe+Mg) = 0.89 and 0.93; Al 2O 3 < 0.1 wt% with 35 and 2065 ppm wt H 2O, respectively) in the laser-heated diamond anvil cell at 1600-2000 K and 25-65 GPa. Combined Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, and ex-situ transmission electron microscopy (TEM) analysis demonstrates little difference in the resulting perovskite as a function of initial water content. Four distinct OHmore » vibrational stretching bands are evident upon cooling below 100 K (3576, 3378, 3274, and 3078 cm -1), suggesting 4 potential bonding sites for OH in perovskite with a maximum water content of 220 ppm wt H 2O, and likely no more than 10 ppm wt H 2O. Complementary, Fe-free, first-principles calculations predict multiple potential bonding sites for hydrogen in perovskite, each with significant solution enthalpy (0.2 eV/defect). We calculate that perovskite can dissolve less than 37 ppm wt H 2O (400 ppm H/Si) at the top of the lower <span class="hlt">mantle</span>, decreasing to 31 ppm wt H 2O (340 ppm H/Si) at 125 GPa and 3000 K in the absence of a melt or fluid phase. Here, we propose that these results resolve a long-standing debate of the perovskite melting curve and explain the order of magnitude increase in viscosity from upper to lower <span class="hlt">mantle</span>.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008Litho.102...12O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008Litho.102...12O"><span>Dynamics of cratons in an evolving <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Neill, C. J.; Lenardic, A.; Griffin, W. L.; O'Reilly, Suzanne Y.</p> <p>2008-04-01</p> <p>The tectonic quiescence of cratons on a tectonically active planet has been attributed to their physical properties such as buoyancy, viscosity, and yield strength. Previous modelling has shown the conditions under which cratons may be stable for the present, but cast doubt on how they survived in a more energetic <span class="hlt">mantle</span> of the past. Here we incorporate an endothermic phase change at 670 km, and a depth-dependent viscosity structure consistent with post-glacial rebound and geoid modelling, to simulate the dynamics of cratons in an "<span class="hlt">Earth</span>-like" convecting system. We find that cratons are unconditionally stable in such systems for plausible ranges of viscosity ratios between the root and asthenosphere (50-150) and the root/oceanic lithosphere yield strength ratio (5-30). Realistic <span class="hlt">mantle</span> viscosity structures have limited effect on the average background cratonic stress state, but do buffer cratons from extreme stress excursions. An endothermic phase change at 670 km introduces an additional time-dependence into the system, with slab breakthrough into the lower <span class="hlt">mantle</span> associated with 2-3 fold stress increases at the surface. Under Precambrian <span class="hlt">mantle</span> conditions, however, the dominant effect is not more violent <span class="hlt">mantle</span> avalanches, or faster <span class="hlt">mantle</span>/plate velocities, but rather the drastic viscosity drop which results from hotter <span class="hlt">mantle</span> conditions in the past. This results in a large decrease in the cratonic stress field, and promotes craton survival under the evolving <span class="hlt">mantle</span> conditions of the <span class="hlt">early</span> <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMMR21C..06B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMMR21C..06B"><span>Eutectic melting in the MgO-SiO2 system and its implication to <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baron, M. A.; Lord, O. T.; Myhill, R.; Thomson, A.; Wang, W.; Tronnes, R. G.; Walter, M. J.</p> <p>2017-12-01</p> <p>Eutectic melting curves in the system MgO-SiO2 have been experimentally studied at lower <span class="hlt">mantle</span> pressures using laser-heated diamond anvil cell (LH-DAC) techniques. We investigated eutectic melting of bridgmanite plus periclase in the MgO-MgSiO3 binary and bridgmanite plus stishovite in the MgSiO3-SiO2 sub-system as the simplest models of natural peridotite and basalt. The eutectic melting have been detected on the basis of the thermal perturbations (i.e. melting plateau) during the experiment but also post-experimental textural and chemical analyses of the recovered samples. We also performed a suite of sub-solidus experiments in order to compare and bracket the eutectic melting experiments. The melting curve of model basalt occurs at lower temperatures, has a shallower dT/dP slope and slightly less curvature than the model peridotitic melting curve. Overall, melting temperatures detected in this study are in good agreement with previous experiments and ab initio simulations at 25 GPa (Liebske and Frost, 2012; de Koker et al., 2013). However, at higher pressures the measured eutectic melting curves are systematically lower in temperature than curves extrapolated on the basis of thermodynamic modelling of low-pressure experimental data, and those calculated from atomistic simulations. In turn, when comparing with previously published solidus curves obtained for natural basalt and peridotite (e.g. Fiquet et al., 2010; Andrault et al. 2011; Nomura et al. 2014; Hirose et al. 1999; Andrault et al. 2014 and Pradhan et al. 2015) the melting curves from this study are higher. However, the difference in temperature is less significant than previously though. Based on the comparison of the curvature of the model peridotite eutectic relative to an MgSiO3 melt adiabat we infer that crystallization in a global magma ocean would begin at 100 GPa rather than at the bottom of the <span class="hlt">mantle</span>, allowing for an <span class="hlt">early</span> basal melt layer. The model peridotite melting curve lies 500 K above</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17720806','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17720806"><span>Time variability in Cenozoic reconstructions of <span class="hlt">mantle</span> heat flow: plate tectonic cycles and implications for <span class="hlt">Earth</span>'s thermal evolution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A</p> <p>2007-09-04</p> <p>The thermal evolution of <span class="hlt">Earth</span> is governed by the rate of secular cooling and the amount of radiogenic heating. If <span class="hlt">mantle</span> heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot <span class="hlt">mantle</span> in the recent past.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1964844','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1964844"><span>Time variability in Cenozoic reconstructions of <span class="hlt">mantle</span> heat flow: Plate tectonic cycles and implications for <span class="hlt">Earth</span>'s thermal evolution</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Loyd, S. J.; Becker, T. W.; Conrad, C. P.; Lithgow-Bertelloni, C.; Corsetti, F. A.</p> <p>2007-01-01</p> <p>The thermal evolution of <span class="hlt">Earth</span> is governed by the rate of secular cooling and the amount of radiogenic heating. If <span class="hlt">mantle</span> heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ∼0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot <span class="hlt">mantle</span> in the recent past. PMID:17720806</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e000888.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e000888.html"><span>BENNU’S JOURNEY - <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href=""></a></p> <p></p> <p>2017-12-08</p> <p>This is an artist's concept of the young <span class="hlt">Earth</span> being bombarded by asteroids. Scientists think these impacts could have delivered significant amounts of organic matter and water to <span class="hlt">Earth</span>. Image Credit: NASA's Goddard Space Flight Center Conceptual Image Lab The Origins Spectral Interpretation Resource Identification Security -- Regolith Explorer spacecraft (OSIRIS-REx) will travel to a near-<span class="hlt">Earth</span> asteroid, called Bennu, and bring a sample back to <span class="hlt">Earth</span> for study. The mission will help scientists investigate how planets formed and how life began, as well as improve our understanding of asteroids that could impact <span class="hlt">Earth</span>. OSIRIS-REx is scheduled for launch in late 2016. As planned, the spacecraft will reach its asteroid target in 2018 and return a sample to <span class="hlt">Earth</span> in 2023. Watch the full video: youtu.be/gtUgarROs08 Learn more about NASA’s OSIRIS-REx mission and the making of Bennu’s Journey: www.nasa.gov/content/goddard/bennus-journey/ More information on the OSIRIS-REx mission is available at: www.nasa.gov/mission_pages/osiris-rex/index.html www.asteroidmission.org NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: <span class="hlt">Earth</span> Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.7748J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.7748J"><span>Identifying <span class="hlt">early</span> <span class="hlt">Earth</span> microfossils in unsilicified sediments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Javaux, Emmanuelle J.; Asael, Dan; Bekker, Andrey; Debaille, Vinciane; Derenne, Sylvie; Hofmann, Axel; Mattielli, Nadine; Poulton, Simon</p> <p>2013-04-01</p> <p>The search for life on the <span class="hlt">early</span> <span class="hlt">Earth</span> or beyond <span class="hlt">Earth</span> requires the definition of biosignatures, or "indices of life". These traditionally include fossil molecules, isotopic fractionations, biosedimentary structures and morphological fossils interpreted as remnants of life preserved in rocks. This research focuses on traces of life preserved in unsilicified siliciclastic sediments. Indeed, these deposits preserve well sedimentary structures indicative of past aqueous environments and organic matter, including the original organic walls of microscopic organisms. They also do not form in hydrothermal conditions which may be source of abiotic organics. At our knowledge, the only reported occurrence of microfossils preserved in unsilicified Archean sediments is a population of large organic-walled vesicles discovered in shales and siltstones of the 3.2 Ga Moodies Group, South Africa. (Javaux et al, Nature 2010). These have been interpreted as microfossils based on petrographic and geochemical evidence for their endogenicity and syngeneity, their carbonaceous composition, cellular morphology and ultrastructure, occurrence in populations, taphonomic features of soft wall deformation, and the geological context plausible for life, as well as lack of abiotic explanation falsifying a biological origin. Demonstrating that carbonaceous objects from Archaean rocks are truly old and truly biological is the subject of considerable debate. Abiotic processes are known to produce organics and isotopic signatures similar to life. Spheroidal pseudofossils may form as self-assembling vesicles from abiotic CM, e.g. in prebiotic chemistry experiments (Shoztak et al, 2001), from meteoritic lipids (Deamer et al, 2006), or hydrothermal fluids (Akashi et al, 1996); by artifact of maceration; by migration of abiotic or biotic CM along microfractures (VanZuilen et al, 2007) or along mineral casts (Brasier et al, 2005), or around silica spheres formed in silica-saturated water (Jones and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4326963','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4326963"><span>Muonium in Stishovite: Implications for the Possible Existence of Neutral Atomic Hydrogen in the <span class="hlt">Earth</span>'s Deep <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Funamori, Nobumasa; Kojima, Kenji M.; Wakabayashi, Daisuke; Sato, Tomoko; Taniguchi, Takashi; Nishiyama, Norimasa; Irifune, Tetsuo; Tomono, Dai; Matsuzaki, Teiichiro; Miyazaki, Masanori; Hiraishi, Masatoshi; Koda, Akihiro; Kadono, Ryosuke</p> <p>2015-01-01</p> <p>Hydrogen in the <span class="hlt">Earth</span>'s deep interior has been thought to exist as a hydroxyl group in high-pressure minerals. We present Muon Spin Rotation experiments on SiO2 stishovite, which is an archetypal high-pressure mineral. Positive muon (which can be considered as a light isotope of proton) implanted in stishovite was found to capture electron to form muonium (corresponding to neutral hydrogen). The hyperfine-coupling parameter and the relaxation rate of spin polarization of muonium in stishovite were measured to be very large, suggesting that muonium is squeezed in small and anisotropic interstitial voids without binding to silicon or oxygen. These results imply that hydrogen may also exist in the form of neutral atomic hydrogen in the deep <span class="hlt">mantle</span>. PMID:25675890</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840057098&hterms=centrifuge&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcentrifuge','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840057098&hterms=centrifuge&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcentrifuge"><span>Convection experiments in a centrifuge and the generation of plumes in a very viscous fluid. [for <span class="hlt">earth</span> <span class="hlt">mantle</span> models</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nataf, H.-C.; Hager, B. H.; Scott, R. F.</p> <p>1984-01-01</p> <p>In this paper, experiments are described for which inertial effects are negligible. A small aspect-ratio tank filled with a very viscous fluid (Pr = 10 to the 6th) is used to observe the behavior of convection for Rayleigh numbers up to 6.3 x 10 to the 5th. These high values are reached by conducting the experiment in a centrifuge which provides a 130-fold increase in apparent gravity. Rotational effects are small, but cannot be totally dismissed. In this geometry, thermal boundary layer instabilities are indeed observed, and are found to be very similar to their lower Prandtl number counterparts. It is tentatively concluded that once given a certain degree of 'vulnerability' convection can develop 'plume' like instabilities, even when the Prandtl number is infinite. The concept is applied to the <span class="hlt">earth</span>'s <span class="hlt">mantle</span> and it is speculated that 'plumes' could well be the dominant mode of small-scale convection under the lithospheric plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015NatSR...5E8437F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015NatSR...5E8437F"><span>Muonium in Stishovite: Implications for the Possible Existence of Neutral Atomic Hydrogen in the <span class="hlt">Earth</span>'s Deep <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Funamori, Nobumasa; Kojima, Kenji M.; Wakabayashi, Daisuke; Sato, Tomoko; Taniguchi, Takashi; Nishiyama, Norimasa; Irifune, Tetsuo; Tomono, Dai; Matsuzaki, Teiichiro; Miyazaki, Masanori; Hiraishi, Masatoshi; Koda, Akihiro; Kadono, Ryosuke</p> <p>2015-02-01</p> <p>Hydrogen in the <span class="hlt">Earth</span>'s deep interior has been thought to exist as a hydroxyl group in high-pressure minerals. We present Muon Spin Rotation experiments on SiO2 stishovite, which is an archetypal high-pressure mineral. Positive muon (which can be considered as a light isotope of proton) implanted in stishovite was found to capture electron to form muonium (corresponding to neutral hydrogen). The hyperfine-coupling parameter and the relaxation rate of spin polarization of muonium in stishovite were measured to be very large, suggesting that muonium is squeezed in small and anisotropic interstitial voids without binding to silicon or oxygen. These results imply that hydrogen may also exist in the form of neutral atomic hydrogen in the deep <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFMMR11A0091G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFMMR11A0091G"><span>Stability of carbonated basaltic melt at the base of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ghosh, S.; Litasov, K.; Ohtani, E.; Suzuki, A.</p> <p>2006-12-01</p> <p>Seismological observations of low velocity zones (LVZ) at the top of the 410-km discontinuity reveal possible existence of dense melt at this boundary (e.g. Reveanugh and Sipkin, 1994). Density measurements of anhydrous basaltic melts indicate that it is denser than surrounding <span class="hlt">mantle</span> near 410-km depth (Ohtani and Maeda, 2001). However, melting temperature of peridotite is much higher than about 1400°C, estimated at 410-km depth. It has been shown recently that hydrous basaltic melt containing up to 2 wt.% H2O is denser than peridotite atop 410-km and therefore can be accumulated at the base of the upper <span class="hlt">mantle</span> (Sakamaki et al., 2006). CO2 is another major volatile component in the <span class="hlt">mantle</span> and it could be also important for explanation of LVZ near 410 km. In the present study, we have measured the density of carbonated basaltic melt at high pressures and high temperatures and discussed its possible stability at the base of the upper <span class="hlt">mantle</span>. The density of the melt was determined using sink/float technique. The starting material was synthetic MORB glass. 5 and 10 wt.% CO2 was added to the glass as CaCO3 and Na2CO3, adjusting to proportions of related oxides. Experiments were carried out at 16-22 GPa and 2200-2300°C using a multianvil apparatus at Tohoku University, Japan. We observed neutral buoyancy of diamond density marker in MORB + 5 wt.% CO2 at 18 GPa and 2300°C, whereas, diamond was completely dissolved in the carbonated MORB melt containing 10 wt.% CO2 in 0.5-1 minute experiments. Based on the buoyancy test, the density of the carbonated basaltic melt, containing 5 wt.% CO2, is 3.56 g/cm3 at 18 GPa and 2300°C using an equation of state of diamond. To calculate the bulk modulus we assume that the pressure derivative of the isothermal bulk modulus is the same as that of the dry MORB melt, dKT/dP=5.0 and zero-pressure partial molar volume of CO2 is 32 cm3/mol (based on low-pressure experiments on carbonated basaltic melts and carbonatites, e.g. Dobson et al</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/fs/2007/3004/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/fs/2007/3004/"><span>Precambrian Time - The Story of the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href=""></a></p> <p>Lindsey, D.A.</p> <p>2007-01-01</p> <p>The Precambrian is the least-understood part of <span class="hlt">Earth</span> history, yet it is arguably the most important. Precambrian time spans almost nine-tenths of <span class="hlt">Earth</span> history, from the formation of the <span class="hlt">Earth</span> to the dawn of the Cambrian Period. It represents time so vast and long ago that it challenges all comprehension. The Precambrian is the time of big questions. How old is the <span class="hlt">Earth</span>? How old are the oldest rocks and continents? What was the <span class="hlt">early</span> <span class="hlt">Earth</span> like? What was the <span class="hlt">early</span> atmosphere like? When did life appear, and what did it look like? And, how do we know this? In recent years, remarkable progress has been made in understanding the <span class="hlt">early</span> evolution of the <span class="hlt">Earth</span> and life itself. Yet, the scientific story of the <span class="hlt">early</span> <span class="hlt">Earth</span> is still a work in progress, humankind's latest attempt to understand the planet. Like previous attempts, it too will change as we learn more about the <span class="hlt">Earth</span>. Read on to discover what we know now, in the <span class="hlt">early</span> 21st century.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=america+AND+conservation&id=EJ1065401','ERIC'); return false;" href="https://eric.ed.gov/?q=america+AND+conservation&id=EJ1065401"><span>Mother <span class="hlt">Earth</span>, <span class="hlt">Earth</span> Mother: Gabriela Mistral as an <span class="hlt">Early</span> Ecofeminist</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Finzer, Erin</p> <p>2015-01-01</p> <p>Historians have noted that male bureaucrats and natural resource experts tended to dominate <span class="hlt">early</span> twentieth-century national and hemispheric conservationist movements in Latin America, but a constellation of female activists, notable among them Gabriela Mistral, strengthened conservationism in the cultural sphere. Capitalizing on her leadership in…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMPP31C1355H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMPP31C1355H"><span>Hygroscopicity of <span class="hlt">Early</span> <span class="hlt">Earth</span> and Titan Laboratory Aerosol Analogs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hasenkopf, C. A.; Beaver, M. R.; Freedman, M. A.; Toon, O. B.; Tolbert, M. A.</p> <p>2009-12-01</p> <p>We have explored the ability of organic hazes, known to exist in the atmosphere of Titan and postulated to have existed in the Archean <span class="hlt">Earth</span> atmosphere, to act as cloud condensation nuclei (CCN). These laboratory aerosol analogs are generated via UV-photolysis of <span class="hlt">early</span> <span class="hlt">Earth</span> and Titan analog gas mixtures and are designed to mimic the present day atmospheric conditions on Titan and the <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere before the rise of oxygen. Water uptake is observed to occur on the <span class="hlt">early</span> <span class="hlt">Earth</span> and Titan aerosol analogs at relative humidities of 80% - 90% via optical growth measurements using cavity ring-down aerosol extinction spectroscopy. We find the optical growth of these aerosols is similar to known slightly-soluble organic acids, such as phthalic and pyromellitic acids. On average, the optical growth of the <span class="hlt">early</span> <span class="hlt">Earth</span> analog is slightly larger than the Titan analog. In order to translate our measurements obtained in a subsaturated regime into the CCN ability of these particles, we rely on the hygroscopicity parameter κ, developed by Petters & Kreidenweis (2007). We retrieve κ = 0.17±0.03 and 0.06±0.01 for the <span class="hlt">early</span> <span class="hlt">Earth</span> and Titan analogs, respectively. This <span class="hlt">early</span> <span class="hlt">Earth</span> analog hygroscopicity value indicates that the aerosol could activate at reasonable water vapor supersaturations. We use previous aerosol mass spectrometry results to correlate the chemical structure of the two types of analog with their hygroscopicity. The hygroscopicity of the <span class="hlt">early</span> <span class="hlt">Earth</span> aerosol analog, coupled with the apparent lack of other good CCN during the Archean, helps explain the role of the organic haze in the indirect effect of clouds on the <span class="hlt">early</span> <span class="hlt">Earth</span> and indicates that it may have had a significant impact on the hydrological cycle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2621O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2621O"><span>Seismic anisotropy; a window on how the <span class="hlt">Earth</span> works: multiple mechanisms and sites, from shallow <span class="hlt">mantle</span> to inner core</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Osmaston, Miles</p> <p>2013-04-01</p> <p>Since the seismic anisotropy (SA) in the uppermost oceanic <span class="hlt">mantle</span> was discovered [1] and attributed to the shearing of olivine by an MOR-divergent flow velocity gradient, rheological mobility interpretations of this type have dominated studies of SA there and elsewhere in the <span class="hlt">Earth</span>. Here I describe two other SA-generating mechanisms. I will reason that one of these, the anisotropic crystallization from melt, bids fair largely to replace the shearing one and be present in even larger volumes of the <span class="hlt">Earth</span>, both within its outer 100km and in the Inner Core. The other, the layered deposition of disparate substances, offers to explain the ULVZs and SA in D''. We start with the Upper <span class="hlt">Mantle</span>. New constraints on its rheological properties and dynamical behaviour have come from two directions. Firstly, contrary to the seismologists' rule-book, the oceanic LVZ is no longer to be thought of as mobile because the presence of interstitial melt strips out the water-weakening of the mineral structure [2, 3]. So we require a substitute for the divergent-flow model for MORs. In fact it also has three other, apparently unrecognized, dynamical inconsistencies. One of these [4] is that there are in the record many rapid changes of spreading rate and direction, and ridge jumps. This cannot happen with a process driven by slow-to-change body forces. Secondly, during the past decade, my work on the global dynamics for the past 150Ma (I will show examples) has shown [4 - 7] that the tectospheres of cratons must extend to very close to the bottom of the upper <span class="hlt">mantle</span>. And that East Antarctica's 'keel' must actually reach it, because its CW rotation [7] suggests it has been picking up an electromagnetic torque from the CMB via the lower <span class="hlt">mantle</span>. Xenoliths suggest that the reason for this downwards extent of 'keels' is the same as [3]. To meet these two sets of constraints I will demonstrate my now not-so-new MOR model, which has a narrow, wall-accreting subaxial crack. Among its many features</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IJEaS.107..787G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IJEaS.107..787G"><span><span class="hlt">Earth</span>'s evolving subcontinental lithospheric <span class="hlt">mantle</span>: inferences from LIP continental flood basalt geochemistry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greenough, John D.; McDivitt, Jordan A.</p> <p>2018-04-01</p> <p>Archean and Proterozoic subcontinental lithospheric <span class="hlt">mantle</span> (SLM) is compared using 83 similarly incompatible element ratios (SIER; minimally affected by % melting or differentiation, e.g., Rb/Ba, Nb/Pb, Ti/Y) for >3700 basalts from ten continental flood basalt (CFB) provinces representing nine large igneous provinces (LIPs). Nine transition metals (TM; Fe, Mn, Sc, V, Cr, Co, Ni, Cu, Zn) in 102 primitive basalts (Mg# = 0.69-0.72) from nine provinces yield additional SLM information. An iterative evaluation of SIER values indicates that, regardless of age, CFB transecting Archean lithosphere are enriched in Rb, K, Pb, Th and heavy REE(?); whereas P, Ti, Nb, Ta and light REE(?) are higher in Proterozoic-and-younger SLM sources. This suggests efficient transfer of alkali metals and Pb to the continental lithosphere perhaps in association with melting of subducted ocean floor to form Archean tonalite-trondhjemite-granodiorite terranes. Titanium, Nb and Ta were not efficiently transferred, perhaps due to the stabilization of oxide phases (e.g., rutile or ilmenite) in down-going Archean slabs. CFB transecting Archean lithosphere have EM1-like SIER that are more extreme than seen in oceanic island basalts (OIB) suggesting an Archean SLM origin for OIB-enriched <span class="hlt">mantle</span> 1 (EM1). In contrast, OIB high U/Pb (HIMU) sources have more extreme SIER than seen in CFB provinces. HIMU may represent subduction-processed ocean floor recycled directly to the convecting <span class="hlt">mantle</span>, but to avoid convective homogenization and produce its unique Pb isotopic signature may require long-term isolation and incubation in SLM. Based on all TM, CFB transecting Proterozoic lithosphere are distinct from those cutting Archean lithosphere. There is a tendency for lower Sc, Cr, Ni and Cu, and higher Zn, in the sources for Archean-cutting CFB and EM1 OIB, than Proterozoic-cutting CFB and HIMU OIB. All CFB have SiO2 (pressure proxy)-Nb/Y (% melting proxy) relationships supporting low pressure, high % melting</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3655C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3655C"><span>Electrical conductivity of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> after one year of SWARM magnetic field measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Civet, François; Thebault, Erwan; Verhoeven, Olivier; Langlais, Benoit; Saturnino, Diana</p> <p>2015-04-01</p> <p>We present a global EM induction study using L1b Swarm satellite magnetic field measurements data down to a depth of 2000 km. Starting from raw measurements, we first derive a model for the main magnetic field, correct the data for a lithospheric field model, and further select the data to reduce the contributions of the ionospheric field. These computations allowed us to keep a full control on the data processes. We correct residual field from outliers and estimate the spherical harmonic coefficients of the transient field for periods between 2 and 256 days. We used full latitude range and all local times to keep a maximum amount of data. We perform a Bayesian inversion and construct a Markov chain during which model parameters are randomly updated at each iteration. We first consider regular layers of equal thickness and extra layers are added where conductivity contrast between successive layers exceed a threshold value. The mean and maximum likelihood of the electrical conductivity profile is then estimated from the probability density function. The obtained profile particularly shows a conductivity jump in the 600-700 km depth range, consistent with the olivine phase transition at 660 km depth. Our study is the first one to show such a conductivity increase in this depth range without any a priori informations on the internal strucutres. Assuming a pyrolitic <span class="hlt">mantle</span> composition, this profile is interpreted in terms of temperature variations in the depth range where the probability density function is the narrowest. We finally obtained a temperature gradient in the lower <span class="hlt">mantle</span> close to adiabatic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.S43D..01X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.S43D..01X"><span>Imaging <span class="hlt">Mantle</span> Convection Processes Beneath the Western USA Using the <span class="hlt">Earth</span>Scope Transportable Array</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xue, M.; Allen, R. M.</p> <p>2007-12-01</p> <p>High resolution velocity models beneath western USA can provide important clues to <span class="hlt">mantle</span> convection processes in this tectonically active region, e.g., the subduction of the Juan de Fuca plate, the upwelling of the Yellowstone plume, and their possible interactions. In this study, we apply the tomography technique using the Transportable Array data complemented by regional networks data resulting in a total of 732 stations. In our preliminary models we use 57 earthquakes sources. We derived two preliminary Vs models and one preliminary Vp model using tangential, radial, and vertical components respectively. Our preliminary tomographic images show some common features which have been imaged before such as the high velocity anomaly beneath the Cascades and the low velocity anomaly beneath the Yellowstone National Park. However, the unprecedented dense station distribution allows us to see deeper and reveals some new features: (1) the imaged Juan de Fuca subduction system goes deeper than previously been imaged. It reaches more than 500 km depth in Washington and northern California while in Oregon it seems break off and is segmented, implying a possible interaction with the proposed Yellowstone plume; (2) immediately south of the Juan de Fuca subduction system, we image low velocity anomalies down to ~{400} km depth, coincident with the proposed location of the slab gap; (3) we image the low velocity anomaly beneath the northeast Oregon down to ~{300} km depth, deeper than has previously been imaged, which has been hypothesized as the depleted <span class="hlt">mantle</span> after the eruption of the Columbia River flood basalts, a result of delamination of the Wallowa plutonic roots [Hales, et. al., 2005]; (4) we see the high velocity Pacific plate abutting against the low velocity North American plate along the trace of the San Andreas Fault System. These observations suggest we are only just beginning to image the complex interactions between geologic objects beneath the western USA.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018A%26ARv..26....2L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018A%26ARv..26....2L"><span>Origin and evolution of the atmospheres of <span class="hlt">early</span> Venus, <span class="hlt">Earth</span> and Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lammer, Helmut; Zerkle, Aubrey L.; Gebauer, Stefanie; Tosi, Nicola; Noack, Lena; Scherf, Manuel; Pilat-Lohinger, Elke; Güdel, Manuel; Grenfell, John Lee; Godolt, Mareike; Nikolaou, Athanasia</p> <p>2018-05-01</p> <p>We review the origin and evolution of the atmospheres of <span class="hlt">Earth</span>, Venus and Mars from the time when their accreting bodies were released from the protoplanetary disk a few million years after the origin of the Sun. If the accreting planetary cores reached masses ≥ 0.5 M_<span class="hlt">Earth</span> before the gas in the disk disappeared, primordial atmospheres consisting mainly of H_2 form around the young planetary body, contrary to late-stage planet formation, where terrestrial planets accrete material after the nebula phase of the disk. The differences between these two scenarios are explored by investigating non-radiogenic atmospheric noble gas isotope anomalies observed on the three terrestrial planets. The role of the young Sun's more efficient EUV radiation and of the plasma environment into the escape of <span class="hlt">early</span> atmospheres is also addressed. We discuss the catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans and we describe the geochemical evidence for additional delivery of volatile-rich chondritic materials during the main stages of terrestrial planet formation. The evolution scenario of <span class="hlt">early</span> <span class="hlt">Earth</span> is then compared with the atmospheric evolution of planets where no active plate tectonics emerged like on Venus and Mars. We look at the diversity between <span class="hlt">early</span> <span class="hlt">Earth</span>, Venus and Mars, which is found to be related to their differing geochemical, geodynamical and geophysical conditions, including plate tectonics, crust and <span class="hlt">mantle</span> oxidation processes and their involvement in degassing processes of secondary N_2 atmospheres. The buildup of atmospheric N_2, O_2, and the role of greenhouse gases such as CO_2 and CH_4 to counter the Faint Young Sun Paradox (FYSP), when the earliest life forms on <span class="hlt">Earth</span> originated until the Great Oxidation Event ≈ 2.3 Gyr ago, are addressed. This review concludes with a discussion on the implications of understanding <span class="hlt">Earth</span>'s geophysical and related atmospheric evolution in relation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000Tectp.322...19D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000Tectp.322...19D"><span><span class="hlt">Early</span> formation and long-term stability of continents resulting from decompression melting in a convecting <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>De Smet, J.; Van den Berg, A. P.; Vlaar, N. J.</p> <p>2000-07-01</p> <p>The origin of stable old continental cratonic roots is still debated. We present numerical modelling results which show rapid initial formation during the Archaean of continental roots of ca. 200 km thick. These results have been obtained from an upper <span class="hlt">mantle</span> thermal convection model including differentiation by pressure release partial melting of <span class="hlt">mantle</span> peridotite. The upper <span class="hlt">mantle</span> model includes time-dependent radiogenic heat production and thermal coupling with a heat reservoir representing the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> and core. This allows for model experiments including secular cooling on a time-scale comparable to the age of the <span class="hlt">Earth</span>. The model results show an initial phase of rapid continental root growth of ca. 0.1 billion year, followed by a more gradual increase of continental volume by addition of depleted material produced through hot diapiric, convective upwellings which penetrate the continental root from below. Within ca. 0.6 Ga after the start of the experiment, secular cooling of the <span class="hlt">mantle</span> brings the average geotherm below the peridotite solidus thereby switching off further continental growth. At this time the thickness of the continental root has grown to ca. 200 km. After 1 Ga of secular cooling small scale thermal instabilities develop at the bottom of the continental root causing continental delamination without breaking up the large scale layering. This delaminated material remixes with the deeper layers. Two more periods, each with a duration of ca. 0.5 Ga and separated by quiescent periods were observed when melting and continental growth was reactivated. Melting ends at 3 Ga. Thereafter secular cooling proceeds and the compositionally buoyant continental root is stabilized further through the increase in mechanical strength induced by the increase of the temperature dependent <span class="hlt">mantle</span> viscosity. Fluctuating convective velocity amplitudes decrease to below 10 mma -1 and the volume average temperature of the sub-continental convecting <span class="hlt">mantle</span> has</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI41A0327I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI41A0327I"><span>Experimental deformation of (Mg,Fe)O ferropericlase in a resistive-heated DAC at conditions of the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Immoor, J.; Marquardt, H.; Miyagi, L. M.; Lin, F.; Speziale, S.; Merkel, S.; Liermann, H. P.</p> <p>2017-12-01</p> <p>Seismic anisotropy in <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span>, resulting from crystallographic preferred orientation (CPO) of elastically anisotropic minerals, is the most promising observable to map <span class="hlt">mantle</span> flow patterns. The shear wave anisotropy observed in the lowermost <span class="hlt">mantle</span> might be caused by CPO of (Mg,Fe)O ferropericlase that is characterized by large elastic anisotropy in the deep lower <span class="hlt">mantle</span>. However, our understanding of the slip system activities of ferropericlase at conditions of the lowermost <span class="hlt">mantle</span> is still incomplete. Here, we present results of an experimental study designed to determine slip system activities in (Mg,Fe)O at P-T conditions of the lower <span class="hlt">mantle</span>. In-situ deformation experiments on powders of (Mg0.8Fe0.2)O were conducted in a graphite heated diamond anvil cell (DAC) up to a temperature of 1400K. Synchrotron x-ray diffraction data were fit with the program MAUD (Materials Analysing Using Diffraction) to extract textures and lattice strains. The experimental results were modelled using the Elasto-Viscoplastic Self Consistent (EVPSC) code. Our data indicate a change in slip system activities from dominant {110} to increasing {100} slip at temperatures above 1150 K and pressures corresponding to the mid-lower <span class="hlt">mantle</span>. Our findings indicate an effect of both pressure and temperature on the plasticity of (Mg,Fe)O and, hence, pave the way to a better understanding of with a potential change of dominant slip system between 40-60 GPa in MgO predicted from numerical models (Amodeo et al., 2012). We use the results to model the possible contribution of ferropericlase CPO to observed seismic anisotropy in the D'' layer in the lowermost <span class="hlt">mantle</span>. Amodeo et al. (2012) Phil Mag, 92, 1523-1541</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4525W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4525W"><span>Complete synthetic seismograms based on a spherical self-gravitating <span class="hlt">Earth</span> model with an atmosphere-ocean-<span class="hlt">mantle</span>-core structure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Rongjiang; Heimann, Sebastian; Zhang, Yong; Wang, Hansheng; Dahm, Torsten</p> <p>2017-04-01</p> <p>A hybrid method is proposed to calculate complete synthetic seismograms based on a spherically symmetric and self-gravitating <span class="hlt">Earth</span> with a multi-layered structure of atmosphere, ocean, <span class="hlt">mantle</span>, liquid core and solid core. For large wavelengths, a numerical scheme is used to solve the geodynamic boundary-value problem without any approximation on the deformation and gravity coupling. With the decreasing wavelength, the gravity effect on the deformation becomes negligible and the analytical propagator scheme can be used. Many useful approaches are used to overcome the numerical problems that may arise in both analytical and numerical schemes. Some of these approaches have been established in the seismological community and the others are developed for the first time. Based on the stable and efficient hybrid algorithm, an all-in-one code QSSP is implemented to cover the complete spectrum of seismological interests. The performance of the code is demonstrated by various tests including the curvature effect on teleseismic body and surface waves, the appearance of multiple reflected, teleseismic core phases, the gravity effect on long period surface waves and free oscillations, the simulation of near-field displacement seismograms with the static offset, the coupling of tsunami and infrasound waves, and free oscillations of the solid <span class="hlt">Earth</span>, the atmosphere and the ocean. QSSP is open source software that can be used as a stand-alone FORTRAN code or may be applied in combination with a Python toolbox to calculate and handle Green's function databases for efficient coding of source inversion problems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.210.1739W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.210.1739W"><span>Complete synthetic seismograms based on a spherical self-gravitating <span class="hlt">Earth</span> model with an atmosphere-ocean-<span class="hlt">mantle</span>-core structure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Rongjiang; Heimann, Sebastian; Zhang, Yong; Wang, Hansheng; Dahm, Torsten</p> <p>2017-09-01</p> <p>A hybrid method is proposed to calculate complete synthetic seismograms based on a spherically symmetric and self-gravitating <span class="hlt">Earth</span> with a multilayered structure of atmosphere, ocean, <span class="hlt">mantle</span>, liquid core and solid core. For large wavelengths, a numerical scheme is used to solve the geodynamic boundary-value problem without any approximation on the deformation and gravity coupling. With decreasing wavelength, the gravity effect on the deformation becomes negligible and the analytical propagator scheme can be used. Many useful approaches are used to overcome the numerical problems that may arise in both analytical and numerical schemes. Some of these approaches have been established in the seismological community and the others are developed for the first time. Based on the stable and efficient hybrid algorithm, an all-in-one code QSSP is implemented to cover the complete spectrum of seismological interests. The performance of the code is demonstrated by various tests including the curvature effect on teleseismic body and surface waves, the appearance of multiple reflected, teleseismic core phases, the gravity effect on long period surface waves and free oscillations, the simulation of near-field displacement seismograms with the static offset, the coupling of tsunami and infrasound waves, and free oscillations of the solid <span class="hlt">Earth</span>, the atmosphere and the ocean. QSSP is open source software that can be used as a stand-alone FORTRAN code or may be applied in combination with a Python toolbox to calculate and handle Green's function databases for efficient coding of source inversion problems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ExFl...58...90F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ExFl...58...90F"><span>The <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> in a microwave oven: thermal convection driven by a heterogeneous distribution of heat sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fourel, Loïc; Limare, Angela; Jaupart, Claude; Surducan, Emanoil; Farnetani, Cinzia G.; Kaminski, Edouard C.; Neamtu, Camelia; Surducan, Vasile</p> <p>2017-08-01</p> <p>Convective motions in silicate planets are largely driven by internal heat sources and secular cooling. The exact amount and distribution of heat sources in the <span class="hlt">Earth</span> are poorly constrained and the latter is likely to change with time due to mixing and to the deformation of boundaries that separate different reservoirs. To improve our understanding of planetary-scale convection in these conditions, we have designed a new laboratory setup allowing a large range of heat source distributions. We illustrate the potential of our new technique with a study of an initially stratified fluid involving two layers with different physical properties and internal heat production rates. A modified microwave oven is used to generate a uniform radiation propagating through the fluids. Experimental fluids are solutions of hydroxyethyl cellulose and salt in water, such that salt increases both the density and the volumetric heating rate. We determine temperature and composition fields in 3D with non-invasive techniques. Two fluorescent dyes are used to determine temperature. A Nd:YAG planar laser beam excites fluorescence, and an optical system, involving a beam splitter and a set of colour filters, captures the fluorescence intensity distribution on two separate spectral bands. The ratio between the two intensities provides an instantaneous determination of temperature with an uncertainty of 5% (typically 1K). We quantify mixing processes by precisely tracking the interfaces separating the two fluids. These novel techniques allow new insights on the generation, morphology and evolution of large-scale heterogeneities in the <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21417943','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21417943"><span>Potential climatic impact of organic haze on <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hasenkopf, Christa A; Freedman, Miriam A; Beaver, Melinda R; Toon, Owen B; Tolbert, Margaret A</p> <p>2011-03-01</p> <p>We have explored the direct and indirect radiative effects on climate of organic particles likely to have been present on <span class="hlt">early</span> <span class="hlt">Earth</span> by measuring their hygroscopicity and cloud nucleating ability. The <span class="hlt">early</span> <span class="hlt">Earth</span> analog aerosol particles were generated via ultraviolet photolysis of an <span class="hlt">early</span> <span class="hlt">Earth</span> analog gas mixture, which was designed to mimic possible atmospheric conditions before the rise of oxygen. An analog aerosol for the present-day atmosphere of Saturn's moon Titan was tested for comparison. We exposed the <span class="hlt">early</span> <span class="hlt">Earth</span> aerosol to a range of relative humidities (RHs). Water uptake onto the aerosol was observed to occur over the entire RH range tested (RH=80-87%). To translate our measurements of hygroscopicity over a specific range of RHs into their water uptake ability at any RH < 100% and into their ability to act as cloud condensation nuclei (CCN) at RH > 100%, we relied on the hygroscopicity parameter κ, developed by Petters and Kreidenweis. We retrieved κ=0.22 ±0.12 for the <span class="hlt">early</span> <span class="hlt">Earth</span> aerosol, which indicates that the humidified aerosol (RH < 100 %) could have contributed to a larger antigreenhouse effect on the <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere than previously modeled with dry aerosol. Such effects would have been of significance in regions where the humidity was larger than 50%, because such high humidities are needed for significant amounts of water to be on the aerosol. Additionally, <span class="hlt">Earth</span> organic aerosol particles could have activated into CCN at reasonable-and even low-water-vapor supersaturations (RH > 100%). In regions where the haze was dominant, it is expected that low particle concentrations, once activated into cloud droplets, would have created short-lived, optically thin clouds. Such clouds, if predominant on <span class="hlt">early</span> <span class="hlt">Earth</span>, would have had a lower albedo than clouds today, thereby warming the planet relative to current-day clouds. © Mary Ann Liebert, Inc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030001111&hterms=Biodiversity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DBiodiversity','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030001111&hterms=Biodiversity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DBiodiversity"><span>Ultramafic Terranes and Associated Springs as Analogs for Mars and <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Blake, David; Schulte, Mitch; Cullings, Ken; DeVincezi, D. (Technical Monitor)</p> <p>2002-01-01</p> <p>Putative extinct or extant Martian organisms, like their terrestrial counterparts, must adopt metabolic strategies based on the environments in which they live. In order for organisms to derive metabolic energy from the natural environment (Martian or terrestrial), a state of thermodynamic disequilibrium must exist. The most widespread environment of chemical disequilibrium on present-day <span class="hlt">Earth</span> results from the interaction of mafic rocks of the ocean crust with liquid water. Such environments were even more pervasive and important on the Archean <span class="hlt">Earth</span> due to increased geothermal heat flow and the absence of widespread continental crust formation. The composition of the lower crust and upper <span class="hlt">mantle</span> of the <span class="hlt">Earth</span> is essentially the-same as that of Mars, and the <span class="hlt">early</span> histories of these two planets are similar. It follows that a knowledge of the mineralogy, water-rock chemistry and microbial ecology of <span class="hlt">Earth</span>'s oceanic crust could be of great value in devising a search strategy for evidence of past or present life on Mars. In some tectonic regimes, cross-sections of lower oceanic crust and upper <span class="hlt">mantle</span> are exposed on land as so-called "ophiolite suites." Such is the case in the state of California (USA) as a result of its location adjacent to active plate margins. These mafic and ultramafic rocks contain numerous springs that offer an easily accessible field laboratory for studying water/rock interactions and the microbial communities that are supported by the resulting geochemical energy. A preliminary screen of Archaean biodiversity was conducted in a cold spring located in a presently serpentinizing ultramafic terrane. PCR and phylogenetic analysis of partial 16s rRNA, sequences were performed on water and sediment samples. Archaea of recent phylogenetic origin were detected with sequences nearly identical to those of organisms living in ultra-high pH lakes of Africa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26493639','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26493639"><span>Crystal structure, equation of state, and elasticity of phase H (MgSiO4H2) at <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span> pressures.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tsuchiya, Jun; Mookherjee, Mainak</p> <p>2015-10-23</p> <p>Dense hydrous magnesium silicate (DHMS) phases play a crucial role in transporting water in to the <span class="hlt">Earth</span>'s interior. A newly discovered DHMS, phase H (MgSiO4H2), is stable at <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>, i.e., at pressures greater than 30 GPa. Here we report the crystal structure and elasticity of phase H and its evolution upon compression. Using first principles simulations, we have explored the relative energetics of the candidate crystal structures with ordered and disordered configurations of magnesium and silicon atoms in the octahedral sites. At conditions relevant to <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>, it is likely that phase H is able to incorporate a significant amount of aluminum, which may enhance the thermodynamic stability of phase H. The sound wave velocities of phase H are ~2-4% smaller than those of isostructural δ-AlOOH. The shear wave impedance contrast due to the transformation of phase D to a mixture of phase H and stishovite at pressures relevant to the upper part of the lower <span class="hlt">mantle</span> could partly explain the geophysical observations. The calculated elastic wave velocities and anisotropies indicate that phase H can be a source of significant seismic anisotropy in the lower <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18..697K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18..697K"><span>Origin of geochemical <span class="hlt">mantle</span> components: Role of spreading ridges and thermal evolution of <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kimura, Jun-Ichi; Gill, James B.; van Keken, Peter E.; Kawabata, Hiroshi; Skora, Susanne</p> <p>2017-02-01</p> <p>We explore the element redistribution at mid-ocean ridges (MOR) using a numerical model to evaluate the role of decompression melting of the <span class="hlt">mantle</span> in <span class="hlt">Earth</span>'s geochemical cycle, with focus on the formation of the depleted <span class="hlt">mantle</span> component. Our model uses a trace element mass balance based on an internally consistent thermodynamic-petrologic computation to explain the composition of MOR basalt (MORB) and residual peridotite. Model results for MORB-like basalts from 3.5 to 0 Ga indicate a high <span class="hlt">mantle</span> potential temperature (Tp) of 1650-1500°C during 3.5-1.5 Ga before decreasing gradually to ˜1300°C today. The source <span class="hlt">mantle</span> composition changed from primitive (PM) to depleted as Tp decreased, but this source <span class="hlt">mantle</span> is variable with an <span class="hlt">early</span> depleted reservoir (EDR) <span class="hlt">mantle</span> periodically present. We examine a two-stage Sr-Nd-Hf-Pb isotopic evolution of <span class="hlt">mantle</span> residues from melting of PM or EDR at MORs. At high-Tp (3.5-1.5 Ga), the MOR process formed extremely depleted DMM. This coincided with formation of the majority of the continental crust, the subcontinental lithospheric <span class="hlt">mantle</span>, and the enriched <span class="hlt">mantle</span> components formed at subduction zones and now found in OIB. During cooler <span class="hlt">mantle</span> conditions (1.5-0 Ga), the MOR process formed most of the modern ocean basin DMM. Changes in the mode of <span class="hlt">mantle</span> convection from vigorous deep <span class="hlt">mantle</span> recharge before ˜1.5 Ga to less vigorous afterward is suggested to explain the thermochemical <span class="hlt">mantle</span> evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMMR31A0136R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMMR31A0136R"><span>Structural State and Elastic Properties of Perovskites in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ross, N. L.; Angel, R. J.; Zhao, J.</p> <p>2005-12-01</p> <p>Recent advances in laboratory-based single-crystal X-ray diffraction techniques for measuring the intensities of diffraction from crystals held in situ at high pressures in the diamond-anvil cell have been used to determine the role of polyhedral compression in the response of 2:4 and 3:3 GdFeO3-type perovskites to high pressure [1]. These new data clearly demonstrate that, contrary to previous belief, the compression of the octahedral sites is significant and that the evolution of the perovskite structure with pressure is controlled by a new principle; that of equipartition of bond-valence strain across the structure [2]. This new paradigm, together with the minimal information available from high- pressure powder diffraction studies, may provide the possibility of predicting the structural state and elastic properties of perovskites of any composition at <span class="hlt">mantle</span> pressures and temperatures. Cation partioning between silicate perovskites and other phases should then be predictable through the application of a Brice-style model [3]. The geochemical implications of this type of analysis will be presented as well as the possibility for extending these measurements to higher pressures. References [1] e.g. Zhao, Ross & Angel (2004) Phys Chem Miner. 31: 299; Ross, Zhao,. & Angel (2004). J. Solid State Chemistry 177:1276. [2] Zhao, Ross, & Angel (2004). Acta Cryst. B60:263 [3] e.g Walter et al. (2004) Geochim Cosmochim Acta 68:4267; Blundy & Wood (1994) Nature 372:452</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18.4110T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18.4110T"><span>Evolving <span class="hlt">Mantle</span> Sources in Postcollisional <span class="hlt">Early</span> Permian-Triassic Magmatic Rocks in the Heart of Tianshan Orogen (Western China)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tang, Gong-Jian; Cawood, Peter A.; Wyman, Derek A.; Wang, Qiang; Zhao, Zhen-Hua</p> <p>2017-11-01</p> <p>Magmatism postdating the initiation of continental collision provides insight into the late stage evolution of orogenic belts including the composition of the contemporaneous underlying subcontinental <span class="hlt">mantle</span>. The Awulale Mountains, in the heart of the Tianshan Orogen, display three types of postcollisional mafic magmatic rocks. (1) A medium to high K calc-alkaline mafic volcanic suite (˜280 Ma), which display low La/Yb ratios (2.2-11.8) and a wide range of ɛNd(t) values from +1.9 to +7.4. This suite of rocks was derived from melting of depleted metasomatized asthenospheric <span class="hlt">mantle</span> followed by upper crustal contamination. (2) Mafic shoshonitic basalts (˜272 Ma), characterized by high La/Yb ratios (14.4-20.5) and more enriched isotope compositions (ɛNd(t) = +0.2 - +0.8). These rocks are considered to have been generated by melting of lithospheric <span class="hlt">mantle</span> enriched by melts from the Tarim continental crust that was subducted beneath the Tianshan during final collisional suturing. (3) Mafic dikes (˜240 Ma), with geochemical and isotope compositions similiar to the ˜280 Ma basaltic rocks. This succession of postcollision mafic rock types suggests there were two stages of magma generation involving the sampling of different <span class="hlt">mantle</span> sources. The first stage, which occurred in the <span class="hlt">early</span> Permian, involved a shift from depleted asthenospheric sources to enriched lithospheric <span class="hlt">mantle</span>. It was most likely triggered by the subduction of Tarim continental crust and thickening of the Tianshan lithospheric <span class="hlt">mantle</span>. During the second stage, in the middle Triassic, there was a reversion to more asthenospheric sources, related to postcollision lithospheric thinning.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI13B..04G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI13B..04G"><span>Towards a New Framework for Interpreting Relations Between <span class="hlt">Mantle</span> Dynamics and Processes at the <span class="hlt">Earth</span>'s Surface: A Case Study Involving the Deccan Traps</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glisovic, P.; Forte, A. M.</p> <p>2017-12-01</p> <p>An outstanding challenge in modern geodynamics is the utilization of <span class="hlt">mantle</span> convection models and geophysical data to successfully explain geological events and processes that alter <span class="hlt">Earth</span>'s biosphere, climate, and surface. A key challenge in this modelling is the determination of the initial (and unknown) configuration of <span class="hlt">mantle</span> heterogeneity in the geological past. The first step in addressing this challenge is recognizing that seismic tomography is our most powerful tool for mapping the present-day, internal structure of the <span class="hlt">mantle</span>. We, therefore, implemented a new back-and-forth iterative method for time-reversed, tomography-based convection modelling to reconstruct <span class="hlt">Earth</span>'s internal 3-D structure and dynamics over the Cenozoic [Glisovic & Forte 2016 (JGR)]. This backward convection modelling also includes another key input - the depth variation of <span class="hlt">mantle</span> viscosity inferred from joint inversions of the global convection-related observables and a suite of glacial isostatic adjustments (GIA) data [Mitrovica & Forte 2004 (EPSL), Forte et al. 2010 (EPSL)]. This state-of-the-art, time-reversed convection model is able to show that massive outpourings of basalt in west-central India, known as the Deccan Traps, about 65 million years ago can be directly linked to the presence of two different deep-<span class="hlt">mantle</span> hotspots: Réunion and Comores [Glisovic & Forte 2017 (Science)]. This work constitutes case study showing how time-reversed convection modelling provides a new framework for interpreting the relations between <span class="hlt">mantle</span> dynamics and changing paleogeography and it provides a roadmap for a new series of studies that will elucidate these linkages.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11543125','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11543125"><span>Accretion and differentiation of carbon in the <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tingle, T N</p> <p>1998-05-15</p> <p>The abundance of C in carbonaceous and ordinary chondrites decreases exponentially with increasing shock pressure as inferred from the petrologic shock classification of Scott et al. [Scott, E.R.D., Keil, K., Stoffler, D., 1992. Shock metamorphism of carbonaceous chondrites. Geochim. Cosmochim. Acta 56, 4281-4293] and Stoffler et al. [Stoffler, D., Keil, K., Scott, E.R.D., 1991. Shock metamorphism of ordinary chondrites. Geochim. Cosmochim. Acta 55, 3845-3867]. This confirms the experimental results of Tyburczy et al. [Tyburczy, J.A., Frisch, B., Ahrens, T.J., 1986. Shock-induced volatile loss from a carbonaceous chondrite: implications for planetary accretion. <span class="hlt">Earth</span> Planet. Sci. Lett. 80, 201-207] on shock-induced devolatization of the Murchison meteorite showing that carbonaceous chondrites appear to be completely devolatilized at impact velocities greater than 2 km s-1. Both of these results suggest that C incorporation would have been most efficient in the <span class="hlt">early</span> stages of accretion, and that the primordial C content of the <span class="hlt">Earth</span> was between 10(24) and 10(25) g C (1-10% efficiency of incorporation). This estimate agrees well with the value of 3-7 x 10(24) g C based on the atmospheric abundance of 36Ar and the chondritic C/36Ar (Marty and Jambon, 1987). Several observations suggest that C likely was incorporated into the <span class="hlt">Earth</span>'s core during accretion. (1) Graphite and carbides are commonly present in iron meteorites, and those iron meteorites with Widmanstatten patterns reflecting the slowest cooling rates (mostly Group I and IIIb) contain the highest C abundances. The C abundance-cooling rate correlation is consistent with dissolution of C into Fe-Ni liquids that segregated to form the cores of the iron meteorite parent bodies. (2) The carbon isotopic composition of graphite in iron meteorites exhibits a uniform value of -5% [Deines, P., Wickman, F.E. 1973. The isotopic composition of 'graphitic' carbon from iron meteorites and some remarks on the troilitic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI24A..08W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI24A..08W"><span>The Stability of Hydrous Silicates in <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span>: Experimental constraints from the System MgO-Al2O3-SiO2-H2O</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walter, M. J.; Thomson, A. R.; Wang, W.; Lord, O. T.; Kleppe, A. K.; Ross, J.; Kohn, S. C.</p> <p>2014-12-01</p> <p>Laser-heated diamond anvil cell experiments were performed at pressures from ~ 30 to 125 GPa on bulk compositions in the system MgO-Al2O3-SiO2-H2O (MASH) to constrain the stability of hydrous phases in <span class="hlt">Earth</span>'s lower <span class="hlt">mantle</span>. Phase identification in run products by synchrotron powder diffraction reveals a consistent set of stability relations for the high-pressure, dense hydrous silicate phases D and H. Experiments show that aluminous phase D is stable to ~ 55 GPa. Aluminous phase H becomes stable at ~ 40 GPa and remains stable to higher pressures throughout the lower <span class="hlt">mantle</span> depth range in both model peridotitic and basaltic lithologies. Preliminary FEG-probe analyses indicate that Phase H is alumina-rich at ~ 50 GPa, with only 5 to 10 wt% each of MgO and SiO2. Variations in ambient unit cell volumes show that Mg-perovskite becomes more aluminous with pressure throughout the pressure range studied, and that Phase H may become more Mg- and Si-rich with pressure. We also find that at pressures above ~ 90 GPa stishovite is replaced in Si-rich compositions by seifertite, at which point there is a corresponding increase in the Al-content of phase H. The melting curves of MASH compositions have been determined using thermal perturbations in power versus temperature curves, and are observed to be shallow with dT/dP slopes of ~ 4K/GPa. Our results show that hydrated peridotitic or basaltic compositions in the lower <span class="hlt">mantle</span> should be partially molten at all depths along an adiabatic <span class="hlt">mantle</span> geotherm. Aluminous Phase H will be stable in colder, hydrated subducting slabs, potentially to the core-<span class="hlt">mantle</span> boundary. Thus, aluminous phase H is the primary vessel for transport of hydrogen to the deepest <span class="hlt">mantle</span>, but hydrous silicate melt will be the host of hydrogen at ambient <span class="hlt">mantle</span> temperatures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930064417&hterms=continental+drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcontinental%2Bdrift','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930064417&hterms=continental+drift&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcontinental%2Bdrift"><span>Hotspots and sunspots - Surface tracers of deep <span class="hlt">mantle</span> convection in the <span class="hlt">earth</span> and sun</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stothers, Richard B.</p> <p>1993-01-01</p> <p>The evolution of the hot-spot distribution on <span class="hlt">earth</span> in time and space is investigated using available age data. The statistics of continental flood basalt eruptions suggests the formation of a total of about 40 hot spots worldwide during the Cenozoic and Mesozoic, with no true antipodal pairs found. It was found that hot spots tend to concentrate mainly in mid-latitudes, but the pattern of new appearances of hot spots may migrate from high to low latitudes in both hemispheres in long cycles, and may also drift in longitude, although much more slowly prograde.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PApGe.174..849C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PApGe.174..849C"><span>The Gassmann-Burgers Model to Simulate Seismic Waves at the <span class="hlt">Earth</span> Crust And <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carcione, José M.; Poletto, Flavio; Farina, Biancamaria; Craglietto, Aronne</p> <p>2017-03-01</p> <p>The upper part of the crust shows generally brittle behaviour while deeper zones, including the <span class="hlt">mantle</span>, may present ductile behaviour, depending on the pressure-temperature conditions; moreover, some parts are melted. Seismic waves can be used to detect these conditions on the basis of reflection and transmission events. Basically, from the elastic-plastic point of view the seismic properties (seismic velocity and density) depend on effective pressure and temperature. Confining and pore pressures have opposite effects on these properties, such that very small effective pressures (the presence of overpressured fluids) may substantially decrease the P- and S-wave velocities, mainly the latter, by opening of cracks and weakening of grain contacts. Similarly, high temperatures induce the same effect by partial melting. To model these effects, we consider a poro-viscoelastic model based on Gassmann equations and Burgers mechanical model to represent the properties of the rock frame and describe ductility in which deformation takes place by shear plastic flow. The Burgers elements allow us to model the effects of seismic attenuation, velocity dispersion and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. Effective pressure effects are taken into account in the dry-rock moduli using exponential functions whose parameters are obtained by fitting experimental data as a function of confining pressure. Since fluid effects are important, the density and bulk modulus of the saturating fluids (water and steam) are modeled using the equations provided by the NIST website, including supercritical behaviour. The theory allows us to obtain the phase velocity and quality factor as a function of depth and geological pressure and temperature as well as time frequency. We then obtain the PS and SH</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.479...34F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.479...34F"><span>Organic chemistry in a CO2 rich <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fleury, Benjamin; Carrasco, Nathalie; Millan, Maëva; Vettier, Ludovic; Szopa, Cyril</p> <p>2017-12-01</p> <p>The emergence of life on the <span class="hlt">Earth</span> has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the <span class="hlt">early</span> <span class="hlt">Earth</span> is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the <span class="hlt">early</span> <span class="hlt">Earth</span> where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an <span class="hlt">early</span> atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the <span class="hlt">early</span> <span class="hlt">Earth</span>. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the <span class="hlt">early</span> <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1838702','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1838702"><span>Organic haze on Titan and the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Trainer, Melissa G.; Pavlov, Alexander A.; DeWitt, H. Langley; Jimenez, Jose L.; McKay, Christopher P.; Toon, Owen B.; Tolbert, Margaret A.</p> <p>2006-01-01</p> <p>Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH4/N2 atmosphere. It has been suggested that a similar haze layer may have formed on the <span class="hlt">early</span> <span class="hlt">Earth</span>. Here we report laboratory experiments that demonstrate the properties of haze likely to form through photochemistry on Titan and <span class="hlt">early</span> <span class="hlt">Earth</span>. We have used a deuterium lamp to initiate particle production in these simulated atmospheres from UV photolysis. Using a unique analysis technique, the aerosol mass spectrometer, we have studied the chemical composition, size, and shape of the particles produced as a function of initial trace gas composition. Our results show that the aerosols produced in the laboratory can serve as analogs for the observed haze in Titan's atmosphere. Experiments performed under possible conditions for <span class="hlt">early</span> <span class="hlt">Earth</span> suggest a significant optical depth of haze may have dominated the <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere. Aerosol size measurements are presented, and implications for the haze layer properties are discussed. We estimate that aerosol production on the <span class="hlt">early</span> <span class="hlt">Earth</span> may have been on the order of 1014 g·year−1 and thus could have served as a primary source of organic material to the surface. PMID:17101962</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2084.4005A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2084.4005A"><span>Meteoritic Evidence for Multiple <span class="hlt">Early</span> Enriched Reservoirs in the Martian <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Armytage, R. M. G.; Debaille, V.; Brandon, A. D.; Agee, C. B.</p> <p>2018-05-01</p> <p>From isotopic systematics, the martian crustal reservoir represented by NWA 7034 cannot be the enriched end-member for the shergottites. This suggests multiple enriched reservoirs in the martian <span class="hlt">mantle</span> formed by several differentiation events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2084.4016J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2084.4016J"><span><span class="hlt">Early</span> Episodes of High-Pressure Core Formation Preserved in Plume <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jackson, C. R. M.; Bennett, N. R.; Du, Z.; Cottrell, E.; Fei, Y.</p> <p>2018-05-01</p> <p>New experiments demonstrate that xenon isotopes are sensitive to core formation. This behavior may be crucial in explaining the co-occurrence xenon and tungsten anomalies recently observed in plume <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22129728','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22129728"><span>The oxidation state of Hadean magmas and implications for <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Trail, Dustin; Watson, E Bruce; Tailby, Nicholas D</p> <p>2011-11-30</p> <p>Magmatic outgassing of volatiles from <span class="hlt">Earth</span>'s interior probably played a critical part in determining the composition of the earliest atmosphere, more than 4,000 million years (Myr) ago. Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen and sulphur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure (fugacity) of oxygen. Reduced melts having oxygen fugacities close to that defined by the iron-wüstite buffer would yield volatile species such as CH(4), H(2), H(2)S, NH(3) and CO, whereas melts close to the fayalite-magnetite-quartz buffer would be similar to present-day conditions and would be dominated by H(2)O, CO(2), SO(2) and N(2) (refs 1-4). Direct constraints on the oxidation state of terrestrial magmas before 3,850 Myr before present (that is, the Hadean eon) are tenuous because the rock record is sparse or absent. Samples from this earliest period of <span class="hlt">Earth</span>'s history are limited to igneous detrital zircons that pre-date the known rock record, with ages approaching ∼4,400 Myr (refs 5-8). Here we report a redox-sensitive calibration to determine the oxidation state of Hadean magmatic melts that is based on the incorporation of cerium into zircon crystals. We find that the melts have average oxygen fugacities that are consistent with an oxidation state defined by the fayalite-magnetite-quartz buffer, similar to present-day conditions. Moreover, selected Hadean zircons (having chemical characteristics consistent with crystallization specifically from <span class="hlt">mantle</span>-derived melts) suggest oxygen fugacities similar to those of Archaean and present-day <span class="hlt">mantle</span>-derived lavas as <span class="hlt">early</span> as ∼4,350 Myr before present. These results suggest that outgassing of <span class="hlt">Earth</span>'s interior later than ∼200 Myr into the history of Solar System formation would not have resulted in a reducing atmosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.482..236G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.482..236G"><span>The effect of fluorine on the stability of wadsleyite: Implications for the nature and depths of the transition zone in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grützner, Tobias; Klemme, Stephan; Rohrbach, Arno; Gervasoni, Fernanda; Berndt, Jasper</p> <p>2018-01-01</p> <p>The <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> contains significant amounts of volatile elements, such as hydrogen (H), carbon (C) and the halogens fluorine (F), chlorine (Cl) and bromine (Br) and iodine (I). There is a wealth of knowledge about the global cycling of H and C, but there is only scant data on the concentrations of halogens in different <span class="hlt">Earth</span> reservoirs and on the behavior of halogens during recycling in subduction zones. Here we focus on the storage potential of F in deeper parts of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. The transition zone is a region in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> (410-660 km) known for its high water storage capacity, as the high pressure polymorphs of olivine, wadsleyite and ringwoodite are known to be able to incorporate several per-cent of water. In order to assess potential fractionation between water and F in the transition zone of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>, we set out to investigate the storage capacity of the halogen F in wadsleyite and olivine at transition zone conditions. Experiments were performed in a simplified <span class="hlt">mantle</span> composition at temperatures from 1400 °C to 1900 °C and pressures from 17 up to 21 GPa in a multi anvil apparatus. The results show that F can shift the olivine-wadsleyite transition towards higher pressure. We find that F has an opposing effect to water, the latter of which extends the transition zone towards lower pressure. Moreover, the F storage capacity of wadsleyite is significantly lower than previously anticipated. F concentrations in wadsleyite range from 1470 ± 60 μg/g to 2110 ± 600 μg/g independent of temperature or pressure. The F storage capacity in wadsleyite is even lower than the F storage capacity of forsterite under transition zone conditions, and the latter can incorporate 3930 ± 140 μg/g F under these conditions. Based on our data we find that the transition zone cannot be a reservoir for F as it is assumed to be for water. Furthermore, we argue that during subduction of a volatile-bearing slab, fractionation of water from F will occur</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17483486','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17483486"><span>Dynamical stability of Fe-H in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and core regions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Isaev, Eyvaz I; Skorodumova, Natalia V; Ahuja, Rajeev; Vekilov, Yuri K; Johansson, Börje</p> <p>2007-05-29</p> <p>The core extends from the depth of 2,900 km to the center of the <span class="hlt">Earth</span> and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp --> hcp --> fcc sequence of structural transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1890465','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1890465"><span>Dynamical stability of Fe-H in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and core regions</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Isaev, Eyvaz I.; Skorodumova, Natalia V.; Ahuja, Rajeev; Vekilov, Yuri K.; Johansson, Börje</p> <p>2007-01-01</p> <p>The core extends from the depth of 2,900 km to the center of the <span class="hlt">Earth</span> and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp → hcp → fcc sequence of structural transitions. PMID:17483486</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4818L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4818L"><span><span class="hlt">Early</span> evolution and dynamics of <span class="hlt">Earth</span> from a molten initial stage</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Louro Lourenço, Diogo; Tackley, Paul J.</p> <p>2016-04-01</p> <p>It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On <span class="hlt">Earth</span>, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the <span class="hlt">mantle</span>. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid <span class="hlt">mantle</span>, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We present results for the evolution of an <span class="hlt">Earth</span>-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much slower</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6125L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6125L"><span><span class="hlt">Early</span> evolution and dynamics of <span class="hlt">Earth</span> from a molten initial stage</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lourenço, Diogo; Tackley, Paul</p> <p>2015-04-01</p> <p>It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On <span class="hlt">Earth</span>, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the <span class="hlt">mantle</span>. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid <span class="hlt">mantle</span>, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We will present results for the evolution of an <span class="hlt">Earth</span>-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.P51A3907L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.P51A3907L"><span><span class="hlt">Early</span> evolution and dynamics of <span class="hlt">Earth</span> from a molten initial stage</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Louro Lourenço, D. J.; Tackley, P. J.</p> <p>2014-12-01</p> <p>It is now well established that most of the terrestrial planets underwent a magma ocean stage during their accretion. On <span class="hlt">Earth</span>, it is probable that at the end of accretion, giant impacts like the hypothesised Moon-forming impact, together with other sources of heat, melted a substantial part of the <span class="hlt">mantle</span>. The thermal and chemical evolution of the resulting magma ocean most certainly had dramatic consequences on the history of the planet. Considerable research has been done on magma oceans using simple 1-D models (e.g.: Abe, PEPI 1997; Solomatov, Treat. Geophys. 2007; Elkins-Tanton EPSL 2008). However, some aspects of the dynamics may not be adequately addressed in 1-D and require the use of 2-D or 3-D models. Moreover, new developments in mineral physics that indicate that melt can be denser than solid at high pressures (e.g.: de Koker et al., EPSL 2013) can have very important impacts on the classical views of the solidification of magma oceans (Labrosse et al., Nature 2007). The goal of our study is to understand and characterize the influence of melting on the long-term thermo-chemical evolution of rocky planet interiors, starting from an initial molten state (magma ocean). Our approach is to model viscous creep of the solid <span class="hlt">mantle</span>, while parameterizing processes that involve melt as previously done in 1-D models, including melt-solid separation at all melt fractions, the use of an effective diffusivity to parameterize turbulent mixing, coupling to a parameterized core heat balance and a radiative surface boundary condition. These enhancements have been made to the numerical code StagYY (Tackley, PEPI 2008). We will present results for the evolution of an <span class="hlt">Earth</span>-like planet from a molten initial state to present day, while testing the effect of uncertainties in parameters such as melt-solid density differences, surface heat loss and efficiency of turbulent mixing. Our results show rapid cooling and crystallization until the rheological transition then much</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22518936-water-formation-upper-atmosphere-early-earth','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22518936-water-formation-upper-atmosphere-early-earth"><span>WATER FORMATION IN THE UPPER ATMOSPHERE OF THE <span class="hlt">EARLY</span> <span class="hlt">EARTH</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Fleury, Benjamin; Carrasco, Nathalie; Marcq, Emmanuel</p> <p>2015-07-10</p> <p>The water concentration and distribution in the <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere are important parameters that contribute to the chemistry and the radiative budget of the atmosphere. If the atmosphere above the troposphere is generally considered as dry, photochemistry is known to be responsible for the production of numerous minor species. Here we used an experimental setup to study the production of water in conditions simulating the chemistry above the troposphere of the <span class="hlt">early</span> <span class="hlt">Earth</span> with an atmospheric composition based on three major molecules: N{sub 2}, CO{sub 2}, and H{sub 2}. The formation of gaseous products was monitored using infrared spectroscopy. Watermore » was found as the major product, with approximately 10% of the gas products detected. This important water formation is discussed in the context of the <span class="hlt">early</span> <span class="hlt">Earth</span>.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850024750&hterms=recycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Drecycling','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850024750&hterms=recycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Drecycling"><span>The relation between the age of the subconducting slab and the recycling of sediments into the <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Abbott, D.; Hoffman, S.</p> <p>1985-01-01</p> <p>The recycling of sediments into the <span class="hlt">mantle</span> has become an important issue because recent papers have suggested that the geochemical inverse models of the evolution of radiogenic isotope abundances over the history of the <span class="hlt">Earth</span> have nonunique solutions. Both the recycling of continent-derived sediments into the <span class="hlt">mantle</span> and mixing in the <span class="hlt">mantle</span> could produce similar geochemical effects in the mean isotopic ratios of new igneous material emplaced in continents. Recent models of Archaean heat flow and of plate tectonics during <span class="hlt">early</span> <span class="hlt">Earth</span> history have demonstrated that higher internal heat production of the <span class="hlt">early</span> <span class="hlt">Earth</span> was mainly dissipated through a higher creation rate of oceanic lithosphere. If the seafloor creation rate was higher on the <span class="hlt">early</span> <span class="hlt">Earth</span>, then the residence time of any one piece of oceanic lithosphere on the surface would have been shorter. It is possible that a higher rate of recycling of oceanic lithosphere into the <span class="hlt">mantle</span> could have resulted in some transport of sediment into the <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NatGe..11...55O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NatGe..11...55O"><span>Effects of primitive photosynthesis on <span class="hlt">Earth</span>'s <span class="hlt">early</span> climate system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ozaki, Kazumi; Tajika, Eiichi; Hong, Peng K.; Nakagawa, Yusuke; Reinhard, Christopher T.</p> <p>2018-01-01</p> <p>The evolution of different forms of photosynthetic life has profoundly altered the activity level of the biosphere, radically reshaping the composition of <span class="hlt">Earth</span>'s oceans and atmosphere over time. However, the mechanistic impacts of a primitive photosynthetic biosphere on <span class="hlt">Earth</span>'s <span class="hlt">early</span> atmospheric chemistry and climate are poorly understood. Here, we use a global redox balance model to explore the biogeochemical and climatological effects of different forms of primitive photosynthesis. We find that a hybrid ecosystem of H2-based and Fe2+-based anoxygenic photoautotrophs—organisms that perform photosynthesis without producing oxygen—gives rise to a strong nonlinear amplification of <span class="hlt">Earth</span>'s methane (CH4) cycle, and would thus have represented a critical component of <span class="hlt">Earth</span>'s <span class="hlt">early</span> climate system before the advent of oxygenic photosynthesis. Using a Monte Carlo approach, we find that a hybrid photosynthetic biosphere widens the range of geochemical conditions that allow for warm climate states well beyond either of these metabolic processes acting in isolation. Our results imply that the <span class="hlt">Earth</span>'s <span class="hlt">early</span> climate was governed by a novel and poorly explored set of regulatory feedbacks linking the anoxic biosphere and the coupled H, C and Fe cycles. We suggest that similar processes should be considered when assessing the potential for sustained habitability on <span class="hlt">Earth</span>-like planets with reducing atmospheres.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AsBio..17...27G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AsBio..17...27G"><span>Evolution of <span class="hlt">Earth</span>-like Extrasolar Planetary Atmospheres: Assessing the Atmospheres and Biospheres of <span class="hlt">Early</span> <span class="hlt">Earth</span> Analog Planets with a Coupled Atmosphere Biogeochemical Model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gebauer, S.; Grenfell, J. L.; Stock, J. W.; Lehmann, R.; Godolt, M.; von Paris, P.; Rauer, H.</p> <p>2017-01-01</p> <p>Understanding the evolution of <span class="hlt">Earth</span> and potentially habitable <span class="hlt">Earth</span>-like worlds is essential to fathom our origin in the Universe. The search for <span class="hlt">Earth</span>-like planets in the habitable zone and investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of <span class="hlt">Earth</span> as a reference for <span class="hlt">Earth</span>-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on <span class="hlt">early</span> <span class="hlt">Earth</span>. The Great Oxidation Event in <span class="hlt">Earth</span>'s history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models. In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O2 concentrations are fixed to values inferred by geological evidence. Applying a unique tool (Pathway Analysis Program), ours is the first quantitative analysis of catalytic cycles that governed O2 in <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere near the Great Oxidation Event. Complicated oxidation pathways play a key role in destroying O2, whereas in the upper atmosphere, most O2 is formed abiotically via CO2 photolysis. The O2 bistability found by Goldblatt et al. (2006) is not observed in our calculations likely due to our detailed CH4 oxidation scheme. We calculate increased CH4 with increasing O2 during the Great Oxidation Event. For a given atmospheric surface flux, different atmospheric states are possible; however, the net primary productivity of the biosphere that produces O2 is unique. Mixing, CH4 fluxes, ocean solubility, and <span class="hlt">mantle</span>/crust properties strongly affect net primary productivity and surface O2 fluxes. Regarding exoplanets, different "states" of O2 could exist for similar biomass output. Strong geological activity could lead to false negatives for life (since our analysis suggests that reducing gases remove O2 that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V13E2898G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V13E2898G"><span>Looking Backwards in Time to the <span class="hlt">Early</span> <span class="hlt">Earth</span> Using the Lens of Stable Isotope Geodynamic Cycles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gregory, R. T.</p> <p>2016-12-01</p> <p>The stable isotope ratios of hydrogen, carbon, oxygen and sulfur provide of means of tracing interactions between the major reservoirs of the <span class="hlt">Earth</span>. The oceans and the dichotomy between continental and oceanic crust are key differences between the <span class="hlt">Earth</span> and other terrestrial bodies. The existence of plate tectonics and the recognition that no primary crust survives at the <span class="hlt">Earth</span>'s surface sets this planet apart from the smaller terrestrial bodies. The thermostatic control of carbonate-silicate cycle works because of the hydrosphere and plate tectonics. Additionally, the contrast between the carbon isotope ratios for reduced and oxidized species appear to also be invariant over geologic time with evidence of old recycled carbon in the form of diamond inclusions in <span class="hlt">mantle</span>-derived igneous rocks. Lessons from comparative planetology suggest that <span class="hlt">early</span> differentiation of the <span class="hlt">Earth</span> would have likely resulted in the rapid formation of the oceans, a water world over the primary crust. Plate tectonics provides a mechanism for buffering the oxygen isotope fractionation between the oceans and the <span class="hlt">mantle</span>. The set point for hydrosphere's oxygen isotope composition is a result of the geometry of mid-ocean ridge accretion that is stable over an order magnitude change in spreading rates with time constants much younger shorter than the age of the <span class="hlt">Earth</span>. The recognition that the "normal" ranges for hydrogen isotope ratios of igneous, metamorphic and sedimentary rocks of any age generally overlap with similar ranges, with the exception of rocks that have interacted with D- and 18O-depleted meteoric waters (generally at high latitudes), is an argument for a constant volume ocean over geologic time. Plate tectonics with a constant volume ocean constrains the thickness of the continental crust because of the rapidity of the mechanical weathering cycle (characteristic times of 10's of millions of years; freeboard of the continents argument). In a plate tectonic regime, chemical</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29915073','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29915073"><span>Ab initio spectroscopy and ionic conductivity of water under <span class="hlt">Earth</span> <span class="hlt">mantle</span> conditions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rozsa, Viktor; Pan, Ding; Giberti, Federico; Galli, Giulia</p> <p>2018-06-18</p> <p>The phase diagram of water at extreme conditions plays a critical role in <span class="hlt">Earth</span> and planetary science, yet remains poorly understood. Here we report a first-principles investigation of the liquid at high temperature, between 11 GPa and 20 GPa-a region where numerous controversial results have been reported over the past three decades. Our results are consistent with the recent estimates of the water melting line below 1,000 K and show that on the 1,000-K isotherm the liquid is rapidly dissociating and recombining through a bimolecular mechanism. We found that short-lived ionic species act as charge carriers, giving rise to an ionic conductivity that at 11 GPa and 20 GPa is six and seven orders of magnitude larger, respectively, than at ambient conditions. Conductivity calculations were performed entirely from first principles, with no a priori assumptions on the nature of charge carriers. Despite frequent dissociative events, we observed that hydrogen bonding persists at high pressure, up to at least 20 GPa. Our computed Raman spectra, which are in excellent agreement with experiment, show no distinctive signatures of the hydronium and hydroxide ions present in our simulations. Instead, we found that infrared spectra are sensitive probes of molecular dissociation, exhibiting a broad band below the OH stretching mode ascribable to vibrations of complex ions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820003818','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820003818"><span>Workshop on <span class="hlt">Early</span> Crustal Genesis: Implications from <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Phinney, W. C. (Compiler)</p> <p>1981-01-01</p> <p>Ways to foster increased study of the <span class="hlt">early</span> evolution of the <span class="hlt">Earth</span>, considering the planet as a whole, were explored and recommendations were made to NASA with the intent of exploring optimal ways for integrating Archean studies with problems of planetary evolution. Major themes addressed include: (1) Archean contribution to constraints for modeling planetary evolution; (2) Archean surface conditions and processes as clues to <span class="hlt">early</span> planetary history; and (3) Archean evidence for physical, chemical and isotopic transfer processes in <span class="hlt">early</span> planetary crusts. Ten <span class="hlt">early</span> crustal evolution problems are outlined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatGe..10..400S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatGe..10..400S"><span>Geodynamics: Hot <span class="hlt">mantle</span> rising</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shorttle, Oliver</p> <p>2017-06-01</p> <p>The long-term cooling of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> is recorded in the declining temperature and volume of its volcanic outpourings over time. However, analyses of 89-million-year-old lavas from Costa Rica suggest that extremely hot <span class="hlt">mantle</span> still lurks below.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMDI13A..05G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMDI13A..05G"><span>Linking the geological record for large igneous provinces and hotspots with tomography-based numerical models of thermal convection in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glisovic, P.; Forte, A. M.; Rowley, D. B.; Simmons, N. A.; Grand, S. P.</p> <p>2013-12-01</p> <p>Current tomographic imaging of the 3-D structure in <span class="hlt">Earth</span>'s interior reveals several large-scale anomalies of strongly reduced seismic velocity in the deep lower <span class="hlt">mantle</span>, in particular beneath the Perm region in Western Siberia, the East Pacific Rise, the West Pacific (Caroline Islands), the Southwest Indian Ocean, as well as under Western and Southern Africa. We have carried out <span class="hlt">mantle</span> dynamic simulations (Glisovic et al., GJI 2012) of the evolution of these large-scale structures that directly incorporate robust constraints provided by joint seismic-geodynamic inversions of <span class="hlt">mantle</span> density structure with further constraints provided by mineral physics data (Simmons et al., GJI 2009, JGR 2010). These tomography-based convection simulations also incorporate constraints on <span class="hlt">mantle</span> viscosity inferred by inversion of a suite of convection-related and glacial isostatic adjustment data sets (Mitrovica & Forte, EPSL 2004) and are characterized by <span class="hlt">Earth</span>-like Rayleigh numbers. The convection simulations provide a detailed insight into the very-long-time evolution of the buoyancy of these lower-<span class="hlt">mantle</span> anomalies. We find, in particular, that the buoyancy associated with the 'Perm Anomaly' generates a very long-lived hot upwelling or 'superplume' that is connected to the paleomagnetic location of the Siberian Traps (Smirnov & Tarduno, EPSL 2010) and also to location of North Atlantic Igneous Provinces (i.e., the opening of North Atlantic Ocean). These convection simulations (both backwards and forwards in time) also reveal stable and long-lived plume-like upwellings under the East Pacific Rise, as previously identified by Rowley et al. (AGU 2011, Nature - in review), in particular beneath the Easter & Pitcairn hotspots. Finally we also provide detailed reconstructions of the 65 Myr evolution of the 'Reunion plume' that gave rise to the Deccan Traps.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999JGR...10415439L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999JGR...10415439L"><span>Nucleogenic production of Ne isotopes in <span class="hlt">Earth</span>'s crust and upper <span class="hlt">mantle</span> induced by alpha particles from the decay of U and Th</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leya, Ingo; Wieler, Rainer</p> <p>1999-07-01</p> <p>The production of nucleogenic Ne in terrestrial crust and upper <span class="hlt">mantle</span> by alpha particles from the decay of U and Th was calculated. The calculations are based on stopping powers for the chemical compounds and thin-target cross sections. This approach is more rigorous than earlier studies using thick-target yields for pure elements, since our results are independent of limiting assumptions about stopping-power ratios. Alpha induced reactions account for >99% of the Ne production in the crust and for most of the 20,21Ne in the upper <span class="hlt">mantle</span>. On the other hand, our 22Ne value for the upper <span class="hlt">mantle</span> is a lower limit because the reaction 25Mg(n,α)22Ne is significant in <span class="hlt">mantle</span> material. Production rates calculated here for hypothetical crustal and upper <span class="hlt">mantle</span> material with average major element composition and homogeneously distributed F, U, and Th are up to 100 times higher than data presented by Kyser and Rison [1982] but agree within error limits with the results by Yatsevich and Honda [1997]. Production of nucleogenic Ne in "mean" crust and <span class="hlt">mantle</span> is also given as a function of the weight fractions of O and F. The alpha dose is calculated by radiogenic 4He as well as by the more retentive fissiogenic 136Xe. U and Th is concentrated in certain accessory minerals. Since the ranges of alpha particles from the three decay chains are comparable to mineral dimensions, most nucleogenic Ne is produced in U- and Th-rich minerals. Therefore nucleogenic Ne production in such accessories was also calculated. The calculated correlation between nucleogenic 21Ne and radiogenic 4He agrees well with experimental data for <span class="hlt">Earth</span>'s crust and accessories. Also, the calculated 22Ne/4He ratios as function of the F concentration and the dependence of 21Ne/22Ne from O/F for zircon and apatite agree with measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.474..128K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.474..128K"><span>Calcium isotopic fractionation in <span class="hlt">mantle</span> peridotites by melting and metasomatism and Ca isotope composition of the Bulk Silicate <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kang, Jin-Ting; Ionov, Dmitri A.; Liu, Fang; Zhang, Chen-Lei; Golovin, Alexander V.; Qin, Li-Ping; Zhang, Zhao-Feng; Huang, Fang</p> <p>2017-09-01</p> <p>To better constrain the Ca isotopic composition of the Bulk Silicate <span class="hlt">Earth</span> (BSE) and explore the Ca isotope fractionation in the <span class="hlt">mantle</span>, we determined the Ca isotopic composition of 28 peridotite xenoliths from Mongolia, southern Siberia and the Siberian craton. The samples are divided in three chemical groups: (1) fertile, unmetasomatized lherzolites (3.7-4.7 wt.% Al2O3); (2) moderately melt-depleted peridotites (1.3-3.0 wt.% Al2O3) with no or very limited metasomatism (LREE-depleted cpx); (3) strongly metasomatized peridotites (LREE-enriched cpx and bulk rock) further divided in subgroups 3a (harzburgites, 0.1-1.0% Al2O3) and 3b (fertile lherzolites, 3.9-4.3% Al2O3). In Group 1, δ44/40Ca of fertile spinel and garnet peridotites, which experienced little or no melting and metasomatism, show a limited variation from 0.90 to 0.99‰ (relative to SRM 915a) and an average of 0.94 ± 0.05‰ (2SD, n = 14), which defines the Ca isotopic composition of the BSE. In Group 2, the δ44/40Ca is the highest for three rocks with the lowest Al2O3, i.e. the greatest melt extraction degrees (average 1.06 ± 0.04 ‰, i.e. ∼0.1‰ heavier than the BSE estimate). Simple modeling of modal melting shows that partial melting of the BSE with 103 ln ⁡αperidotite-melt ranging from 0.10 to 0.25 can explain the Group 2 data. By contrast, δ44/40Ca in eight out of nine metasomatized Group 3 peridotites are lower than the BSE estimate. The Group 3a harzburgites show the greatest δ44/40Ca variation range (0.25-0.96‰), with δ44/40Ca positively correlated with CaO and negatively correlated with Ce/Eu. Chemical evidence suggests that the residual, melt-depleted, low-Ca protoliths of the Group 3a harzburgites were metasomatized, likely by carbonate-rich melts/fluids. We argue that such fluids may have low (≤0.25‰) δ44/40Ca either because they contain recycled crustal components or because Ca isotopes, similar to trace elements and their ratios, may be fractionated by kinetic and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10455043','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10455043"><span>Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ishii; Tromp</p> <p>1999-08-20</p> <p>With the use of a large collection of free-oscillation data and additional constraints imposed by the free-air gravity anomaly, lateral variations in shear velocity, compressional velocity, and density within the <span class="hlt">mantle</span>; dynamic topography on the free surface; and topography on the 660-km discontinuity and the core-<span class="hlt">mantle</span> boundary were determined. The velocity models are consistent with existing models based on travel-time and waveform inversions. In the lowermost <span class="hlt">mantle</span>, near the core-<span class="hlt">mantle</span> boundary, denser than average material is found beneath regions of upwellings centered on the Pacific Ocean and Africa that are characterized by slow shear velocities. These anomalies suggest the existence of compositional heterogeneity near the core-<span class="hlt">mantle</span> boundary.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V43D..06Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V43D..06Z"><span><span class="hlt">Mantle</span> Degassing and Atmosphere Evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Y.</p> <p>2011-12-01</p> <p>Noble gas isotopes have provided much of our understanding of <span class="hlt">Earth</span>'s <span class="hlt">early</span> history [1-3]. Various degassing models have been developed, including degassing of the whole <span class="hlt">mantle</span>, degassing of all gases at similar relative rate [1], solubility-controlled degassing [2], and steady-state degassing models [4]. This report will evaluate various degassing models using recent data. For example, helium outgassing flux has been lowered by more than a factor of two based on sophisticated ocean general circulation models [5], which also impacts on the estimated degassing flux of carbon. Years of measurements and progress have allowed isotopic ratios of various <span class="hlt">mantle</span> reservoirs being pieced together [6]. For example, 129Xe/130Xe in OIB <span class="hlt">mantle</span> is found to be lower than that in MORB <span class="hlt">mantle</span> [7]. Missing Xe has been found to be a non-issue [8]. Nucleogenic 21Ne production rate relative radiogenic 4He has been revised [9-10], which leads to an interesting neon paradox that nucleogenic 21Ne production in the whole silicate <span class="hlt">Earth</span> is barely enough to supply nucleogenic 21Ne in air. 40Ar/36Ar ratio in BSE seems to be much lower than any OIB samples, another interesting paradox. Although non-nucleogenic <span class="hlt">mantle</span> neon is solar, nonradiogenic <span class="hlt">mantle</span> argon is atmospheric [11]. For Kr and Xe, the jury is still out. When <span class="hlt">mantle</span> degassing models are evaluated using volatile data of the MORB and OIB, solubility-controlled degassing is able to reconcile more data than other degassing models. On the other hand, the vailable data seem to indicate that atmosphere evolution is more than <span class="hlt">mantle</span> degassing; there may be significant contribution to the atmosphere from impact degassing and other sources. Furthermore, we are now suffering from too many data so that understanding the whole picture is elusive. [1] Allegre et al. (1986/87) EPSL 81, 127-150. [2] Zhang & Zindler (1989) J. Geophys. Res. 94, 13719-13737. [3] Zhang (1998) Geochim. Cosmochim. Acta 62, 3185-3189. [4] Pocelli & Wasserburg (1995</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EPSC...11..625C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EPSC...11..625C"><span>3D climate-carbon modelling of the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Charnay, B.; Le Hir, G.; Fluteau, F.; Forget, F.; Catling, D.</p> <p>2017-09-01</p> <p>We revisit the climate and carbon cycle of the <span class="hlt">early</span> <span class="hlt">Earth</span> at 3.8 Ga using a 3D climate-carbon model. Our resultsfavor cold or temperate climates with global mean temperatures between around 8°C (281 K) and 30°C (303 K) and with 0.1-0.36 bar of CO2 for the late Hadean and <span class="hlt">early</span> Archean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11157025','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11157025"><span>Results of a prospective trial of <span class="hlt">mantle</span> irradiation alone for selected patients with <span class="hlt">early</span>-stage Hodgkin's disease.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Backstrand, K H; Ng, A K; Takvorian, R W; Jones, E L; Fisher, D C; Molnar-Griffin, B J; Silver, B; Tarbell, N J; Mauch, P M</p> <p>2001-02-01</p> <p>To determine the efficacy of <span class="hlt">mantle</span> radiation therapy alone in selected patients with <span class="hlt">early</span>-stage Hodgkin's disease. Between October 1988 and June 2000, 87 selected patients with pathologic stage (PS) IA to IIA or clinical stage (CS) IA Hodgkin's disease were entered onto a single-arm prospective trial of treatment with <span class="hlt">mantle</span> irradiation alone. Eighty-three of 87 patients had > or = 1 year of follow-up after completion of <span class="hlt">mantle</span> irradiation and were included for analysis in this study. Thirty-seven patients had PS IA, 40 had PS IIA, and six had CS IA disease. Histologic distribution was as follows: nodular sclerosis (n = 64), lymphocyte predominant (n = 15), mixed cellularity (n = 3), and unclassified (n = 1). Median follow-up time was 61 months. The 5-year actuarial rates of freedom from treatment failure (FFTF) and overall survival were 86% and 100%, respectively. Eleven of 83 patients relapsed at a median time of 27 months. Nine of the 11 relapses contained at least a component below the diaphragm. All 11 patients who developed recurrent disease were alive without evidence of Hodgkin's disease at the time of last follow-up. The 5-year FFTF in the 43 stage I patients was 92% compared with 78% in the 40 stage II patients (P =.04). Significant differences in FFTF were not seen by histology (P =.26) or by European Organization for Research and Treatment of Cancer H-5F eligibility (P =.25). <span class="hlt">Mantle</span> irradiation alone in selected patients with <span class="hlt">early</span>-stage Hodgkin's disease is associated with disease control rates comparable to those seen with extended field irradiation. The FFTF is especially favorable among stage I patients.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910030599&hterms=Earths+last+life&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DEarths%2Blast%2Blife','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910030599&hterms=Earths+last+life&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DEarths%2Blast%2Blife"><span>The origin and <span class="hlt">early</span> evolution of life on <span class="hlt">earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Oro, J.; Miller, Stanley L.; Lazcano, Antonio</p> <p>1990-01-01</p> <p>Results of the studies that have provided insights into the cosmic and primitive <span class="hlt">earth</span> environments are reviewed with emphasis on those environments in which life is thought to have originated. The evidence bearing on the antiquity of life on the <span class="hlt">earth</span> and the prebiotic significance of organic compounds found in interstellar clouds and in primitive solar-system bodies such as comets, dark asteroids, and carbonaceous chondrites are assessed. The environmental models of the Hadean and <span class="hlt">early</span> Archean <span class="hlt">earth</span> are discussed, as well as the prebiotic formation of organic monomers and polymers essential to life. The processes that may have led to the appearance in the Archean of the first cells are considered, and possible effects of these processes on the <span class="hlt">early</span> steps of biological evolution are analyzed. The significance of these results to the study of the distribution of life in the universe is evaluated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150003797','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150003797"><span><span class="hlt">Early</span> Life on <span class="hlt">Earth</span> and the Search for Extraterrestrial Biosignatures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Oehler, Dorothy Z.; House, Christopher</p> <p>2014-01-01</p> <p>In the last 2 years, scientists within the ARES Directorate at JSC have applied the technology of Secondary Ion Mass Spectrometry (SIMS) to individual organic structures preserved in Archean (approximately 3 billion years old) sediments on <span class="hlt">Earth</span>. These organic structures are among the oldest on <span class="hlt">Earth</span> that may be microfossils - structurally preserved remnants of ancient microbes. The SIMS work was done to determine the microfossils' stable carbon isotopic composition (delta C-13 values). This is the first time that such ancient, potential microfossils have been successfully analyzed for their individual delta C-13 values. The results support the interpretation that these structures are remnants of <span class="hlt">early</span> life on <span class="hlt">Earth</span> and that they may represent planktonic organisms that were widely distributed in the <span class="hlt">Earth</span>'s earliest oceans. This study has been accepted for publication in the journal Geology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16400134','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16400134"><span>Comment on "A hydrogen-rich <span class="hlt">early</span> <span class="hlt">Earth</span> atmosphere".</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Catling, David C</p> <p>2006-01-06</p> <p>Tian et al. (Reports, 13 May 2005, p. 1014) proposed a hydrogen-rich <span class="hlt">early</span> atmosphere with slow hydrogen escape from a cold thermosphere. However, their model neglects the ultraviolet absorption of all gases other than H2. The model also neglects <span class="hlt">Earth</span>'s magnetic field, which affects the temperature and density of ions and promotes nonthermal escape of neutral hydrogen.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tectp.662..434G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tectp.662..434G"><span>A hypothesis for Proterozoic-Phanerozoic supercontinent cyclicity, with implications for <span class="hlt">mantle</span> convection, plate tectonics and <span class="hlt">Earth</span> system evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grenholm, Mikael; Scherstén, Anders</p> <p>2015-11-01</p> <p> relation to <span class="hlt">mantle</span> convection and <span class="hlt">Earth</span> system evolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.448..150P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.448..150P"><span><span class="hlt">Early</span> <span class="hlt">mantle</span> heterogeneities in the Réunion hotspot source inferred from highly siderophile elements in cumulate xenoliths</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peters, Bradley J.; Day, James M. D.; Taylor, Lawrence A.</p> <p>2016-08-01</p> <p> remarkably homogeneous Os, Pb, and noble-gas isotopic signatures of Réunion, which plot near the convergence point of isotopic data for many hotspots, such a conclusion provides evidence for an <span class="hlt">early</span> differentiated and subsequently isolated <span class="hlt">mantle</span> domain that may be partially sampled by some ocean island basalts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24553238','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24553238"><span>The rise of oxygen in <span class="hlt">Earth</span>'s <span class="hlt">early</span> ocean and atmosphere.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lyons, Timothy W; Reinhard, Christopher T; Planavsky, Noah J</p> <p>2014-02-20</p> <p>The rapid increase of carbon dioxide concentration in <span class="hlt">Earth</span>'s modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by <span class="hlt">early</span> biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in <span class="hlt">Earth</span>'s history.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.6241B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.6241B"><span>The mechanism of translational displacements of the core of the <span class="hlt">Earth</span> at inversion molten and solidification of substance at core-<span class="hlt">mantle</span> boundary in opposite hemispheres</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barkin, Yu. V.</p> <p>2009-04-01</p> <p>Shell dynamics. "The <span class="hlt">Earth</span> represents system of non-spherical eccentric shells (the core, the <span class="hlt">mantle</span>, a rigid core etc.) which have various structure and distribution of density. Their moments of inertia and dynamic oblatenesses are various. From the point of view of the mechanics it means, that external celestial bodies (the Moon and the Sun) on miscellaneous (differentially) gravitationally act on the separate shells. They try to cause various accelerations to the centers of masses of shells and various angular accelerations to their rotary motions. It the most external celestial bodies put shells of forced body in difficult state, forcing them to push each other to prevent each other and to struggle with each other. That is between shells there are powerful force interactions: additional forces, and more significant on value, than tidal forces, and the huge moments of forces which all time aspire to turn one of shells relatively to another. The external influence is stronger, the shells are pressed more strongly or taken away. If external action weakens, also shells mutually exist more quietly. External influence depends on position of perturbing celestial bodies. But the last vary cyclically in various time scales. It means, that interactions of shells with each other also are cyclic with the set of frequencies being a derivative from basic frequencies of orbital motions of celestial bodies (coincide with basic frequencies or are their various combinations). Clearly, that the specified mechanical interactions are as though primary which generate then a sequence of every possible interactions of all layers of shells, geodynamic and geophysical processes (which are naturally also cyclic). Elastic layers will test deformations, thus absorbing, and then returning a mechanical energy of translatory - rotary motion of shells and their relative swing. Plastic properties of layers of shells will result in absorption of mechanical energy and to its transformation to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11541323','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11541323"><span>Isotopic constraints on the age and <span class="hlt">early</span> differentiation of the <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McCulloch, M T</p> <p>1996-03-01</p> <p>The <span class="hlt">Earth</span>'s age and <span class="hlt">early</span> differentiation history are re-evaluated using updated isotopic constraints. From the most primitive terrestrial Pb isotopic compositions found at Isua Greenland, and the Pilbara of Western Australia, combined with precise geochronology of these localities, an age 4.49 +/- 0.02 Ga is obtained. This is interpreted as the mean age of core formation as U/Pb is fractionated due to sequestering of Pb into the <span class="hlt">Earth</span>'s core. The long-lived Rb-Sr isotopic system provides constraints on the time interval for the accretion of the <span class="hlt">Earth</span> as Rb underwent significant depletion by volatile loss during accretion of the <span class="hlt">Earth</span> or its precursor planetesimals. A primitive measured 87Sr/86Sr initial ratio of 0.700502 +/- 10 has been obtained for an <span class="hlt">early</span> Archean (3.46 Ga) barite from the Pilbara Block of Western Australia. Using conservative models for the evolution of Rb/Sr in the <span class="hlt">early</span> Archean <span class="hlt">mantle</span> allows an estimate to be placed on the <span class="hlt">Earth</span>'s initial Sr ratio at approximately 4.50 Ga, of 0.69940 +/- 10. This is significantly higher than that measured for the Moon (0.69900 +/- 2) or in the achondrite, Angra dos Reis (0.69894 +/- 2) and for a Rb/Sr ratio of approximately 1/2 of chondrites corresponds to a mean age for accretion of the <span class="hlt">Earth</span> of 4.48 + /- 0.04 Ga. The now extinct 146Sm-142Nd (T1/2(146)=103 l0(6)yrs) combined with the long-lived 147Sm-143Nd isotopic systematics can also be used to provide limits on the time of <span class="hlt">early</span> differentiation of the <span class="hlt">Earth</span>. High precision analyses of the oldest (3.8-3.9 Ga) Archean gneisses from Greenland (Amitsoq and Akilia gneisses), and Canada (Acasta gneiss) do not show measurable (> +/- l0ppm) variations of 142Nd, in contrast to the 33 ppm 142Nd excess reported for an Archean sample. The general lack of 142Nd variations, combined with the presence of highly positive epsilon 143 values (+4.0) at 3.9 Ga, indicates that the record of large-scale Sm/Nd fractionation events was not preserved in the <span class="hlt">early-Earth</span> from 4</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28103105','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28103105"><span>Evolution of <span class="hlt">Earth</span>-like Extrasolar Planetary Atmospheres: Assessing the Atmospheres and Biospheres of <span class="hlt">Early</span> <span class="hlt">Earth</span> Analog Planets with a Coupled Atmosphere Biogeochemical Model.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gebauer, S; Grenfell, J L; Stock, J W; Lehmann, R; Godolt, M; von Paris, P; Rauer, H</p> <p>2017-01-01</p> <p>Understanding the evolution of <span class="hlt">Earth</span> and potentially habitable <span class="hlt">Earth</span>-like worlds is essential to fathom our origin in the Universe. The search for <span class="hlt">Earth</span>-like planets in the habitable zone and investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of <span class="hlt">Earth</span> as a reference for <span class="hlt">Earth</span>-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on <span class="hlt">early</span> <span class="hlt">Earth</span>. The Great Oxidation Event in <span class="hlt">Earth</span>'s history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models. In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O 2 concentrations are fixed to values inferred by geological evidence. Applying a unique tool (Pathway Analysis Program), ours is the first quantitative analysis of catalytic cycles that governed O 2 in <span class="hlt">early</span> <span class="hlt">Earth</span>'s atmosphere near the Great Oxidation Event. Complicated oxidation pathways play a key role in destroying O 2 , whereas in the upper atmosphere, most O 2 is formed abiotically via CO 2 photolysis. The O 2 bistability found by Goldblatt et al. ( 2006 ) is not observed in our calculations likely due to our detailed CH 4 oxidation scheme. We calculate increased CH 4 with increasing O 2 during the Great Oxidation Event. For a given atmospheric surface flux, different atmospheric states are possible; however, the net primary productivity of the biosphere that produces O 2 is unique. Mixing, CH 4 fluxes, ocean solubility, and <span class="hlt">mantle</span>/crust properties strongly affect net primary productivity and surface O 2 fluxes. Regarding exoplanets, different "states" of O 2 could exist for similar biomass output. Strong geological activity could lead to false negatives for life (since our analysis suggests that reducing gases</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.209.1660N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.209.1660N"><span>Secular variations in zonal harmonics of <span class="hlt">Earth</span>'s geopotential and their implications for <span class="hlt">mantle</span> viscosity and Antarctic melting history due to the last deglaciation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakada, Masao; Okuno, Jun'ichi</p> <p>2017-06-01</p> <p>Secular variations in zonal harmonics of <span class="hlt">Earth</span>'s geopotential based on the satellite laser ranging observations, {\\dot{J}_n}, contain important information about the <span class="hlt">Earth</span>'s deformation due to the glacial isostatic adjustment (GIA) and recent melting of glaciers and the Greenland and Antarctic ice sheets. Here, we examine the GIA-induced {\\dot{J}_n}, \\dot{J}_n^{GIA} (2 ≤ n ≤ 6), derived from the available geopotential zonal secular rate and recent melting taken from the IPCC 2013 Report (AR5) to explore the possibility of additional information on the depth-dependent lower-<span class="hlt">mantle</span> viscosity and GIA ice model inferred from the analyses of the \\dot{J}_2^{GIA} and relative sea level changes. The sensitivities of the \\dot{J}_n^{GIA} to lower-<span class="hlt">mantle</span> viscosity and GIA ice model with a global averaged eustatic sea level (ESL) of ∼130 m indicate that the secular rates for n = 3 and 4 are mainly caused by the viscous response of the lower <span class="hlt">mantle</span> to the melting of the Antarctic ice sheet regardless of GIA ice models adopted in this study. Also, the analyses of the \\dot{J}_n^{GIA} based on the available geopotential zonal secular rates indicate that permissible lower-<span class="hlt">mantle</span> viscosity structure satisfying even zonal secular rates of n = 2, 4 and 6 is obtained for the GIA ice model with an Antarctic ESL component of ∼20 or ∼30 m, but there is no viscosity solution satisfying \\dot{J}_3^{GIA} and \\dot{J}_5^{GIA} values. Moreover, the inference model for the lower-<span class="hlt">mantle</span> viscosity and GIA ice model from each odd zonal secular rate is distinctly different from that satisfying GIA-induced even zonal secular rate. The discrepancy between the inference models for the even and odd zonal secular rates may partly be attributed to uncertainties of the geopotential zonal secular rates for n > 2 and particularly those for odd zonal secular rates due to weakness in the orbital geometry. If this problem is overcome at least for the secular rates of n < 5, then the analyses of</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70014931','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70014931"><span>Mineral remains of <span class="hlt">early</span> life on <span class="hlt">Earth</span>? On Mars?</span></a></p> <p><a target="_blank" href=""></a></p> <p>Iberall, Robbins E.; Iberall, A.S.</p> <p>1991-01-01</p> <p>The oldest sedimentary rocks on <span class="hlt">Earth</span>, the 3.8-Ga Isua Iron-Formation in southwestern Greenland, are metamorphosed past the point where organic-walled fossils would remain. Acid residues and thin sections of these rocks reveal ferric microstructures that have filamentous, hollow rod, and spherical shapes not characteristic of crystalline minerals. Instead, they resemble ferric-coated remains of bacteria. Because there are no earlier sedimentary rocks to study on <span class="hlt">Earth</span>, it may be necessary to expand the search elsewhere in the solar system for clues to any biotic precursors or other types of <span class="hlt">early</span> life. A study of morphologies of iron oxide minerals collected in the southern highlands during a Mars sample return mission may therefore help to fill in important gaps in the history of <span class="hlt">Earth</span>'s earliest biosphere. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004IJEaS..93.1025X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004IJEaS..93.1025X"><span><span class="hlt">Early</span> Cretaceous gabbroic complex from Yinan, Shandong Province: petrogenesis and <span class="hlt">mantle</span> domains beneath the North China Craton</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Yi-Gang; Ma, Jin-Long; Huang, Xiao-Long; Iizuka, Yoshiyuki; Chung, Sun-Lin; Wang, Yan-Bin; Wu, Xiang-Yang</p> <p>2004-12-01</p> <p>Sensitive high resolution ion microprobe (SHRIMP) zircon U Pb ages, geochemical and Sr-Nd-Pb isotopic data are reported for the gabbroic complex from Yinan (Shandong Province) with the aims of characterizing the nature of the Mesozoic <span class="hlt">mantle</span> beneath the North China Craton. The Yinan gabbros contain alkali feldspar and biotite, and are characterized by moderate Mg#, high SiO2, low FeO and TiO2 contents and a strong enrichment of light rare <span class="hlt">earth</span> elements [(La/Yb)n=11 50], but no Eu anomaly. They have low Nb/La (0.07 0.29), radiogenic 87Sr/86Sr (0.710) and unradiogenic ɛNd(t) (-15 to -13). These “crustal fingerprints” cannot be attributed to crustal contamination, given the lack of correlation between isotopic ratios and differentiation indices and the unreasonably high proportion of crustal contaminant (>20%) required in modeling. Instead, compositional similarities to contemporaneous basalts from nearby regions imply that the Yinan gabbros were not significantly affected by crystal cumulation. Isotopic data available for the Mesozoic mafic magmas reveal two distinct <span class="hlt">mantle</span> domains beneath Shandong. While the EM1-like domain (with low 87Sr/86Sr) is confined to western Shandong, the <span class="hlt">mantle</span> beneath eastern Shandong is dominated by EM2-type (with high 87Sr/86Sr) affinities. This aerial distinction suggests that the EM2-like signature of the Yinan gabbros may have been inherited from westerly-subducted Yangtze crust during the Triassic North China-South China collision. Emplacement of the Yinan gabbros (127 Ma) is likely affiliated with the widespread and protracted extension during the late Mesozoic in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910069328&hterms=carl+sagan&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcarl%2Bsagan','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910069328&hterms=carl+sagan&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcarl%2Bsagan"><span>Electrical energy sources for organic synthesis on the <span class="hlt">early</span> <span class="hlt">earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chyba, Christopher; Sagan, Carl</p> <p>1991-01-01</p> <p>It is pointed out that much of the contemporary origin-of-life research uses the original estimates of Miller and Urey (1959) for terrestrial energy dissipation by lightning and coronal discharges being equal to 2 x 10 to the 19th J/yr and 6 x 10 to the 19th J/yr, respectively. However, data from experiments that provide analogues to naturally-occurring lightning and coronal discharges indicate that lightning energy yields for organic synthesis (nmole/J) are about one order of magnitude higher than the coronal discharge yields. This suggests that, on <span class="hlt">early</span> <span class="hlt">earth</span>, organic production by lightning may have dominated that due to coronal emission. New values are recommended for lightning and coronal discharge dissipation rates on the <span class="hlt">early</span> <span class="hlt">earth</span>, 1 x 10 to the 18th J/yr and 5 x 10 to the 17th J/yr, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23288536','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23288536"><span>Hydrogen-nitrogen greenhouse warming in <span class="hlt">Earth</span>'s <span class="hlt">early</span> atmosphere.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wordsworth, Robin; Pierrehumbert, Raymond</p> <p>2013-01-04</p> <p>Understanding how <span class="hlt">Earth</span> has sustained surface liquid water throughout its history remains a key challenge, given that the Sun's luminosity was much lower in the past. Here we show that with an atmospheric composition consistent with the most recent constraints, the <span class="hlt">early</span> <span class="hlt">Earth</span> would have been significantly warmed by H(2)-N(2) collision-induced absorption. With two to three times the present-day atmospheric mass of N(2) and a H(2) mixing ratio of 0.1, H(2)-N(2) warming would be sufficient to raise global mean surface temperatures above 0°C under 75% of present-day solar flux, with CO(2) levels only 2 to 25 times the present-day values. Depending on their time of emergence and diversification, <span class="hlt">early</span> methanogens may have caused global cooling via the conversion of H(2) and CO(2) to CH(4), with potentially observable consequences in the geological record.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27870584','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27870584"><span>Follow the Carbon: Isotopic Labeling Studies of <span class="hlt">Early</span> <span class="hlt">Earth</span> Aerosol.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hicks, Raea K; Day, Douglas A; Jimenez, Jose L; Tolbert, Margaret A</p> <p>2016-11-01</p> <p>Despite the faint young Sun, <span class="hlt">early</span> <span class="hlt">Earth</span> might have been kept warm by an atmosphere containing the greenhouse gases CH 4 and CO 2 in mixing ratios higher than those found on <span class="hlt">Earth</span> today. Laboratory and modeling studies suggest that an atmosphere containing these trace gases could lead to the formation of organic aerosol haze due to UV photochemistry. Chemical mechanisms proposed to explain haze formation rely on CH 4 as the source of carbon and treat CO 2 as a source of oxygen only, but this has not previously been verified experimentally. In the present work, we use isotopically labeled precursor gases and unit-mass resolution (UMR) and high-resolution (HR) aerosol mass spectrometry to examine the sources of carbon and oxygen to photochemical aerosol formed in a CH 4 /CO 2 /N 2 atmosphere. UMR results suggest that CH 4 contributes 70-100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO 2 contributes approximately 10% of the total mass to the aerosol as oxygen. These results have implications for the geochemical interpretations of inclusions found in Archean rocks on <span class="hlt">Earth</span> and for the astrobiological potential of other planetary atmospheres. Key Words: Atmosphere-<span class="hlt">Early</span> <span class="hlt">Earth</span>-Planetary atmospheres-Carbon dioxide-Methane. Astrobiology 16, 822-830.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRB..122.8431N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRB..122.8431N"><span>Long-Term Stability of Plate-Like Behavior Caused by Hydrous <span class="hlt">Mantle</span> Convection and Water Absorption in the Deep <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakagawa, Takashi; Iwamori, Hikaru</p> <p>2017-10-01</p> <p>We investigate the cycling of water (regassing, dehydration, and degassing) in <span class="hlt">mantle</span> convection simulations as a function of the strength of the oceanic lithosphere and its influence on the evolution of <span class="hlt">mantle</span> water content. We also consider pseudo-plastic yielding with a friction coefficient for simulating brittle behavior of the plates and the water-weakening effect of <span class="hlt">mantle</span> materials. This model can generate long-term plate-like behavior as a consequence of the water-weakening effect of <span class="hlt">mantle</span> minerals. This finding indicates that water cycling plays an essential role in generating tectonic plates. In vigorous plate motion, the <span class="hlt">mantle</span> water content rapidly increases by up to approximately 4-5 ocean masses, which we define as the "burst" effect. A burst is related to the <span class="hlt">mantle</span> temperature and water solubility in the <span class="hlt">mantle</span> transition zone. When the <span class="hlt">mantle</span> is efficiently cooled down, the <span class="hlt">mantle</span> transition zone can store water transported by the subducted slabs that can pass through the "choke point" of water solubility. The onset of the burst effect is strongly dependent on the friction coefficient. The burst effect of the <span class="hlt">mantle</span> water content could have significantly influenced the evolution of the surface water if the burst started <span class="hlt">early</span>, in which case the <span class="hlt">Earth</span>'s surface cannot preserve the surface water over the age of the <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.B53A1947H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.B53A1947H"><span>Electrochemistry of Prebiotic <span class="hlt">Early</span> <span class="hlt">Earth</span> Hydrothermal Chimney Systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hermis, N.; Barge, L. M.; Chin, K. B.; LeBlanc, G.; Cameron, R.</p> <p>2017-12-01</p> <p>Hydrothermal chimneys are self-organizing chemical garden precipitates generated from geochemical disequilibria within sea-vent environments, and have been proposed as a possible setting for the emergence of life because they contain mineral catalysts and transect ambient pH / Eh / chemical gradients [1]. We simulated the growth of hydrothermal chimneys in <span class="hlt">early</span> <span class="hlt">Earth</span> vent systems by using different hydrothermal simulants such as sodium sulfide (optionally doped with organic molecules) which were injected into an <span class="hlt">early</span> <span class="hlt">Earth</span> ocean simulant containing dissolved ferrous iron, nickel, and bicarbonate [2]. Chimneys on the <span class="hlt">early</span> <span class="hlt">Earth</span> would have constituted flow-through reactors, likely containing Fe/Ni-sulfide catalysts that could have driven proto-metabolic electrochemical reactions. The electrochemical activity of the chimney system was characterized non-invasively by placing electrodes at different locations across the chimney wall and in the ocean to analyze the bulk properties of surface charge potential in the chimney / ocean / hydrothermal fluid system. We performed in-situ characterization of the chimney using electrochemical impedance spectroscopy (EIS) which allowed us to observe the changes in physio-chemical behavior of the system through electrical spectra of capacitance and impedance over a wide range of frequencies during the metal sulfide chimney growth. The electrochemical properties of hydrothermal chimneys in natural systems persist due to the disequilibria maintained between the ocean and hydrothermal fluid. When the injection in our experiment (analogous to fluid flow in a vent) stopped, we observed a corresponding decline in open circuit voltage across the chimney wall, though the impedance of the precipitate remained lor. Further work is needed to characterize the electrochemistry of simulated chimney systems by controlling response factors such as electrode geometry and environmental conditions, in order to simulate electrochemical reactions</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900005420','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900005420"><span>Workshop on the Archean <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ashwal, L. D. (Editor)</p> <p>1989-01-01</p> <p>The Workshop on the Archaen <span class="hlt">mantle</span> considers and discusses evidence for the nature of <span class="hlt">earth</span>'s Archaen <span class="hlt">mantle</span>, including its composition, age and structure, influence on the origin and evolution of <span class="hlt">earth</span>'s crust, and relationship to <span class="hlt">mantle</span> and crustal evolution of the other terrestrial planets. The summaries of presentations and discussions are based on recordings made during the workshop and on notes taken by those who agreed to serve as summarizers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19760059761&hterms=Solar+system+facts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DSolar%2Bsystem%2Bfacts','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19760059761&hterms=Solar+system+facts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DSolar%2Bsystem%2Bfacts"><span>Development of the <span class="hlt">earth</span>-moon system with implications for the geology of the <span class="hlt">early</span> <span class="hlt">earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, J. V.</p> <p>1976-01-01</p> <p>Established facts regarding the basic features of the <span class="hlt">earth</span> and the moon are reviewed, and some important problems involving the moon are discussed (extent of melting, time of crustal differentiation and nature of bombardment, bulk chemical composition, and nature and source of mare basins), with attention given to the various existing theories concerning these problems. Models of the development of the <span class="hlt">earth</span>-moon system from the solar nebula are examined, with particular attention focused on those that use the concept of capture with disintegration. Impact processes in the <span class="hlt">early</span> crust of the <span class="hlt">earth</span> are briefly considered, with attention paid to Green's (1972) suggestion that Archaean greenstone belts may be the terrestrial equivalent of lunar maria.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI21A4272D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI21A4272D"><span>The Fate of Sulfur during Decompression Melting of Peridotite and Crystallization of Basalts - Implications for Sulfur Geochemistry of MORB and the <span class="hlt">Earth</span>'s Upper <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ding, S.; Dasgupta, R.</p> <p>2014-12-01</p> <p>Magmatism in mid-ocean ridges is the main pathway of sulfur (S) from the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> to the surficial reservoir. MORB is generally considered sulfide saturated due to the positive correlation between S and FeOT concentration (e.g., [1]). However, most MORBs are differentiated, and both S content and sulfur concentration at sulfide saturation (SCSS) change with P, T, and magma composition (e.g., [2]). Therefore, it remains uncertain, from the MORB chemistry alone, whether <span class="hlt">mantle</span> melts parental to MORB are sulfide saturated. In this study, we modeled the behavior of S during isentropic partial melting of a fertile peridotite using pMELTS [3] and an SCSS parameterization [4]. Our results show that during decompression melting, at a fixed <span class="hlt">mantle</span> potential temperature, TP (e.g., 1300 °C), SCSS of aggregate melt first slightly increases then decreases at shallower depth with total variation <200 ppm. However, an increase of TP results in a significant increase of SCSS of primitive melts. Our model shows that at 15% melting (F), sulfide in the residue is exhausted for a <span class="hlt">mantle</span> with <200 ppm S. The resulted sulfide-undersaturated partial melts contain <1000 ppm S and are 4-6 times enriched in Cu compared to the source. In order to compare our modeled results directly to the differentiated basalts, isobaric crystallization calculation was performed on 5, 10, and 15% aggregate melts. SCSS changes along liquid line of descent with a decrease in T and increase in FeOT. Comparison of S contents between the model results and MORB glasses [5] reveals that many MORBs derive from sulfide undersaturated melts. Further, for a TP of 1300-1350 °C and F of 10-15 wt.%, reproduction of self-consistent S, and Cu budget of many MORB glasses requires that S of their <span class="hlt">mantle</span> source be ~25-200 ppm. We will discuss the interplay of TP, average F, and the conditions of differentiation to bracket the S geochemistry of MORB and MORB source <span class="hlt">mantle</span> and develop similar systematics for OIBs and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3510B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3510B"><span>Petrogenesis of siliceous high-Mg series rocks as exemplified by the <span class="hlt">Early</span> Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched <span class="hlt">mantle</span> versus crustal contamination</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii</p> <p>2015-04-01</p> <p>The <span class="hlt">Early</span> Paleoproterozoic stage in the <span class="hlt">Earth</span>'s evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of <span class="hlt">mantle</span> melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted <span class="hlt">mantle</span> melts, and by generation from a <span class="hlt">mantle</span> source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11538678','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11538678"><span>The origin and <span class="hlt">early</span> evolution of life on <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Oró, J; Miller, S L; Lazcano, A</p> <p>1990-01-01</p> <p>We do not have a detailed knowledge of the processes that led to the appearance of life on <span class="hlt">Earth</span>. In this review we bring together some of the most important results that have provided insights into the cosmic and primitive <span class="hlt">Earth</span> environments, particularly those environments in which life is thought to have originated. To do so, we first discuss the evidence bearing on the antiquity of life on our planet and the prebiotic significance of organic compounds found in interstellar clouds and in primitive solar system bodies such as comets, dark asteroids, and carbonaceous chondrites. This is followed by a discussion on the environmental models of the Hadean and <span class="hlt">early</span> Archean <span class="hlt">Earth</span>, as well as on the prebiotic formation of organic monomers and polymers essential to life. We then consider the processes that may have led to the appearance in the Archean of the first cells, and how these processes may have affected the <span class="hlt">early</span> steps of biological evolution. Finally, the significance of these results to the study of the distribution of life in the Universe is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V33D2802W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V33D2802W"><span>A new model for <span class="hlt">early</span> <span class="hlt">Earth</span>: heat-pipe cooling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Webb, A. G.; Moore, W. B.</p> <p>2013-12-01</p> <p>In the study of heat transport and lithospheric dynamics of <span class="hlt">early</span> <span class="hlt">Earth</span>, current models depend upon plate tectonic and vertical tectonic concepts. Plate tectonic models adequately account for regions with diverse lithologies juxtaposed along ancient shear zones, as seen at the famous Eoarchean Isua supracrustal belt of West Greenland. Vertical tectonic models to date have involved volcanism, sub- and intra-lithospheric diapirism, and sagduction, and can explain the geology of the best-preserved low-grade ancient terranes, such as the Paleoarchean Barberton and Pilbara greenstone belts. However, these models do not offer a globally-complete framework consistent with the geologic record. Plate tectonics models suggest that paired metamorphic belts and passive margins are among the most likely features to be preserved, but the <span class="hlt">early</span> rock record shows no evidence of these terranes. Existing vertical tectonics models account for the >300 million years of semi-continuous volcanism and diapirism at Barberton and Pilbara, but when they explain the shearing record at Isua, they typically invoke some horizontal motion that cannot be differentiated from plate motion and is not a salient feature of the lengthy Barberton and Pilbara records. Despite the strengths of these models, substantial uncertainty remains about how <span class="hlt">early</span> <span class="hlt">Earth</span> evolved from magma ocean to plate tectonics. We have developed a new model, based on numerical simulations and analysis of the geologic record, that provides a coherent, global geodynamic framework for <span class="hlt">Earth</span>'s evolution from magma ocean to subduction tectonics. We hypothesize that heat-pipe cooling offers a viable mechanism for the lithospheric dynamics of <span class="hlt">early</span> <span class="hlt">Earth</span>. Our numerical simulations of heat-pipe cooling on <span class="hlt">early</span> <span class="hlt">Earth</span> indicate that a cold, thick, single-plate lithosphere developed as a result of frequent volcanic eruptions that advected surface materials downward. The constant resurfacing and downward advection caused compression as the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S21C2442C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S21C2442C"><span>Travel-time Tomography of the Upper <span class="hlt">Mantle</span> using Amphibious Array Seismic Data from the Cascadia Initiative and <span class="hlt">Earth</span>Scope</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cafferky, S.; Schmandt, B.</p> <p>2013-12-01</p> <p>Offshore and onshore broadband seismic data from the Cascadia Initiative and <span class="hlt">Earth</span>Scope provide a unique opportunity to image 3-D <span class="hlt">mantle</span> structure continuously from a spreading ridge across a subduction zone and into continental back-arc provinces. Year one data from the Cascadia Initiative primarily covers the northern half of the Juan de Fuca plate and the Cascadia forearc and arc provinces. These new data are used in concert with previously collected onshore data for a travel-time tomography investigation of <span class="hlt">mantle</span> structure. Measurement of relative teleseismic P travel times for land-based and ocean-bottom stations operating during year one was completed for 16 events using waveform cross-correlation, after bandpass filtering the data from 0.05 - 0.1 Hz with a second order Butterworth filter. Maps of travel-time delays show changing patterns with event azimuth suggesting that structural variations exist beneath the oceanic plate. The data from year one and prior onshore travel time measurements were used in a tomographic inversion for 3-D <span class="hlt">mantle</span> P-velocity structure. Inversions conducted to date use ray paths determined by a 1-D velocity model. By meeting time we plan to present models using ray paths that are iteratively updated to account for 3-D structure. Additionally, we are testing the importance of corrections for sediment and crust thickness on imaging of <span class="hlt">mantle</span> structure near the subduction zone. Low-velocities beneath the Juan de Fuca slab that were previously suggested by onshore data are further supported by our preliminary tomographic inversions using the amphibious array data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V31A4720B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V31A4720B"><span><span class="hlt">Early</span> <span class="hlt">Earth</span> evolution: new insight from Sm and Nd isotopes in meteoritic inclusions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bouvier, A.; Boyet, M.</p> <p>2014-12-01</p> <p>The interpretation of Sm-Nd systematics for the <span class="hlt">early</span> <span class="hlt">Earth</span> relies on knowing the composition of the silicate <span class="hlt">Earth</span> and the 146Sm decay constant. We have measured both 146Sm-142Nd and 147Sm-143Nd internal systematics of four individual Calcium, Aluminum-rich Inclusions (CAIs), the first solids formed in the Solar System [1], from 3 different carbonaceous chondrites from the CV3 group: Allende, Northwest Africa (NWA) 2364 and NWA 6991. Results obtained on NWA 6991 plot on a well-defined mineral and bulk isochron with a Solar System initial 146Sm/144Sm ratio of 0.0070 ±0.0024. This ratio is more consistent with the ratio defined from internal isochrons of differentiated meteorites using the half-life of 103 Ma for 146Sm [2], instead of the value obtained considering the half-life of 68 Ma [3]. On the basis of nucleosynthethic anomalies in Sm and Nd isotopes [4], the ordinary (O) and enstatite (E) chondrites remain potential candidates for the <span class="hlt">Earth</span>'s building blocks. OC have an average deficit of -18±3 ppm relative to modern terrestrial 142Nd/144Nd, whereas EC range from the OC to the terrestrial values [4-6]. Sm stable isotope compositions of the analyzed CAIs indicate that galactic cosmic rays did not affect the 142Nd/144Nd compositions, but deficits are found in the pure p-process 144Sm nuclide (-240 to -290 ppm/ standard). These deficits may translate to 142Nd deficits of a few ppm. NWA 6991 CAI 146Sm-142Nd internal isochron passes through a 142Nd/144Nd ratio of -6 ±6 ppm relative to the terrestrial standard at a chondritic 147Sm/144Nd of 0.1960. We note that this value is identical to the enstatite chondrite average and the 142Nd/144Nd ratio of the lunar <span class="hlt">mantle</span>, as defined recently by [7] using a chondritic Sm/Nd and Lu/Hf for the bulk Moon. While the determination of the Sm-Nd reference parameters for the bulk <span class="hlt">Earth</span> is still contentious, the difference in 142Nd/144Nd between modern terrestrial rocks and meteorites analyzed so far is <10ppm. [1] Bouvier and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011E%26PSL.306..205Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011E%26PSL.306..205Z"><span>Heat fluxes at the <span class="hlt">Earth</span>'s surface and core-<span class="hlt">mantle</span> boundary since Pangea formation and their implications for the geomagnetic superchrons</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Nan; Zhong, Shijie</p> <p>2011-06-01</p> <p>The <span class="hlt">Earth</span>'s surface and core-<span class="hlt">mantle</span> boundary (CMB) heat fluxes are controlled by <span class="hlt">mantle</span> convection and have important influences on <span class="hlt">Earth</span>'s thermal evolution and geodynamo processes in the core. However, the long-term variations of the surface and CMB heat fluxes remain poorly understood, particularly in response to the supercontinent Pangea — likely the most significant global tectonic event in the last 500 Ma. In this study, we reconstruct temporal evolution of the surface and CMB heat fluxes since the Paleozoic by formulating three-dimensional spherical models of <span class="hlt">mantle</span> convection with plate motion history for the last 450 Ma that includes the assembly and break-up of supercontinent Pangea. Our models reproduce well present-day observations of the surface heat flux and seafloor age distribution. Our models show that the present-day CMB heat flux is low below the central Pacific and Africa but high elsewhere due to subducted slabs, particularly when chemically dense piles are present above the CMB. We show that while the surface heat flux may not change significantly in response to Pangea assembly, it increases by ~ 16% from 200 to 120 Ma ago as a result of Pangea breakup and then decreases for the last 120 Ma to approximately the pre-200 Ma value. As consequences of the assembly and breakup of Pangea, equatorial CMB heat flux reaches minimum at ~ 270 Ma and again at ~ 100 Ma ago, while global CMB heat flux is a maximum at ~ 100 Ma ago. These extrema in CMB heat fluxes coincide with the Kiaman (316-262 Ma) and Cretaceous (118-83 Ma) Superchrons, respectively, and may be responsible for the Superchrons.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP41B1297O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP41B1297O"><span>Atmospheric Expression of Seasonality on the <span class="hlt">Early</span> <span class="hlt">Earth</span> and <span class="hlt">Earth</span>-like Exoplanets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Olson, S. L.; Schwieterman, E. W.; Reinhard, C. T.; Ridgwell, A.; Lyons, T. W.</p> <p>2017-12-01</p> <p>Biologically modulated seasonality impacts nearly every chemical constituent of <span class="hlt">Earth</span>'s atmosphere. For example, seasonal shifts in the balance of photosynthesis and respiration manifest as striking oscillation in the atmospheric abundance of CO2 and O2. Similar temporal variability is likely on other inhabited worlds, and seasonality is often regarded as a potential exoplanetary biosignature. Seasonality is a particularly intriguing biosignature because it may allow us to identify life through the abundance of spectrally active gases that are not uniquely biological in origin (e.g., CO2 or CH4). To date, however, the discussion of seasonality as a biosignature has been exclusively qualitative. We lack both quantitative constraints on the likelihood of spectrally detectable seasonality elsewhere and a framework for evaluating potential false positive scenarios (e.g., seasonal CO2 ice sublimation). That is, we do not yet know for which gases, and under which conditions, we could expect to detect seasonality and reliably infer the presence of an active biosphere. The composition of <span class="hlt">Earth</span>'s atmosphere has changed dramatically through time, and consequently, the atmospheric expression of seasonality has necessarily changed throughout <span class="hlt">Earth</span> history as well. Thus, <span class="hlt">Earth</span> offers several case studies for examining the potential for observable seasonality on chemically and tectonically diverse exoplanets. We outline an approach for exploring the history of seasonality on <span class="hlt">Earth</span> via coupled biogeochemical and photochemical models, with particular emphasis on the seasonal cycles of CO2, CH4, and O2/O3. We also discuss the remote detectability of these seasonal signals on directly imaged exoplanets via reflectance and emission spectra. We suggest that seasonality in O2 on the <span class="hlt">early</span> <span class="hlt">Earth</span> was biogeochemically significant—and that seasonal cycles in O3, an indirect biological product coupled to biogenic O2, may be a readily detectable fingerprint of life in the absence of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/1409631-tracking-silica-earth-upper-mantle-using-new-sound-velocity-data-coesite-tracking-silica-earth-upper-mantle','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1409631-tracking-silica-earth-upper-mantle-using-new-sound-velocity-data-coesite-tracking-silica-earth-upper-mantle"><span>Tracking silica in <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> using new sound velocity data for coesite to 5.8 GPa and 1073 K: Tracking Silica in <span class="hlt">Earth</span>'s Upper <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciT</a></p> <p>Chen, Ting; Liebermann, Robert C.; Zou, Yongtao</p> <p></p> <p>The compressional and shear wave velocities for coesite have been measured simultaneously up to 5.8 GPa and 1073 K by ultrasonic interferometry for the first time. The shear wave velocity decreases with pressure along all isotherms. The resulting contrasts between coesite and stishovite reach ~34% and ~45% for P and S wave velocities, respectively, and ~64% and ~75% for their impedance at <span class="hlt">mantle</span> conditions. The large velocity and impedance contrasts across coesite-stishovite transition imply that to generate the velocity and impedance contrasts observed at the X-discontinuity, only a small amount of silica would be required. The velocity jump dependences onmore » silica, d(lnVP)/d(SiO2) = 0.38 (wt %)-1 and d(lnVS)/d(SiO2) = 0.52 (wt %)-1, are utilized to place constraints on the amount of silica in the upper <span class="hlt">mantle</span> and provide a geophysical approach to track <span class="hlt">mantle</span> eclogite materials and ancient subducted oceanic slabs.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.304..230D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.304..230D"><span><span class="hlt">Mantle</span> contribution and tectonic transition in the Aqishan-Yamansu Belt, Eastern Tianshan, NW China: Insights from geochronology and geochemistry of <span class="hlt">Early</span> Carboniferous to <span class="hlt">Early</span> Permian felsic intrusions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Du, Long; Long, Xiaoping; Yuan, Chao; Zhang, Yunying; Huang, Zongying; Wang, Xinyu; Yang, Yueheng</p> <p>2018-04-01</p> <p>Late Paleozoic is a key period for the accretion and collision of the southern Central Asian Orogenic Belt (CAOB). Here, we present new zircon U-Pb ages, whole-rock geochemistry and Sr-Nd isotopic compositions for four Late Paleozoic felsic plutons in Eastern Tianshan (or Tienshan in some literatures) in order to constrain the tectonic evolution of the southern CAOB. The granodioritic pluton and its dioritic enclaves were synchronously formed in the <span class="hlt">Early</span> Carboniferous (336 ± 3 Ma and 335 ± 2 Ma, respectively). These rocks are depleted in Nb, Ta and Ti, and enriched in Rb, Ba, Th and U related to the primitive <span class="hlt">mantle</span>, which show typical features of arc rocks. They both have similar Sr-Nd isotopic ratios to those granitic rocks from the eastern Central Tianshan Block and have the latest Mesoproterozoic two stage Nd model ages (TDM2) (1111-1195 Ma for the granodioritic pluton and 1104-1108 Ma for the enclaves, respectively), indicating that their source magmas may have been derived from the Mesoproterozoic crust. The albitophyric pluton was also emplaced in the <span class="hlt">Early</span> Carboniferous (333 ± 3 Ma). Rocks of this pluton have similar εNd(t) values (-0.69 to -0.37) and TDM2 ages (1135-1161 Ma) to those of the granodioritic rocks, suggest similar crustal source for both types of rocks. In contrast, the K-feldspar granitic and monzonitic plutons were emplaced in the <span class="hlt">Early</span> Permian (292 ± 3 Ma and 281 ± 2 Ma, respectively). Samples of the K-feldspar granitic pluton have high K2O + Na2O, FeO/MgO, Ga/Al, HFSE (e.g., Zr and Hf) and low CaO, Sr and Ba, exhibiting characteristics of A2-type granites, which probably emplaced in a post-collisional extension environment. They have higher εNd(t) values (+2.77 to +3.27) and more juvenile TDM2 ages (799-841 Ma) than the <span class="hlt">Early</span> Carboniferous plutons, suggesting that they were derived from relatively younger crustal sources. The monzonitic granites are metaluminous to weakly peraluminous with A/CNK ranging from 0.93 to 1.05, and have</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1986JGR....91E.291A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986JGR....91E.291A"><span><span class="hlt">Early</span> evolution of the <span class="hlt">Earth</span>: Accretion, atmosphere formation, and thermal history</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abe, Yutaka; Matsui, Takafumi</p> <p>1986-03-01</p> <p>Atmospheric and thermal evolution of the <span class="hlt">earth</span> growing by planetesimal impacts was modeled by taking into account the blanketing effect of an impact-induced H2O atmosphere and the temperature dependence of H2O degassing. When the water content of planetesimals is larger than 0.1% by weight and the accretion time of the <span class="hlt">earth</span> is less than 5 × 107 years, the surface of the accreting <span class="hlt">earth</span> melts and thus a “magma ocean” forms and covers the surface. The formation of a “magma ocean” will result in the initiation of core-<span class="hlt">mantle</span> separation and <span class="hlt">mantle</span> differentiation during accretion. Once a magma ocean is formed, the surface temperature, the degree of melting in the magma ocean, and the mass of the H2O atmosphere are nearly constant as the protoplanet grows further. The final mass of the H2O atmosphere is about 1021 kg, a value which is insensitive to variations in the model parameter values such as the accretion time and the water content of planetesimals. That the final mass of the H2O atmosphere is close to the mass of the present oceans suggests an impact origin for the <span class="hlt">earth</span>'s hydrosphere. On the other hand, most of the H2O retained in planetesimals will be deposited in the solid <span class="hlt">earth</span>. Free water within the proto-<span class="hlt">earth</span> may affect differentiation of the proto-<span class="hlt">mantle</span>, in particular, the <span class="hlt">mantle</span> FeO abundance and the incorporation of a light element in the outer core.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.204.1237N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.204.1237N"><span>Total meltwater volume since the Last Glacial Maximum and viscosity structure of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> inferred from relative sea level changes at Barbados and Bonaparte Gulf and GIA-induced J˙2</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakada, Masao; Okuno, Jun'ichi; Yokoyama, Yusuke</p> <p>2016-02-01</p> <p>Inference of globally averaged eustatic sea level (ESL) rise since the Last Glacial Maximum (LGM) highly depends on the interpretation of relative sea level (RSL) observations at Barbados and Bonaparte Gulf, Australia, which are sensitive to the viscosity structure of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Here we examine the RSL changes at the LGM for Barbados and Bonaparte Gulf ({{RSL}}_{{L}}^{{{Bar}}} and {{RSL}}_{{L}}^{{{Bon}}}), differential RSL for both sites (Δ {{RSL}}_{{L}}^{{{Bar}},{{Bon}}}) and rate of change of degree-two harmonics of <span class="hlt">Earth</span>'s geopotential due to glacial isostatic adjustment (GIA) process (GIA-induced J˙2) to infer the ESL component and viscosity structure of <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Differential RSL, Δ {{RSL}}_{{L}}^{{{Bar}},{{Bon}}} and GIA-induced J˙2 are dominantly sensitive to the lower-<span class="hlt">mantle</span> viscosity, and nearly insensitive to the upper-<span class="hlt">mantle</span> rheological structure and GIA ice models with an ESL component of about (120-130) m. The comparison between the predicted and observationally derived Δ {{RSL}}_{{L}}^{{{Bar}},{{Bon}}} indicates the lower-<span class="hlt">mantle</span> viscosity higher than ˜2 × 1022 Pa s, and the observationally derived GIA-induced J˙2 of -(6.0-6.5) × 10-11 yr-1 indicates two permissible solutions for the lower <span class="hlt">mantle</span>, ˜1022 and (5-10) × 1022 Pa s. That is, the effective lower-<span class="hlt">mantle</span> viscosity inferred from these two observational constraints is (5-10) × 1022 Pa s. The LGM RSL changes at both sites, {{RSL}}_{{L}}^{{{Bar}}} and {{RSL}}_{{L}}^{{{Bon}}}, are also sensitive to the ESL component and upper-<span class="hlt">mantle</span> viscosity as well as the lower-<span class="hlt">mantle</span> viscosity. The permissible upper-<span class="hlt">mantle</span> viscosity increases with decreasing ESL component due to the sensitivity of the LGM sea level at Bonaparte Gulf ({{RSL}}_{{L}}^{{{Bon}}}) to the upper-<span class="hlt">mantle</span> viscosity, and inferred upper-<span class="hlt">mantle</span> viscosity for adopted lithospheric thicknesses of 65 and 100 km is (1-3) × 1020 Pa s for ESL˜130 m and (4-10) × 1020 Pa s for ESL˜125 m. The former solution of (1-3) × 1020</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004ASSL..305..287W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004ASSL..305..287W"><span><span class="hlt">Early</span> Life on <span class="hlt">Earth</span>: the Ancient Fossil Record</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Westall, F.</p> <p>2004-07-01</p> <p>The evidence for <span class="hlt">early</span> life and its initial evolution on <span class="hlt">Earth</span> is lin= ked intimately with the geological evolution of the <span class="hlt">early</span> <span class="hlt">Earth</span>. The environment of the <span class="hlt">early</span> <span class="hlt">Earth</span> would be considered extreme by modern standards: hot (50-80=B0C), volcanically and hydrothermally active, a= noxic, high UV flux, and a high flux of extraterrestrial impacts. Habitats = for life were more limited until continent-building processes resulted in= the formation of stable cratons with wide, shallow, continental platforms= in the Mid-Late Archaean. Unfortunately there are no records of the first appearance of life and the earliest isotopic indications of the exist= ence of organisms fractionating carbon in ~3.8 Ga rocks from the Isua greenst= one belt in Greenland are tenuous. Well-preserved microfossils and micro= bial mats (in the form of tabular and domical stromatolites) occur in 3.5-= 3.3 Ga, <span class="hlt">Early</span> Archaean, sedimentary formations from the Barberton (South Afri= ca) and Pilbara (Australia) greenstone belts. They document life forms that = show a relatively advanced level of evolution. Microfossil morphology inclu= des filamentous, coccoid, rod and vibroid shapes. Colonial microorganism= s formed biofilms and microbial mats at the surfaces of volcaniclastic = and chemical sediments, some of which created (small) macroscopic microbi= alites such as stromatolites. Anoxygenic photosynthesis may already have developed. Carbon, nitrogen and sulphur isotopes ratios are in the r= ange of those for organisms with anaerobic metabolisms, such as methanogenesi= s, sulphate reduction and photosynthesis. Life was apparently distribute= d widely in shallow-water to littoral environments, including exposed, evaporitic basins and regions of hydrothermal activity. Biomass in t= he <span class="hlt">early</span> Archaean was restricted owing to the limited amount of energy t= hat could be produced by anaerobic metabolisms. Microfossils resembling o= xygenic photosynthesisers, such as cyanobacteria, probably first occurred in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010083381&hterms=cyanobacteria+reduction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dcyanobacteria%2Breduction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010083381&hterms=cyanobacteria+reduction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dcyanobacteria%2Breduction"><span>Hydrogen Fluxes from Photosynthetic Communities: Implications for <span class="hlt">Early</span> <span class="hlt">Earth</span> Biogeochemistry</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hoehler, Tori M.; Bebout, Brad M.; DesMarais, David J.; DeVincenzi, Donald L. (Technical Monitor)</p> <p>2000-01-01</p> <p>More than half the history of life on <span class="hlt">Earth</span> was dominated by photosynthetic microbial mats, which must have represented the preeminent biological influence on global geochemical cycling during that time. In modem analogs of then ancient communities, hypersaline microbial mats from Guerrero Negro, Mexico, we have observed a large flux of molecular hydrogen originating in the cyanobacteria-dominated surface layers. Hydrogen production follows a distinct diel pattern and is sensitive to both oxygen tension and microbial species composition within the mat. On an <span class="hlt">early</span> <span class="hlt">Earth</span> dominated by microbial mats, the observed H2 fluxes would scale to global levels far in excess of geothermal emissions. A hydrogen flux of this magnitude represents a profound transmission of reducing power from oxygenic photosynthesis, both to the anaerobic biosphere, where H2 is an almost universally-utilized substrate and regulator of microbial redox chemistry, and to the atmosphere, where subsequent escape to space could provide an important mechanism for the net oxidation of <span class="hlt">Earth</span>'s surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1664678','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1664678"><span>Prebiotic materials from on and off the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bernstein, Max</p> <p>2006-01-01</p> <p>One of the greatest puzzles of all time is how did life arise? It has been universally presumed that life arose in a soup rich in carbon compounds, but from where did these organic molecules come? In this article, I will review proposed terrestrial sources of prebiotic organic molecules, such as Miller–Urey synthesis (including how they would depend on the oxidation state of the atmosphere) and hydrothermal vents and also input from space. While the former is perhaps better known and more commonly taught in school, we now know that comet and asteroid dust deliver tons of organics to the <span class="hlt">Earth</span> every day, therefore this flux of reduced carbon from space probably also played a role in making the <span class="hlt">Earth</span> habitable. We will compare and contrast the types and abundances of organics from on and off the <span class="hlt">Earth</span> given standard assumptions. Perhaps each process provided specific compounds (amino acids, sugars, amphiphiles) that were directly related to the origin or <span class="hlt">early</span> evolution of life. In any case, whether planetary, nebular or interstellar, we will consider how one might attempt to distinguish between abiotic organic molecules from actual signs of life as part of a robotic search for life in the Solar System. PMID:17008210</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17008210','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17008210"><span>Prebiotic materials from on and off the <span class="hlt">early</span> <span class="hlt">Earth</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bernstein, Max</p> <p>2006-10-29</p> <p>One of the greatest puzzles of all time is how did life arise? It has been universally presumed that life arose in a soup rich in carbon compounds, but from where did these organic molecules come? In this article, I will review proposed terrestrial sources of prebiotic organic molecules, such as Miller-Urey synthesis (including how they would depend on the oxidation state of the atmosphere) and hydrothermal vents and also input from space. While the former is perhaps better known and more commonly taught in school, we now know that comet and asteroid dust deliver tons of organics to the <span class="hlt">Earth</span> every day, therefore this flux of reduced carbon from space probably also played a role in making the <span class="hlt">Earth</span> habitable. We will compare and contrast the types and abundances of organics from on and off the <span class="hlt">Earth</span> given standard assumptions. Perhaps each process provided specific compounds (amino acids, sugars, amphiphiles) that were directly related to the origin or <span class="hlt">early</span> evolution of life. In any case, whether planetary, nebular or interstellar, we will consider how one might attempt to distinguish between abiotic organic molecules from actual signs of life as part of a robotic search for life in the Solar System.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI11A2321Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI11A2321Z"><span>Small-scale heterogeneity spectra in the <span class="hlt">Earth</span> <span class="hlt">mantle</span> resolved by PKP-ab,-bc and -df waves</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zheng, Y.</p> <p>2016-12-01</p> <p>Plate tectonics creates heterogeneities at mid ocean ridges and subducts the heterogeneities back to the <span class="hlt">mantle</span> at subduction zones. Heterogeneities manifest themselves by different densities and seismic wave speeds. The length scales and spatial distribution of the heterogeneities measure the mixing mechanism of the plate tectonics. This information can be mathematically captured as the heterogeneity spatial Fourier spectrum. Since most heterogeneities created are on the order of 10s of km, global seismic tomography is not able to resolve them directly. Here, we use seismic P-waves that transmit through the outer core (phases: PKP-ab and PKP-bc) and through the inner core (PKP-df) to probe the lower-<span class="hlt">mantle</span> heterogeneities. The differential traveltimes (PKP-ab versus PKP-df; PKP-bc versus PKP-df) are sensitive to lower <span class="hlt">mantle</span> structures. We have collected more than 10,000 PKP phases recorded by Japan Hi-Net short-period seismic network. We found that the lower <span class="hlt">mantle</span> was filled with seismic heterogeneities from scale 20km to 200km. The heterogeneity spectrum is similar to an exponential distribution but is more enriched in small-scale heterogeneities at the high-wavenumber end. The spectrum is "red" meaning large scales have more power and heterogeneities show a multiscale nature: small-scale heterogeneities are embedded in large-scale heterogeneities. These small-scale heterogeneities cannot be due to thermal origin and they must be compositional. If all these heterogeneities were located in the D" layer, statistically, it would have a root-mean-square P-wave velocity fluctuation of 1% (i.e., -3% to 3%).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA568794','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA568794"><span>A Global 3D P-Velocity Model of the <span class="hlt">Earth</span>’s Crust and <span class="hlt">Mantle</span> for Improved Event Location</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2011-09-01</p> <p>starting model, we use a simplified layer crustal model derived from the NNSA Unified model in Eurasia and Crust 2.0 model everywhere else, over a...geographic and radial dimensions. For our starting model, we use a simplified layer crustal model derived from the NNSA Unified model in Eurasia and...tessellation with 4° triangles to the transition zone and upper <span class="hlt">mantle</span>, and a third tessellation with variable resolution to all crustal layers. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.417...67C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.417...67C"><span>Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for <span class="hlt">early</span> core-<span class="hlt">mantle</span> differentiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cerantola, V.; Walte, N. P.; Rubie, D. C.</p> <p>2015-05-01</p> <p>Deformation-assisted segregation of metallic and sulphidic liquid from a solid peridotitic matrix is a process that may contribute to the <span class="hlt">early</span> differentiation of small planetesimals into a metallic core and a silicate <span class="hlt">mantle</span>. Here we present results of an experimental study using a simplified system consisting of a polycrystalline Fo90-olivine matrix containing a small percentage of iron sulphide and a synthetic primitive MORB melt, in order to investigate whether the silicate melt enhances the interconnection and segregation of FeS liquid under deformation conditions at varying strain rates. The experiments have been performed at 2 GPa, 1450 °C and strain rates between 1 ×10-3s-1 to 1 ×10-5s-1. Our results show that the presence of silicate melt actually hinders the migration and segregation of sulphide liquid by reducing its interconnectivity. At low to moderate strain rates the sulphide liquid pockets preserved a roundish shape, showing the liquid behavior is governed mainly by surface tension rather than by differential stress. Even at the highest strain rates, insignificant FeS segregation and interconnection were observed. On the other hand the basaltic melt was very mobile during deformation, accommodating part of the strain, which led to its segregation from the matrix at high bulk strains leaving the sulphide liquid stranded in the olivine matrix. Hence, we conclude that deformation-induced percolation of sulphide liquid does not contribute to the formation of planetary cores after the silicate solidus is overstepped. A possible <span class="hlt">early</span> deformation enhanced core-<span class="hlt">mantle</span> differentiation after overstepping the Fe-S solidus is not possible between the initial formation of silicate melt and the formation of a widespread magma ocean.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006E%26PSL.250..306L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006E%26PSL.250..306L"><span>Constraints on the coupled thermal evolution of the <span class="hlt">Earth</span>'s core and <span class="hlt">mantle</span>, the age of the inner core, and the origin of the 186Os/188Os “core signal” in plume-derived lavas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lassiter, J. C.</p> <p>2006-10-01</p> <p>The possibility that some <span class="hlt">mantle</span> plumes may carry a geochemical signature of core/<span class="hlt">mantle</span> interaction has rightly generated considerable interest and attention in recent years. Correlated 186Os- 187Os enrichments in some plume-derived lavas (Hawaii, Gorgona, Kostomuksha) have been interpreted as deriving from an outer core with elevated Pt/Os and Re/Os ratios due to the solidification of the <span class="hlt">Earth</span>'s inner core (c.f., [A.D. Brandon, R.J. Walker, The debate over core-<span class="hlt">mantle</span> interaction, <span class="hlt">Earth</span> Planet. Sci. Lett. 232 (2005) 211-225.] and references therein). Conclusive identification of a "core signal" in plume-derived lavas would profoundly influence our understanding of <span class="hlt">mantle</span> convection and evolution. This paper reevaluates the Os-isotope evidence for core/<span class="hlt">mantle</span> interaction by examining other geochemical constraints on core/<span class="hlt">mantle</span> interaction, geophysical constraints on the thermal evolution of the outer core, and geochemical and cosmochemical constraints on the abundance of heat-producing elements in the core. Additional study of metal/silicate and sulfide/silicate partitioning of K, Pb, and other trace elements is needed to more tightly constrain the likely starting composition of the <span class="hlt">Earth</span>'s core. However, available data suggest that the observed 186Os enrichments in Hawaiian and other plume-derived lavas are unlikely to derive from core/<span class="hlt">mantle</span> interaction. 1) Core/<span class="hlt">mantle</span> interaction sufficient to produce the observed 186Os enrichments would likely have significant effects on other tracers such as Pb- and W-isotopes that are not observed. 2) Significant partitioning of K or other heat-producing elements into the core would produce a "core depletion" pattern in the Silicate <span class="hlt">Earth</span> very different from that observed. 3) In the absence of heat-producing elements in the core, core/<span class="hlt">mantle</span> heat flow of ˜ 6-15 TW estimated from several independent geophysical constraints suggests an inner core age (< ˜ 2.5 Ga) too young for the outer core to have developed a significant</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....2691B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....2691B"><span>Life and the solar uv environment on the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bérces, A.; Kovács, G.; Rontó, G.; Lammer, H.; Kargl, G.; Kömle, N.; Bauer, S.</p> <p>2003-04-01</p> <p>The solar UV radiation environment on planetary surfaces and within their atmospheres is of importance in a wide range of scientific disciplines. Solar UV radiation is the driving force of chemical and organic evolution and serves also as a constraint in biological evolution. Studies of the solar UV environment of the <span class="hlt">early</span> <span class="hlt">Earth</span> 2.0 Gyr to 3.8 Gyr ago suggest that the terrestrial atmosphere was essentially anoxic, resulting in an ozone column abundance insufficient for protecting the planetary surface in the UV-B and the UV-C ranges. Since, short wavelength solar UV radiation in the UV-B ind UV-C range penetrated through the unprotected atmosphere to the surface on <span class="hlt">early</span> <span class="hlt">Earth</span>, associated biological consequences may be expected. For DNA-based terrestrial solar UV dosimetry, bacteriophage T7, isolated phage-DNA ind polycrystalline Uracil samples have been used. The effect of solar UV radiation can be measured by detecting the biological-structural consequences of the damage induced by UV photons. We show model calculations for the Biological Effective Dose (BED) rate of Uracil and bacteriophage T7, for various ozone concentrations representing <span class="hlt">early</span> atmospheric conditions on <span class="hlt">Earth</span> up to a UV protecting ozone layer comparable to present times. Further, we discuss experimental data which show the photo-reverse effect of Uracil molecules caused by short UV wavelengths. These photoreversion effect highly depend on the wavelength of the radiation. Shorter wavelength UV radiation of about 200 nm is strongly effective in monomerisation, while the longer wavelengths prefer the production of dimerisation. We could demonstrate experimentally, for the case of an Uracil thin-layer that the photo-reaction process of the nucleotides can be both, dimerization and the reverse process: monomerization. These results are important for the study of solar UV exposure on organisms in the terrestrial environment more than 2 Gyr ago where <span class="hlt">Earth</span> had no UV protecting ozone layer as well as</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V12B..04R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V12B..04R"><span>What do we really know about <span class="hlt">Earth</span>'s <span class="hlt">early</span> crust?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rudnick, R. L.; Tang, M.</p> <p>2016-12-01</p> <p>The oldest minerals on <span class="hlt">Earth</span>, the detrital Hadean Jack Hills zircons from western Australia, show evidence for their crystallization from hydrous, low temperature, granitic magmas. However, considerable debate centers on whether the parental melts are minimum-melt granites formed in subduction zone settings and implying widespread, evolved continental crust (e.g., Harrison, 2009, AREPS), or crystallized from the last differentiates of mafic magmas (Darling et al., 2009, Geology), or even late differentiates of impact melt sheets on a largely water-covered <span class="hlt">Earth</span> (Kenny et al., 2016, Geology). Another means by which to interrogate the nature of <span class="hlt">Earth</span>'s <span class="hlt">early</span> crust is through analyses of ancient fine-grained terrigenous sedimentary rocks such as shales or glacial diamictites, which provide averages of the surface of the <span class="hlt">Earth</span> that is exposed to chemical weathering and erosion. From these studies it has long been known that Archean crust contained a higher proportion of mafic rocks. However, only recently has that proportion been constrained based on a change in the average MgO content of the upper continental crust from 15 wt.% at 3.2 Ga, to 4 wt.% at 2.6 Ga (Tang et al., 2016, Science). These data for terrigeneous sediments require the pre 3.2 Ga crust to be dominated by mafic rocks (only 10-40% `granite' s.l.) and to be high-standing and susceptible to subareal weathering and erosion, implying the mafic crust was thick (see Tang and Rudnick, this meeting). The dramatic transition that occurred in upper crustal composition between 3.2 and 2.6 Ga likely marks the onset of widespread subduction as a means of generating voluminous granite.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMMR23C2423B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMMR23C2423B"><span>Deformation of polyphase aggregates, forsterite+MgO, at pressures and temperatures of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bejina, F.; Bystricky, M.; Ingrin, J.</p> <p>2012-12-01</p> <p>Modelling the solid-state flow of the upper <span class="hlt">mantle</span> requires a thorough understanding of its rheology and therefore necessitates to perform deformation experiments on <span class="hlt">mantle</span> rocks (or analogues) at very high pressures and temperatures. Minerals other than olivine constitute up to 40 vol% of upper <span class="hlt">mantle</span> rocks and may have a significant effect on the rheological behavior of these rocks. Nevertheless, most experimental studies to date have focused on the deformation properties of olivine single crystals or monomineralic olivine aggregates. In this study, and as a first step before focusing on more realistic <span class="hlt">mantle</span>-like compositions, we have performed deformation experiments on polymineralic model aggregates of forsterite and MgO, at upper <span class="hlt">mantle</span> pressures and temperatures. Commercial powders of Mg2SiO4 and MgO were mixed and ground in WC grinders and dried in a one-atmosphere furnace at 1000°C. Powders with different volume proportions of the two phases were sintered by spark plasma sintering (SPS) at temperatures of 1300-1400°C and 100 MPa for a few minutes, resulting in dense pellets 8 mm in diameter and 3-4 mm in length. Microstructural analysis by SEM reveals equilibrated microstructures with forsterite and MgO grain sizes of a few microns. Deformation experiments on samples 1.2 mm in diameter and 1.2 mm in length were performed at 3-8 GPa and 1000-1300°C in a D-DIA apparatus coupled with synchrotron X-ray radiation. The technique permits in situ measurement of macroscopic strain rates as well as stress levels sustained by different subpopulations of grains of each phase. Typically, two specimens, respectively a monomineralic and a polyphase aggregate, were deformed concurrently in order to minimize the relative uncertainties in temperature and pressure and to facilitate the comparison of their rheological properties. The samples were deformed to total strains of 15-25%. As expected, the harder phase, forsterite, sustains much higher stress levels than MgO, in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V13A0375H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V13A0375H"><span>Upper <span class="hlt">mantle</span> fluids evolution, diamond formation, and <span class="hlt">mantle</span> metasomatism</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huang, F.; Sverjensky, D. A.</p> <p>2017-12-01</p> <p>During <span class="hlt">mantle</span> metasomatism, fluid-rock interactions in the <span class="hlt">mantle</span> modify wall-rock compositions. Previous studies usually either investigated mineral compositions in xenoliths and xenocrysts brought up by magmas, or examined fluid compositions preserved in fluid inclusions in diamonds. However, a key study of Panda diamonds analysed both mineral and fluid inclusions in the diamonds [1] which we used to develop a quantitative characterization of <span class="hlt">mantle</span> metasomatic processes. In the present study, we used an extended Deep <span class="hlt">Earth</span> Water model [2] to simulate fluid-rock interactions at upper <span class="hlt">mantle</span> conditions, and examine the fluids and mineral assemblages together simultaneously. Three types of end-member fluids in the Panda diamond fluid inclusions include saline, rich in Na+K+Cl; silicic, rich in Si+Al; and carbonatitic, rich in Ca+Mg+Fe [1, 3]. We used the carbonatitic end-member to represent fluid from a subducting slab reacting with an excess of peridotite + some saline fluid in the host environment. During simultaneous fluid mixing and reaction with the host rock, the logfO2 increased by about 1.6 units, and the pH increased by 0.7 units. The final minerals were olivine, garnet and diamond. The Mg# of olivine decreased from 0.92 to 0.85. Garnet precipitated at an <span class="hlt">early</span> stage, and its Mg# also decreased with reaction progress, in agreement with the solid inclusions in the Panda diamonds. Phlogopite precipitated as an intermediate mineral and then disappeared. The aqueous Ca, Mg, Fe, Si and Al concentrations all increased, while Na, K, and Cl concentrations decreased during the reaction, consistent with trends in the fluid inclusion compositions. Our study demonstrates that fluids coming from subducting slabs could trigger <span class="hlt">mantle</span> metasomatism, influence the compositions of sub-lithospherc cratonic <span class="hlt">mantle</span>, precipitate diamonds, and change the oxygen fugacity and pH of the upper <span class="hlt">mantle</span> fluids. [1] Tomlinson et al. EPSL (2006); [2] Sverjensky, DA et al., GCA (2014</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12460481','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12460481"><span>Zoned <span class="hlt">mantle</span> convection.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Albarède, Francis; Van Der Hilst, Rob D</p> <p>2002-11-15</p> <p>We review the present state of our understanding of <span class="hlt">mantle</span> convection with respect to geochemical and geophysical evidence and we suggest a model for <span class="hlt">mantle</span> convection and its evolution over the <span class="hlt">Earth</span>'s history that can reconcile this evidence. Whole-<span class="hlt">mantle</span> convection, even with material segregated within the D" region just above the core-<span class="hlt">mantle</span> boundary, is incompatible with the budget of argon and helium and with the inventory of heat sources required by the thermal evolution of the <span class="hlt">Earth</span>. We show that the deep-<span class="hlt">mantle</span> composition in lithophilic incompatible elements is inconsistent with the storage of old plates of ordinary oceanic lithosphere, i.e. with the concept of a plate graveyard. Isotopic inventories indicate that the deep-<span class="hlt">mantle</span> composition is not correctly accounted for by continental debris, primitive material or subducted slabs containing normal oceanic crust. Seismological observations have begun to hint at compositional heterogeneity in the bottom 1000 km or so of the <span class="hlt">mantle</span>, but there is no compelling evidence in support of an interface between deep and shallow <span class="hlt">mantle</span> at mid-depth. We suggest that in a system of thermochemical convection, lithospheric plates subduct to a depth that depends - in a complicated fashion - on their composition and thermal structure. The thermal structure of the sinking plates is primarily determined by the direction and rate of convergence, the age of the lithosphere at the trench, the sinking rate and the variation of these parameters over time (i.e. plate-tectonic history) and is not the same for all subduction systems. The sinking rate in the <span class="hlt">mantle</span> is determined by a combination of thermal (negative) and compositional buoyancy and as regards the latter we consider in particular the effect of the loading of plates with basaltic plateaux produced by plume heads. Barren oceanic plates are relatively buoyant and may be recycled preferentially in the shallow <span class="hlt">mantle</span>. Oceanic plateau-laden plates have a more pronounced</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NatGe..11..139A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NatGe..11..139A"><span>Deep and persistent melt layer in the Archaean <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andrault, Denis; Pesce, Giacomo; Manthilake, Geeth; Monteux, Julien; Bolfan-Casanova, Nathalie; Chantel, Julien; Novella, Davide; Guignot, Nicolas; King, Andrew; Itié, Jean-Paul; Hennet, Louis</p> <p>2018-02-01</p> <p>The transition from the Archaean to the Proterozoic eon ended a period of great instability at the <span class="hlt">Earth</span>'s surface. The origin of this transition could be a change in the dynamic regime of the <span class="hlt">Earth</span>'s interior. Here we use laboratory experiments to investigate the solidus of samples representative of the Archaean upper <span class="hlt">mantle</span>. Our two complementary in situ measurements of the melting curve reveal a solidus that is 200-250 K lower than previously reported at depths higher than about 100 km. Such a lower solidus temperature makes partial melting today easier than previously thought, particularly in the presence of volatiles (H2O and CO2). A lower solidus could also account for the <span class="hlt">early</span> high production of melts such as komatiites. For an Archaean <span class="hlt">mantle</span> that was 200-300 K hotter than today, significant melting is expected at depths from 100-150 km to more than 400 km. Thus, a persistent layer of melt may have existed in the Archaean upper <span class="hlt">mantle</span>. This shell of molten material may have progressively disappeared because of secular cooling of the <span class="hlt">mantle</span>. Crystallization would have increased the upper <span class="hlt">mantle</span> viscosity and could have enhanced mechanical coupling between the lithosphere and the asthenosphere. Such a change might explain the transition from surface dynamics dominated by a stagnant lid on the <span class="hlt">early</span> <span class="hlt">Earth</span> to modern-like plate tectonics with deep slab subduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11002893','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11002893"><span>Ultraviolet radiation and the photobiology of <span class="hlt">earth</span>'s <span class="hlt">early</span> oceans.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cockell, C S</p> <p>2000-10-01</p> <p>During the Archean era (3.9-2.5 Ga ago) the <span class="hlt">earth</span> was dominated by an oceanic lithosphere. Thus, understanding how life arose and persisted in the Archean oceans constitutes a major challenge in understanding <span class="hlt">early</span> life on <span class="hlt">earth</span>. Using a radiative transfer model of the late Archean oceans, the photobiological environment of the photic zone and the surface microlayer is explored at the time before the formation of a significant ozone column. DNA damage rates might have been approximately three orders of magnitude higher in the surface layer of the Archean oceans than on the present-day oceans, but at 30 m depth, damage may have been similar to the surface of the present-day oceans. However at this depth the risk of being transported to surface waters in the mixed layer was high. The mixed layer may have been inhabited by a low diversity UV-resistant biota. But it could have been numerically abundant. Repair capabilities similar to Deinococcus radiodurans would be sufficient to survive in the mixed layer. Diversity may have been greater in the region below the mixed layer and above the light compensation point corresponding to today's 'deep chlorophyll maximum'. During much of the Archean the air-water interface was probably an uninhabitable extreme environment for neuston. The habitability of some regions of the photic zone is consistent with the evidence embodied in the geologic record, which suggests an oxygenated upper layer in the Archean oceans. During the <span class="hlt">early</span> Proterozoic, as ozone concentrations increased to a column abundance above 1 x 10(17) cm-2, UV stress would have been reduced and possibly a greater diversity of organisms could have inhabited the mixed layer. However, nutrient upwelling from newly emergent continental crusts may have been more significant in increasing total planktonic abundance in the open oceans and coastal regions than photobiological factors. The phohobiological environment of the Archean oceans has implications for the potential</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040142208&hterms=structure+lipids&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dstructure%2Blipids','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040142208&hterms=structure+lipids&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dstructure%2Blipids"><span>Biomarkers as tracers for life on <span class="hlt">early</span> <span class="hlt">earth</span> and Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Simoneit, B. R.; Summons, R. E.; Jahnke, L. L.</p> <p>1998-01-01</p> <p>Biomarkers in geological samples are products derived from biochemical (natural product) precursors by reductive and oxidative processes (e.g., cholestanes from cholesterol). Generally, lipids, pigments and biomembranes are preserved best over longer geological times and labile compounds such as amino acids, sugars, etc. are useful biomarkers for recent times. Thus, the detailed characterization of biomarker compositions permits the assessment of the major contributing species of extinct and/or extant life. In the case of the <span class="hlt">early</span> <span class="hlt">Earth</span>, work has progressed to elucidate molecular structure and carbon isotropic signals preserved in ancient sedimentary rocks. In addition, the combination of bacterial biochemistry with the organic geochemistry of contemporary and ancient hydrothermal ecosystems permits the modeling of the nature, behavior and preservation potential of primitive microbial communities. This approach uses combined molecular and isotopic analyses to characterize lipids produced by cultured bacteria (representative of ancient strains) and to test a variety of culture conditions which affect their biosynthesis. On considering Mars, the biomarkers from lipids and biopolymers would be expected to be preserved best if life flourished there during its <span class="hlt">early</span> history (3.5-4 x 10(9) yr ago). Both oxidized and reduced products would be expected. This is based on the inferred occurrence of hydrothermal activity during that time with the concomitant preservation of biochemically-derived organic matter. Both known biomarkers (i.e., as elucidated for <span class="hlt">early</span> terrestrial samples and for primitive terrestrial microbiota) and novel, potentially unknown compounds should be characterized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeoRL..45.1330Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeoRL..45.1330Y"><span>Chemical Reactions Between Fe and H2O up to Megabar Pressures and Implications for Water Storage in the <span class="hlt">Earth</span>'s <span class="hlt">Mantle</span> and Core</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yuan, Liang; Ohtani, Eiji; Ikuta, Daijo; Kamada, Seiji; Tsuchiya, Jun; Naohisa, Hirao; Ohishi, Yasuo; Suzuki, Akio</p> <p>2018-02-01</p> <p>We investigated the phase relations of the Fe-H2O system at high pressures based on in situ X-ray diffraction experiments and first-principles calculations and demonstrate that FeH<fi>x</fi> and FeO are present at pressures less than 78 GPa. A recently reported pyrite-structured FeO2 was identified in the Fe-H2O system at pressures greater than 78 GPa after laser heating. The phase observed in this study has a unit cell volume 8%-11% larger than that of FeO2, produced in the Fe-O binary system reported previously, suggesting that hydrogen might be retained in a FeO2H<fi>x</fi> crystal structure. Our observations indicate that H2O is likely introduced into the deep <span class="hlt">Earth</span> through reaction between iron and water during the accretion and separation of the metallic core. Additionally, reaction between Fe and H2O would occur at the core-<span class="hlt">mantle</span> boundary, given water released from hydrous subducting slabs that intersect with the metallic core. Accumulation of volatile-bearing iron compounds may provide new insights into the enigmatic seismic structures observed at the base of the lower <span class="hlt">mantle</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=34063','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=34063"><span><span class="hlt">Mantle</span> dynamics and seismic tomography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tanimoto, Toshiro; Lay, Thorne</p> <p>2000-01-01</p> <p>Three-dimensional imaging of the <span class="hlt">Earth</span>'s interior, called seismic tomography, has achieved breakthrough advances in the last two decades, revealing fundamental geodynamical processes throughout the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and core. Convective circulation of the entire <span class="hlt">mantle</span> is taking place, with subducted oceanic lithosphere sinking into the lower <span class="hlt">mantle</span>, overcoming the resistance to penetration provided by the phase boundary near 650-km depth that separates the upper and lower <span class="hlt">mantle</span>. The boundary layer at the base of the <span class="hlt">mantle</span> has been revealed to have complex structure, involving local stratification, extensive structural anisotropy, and massive regions of partial melt. The <span class="hlt">Earth</span>'s high Rayleigh number convective regime now is recognized to be much more interesting and complex than suggested by textbook cartoons, and continued advances in seismic tomography, geodynamical modeling, and high-pressure–high-temperature mineral physics will be needed to fully quantify the complex dynamics of our planet's interior. PMID:11035784</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatGe..10..788S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatGe..10..788S"><span><span class="hlt">Earth</span>'s <span class="hlt">early</span> O2 cycle suppressed by primitive continents</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smit, Matthijs A.; Mezger, Klaus</p> <p>2017-10-01</p> <p>Free oxygen began to accumulate in <span class="hlt">Earth</span>'s surface environments between 3.0 and 2.4 billion years ago. Links between oxygenation and changes in the composition of continental crust during this time are suspected, but have been difficult to demonstrate. Here we constrain the average composition of the exposed continental crust since 3.7 billion years ago by compiling records of the Cr/U ratio of terrigenous sediments. The resulting record is consistent with a predominantly mafic crust prior to 3.0 billion years ago, followed by a 500- to 700-million-year transition to a crust of modern andesitic composition. Olivine and other Mg-rich minerals in the mafic Archaean crust formed serpentine minerals upon hydration, continuously releasing O2-scavenging agents such as dihydrogen, hydrogen sulfide and methane to the environment. Temporally, the decline in mafic crust capable of such process coincides with the first accumulation of O2 in the oceans, and subsequently the atmosphere. We therefore suggest that <span class="hlt">Earth</span>'s <span class="hlt">early</span> O2 cycle was ultimately limited by the composition of the exposed upper crust, and remained underdeveloped until modern andesitic continents emerged.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900056330&hterms=carl+sagan&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcarl%2Bsagan','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900056330&hterms=carl+sagan&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcarl%2Bsagan"><span>Cometary delivery of organic molecules to the <span class="hlt">early</span> <span class="hlt">earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chyba, Christopher F.; Thomas, Paul J.; Sagan, Carl; Brookshaw, Leigh</p> <p>1990-01-01</p> <p>It has long been speculated that <span class="hlt">earth</span> accreted prebiotic organic molecules important for the origins of life from impacts of carbonaceous asteroids and comets during the period of heavy bombardment 4.5 x 10 to the 9th to 3.8 x 10 to the 9th years ago. A comprehensive treatment of comet-asteroid interaction with the atmosphere, surface impact, and resulting organic pyrolysis demonstrates that organics will not survive impacts at velocities greater than about 10 kilometers per second and that even comets and asteroids as small as 100 meters in radius cannot be aerobraked to below this velocity in 1-bar atmospheres. However, for plausible dense (10-bar carbon dioxide) <span class="hlt">early</span> atmospheres, it is found that 4.5 x 10 to the 9th years ago <span class="hlt">earth</span> was accreting intact cometary organics at a rate of at least about 10 to the 6th to 10 to the 7th kilograms per year, a flux that thereafter declined with a half-life of about 10 to the 8th years. These results may be put in context by comparison with terrestrial oceanic and total biomasses, about 3 x 10 to the 12th kilograms and about 6 x 10 to the 14th kilograms, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4931454','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4931454"><span>Prebiotic Lipidic Amphiphiles and Condensing Agents on the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Fiore, Michele; Strazewski, Peter</p> <p>2016-01-01</p> <p>It is still uncertain how the first minimal cellular systems evolved to the complexity required for life to begin, but it is obvious that the role of amphiphilic compounds in the origin of life is one of huge relevance. Over the last four decades a number of studies have demonstrated how amphiphilic molecules can be synthesized under plausibly prebiotic conditions. The majority of these experiments also gave evidence for the ability of so formed amphiphiles to assemble in closed membranes of vesicles that, in principle, could have compartmented first biological processes on <span class="hlt">early</span> <span class="hlt">Earth</span>, including the emergence of self-replicating systems. For a competitive selection of the best performing molecular replicators to become operative, some kind of bounded units capable of harboring them are indispensable. Without the competition between dynamic populations of different compartments, life itself could not be distinguished from an otherwise disparate array or network of molecular interactions. In this review, we describe experiments that demonstrate how different prebiotically-available building blocks can become precursors of phospholipids that form vesicles. We discuss the experimental conditions that resemble plausibly those of the <span class="hlt">early</span> <span class="hlt">Earth</span> (or elsewhere) and consider the analytical methods that were used to characterize synthetic products. Two brief sections focus on phosphorylating agents, catalysts and coupling agents with particular attention given to their geochemical context. In Section 5, we describe how condensing agents such as cyanamide and urea can promote the abiotic synthesis of phospholipids. We conclude the review by reflecting on future studies of phospholipid compartments, particularly, on evolvable chemical systems that include giant vesicles composed of different lipidic amphiphiles. PMID:27043635</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhDT........99H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhDT........99H"><span>Evolution of the viscosity of <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span>: Grain-boundary sliding and the role of microstructure in olivine deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hansen, Lars N.</p> <p></p> <p>Many features of plate tectonics cannot be explained with standard rheological models of the upper <span class="hlt">mantle</span>. In particular, the localization of deformation at plate boundaries requires the viscosity of the constituent rocks to evolve spatially and temporally. Such rheological complexity may arise from changing microstructural state variables (e.g., grain size and crystallographic-fabric strength), but the degree to which microstructure contributes to the evolution of viscosity is unclear given our current understanding of deformation mechanisms in <span class="hlt">mantle</span> minerals. Dislocation-accommodated grain-boundary sliding (GBS) is a potentially critical mechanism for localizing deformation in olivine because it imparts a sensitivity of the viscosity to the state of the microstructure while simultaneously providing mechanisms for changing the microstructure. However, many details of GBS in olivine are currently unknown including 1) the magnitude of the sensitivity of strain rate to crystallographic fabric and grain size, 2) the strength of the crystallographic fabrics produced, and 3) the anisotropy in viscosity of polycrystalline aggregates. Detailed knowledge of these unknowns is necessary to assess the importance of microstructural evolution in the operation of plate tectonics. This dissertation investigates the details of GBS in olivine through four sets of laboratory-based experiments. In Chapter 2, triaxial compressive creep experiments on aggregates of San Carlos olivine are used to develop a flow law for olivine deforming by GBS. Extrapolations of strain rate to geological conditions using the derived flow law indicate that GBS is the dominant deformation mechanism throughout the uppermost <span class="hlt">mantle</span>. Crystallographic fabrics observed in deformed samples are consistent with upper-<span class="hlt">mantle</span> seismic anisotropy. In Chapter 3, torsion experiments on iron-rich olivine are used to determine the rheological behavior of olivine deforming by GBS at large strains. The sensitivity of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeCoA.232..303V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeCoA.232..303V"><span>Genesis of ultra-high pressure garnet pyroxenites in orogenic peridotites and its bearing on the compositional heterogeneity of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Varas-Reus, María Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Károly</p> <p>2018-07-01</p> <p> degrees of partial melting than sources with higher Mg#. Positive Eu and Sr anomalies in bulk rocks, indicative of their origin from cumulitic crustal gabbros, are preserved mostly in high Mg# pyroxenites due to their higher melting temperatures and consequent lower partial melting degrees. The results of this study show that the genesis of UHP garnet pyroxenites in orogenic peridotites requires a new recipe for the marble cake <span class="hlt">mantle</span> hypothesis, combining significant recycling and stirring of both oceanic and continental lower crust in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. Furthermore, this study establishes a firm connection between the isotopic signatures of UHP pyroxenite heterogeneities in the <span class="hlt">mantle</span> and the continental lower crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMMR22A..07H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMMR22A..07H"><span>Effects of Composition and Iron Spin State on the Structural Transition of (Mg,Fe)CO3 in the <span class="hlt">Earth</span>'s Lower <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsu, H.; Huang, S. C.; Wei, C. M.; Hsing, C. R.</p> <p>2015-12-01</p> <p>Iron-bearing magnesium carbonates (Mg,Fe)CO3 are believed the major carbon carriers in the <span class="hlt">Earth</span>'s deep lower <span class="hlt">mantle</span>; they may play a crucial role in the <span class="hlt">Earth</span>'s deep carbon cycle. Knowledge of the physical and chemical properties of these carbonates is thus essential for our understanding of the <span class="hlt">mantle</span>'s role in global carbon cycle. Experiments have shown that (Mg,Fe)CO3 ferromagnesite (calcite structure) can be stable up to 80-100 GPa. At 45-50 GPa, ferromangsite undergoes a high-spin to low-spin transition, accompanied by a volume reduction and elastic anomalies. Starting ~100 GPa, ferromagnesite goes through a complicated structural transition. The detail of this transition and the atomic structures of high-pressure (Mg,Fe)CO3 phases are still highly debated. Experimental observations and theoretical results are inconsistent so far. In experiments, several distinct high-pressure (Mg,Fe)CO3 structures have been reported, including a P21/c phase [1] and a Pmm2 phase [2]. In theory, a C2/m phase [3] and a P-1 phase [4] have been suggested, while the Pmm2 phase is not found. One possible reason for such a discrepancy is that all available theoretical calculations so far are based on pure MgCO3, while experimental works are performed using (Mg,Fe)CO3 with high iron concentration ( > 50%). Clearly, the concentration of iron and the possible iron spin crossover can significantly affect the stability of these high-pressure (Mg,Fe)CO3 phases. Here, we use density functional theory + self-consistent Hubbard U (DFT+Usc) calculations to study this structural transition. The effects of composition and iron spin state on these (Mg,Fe)CO3 phases are also discussed. Our results can be expected to provide insightful information for better understanding the <span class="hlt">Earth</span>'s deep carbon cycle.[1] E. Boulard et al., Proc. Natl. Acad. Sci. USA 108, 5184 (2011).[2] J. Liu et al., Sci. Rep. 5, 7640 (2015). [3] A. R. Oganov et al., <span class="hlt">Earth</span> Planet. Sci. Lett. 273, 38 (2008). [4] C. J. Pickard and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Natur.533...82C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Natur.533...82C"><span>Chondritic xenon in the Earth’s <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caracausi, Antonio; Avice, Guillaume; Burnard, Peter G.; Füri, Evelyn; Marty, Bernard</p> <p>2016-05-01</p> <p>Noble gas isotopes are powerful tracers of the origins of planetary volatiles, and the accretion and evolution of the <span class="hlt">Earth</span>. The compositions of magmatic gases provide insights into the evolution of the Earth’s <span class="hlt">mantle</span> and atmosphere. Despite recent analytical progress in the study of planetary materials and <span class="hlt">mantle</span>-derived gases, the possible dual origin of the planetary gases in the <span class="hlt">mantle</span> and the atmosphere remains unconstrained. Evidence relating to the relationship between the volatiles within our planet and the potential cosmochemical end-members is scarce. Here we show, using high-precision analysis of magmatic gas from the Eifel volcanic area (in Germany), that the light xenon isotopes identify a chondritic primordial component that differs from the precursor of atmospheric xenon. This is consistent with an asteroidal origin for the volatiles in the Earth’s <span class="hlt">mantle</span>, and indicates that the volatiles in the atmosphere and <span class="hlt">mantle</span> originated from distinct cosmochemical sources. Furthermore, our data are consistent with the origin of Eifel magmatism being a deep <span class="hlt">mantle</span> plume. The corresponding <span class="hlt">mantle</span> source has been isolated from the convective <span class="hlt">mantle</span> since about 4.45 billion years ago, in agreement with models that predict the <span class="hlt">early</span> isolation of <span class="hlt">mantle</span> domains. Xenon isotope systematics support a clear distinction between mid-ocean-ridge and continental or oceanic plume sources, with chemical heterogeneities dating back to the Earth’s accretion. The deep reservoir now sampled by the Eifel gas had a lower volatile/refractory (iodine/plutonium) composition than the shallower <span class="hlt">mantle</span> sampled by mid-ocean-ridge volcanism, highlighting the increasing contribution of volatile-rich material during the first tens of millions of years of terrestrial accretion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930049231&hterms=chemistry+elements&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dchemistry%2Belements','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930049231&hterms=chemistry+elements&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dchemistry%2Belements"><span>Metal-silicate thermochemistry at high temperature - Magma oceans and the 'excess siderophile element' problem of the <span class="hlt">earth</span>'s upper <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Capobianco, Christopher J.; Jones, John H.; Drake, Michael J.</p> <p>1993-01-01</p> <p>Low-temperature metal-silicate partition coefficients are extrapolated to magma ocean temperatures. If the low-temperature chemistry data is found to be applicable at high temperatures, an important assumption, then the results indicate that high temperature alone cannot account for the excess siderophile element problem of the upper <span class="hlt">mantle</span>. For most elements, a rise in temperature will result in a modest increase in siderophile behavior if an iron-wuestite redox buffer is paralleled. However, long-range extrapolation of experimental data is hazardous when the data contains even modest experimental errors. For a given element, extrapolated high-temperature partition coefficients can differ by orders of magnitude, even when data from independent studies is consistent within quoted errors. In order to accurately assess siderophile element behavior in a magma ocean, it will be necessary to obtain direct experimental measurements for at least some of the siderophile elements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMDI21A2263K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMDI21A2263K"><span><span class="hlt">Mantle</span> Plumes and Geologically Recent Volcanism on Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kiefer, W. S.</p> <p>2013-12-01</p> <p>Despite its small size, Mars has remained volcanically active until the geologically recent past. Crater retention ages on the volcanos Arsia Mon, Olympus Mons, and Pavonis Mons indicate significant volcanic activity in the last 100-200 million years. The radiometric ages of many shergottites, a type of igneous martian meteorite, indicate igneous activity at about 180 million years ago. These ages correspond to the most recent 2-4% of the age of the Solar System. The most likely explanation for this young martian volcanism is adiabatic decompression melting in upwelling <span class="hlt">mantle</span> plumes. Multiple plumes may be active at any time, with each of the major volcanos in the Tharsis region being formed by a separate plume. Like at least some terrestrial <span class="hlt">mantle</span> plumes, <span class="hlt">mantle</span> plumes on Mars likely form via an instability of the thermal boundary layer at the base of the <span class="hlt">mantle</span>. Because Mars operates in the stagnant lid convection regime, the temperature difference between <span class="hlt">mantle</span> and core is lower than on <span class="hlt">Earth</span>. This reduces the temperature contrast between <span class="hlt">mantle</span> and core, resulting in <span class="hlt">mantle</span> plumes on Mars that are about 100 K hotter than the average <span class="hlt">mantle</span>. The chemical composition of the martian meteorites indicates that the martian <span class="hlt">mantle</span> is enriched in both iron and sodium relative to <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. This lowers the dry solidus on <span class="hlt">early</span> Mars by 30-40 K relative to <span class="hlt">Earth</span>. Migration of sodium to the crust over time decreases this difference in solidus temperature to about 15 K at present, but that is sufficient to increase the current plume magma production rate by a factor of about 2. Hydrous phases in the martian meteorites indicate the presence of a few hundred ppm water in the <span class="hlt">mantle</span> source region, roughly the same as <span class="hlt">Earth</span>. Finite element simulations of martian plumes using temperature-dependent viscosity and realistic Rayleigh numbers can reproduce the geologically recent magma production rate that is inferred from geologic mapping and the melt fraction inferred from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992Metic..27Q.259M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992Metic..27Q.259M"><span><span class="hlt">Mantle</span> Mineral/Silicate Melt Partitioning</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McFarlane, E. A.; Drake, M. J.</p> <p>1992-07-01</p> <p>Introduction: The partitioning of elements among <span class="hlt">mantle</span> phases and silicate melts is of interest in unraveling the <span class="hlt">early</span> thermal history of the <span class="hlt">Earth</span>. It has been proposed that the elevated Mg/Si ratio of the upper <span class="hlt">mantle</span> of the <span class="hlt">Earth</span> is a consequence of the flotation of olivine into the upper <span class="hlt">mantle</span> (Agee and Walker, 1988). Agee and Walker (1988) have generated a model via mass balance by assuming average mineral compositions to generate upper <span class="hlt">mantle</span> peridotite. This model determines that upper <span class="hlt">mantle</span> peridotite could result from the addition of 32.7% olivine and 0.9% majorite garnet into the upper <span class="hlt">mantle</span>, and subtraction of 27.6% perovskite from the upper <span class="hlt">mantle</span> (Agee and Walker, 1988). The present contribution uses experimental data to examine the consequences of such multiple phase fractionations enabling an independent evaluation of the above mentioned model. Here we use Mg-perovskite/melt partition coefficients from both a synthetic and a natural system (KLB-1) obtained from this laboratory. Also used are partition coefficient values for majorite garnet/melt, beta spinel/melt and olivine/melt partitioning (McFarlane et al., 1991b; McFarlane et al., 1992). Multiple phase fractionations are examined using the equilibrium crystallization equation and partition coefficient values. The mineral proportions determined by Agee and Walker (1988) are converted into weight fractions and used to compute a bulk partition coefficient value. Discussion: There has been a significant debate concerning whether measured values of trace element partition coefficients permit large-scale fractionation of liquidus phases from an <span class="hlt">early</span> terrestrial magma ocean (Kato et al., 1988a,b; Walker and Agee, 1989; Drake, 1989; Drake et al., 1991; McFarlane et al., 1990, 1991). It should be noted that it is unclear which, if any, numerical values of partition coefficients are appropriate for examining this question, and certainly the assumptions for the current model must be more fully</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P52A..07S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P52A..07S"><span>Subduction on Venus and Implications for Volatile Cycling, <span class="hlt">Early</span> <span class="hlt">Earth</span> and Exoplanets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smrekar, S. E.; Davaille, A.; Mueller, N. T.; Dyar, M. D.; Helbert, J.; Barnes, H.</p> <p>2017-12-01</p> <p>Plate tectonics plays a key role in long-term climate evolution by cycling volatiles between the interior, surface and atmosphere. Subduction is a critical process. It is the first step in transitioning between a stagnant and a mobile lid, a means for conveying volatiles into the <span class="hlt">mantle</span>, and a mechanism for creating felsic crust. Laboratory experiments using realistic rheology illuminate the deformation produced by plume-induced subduction (Davaille abstract). Characteristics include internal rifting and volcanism, external rift branches, with a partial arc of subduction creating a trench on the margins of the plume head, and an exterior flexural bulge with small strain extension perpendicular to the trench. These characteristics, along with a consistent gravity signature, occur at the two largest coronae (quasi-circular volcano-tectonic features) on Venus (Davaille et al. Nature Geos. 2017). This interpretation resolves a long-standing debate about the dual plume and subduction characteristics of these features. Numerous coronae also show signs of plume-induced subduction. At Astkhik Planum, subduction appears to have migrated beyond the margins of Selu Corona to create a 1600 km-long, linear subduction zone, along Vaidilute Rupes. The fractures that define Selu Corona merge with the trench to the north and a rift zone to the east, consistent with plume-induced subduction migrating outward from the corona. The lithosphere and crust are much thinner here than in other potential subduction zones. Subduction appears to have generated massive volcanism which could explain the 400 m elevation of the plateau. Within the plateau there are low-viscosity flow sets nearly 1000 km that may be associated with near infrared low emissivity in VIRTIS data. Unusual lava compositions might be indicative of recycling of CO2 or other volatiles into the lithosphere. Little evidence exists to illustrate how plate tectonics initiated on <span class="hlt">Earth</span>, but Venus' high surface temperature makes</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010cosp...38.3548F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010cosp...38.3548F"><span>ISS COLUMBUS laboratory experiment `GeoFlow I and II' -fluid physics research in microgravity environment to study convection phenomena inside deep <span class="hlt">Earth</span> and <span class="hlt">mantle</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Futterer, Birgit; Egbers, Christoph; Chossat, Pascal; Hollerbach, Rainer; Breuer, Doris; Feudel, Fred; Mutabazi, Innocent; Tuckerman, Laurette</p> <p></p> <p>Overall driving mechanism of flow in inner <span class="hlt">Earth</span> is convection in its gravitational buoyancy field. A lot of effort has been involved in theoretical prediction and numerical simulation of both the geodynamo, which is maintained by convection, and <span class="hlt">mantle</span> convection, which is the main cause for plate tectonics. Especially resolution of convective patterns and heat transfer mechanisms has been in focus to reach the real, highly turbulent conditions inside <span class="hlt">Earth</span>. To study specific phenomena experimentally different approaches has been observed, against the background of magneto-hydrodynamic but also on the pure hydrodynamic physics of fluids. With the experiment `GeoFlow' (Geophysical Flow Simulation) instability and transition of convection in spherical shells under the influence of central-symmetry buoyancy force field are traced for a wide range of rotation regimes within the limits between non-rotating and rapid rotating spheres. The special set-up of high voltage potential between inner and outer sphere and use of a dielectric fluid as working fluid induce an electro-hydrodynamic force, which is comparable to gravitational buoyancy force inside <span class="hlt">Earth</span>. To reduce overall gravity in a laboratory this technique requires microgravity conditions. The `GeoFlow I' experiment was accomplished on International Space Station's module COLUM-BUS inside Fluid Science Laboratory FSL und supported by EADS Astrium, Friedrichshafen, User Support und Operations Centre E-USOC in Madrid, Microgravity Advanced Research and Support Centre MARS in Naples, as well as COLUMBUS Control Center COL-CC Munich. Running from August 2008 until January 2009 it delivered 100.000 images from FSL's optical diagnostics module; here more precisely the Wollaston shearing interferometry was used. Here we present the experimental alignment with numerical prediction for the non-rotating and rapid rotation case. The non-rotating case is characterized by a co-existence of several stationary supercritical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1213792B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1213792B"><span>Forced relative displacements of the core and <span class="hlt">mantle</span> as the basic mechanism of secular changes of the <span class="hlt">Earth</span> shape and lithosphere plates tectonics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barkin, Yury</p> <p>2010-05-01</p> <p>The summary. In the work planetary changes of a figure of the <span class="hlt">Earth</span> and geoid in present epoch are discussed. Contrast and asymmetric geodetic changes of northern and southern hemispheres are revealed. The phenomenon of lengthening of latitude circles of a southern hemisphere and shortening of lengths of latitude circles of northern hemisphere, the phenomenon of expansion of a southern hemisphere and, accordingly, compression of northern hemisphere in relation to the center of mass of the <span class="hlt">Earth</span> have been predicted. The reasons of the planetary tendency of displacement (drift) of plates in northern direction are studied. The geodynamic model is developed, on which the basic moving force in tectonics of plates is a gravitational influence of a moveable core of the <span class="hlt">Earth</span> on all layers of the <span class="hlt">mantle</span>, and also on blocks of the crust and lithosphere plates. In a base of all tectonic and geological reorganizations the mechanism of the forced relative oscillations and swings of the core and the <span class="hlt">mantle</span> of the <span class="hlt">Earth</span> in various time scales, including geological timescale lays. 1 Mechanism of formation and changes of the pear-shaped form of the <span class="hlt">Earth</span>. According to developed geodynamic model a pear-shaped form of planets is not their given property for all time (as believed before scientists), and is the dynamic response to the slow forced relative displacements of the core and <span class="hlt">mantle</span> [1]. Than more a relative displacement of the core and <span class="hlt">mantle</span> (eccentricity of the core in some geology epoch), is especially clearly expressed pear-shaped form. The planet Mars possesses a big pear-shaped form and by our estimations the core of this planet is displaced in northern direction (to latitude in approximately 60° N) on 20-25 km [2]. An eccentricity of the <span class="hlt">Earth</span> core is less (estimations give displacement about 3-4 km in direction to Brazil [3]) and it pear-shaped form is much less. 2 The phenomenon of asymmetric lengthening of latitude circles of southern and northern hemispheres of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017liun.book...91P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017liun.book...91P"><span><span class="hlt">Early</span> Stage of Origin of <span class="hlt">Earth</span> (interval after Emergence of Sun, Formation of Liquid Core, Formation of Solid Core)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pechernikova, G. V.; Sergeev, V. N.</p> <p>2017-05-01</p> <p>Gravitational collapse of interstellar molecular cloud fragment has led to the formation of the Sun and its surrounding protoplanetary disk, consisting of 5 × 10^5 dust and gas. The collapse continued (1 years. Age of solar system (about 4.57×10^9 years) determine by age calcium-aluminum inclusions (CAI) which are present at samples of some meteorites (chondrites). Subsidence of dust to the central plane of a protoplanetary disk has led to formation of a dust subdisk which as a result of gravitational instability has broken up to condensations. In the process of collisional evolution they turned into dense planetesimals from which the planets formed. The accounting of a role of large bodies in evolution of a protoplanetary swarm in the field of terrestrial planets has allowed to define times of formation of the massive bodies permitting their <span class="hlt">early</span> differentiation at the expense of short-lived isotopes heating and impacts to the melting temperature of the depths. The total time of <span class="hlt">Earth</span>'s growth is estimated about 10^8 years. Hf geochronometer showed that the core of the <span class="hlt">Earth</span> has existed for Using W about 3×10^7 Hf geohronometer years since the formation of the CAI. Thus data W point to the formation of the <span class="hlt">Earth</span>'s core during its accretion. The paleomagnetic data indicate the existence of <span class="hlt">Earth</span>'s magnetic field past 3.5×10^9 years. But the age of the solid core, estimated by heat flow at the core-<span class="hlt">mantle</span> boundary is 1.7×10^9 (0.5 years). Measurements of the thermal conductivity of liquid iron under the conditions that exist in the <span class="hlt">Earth</span>'s core, indicate the absence of the need for a solid core of existence to support the work geodynamo, although electrical resistivity measurements yield the opposite result.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2084.4041S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2084.4041S"><span>Source Regions for the <span class="hlt">Earth</span>'s Magnetic Field During the First Billion Years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stegman, D. R.; Badro, J.</p> <p>2018-05-01</p> <p><span class="hlt">Earth</span>'s <span class="hlt">early</span> magnetic field places a severe constraint on the thermal evolution of the <span class="hlt">mantle</span> and core. We will present how a dynamo in a basal magma ocean can reconcile major outstanding issues with present models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23803848','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23803848"><span>Stability of active <span class="hlt">mantle</span> upwelling revealed by net characteristics of plate tectonics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Conrad, Clinton P; Steinberger, Bernhard; Torsvik, Trond H</p> <p>2013-06-27</p> <p>Viscous convection within the <span class="hlt">mantle</span> is linked to tectonic plate motions and deforms <span class="hlt">Earth</span>'s surface across wide areas. Such close links between surface geology and deep <span class="hlt">mantle</span> dynamics presumably operated throughout <span class="hlt">Earth</span>'s history, but are difficult to investigate for past times because the history of <span class="hlt">mantle</span> flow is poorly known. Here we show that the time dependence of global-scale <span class="hlt">mantle</span> flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the <span class="hlt">early</span> Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying <span class="hlt">mantle</span> flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of <span class="hlt">mantle</span> upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost <span class="hlt">mantle</span>, which may organize global <span class="hlt">mantle</span> flow as they remain stationary over geologic time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19970025398&hterms=body+need+sleep&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dbody%2Bneed%2Bsleep','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19970025398&hterms=body+need+sleep&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dbody%2Bneed%2Bsleep"><span>Planetary Perspective on Life on <span class="hlt">Early</span> Mars and the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sleep, Norman H.; Zahnle, Kevin</p> <p>1996-01-01</p> <p>Impacts of asteroids and comets posed a major hazard to the continuous existence of <span class="hlt">early</span> life on Mars as on the <span class="hlt">Earth</span>. The chief danger was presented by globally distributed ejecta, which for very large impacts takes the form of transient thick rock vapor atmospheres; both planets suffered such impacts repeatedly. The exposed surface on both planets was sterilized when it was quickly heated to the temperature of condensed rock vapor by radiation and rock rain. Shallow water bodies were quickly evaporated and sterilized. Any surviving life must have been either in deep water or well below the surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2007/1047/srp/srp039/of2007-1047srp039.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2007/1047/srp/srp039/of2007-1047srp039.pdf"><span><span class="hlt">Early</span> Precambrian <span class="hlt">mantle</span> derived rocks in the southern Prince Charles Mountains, East Antarctica: age and isotopic constraints</span></a></p> <p><a target="_blank" href=""></a></p> <p>Mikhalsky, E.V.; Henjes-Kunst, F.; Roland, N.W.</p> <p>2007-01-01</p> <p>Mafic and ultramafic rocks occurring as lenses, boudins, and tectonic slabs within metamorphic units in the southern Mawson Escarpment display <span class="hlt">mantle</span> characteristics of either a highly enriched, or highly depleted nature. Fractionation of these <span class="hlt">mantle</span> rocks from their sources may be as old as Eoarchaean (ca 3850 Ma) while their tectonic emplacement probably occurred prior to 2550 Ma (U-Pb SHRIMP data). These results provide for the first time evidence for Archaean suturing within East Antarctica. Similar upper <span class="hlt">mantle</span> sources are likely present in the northern Mawson Escarpment. A younger age limit of these rocks is 2200 Ma, as indicated by presumably metamorphic zircon ages while their magmatic age may be constrained by single zircon dates at 2450-2250 Ma. The area of the northern Mawson Escarpment is most likely of ensimatic origin and includes mafic rocks which were derived from distinct <span class="hlt">mantle</span> source(s) during Palaeoproterozoic time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA262753','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA262753"><span>Geochemical and Fluid Dynamic Investigations into the Nature of Chemical Heterogeneity in the <span class="hlt">Earth</span>’s <span class="hlt">Mantle</span></span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1992-09-01</p> <p>21 ’ N on the East Pacific Rise . <span class="hlt">Earth</span> Planet. Sci. Lett., 65, 17-33. Newsom, H. E., W. M. White, K. P. Jochum and A. W...peridotites. In addition, abyssal peridotites from the fast-spreading East Pacific Rise have not been analyzed for their trace element compositions. Given...Garcia, and D.W. Muenow (1986) Volatiles in basaltic glasses from the East Pacific Rise at 2 IN: implications for MORB sources and submarine lava</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860013631','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860013631"><span>Komatiite genesis in the Archaean <span class="hlt">mantle</span>, with implications for the tectonics of Archaean greenstone belts</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Elthon, D.</p> <p>1986-01-01</p> <p>The presence of ultramafic lavas (komatiites) associated with Archean greenstone belts has been suggested to indicate very high increments (50-80%) of partial melting of the Archean <span class="hlt">mantle</span>. Such extensive melting of the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> during the Archean might have profound effects on the <span class="hlt">early</span> tectonic and chemical evolution of the planet, although problems associated with keeping the komatiite liquid in equilibrium with the residual <span class="hlt">mantle</span> at such high increments of melting has cast doubt upon aspects of extensive melting. Two important aspects of the origin of komatiites are discussed below.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T13D0550S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T13D0550S"><span>Evolution of Plate Tectonics on <span class="hlt">Earth</span> since the Mid-Mesoarchean was Controlled by Sedimentary Fluxes from Continents to Oceans and <span class="hlt">Mantle</span> Temperature</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sobolev, S. V.; Brown, M.</p> <p>2017-12-01</p> <p> <span class="hlt">Earth</span> since the mid-Mesoarchean (the so-called `supercontinent cycle') can be interpreted in terms of the balance of power between PT, driven by slab pull and controlled by the temperature of the upper <span class="hlt">mantle</span>, and the efficiency of lubrication in the subduction zones, controlled by accumulation of continental sediment in the trenches.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70017502','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70017502"><span>Rare <span class="hlt">earth</span> element contents and multiple <span class="hlt">mantle</span> sources of the transform-related Mount Edgecumbe basalts, southeastern Alaska</span></a></p> <p><a target="_blank" href=""></a></p> <p>Riehle, J.R.; Budahn, J.R.; Lanphere, M.A.; Brew, D.A.</p> <p>1994-01-01</p> <p>Pleistocene basalt of the Mount Edgecumbe volcanic field (MEF) is subdivided into a plagioclase type and an olivine type. Th/La ratios of plagioclase basalt are similar to those of mid-ocean-ridge basalt (MORB), whereas those of olivine basalt are of continental affinity. Rare <span class="hlt">earth</span> element (REE) contents of the olivine basalt, which resemble those of transitional MORB, are modelled by 10-15% partial melting of fertile spinel-plagioclase lherzolite followed by removal of 8-13% olivine. It is concluded that olivine basalt originated in subcontinental spinel lherzolite and that plagioclase basalt may have originated in suboceanic lithosphere of the Pacific plate. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T41E..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T41E..02S"><span>Tracking the Progress of <span class="hlt">Earth</span>Scope/USArray: The crust and upper <span class="hlt">mantle</span> beneath the transition region between tectonic western US and cratonic eastern US</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shen, W.; Lin, F.; Ritzwoller, M. H.</p> <p>2010-12-01</p> <p>The transition region between the tectonic western US and the cratonic eastern US contains numerous significant geological regions (e.g., the Rocky Mountains, the Colorado Plateau, and the Rio Grande Rift), and also, unknowns (e.g, the location or extent of the east-west US dichotomy, the compensation of the high topography of the western Great Plains, the extensional mechanics of the Rio Grande Rift, and the structure of the <span class="hlt">mantle</span> beneath the Colorado Plateau). The answers to these questions and others are critical to an understanding of the tectonics and tectonic history of this region and its impact on the cratonic eastern US. The recent deployments of seismic stations, particularly the <span class="hlt">Earth</span>Scope USArray Transportable Array (TA), provide an opportunity to construct a detailed 3-D structural model of the crust and upper <span class="hlt">mantle</span> beneath this transition region, and thus allow us to address some of the questions listed above. We present results from ambient noise tomography (ANT) and teleseismic earthquake tomography by using data from TA stations within the western and central US. We processed continuous seismic noise data from ~600 TA stations from August 2008 to March 2010, which after data selection produces a data set with ~100,000 inter-station paths. Rayleigh wave phase speed maps between 6 and 40 sec period and Love wave phase speed maps between 8 and 30 sec with a resolution of ~60 km are constructed using eikonal tomography. In addition, we applied eikonal tomography (ET) to about 300 teleseismic earthquakes to obtain long-period (30 - 100 sec) Rayleigh wave phase speed maps and Love wave phase speeds maps (30 - 60 sec). By jointly inverting Rayleigh and Love phase speeds maps from ANT and earthquake tomography, we constructed a 3-D isotropic and radially anisotropic shear velocity model of the crust and upper <span class="hlt">mantle</span> to ~150 km depth together with model uncertainties constrained by a Monte-Carlo inversion. The 3-D isotropic model reveals a variety of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Natur.542..340J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Natur.542..340J"><span>Primordial helium entrained by the hottest <span class="hlt">mantle</span> plumes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jackson, M. G.; Konter, J. G.; Becker, T. W.</p> <p>2017-02-01</p> <p>Helium isotopes provide an important tool for tracing <span class="hlt">early-Earth</span>, primordial reservoirs that have survived in the planet’s interior. Volcanic hotspot lavas, like those erupted at Hawaii and Iceland, can host rare, high 3He/4He isotopic ratios (up to 50 times the present atmospheric ratio, Ra) compared to the lower 3He/4He ratios identified in mid-ocean-ridge basalts that form by melting the upper <span class="hlt">mantle</span> (about 8Ra; ref. 5). A long-standing hypothesis maintains that the high-3He/4He domain resides in the deep <span class="hlt">mantle</span>, beneath the upper <span class="hlt">mantle</span> sampled by mid-ocean-ridge basalts, and that buoyantly upwelling plumes from the deep <span class="hlt">mantle</span> transport high-3He/4He material to the shallow <span class="hlt">mantle</span> beneath plume-fed hotspots. One problem with this hypothesis is that, while some hotspots have 3He/4He values ranging from low to high, other hotspots exhibit only low 3He/4He ratios. Here we show that, among hotspots suggested to overlie <span class="hlt">mantle</span> plumes, those with the highest maximum 3He/4He ratios have high hotspot buoyancy fluxes and overlie regions with seismic low-velocity anomalies in the upper <span class="hlt">mantle</span>, unlike plume-fed hotspots with only low maximum 3He/4He ratios. We interpret the relationships between 3He/4He values, hotspot buoyancy flux, and upper-<span class="hlt">mantle</span> shear wave velocity to mean that hot plumes—which exhibit seismic low-velocity anomalies at depths of 200 kilometres—are more buoyant and entrain both high-3He/4He and low-3He/4He material. In contrast, cooler, less buoyant plumes do not entrain this high-3He/4He material. This can be explained if the high-3He/4He domain is denser than low-3He/4He <span class="hlt">mantle</span> components hosted in plumes, and if high-3He/4He material is entrained from the deep <span class="hlt">mantle</span> only by the hottest, most buoyant plumes. Such a dense, deep-<span class="hlt">mantle</span> high-3He/4He domain could remain isolated from the convecting <span class="hlt">mantle</span>, which may help to explain the preservation of <span class="hlt">early</span> Hadean (>4.5 billion years ago) geochemical anomalies in lavas sampling this reservoir.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://eric.ed.gov/?q=wind&pg=5&id=EJ1115363','ERIC'); return false;" href="https://eric.ed.gov/?q=wind&pg=5&id=EJ1115363"><span>The <span class="hlt">Early</span> Years: The <span class="hlt">Earth</span>-Sun System</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Ashbrook, Peggy</p> <p>2015-01-01</p> <p>We all experience firsthand many of the phenomena caused by <span class="hlt">Earth</span>'s Place in the Universe (Next Generation Science Standard 5-ESS1; NGSS Lead States 2013) and the relative motion of the <span class="hlt">Earth</span>, Sun, and Moon. Young children can investigate phenomena such as changes in times of sunrise and sunset (number of daylight hours), Moon phases, seasonal…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040090318&hterms=evolution+rock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Devolution%2Brock','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040090318&hterms=evolution+rock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Devolution%2Brock"><span><span class="hlt">Mantle</span> redox evolution and the oxidation state of the Archean atmosphere</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kasting, J. F.; Eggler, D. H.; Raeburn, S. P.</p> <p>1993-01-01</p> <p>Current models predict that the <span class="hlt">early</span> atmosphere consisted mostly of CO2, N2, and H2O, along with traces of H2 and CO. Such models are based on the assumption that the redox state of the upper <span class="hlt">mantle</span> has not changed, so that volcanic gas composition has remained approximately constant with time. We argue here that this assumption is probably incorrect: the upper <span class="hlt">mantle</span> was originally more reduced than today, although not as reduced as the metal arrest level, and has become progressively more oxidized as a consequence of the release of reduced volcanic gases and the subduction of hydrated, oxidized seafloor. Data on the redox state of sulfide and chromite inclusions in diamonds imply that the process of <span class="hlt">mantle</span> oxidation was slow, so that reduced conditions could have prevailed for as much as half of the <span class="hlt">earth</span>'s history. To be sure, other oxybarometers of ancient rocks give different results, so the question of when the <span class="hlt">mantle</span> redox state has changed remains unresolved. <span class="hlt">Mantle</span> redox evolution is intimately linked to the oxidation state of the primitive atmosphere: A reduced Archean atmosphere would have had a high hydrogen escape rate and should correspond to a changing <span class="hlt">mantle</span> redox state; an oxidized Archean atmosphere should be associated with a constant <span class="hlt">mantle</span> redox state. The converses of these statements are also true. Finally, our theory of <span class="hlt">mantle</span> redox evolution may explain why the Archean atmosphere remained oxygen-deficient until approximately 2.0 billion years ago (Ga) despite a probable <span class="hlt">early</span> origin for photosynthesis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018AcGeo.tmp...20L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018AcGeo.tmp...20L"><span>Electric resistivity distribution in the <span class="hlt">Earth</span>'s crust and upper <span class="hlt">mantle</span> for the southern East European Platform and Crimea from area-wide 2D models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Logvinov, Igor M.; Tarasov, Viktor N.</p> <p>2018-03-01</p> <p>Previously obtained magnetotelluric 2D models for 30 profiles made it possible to create an overview model of electric resistivity for the territory between 28°E and 36°E and between 44.5°N and 52.5°N. It allows us to distinguish a number of low resistivity objects (LRO) with resistivities lower than 100 Ω m the <span class="hlt">Earth</span>'s crust and <span class="hlt">mantle</span>. Two regional conductivity anomalies are traced. The Kirovograd conductivity anomaly extends south to the Crimea mountains. A new regional conductivity anomaly (Konkskaya) can be distinguished along the southern slope of the Ukrainian Shield from 29° to 34°E. In addition, many local LROs have been identified. According to the modeling results, the local low resistivity objects on the East European Platform appear along fault zones activated during last 5-7 M years and the model suggests their relation to known zones of graphitization and polymetallic ore deposits. Local LROs in the Dnieper-Donets Basin correlate with the main oil and natural gas fields in this area. The depth of the anomalous objects amounts to 5-22 km. This is consistent with the hypotheses that hydrocarbon deposits are related to generation and transport zones of carbon-bearing fluids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930002475','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930002475"><span>The <span class="hlt">early</span> <span class="hlt">Earth</span> Observing System reference handbook: <span class="hlt">Earth</span> Science and Applications Division missions, 1990-1997</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1990-01-01</p> <p>Prior to the launch of the <span class="hlt">Earth</span> Observing System (EOS) series, NASA will launch and operate a wide variety of new <span class="hlt">earth</span> science satellites and instruments, as well as undertake several efforts collecting and using the data from existing and planned satellites from other agencies and nations. These initiatives will augment the knowledge base gained from ongoing <span class="hlt">Earth</span> Science and Applications Division (ESAD) programs. This volume describes three sets of ESAD activities -- ongoing exploitation of operational satellite data, research missions with upcoming launches between now and the first launch of EOS, and candidate <span class="hlt">earth</span> probes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PEPI..277...10L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PEPI..277...10L"><span>Linking lowermost <span class="hlt">mantle</span> structure, core-<span class="hlt">mantle</span> boundary heat flux and <span class="hlt">mantle</span> plume formation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Mingming; Zhong, Shijie; Olson, Peter</p> <p>2018-04-01</p> <p>The dynamics of <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span> exert significant control on the formation of <span class="hlt">mantle</span> plumes and the core-<span class="hlt">mantle</span> boundary (CMB) heat flux. However, it is not clear if and how the variation of CMB heat flux and <span class="hlt">mantle</span> plume activity are related. Here, we perform geodynamic model experiments that show how temporal variations in CMB heat flux and pulses of <span class="hlt">mantle</span> plumes are related to morphologic changes of the thermochemical piles of large-scale compositional heterogeneities in <span class="hlt">Earth</span>'s lowermost <span class="hlt">mantle</span>, represented by the large low shear velocity provinces (LLSVPs). We find good correlation between the morphologic changes of the thermochemical piles and the time variation of CMB heat flux. The morphology of the thermochemical piles is significantly altered during the initiation and ascent of strong <span class="hlt">mantle</span> plumes, and the changes in pile morphology cause variations in the local and the total CMB heat flux. Our modeling results indicate that plume-induced episodic variations of CMB heat flux link geomagnetic superchrons to pulses of surface volcanism, although the relative timing of these two phenomena remains problematic. We also find that the density distribution in thermochemical piles is heterogeneous, and that the piles are denser on average than the surrounding <span class="hlt">mantle</span> when both thermal and chemical effects are included.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810009125','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810009125"><span>The electrical conductivity of the <span class="hlt">Earth</span>'s upper <span class="hlt">mantle</span> as estimated from satellite measured magnetic field variations. Ph.D. Thesis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Didwall, E. M.</p> <p>1981-01-01</p> <p>Low latitude magnetic field variations (magnetic storms) caused by large fluctuations in the equatorial ring current were derived from magnetic field magnitude data obtained by OGO 2, 4, and 6 satellites over an almost 5 year period. Analysis procedures consisted of (1) separating the disturbance field into internal and external parts relative to the surface of the <span class="hlt">Earth</span>; (2) estimating the response function which related to the internally generated magnetic field variations to the external variations due to the ring current; and (3) interpreting the estimated response function using theoretical response functions for known conductivity profiles. Special consideration is given to possible ocean effects. A temperature profile is proposed using conductivity temperature data for single crystal olivine. The resulting temperature profile is reasonable for depths below 150-200 km, but is too high for shallower depths. Apparently, conductivity is not controlled solely by olivine at shallow depths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PNAS..104.9168I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PNAS..104.9168I"><span>High-Pressure Geoscience Special Feature: Dynamical stability of Fe-H in the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span> and core regions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Isaev, Eyvaz I.; Skorodumova, Natalia V.; Ahuja, Rajeev; Vekilov, Yuri K.; Johansson, Börje</p> <p>2007-05-01</p> <p>The core extends from the depth of 2,900 km to the center of the <span class="hlt">Earth</span> and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp → hcp → fcc sequence of structural transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.256..311C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.256..311C"><span>Petrogenesis of <span class="hlt">early</span> Jurassic basalts in southern Jiangxi Province, South China: Implications for the thermal state of the Mesozoic <span class="hlt">mantle</span> beneath South China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cen, Tao; Li, Wu-xian; Wang, Xuan-ce; Pang, Chong-jin; Li, Zheng-xiang; Xing, Guang-fu; Zhao, Xi-lin; Tao, Jihua</p> <p>2016-07-01</p> <p><span class="hlt">Early</span> Jurassic bimodal volcanic and intrusive rocks in southern South China show distinct associations and distribution patterns in comparison with those of the Middle Jurassic and Cretaceous rocks in the area. It is widely accepted that these rocks formed in an extensional setting, although the timing of the onset and the tectonic driver for extension are debated. Here, we present systematic LA-ICP-MS zircon U-Pb ages, whole-rock geochemistry and Sr-Nd isotope data for bimodal volcanic rocks from the Changpu Formation in the Changpu-Baimianshi and Dongkeng-Linjiang basins in southern Jiangxi Province, South China. Zircon U-Pb ages indicate that the bimodal volcanic rocks erupted at ca. 190 Ma, contemporaneous with the Fankeng basalts ( 183 Ma). A compilation of geochronological results demonstrates that basin-scale basaltic eruptions occurred during the <span class="hlt">Early</span> Jurassic within a relatively short interval (< 5 Ma). These <span class="hlt">Early</span> Jurassic basalts have tholeiitic compositions and OIB-like trace element distribution patterns. Geochemical analyses show that the basalts were derived from depleted asthenospheric <span class="hlt">mantle</span>, dominated by a volatile-free peridotite source. The calculated primary melt compositions suggest that the basalts formed at 1.9-2.1 GPa, with melting temperatures of 1378 °C-1405 °C and a <span class="hlt">mantle</span> potential temperature (TP) ranging from 1383 °C to 1407 °C. The temperature range is somewhat hotter than normal mid-ocean-basalt (MORB) <span class="hlt">mantle</span> but similar to an intra-plate continental <span class="hlt">mantle</span> setting, such as the Basin and Range Province in western North America. This study provides an important constraint on the <span class="hlt">Early</span> Jurassic <span class="hlt">mantle</span> thermal state beneath South China. Reference: Raczek, I., Stoll, B., Hofmann, A.W., Jochum, K.P. 2001. High-precision trace element data for the USGS reference materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, DTS-1, DTS-2, GSP-1 and GSP-2 by ID-TIMS and MIC-SSMS. Geostandards Newsletter 25(1), 77-86.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010083360&hterms=cycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D60%26Ntt%3Dcycling','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010083360&hterms=cycling&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DTitle%26N%3D0%26No%3D60%26Ntt%3Dcycling"><span>Reduced Gas Cycling in Microbial Mats: Implications for <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hoehler, Tori M.; Bebout, Brad M.; DesMarais, David J.; DeVincenzi, Donald L. (Technical Monitor)</p> <p>2000-01-01</p> <p>For more than half the history of life on <span class="hlt">Earth</span>, biological productivity was dominated by photosynthetic microbial mats. During this time, mats served as the preeminent biological influence on <span class="hlt">earth</span>'s surface and atmospheric chemistry and also as the primary crucible for microbial evolution. We find that modern analogs of these ancient mat communities generate substantial quantities of hydrogen, carbon monoxide, and methane. Escape of these gases from the biosphere would contribute strongly to atmospheric evolution and potentially to the net oxidation of <span class="hlt">earth</span>'s surface; sequestration within the biosphere carries equally important implications for the structure, function, and evolution of anaerobic microbial communities within the context of mat biology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFM.U42B..03O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFM.U42B..03O"><span>Noble gas Records of <span class="hlt">Early</span> Evolution of the <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ozima, M.; Podoesk, F. A.</p> <p>2001-12-01</p> <p>Comparison between atmospheric noble gases (except for He) and solar (or meteoritic) noble gases clearly suggests that the <span class="hlt">Earth</span> should have much more Xe than is present in air, and thus that up to about 90 percent of terrestrial Xe is missing from the <span class="hlt">Earth</span> (1). In this report, we discuss implications of these observations on I-Pu chronology of the <span class="hlt">Earth</span> and on the origin of terrestrial He3. Whetherill (2) first noted that an estimated I129/I127 ratio (3x10-6) in the proto-<span class="hlt">Earth</span> was about two orders of magnitude smaller than values commonly observed in meteorites (10-4), and pointed out the possibility that <span class="hlt">Earth</span> formation postdated meteorites by about 100Ma. Ozima and Podosek (1999) came to a similar conclusion on the basis of I129/I127-Pu244/U238 systematics (1). In this report, we reexamine I-Pu systematics with new data for crustal I content (295 ppb for a bulk crust, (3)). With imposition of an estimated value of 86 percent missing Xe as a constraint on terrestrial Xe inventory, we conclude that the best estimate for a formation age of the <span class="hlt">Earth</span> is about 28Ma after the initial condensation of the solar nebula (at 4.57Ga). The formation age thus estimated is significantly later than the generally assumed age of meteorites. We also argue from the I-Pu systematics that the missing Xe became missing place about 120Ma after <span class="hlt">Earth</span> formation. Assuming that the <span class="hlt">Earth</span> is mostly degassed, the I-Pu formation age of the <span class="hlt">Earth</span> can be reasonably assumed to represent a whole <span class="hlt">Earth</span> event. Therefore, we interpret that the I-Pu age of the <span class="hlt">Earth</span> represents the time when the <span class="hlt">Earth</span> started to retain noble gases. More specifically, this may correspond to the time when the proto-<span class="hlt">Earth</span> attained a sufficient size to exert the necessary gravitational force. A giant impact could be another possibility, but it remains to be seen whether or not a giant impact could quantitatively remove heavier noble gases from the <span class="hlt">Earth</span>. It is interesting to speculate that missing Xe was sequestered in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016LPICo1912.2042U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016LPICo1912.2042U"><span>Ocean Fertilization from Giant Icebergs on <span class="hlt">Earth</span> and <span class="hlt">Early</span> Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Uceda, E. R.; Fairen, A. G.; Rodriguez, J. A. P.; Woodworth-Lynas, C.</p> <p>2016-05-01</p> <p>Assuming that life existed on Mars coeval to glacial activity, enhanced concentrations of organic carbon could be anticipated near iceberg trails, analogous to what is observed in polar oceans on <span class="hlt">Earth</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004Litho..74....1G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004Litho..74....1G"><span>The thermal regimes of the upper <span class="hlt">mantle</span> beneath Precambrian and Phanerozoic structures up to the thermobarometry data of <span class="hlt">mantle</span> xenoliths</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glebovitsky, V. A.; Nikitina, L. P.; Khiltova, V. Ya.; Ovchinnikov, N. O.</p> <p>2004-05-01</p> <p>The thermal state of the upper <span class="hlt">mantle</span> beneath tectonic structures of various ages and types (Archaean cratons, <span class="hlt">Early</span> Proterozoic accretionary and collisional orogens, and Phanerozoic structures) is characterized by geotherms and by thermal gradients (TG) derived from data on the P- T conditions of mineral equilibria in garnet and garnet-spinel peridotite xenoliths from kimberlites (East Siberia, Northeastern Europe, India, Central Africa, North America, and Canada) and alkali basalts (Southeastern Siberia, Mongolia, southeastern China, southeastern Australia, Central Africa, South America, and the Solomon and Hawaiian islands). The use of the same garnet-orthopyroxene thermobarometer (Theophrastus Contributions to Advanced Studies in Geology. 3: Capricious <span class="hlt">Earth</span>: Models and Modelling of Geologic Processes and Objects 2000 44) for all xenoliths allowed us to avoid discrepancies in estimation of the P- T conditions, which may be a result of the mismatch between different thermometers and barometers, and to compare the thermal regimes in the <span class="hlt">mantle</span> in various regions. Thus, it was established that (1) <span class="hlt">mantle</span> geotherms and geothermal gradients, obtained from the estimation of P- T equilibrium conditions of deep xenoliths, correspond to the age of crust tectonic structures and respectively to the time of lithosphere stabilization; it can be suggested that the ancient structures of the upper <span class="hlt">mantle</span> were preserved within continental roots; (2) thermal regimes under continental <span class="hlt">mantle</span> between the Archaean cratons and Palaeoproterozoic belts are different today; (3) the continental <span class="hlt">mantle</span> under Neoproterozoic and Phanerozoic belts is characterized by significantly higher values of geothermal gradient compared to the <span class="hlt">mantle</span> under <span class="hlt">Early</span> Precambrian structures; (4) lithosphere dynamics seems to change at the boundary between <span class="hlt">Early</span> and Mezo-Neoproterozoic and Precambrian and Phanerozoic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850024749','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850024749"><span>Workshop on the <span class="hlt">Early</span> <span class="hlt">Earth</span>: The Interval from Accretion to the Older Archean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burke, K. (Editor); Ashwal, L. D. (Editor)</p> <p>1985-01-01</p> <p>Presentation abstracts are compiled which address various issues in <span class="hlt">Earth</span> developmental processes in the first one hundred million years. The session topics included: accretion of the <span class="hlt">Earth</span> (processes accompanying immediately following the accretion, including core formation); impact records and other information from planets and the Moon relevant to <span class="hlt">early</span> <span class="hlt">Earth</span> history; isotopic patterns of the oldest rocks; and igneous, sedimentary, and metamorphic petrology of the oldest rocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70030510','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70030510"><span>Isotope geochemistry of <span class="hlt">early</span> Kilauea magmas from the submarine Hilina bench: The nature of the Hilina <span class="hlt">mantle</span> component</span></a></p> <p><a target="_blank" href=""></a></p> <p>Kimura, Jun-Ichi; Sisson, Thomas W.; Nakano, Natsuko; Coombs, Michelle L.; Lipman, Peter W.</p> <p>2006-01-01</p> <p>Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr–Nd–Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of <span class="hlt">early</span> Kilauea magmas (Sisson et al., 2002). These samples are among the highest 206Pb/204Pb known from Hawaii and may represent melts from a distinct geochemical and isotopic end-member involved in the generation of most Hawaiian tholeiites. This end-member is similar to the postulated literature Kea component, but we propose that it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina end-member but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both “Koolau” (high 87Sr/86Sr, low 206Pb/204Pb) and depleted (low 87Sr/86Sr, intermediate 206Pb/204Pb) source materials. This shift in isotopic character from nearly uniform, end-member, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea's magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling <span class="hlt">mantle</span> source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870038401&hterms=history+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dhistory%2BEarth','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870038401&hterms=history+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dhistory%2BEarth"><span><span class="hlt">Early</span> evolution of the <span class="hlt">earth</span> - Accretion, atmosphere formation, and thermal history</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Abe, Yutaka; Matsui, Takafumi</p> <p>1986-01-01</p> <p>The thermal and atmospheric evolution of the <span class="hlt">earth</span> growing planetesimal impacts are studied. The generation of an H2O protoatmosphere is examined, and the surface temperatures are estimated. The evolution of an impact-induced H2O atmosphere is analyzed. Consideration is given to the formation time of a 'magma ocean'and internal water budgets. The thermal history of an accreting <span class="hlt">earth</span> is reviewed. The wet convection and greenhouse effects are discussed, and the role of Fe oxidation on the evolution of an impact-induced H2O atmopshere is described. The relationship between differentiation processes and core segregation, the H2O and FeO content of the <span class="hlt">mantle</span>, and the origin of the hydrosphere is also examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P51A2575H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P51A2575H"><span>Self-Organized <span class="hlt">Mantle</span> Layering After the Magma-Ocean Period</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hansen, U.; Dude, S.</p> <p>2017-12-01</p> <p>The thermal history of the <span class="hlt">Earth</span>, it's chemical differentiation and also the reaction of the interior with the atmosphere is largely determined by convective processes within the <span class="hlt">Earth</span>'s <span class="hlt">mantle</span>. A simple physical model, resembling the situation, shortly after core formation, consists of a compositionally stable stratified <span class="hlt">mantle</span>, as resulting from fractional crystallization of the magma ocean. The <span class="hlt">early</span> <span class="hlt">mantle</span> is subject to heating from below by the <span class="hlt">Earth</span>'s core and cooling from the top through the atmosphere. Additionally internal heat sources will serve to power the <span class="hlt">mantle</span> dynamics. Under such circumstances double diffusive convection will eventually lead to self -organized layer formation, even without the preexisting jumps is material properties. We have conducted 2D and 3D numerical experiments in Cartesian and spherical geometry, taking into account <span class="hlt">mantle</span> realistic values, especially a strong temperature dependent viscosity and a pressure dependent thermal expansivity . The experiments show that in a wide parameter range. distinct convective layers evolve in this scenario. The layering strongly controls the heat loss from the core and decouples the dynamics in the lower <span class="hlt">mantle</span> from the upper part. With time, individual layers grow on the expense of others and merging of layers does occur. We observe several events of intermittent breakdown of individual layers. Altogether an evolution emerges, characterized by continuous but also spontaneous changes in the <span class="hlt">mantle</span> structure, ranging from multiple to single layer flow. Such an evolutionary path of <span class="hlt">mantle</span> convection allows to interpret phenomena ranging from stagnation of slabs at various depth to variations in the chemical signature of <span class="hlt">mantle</span> upwellings in a new framework.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17008211','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17008211"><span>The carbon cycle on <span class="hlt">early</span> <span class="hlt">Earth</span>--and on Mars?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Grady, Monica M; Wright, Ian</p> <p>2006-10-29</p> <p>One of the goals of the present Martian exploration is to search for evidence of extinct (or even extant) life. This could be redefined as a search for carbon. The carbon cycle (or, more properly, cycles) on <span class="hlt">Earth</span> is a complex interaction among three reservoirs: the atmosphere; the hydrosphere; and the lithosphere. Superimposed on this is the biosphere, and its presence influences the fixing and release of carbon in these reservoirs over different time-scales. The overall carbon balance is kept at equilibrium on the surface by a combination of tectonic processes (which bury carbon), volcanism (which releases it) and biology (which mediates it). In contrast to <span class="hlt">Earth</span>, Mars presently has no active tectonic system; neither does it possess a significant biosphere. However, these observations might not necessarily have held in the past. By looking at how <span class="hlt">Earth</span>'s carbon cycles have changed with time, as both the <span class="hlt">Earth</span>'s tectonic structure and a more sophisticated biology have evolved, and also by constructing a carbon cycle for Mars based on the carbon chemistry of Martian meteorites, we investigate whether or not there is evidence for a Martian biosphere.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850025554&hterms=modulation+reactions+chemical&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmodulation%2Breactions%2Bchemical','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850025554&hterms=modulation+reactions+chemical&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmodulation%2Breactions%2Bchemical"><span>Biological modulation of planetary atmospheres: The <span class="hlt">early</span> <span class="hlt">Earth</span> scenario</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schidlowski, M.</p> <p>1985-01-01</p> <p>The establishment and subsequent evolution of life on <span class="hlt">Earth</span> had a profound impact on the chemical regime at the planet's surface and its atmosphere. A thermodynamic gradient was imposed on near-surface environments that served as the driving force for a number on important geochemical transformations. An example is the redox imbalance between the modern atmosphere and the material of the <span class="hlt">Earth</span>'s crust. Current photochemical models predict extremely low partial pressures of oxygen in the <span class="hlt">Earth</span>'s prebiological atmosphere. There is widespread consensus that any large-scale oxygenation of the primitive atmosphere was contingent on the advent of biological (autotrophic) carbon fixation. It is suggested that photoautotrophy existed both as a biochemical process and as a geochemical agent since at least 3.8 Ga ago. Combining the stoichiometry of the photosynthesis reaction with a carbon isotope mass balance and current concepts for the evolution of the stationary sedimentary mass as a funion of time, it is possible to quantify, the accumulation of oxygen and its photosynthetic oxidation equivalents through <span class="hlt">Earth</span> history.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900065927&hterms=manuel+cruz&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dmanuel%2Bcruz','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900065927&hterms=manuel+cruz&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dmanuel%2Bcruz"><span>21st century <span class="hlt">early</span> mission concepts for Mars delivery and <span class="hlt">earth</span> return</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cruz, Manuel I.; Ilgen, Marc R.</p> <p>1990-01-01</p> <p>In the 21st century, the <span class="hlt">early</span> missions to Mars will entail unmanned Rover and Sample Return reconnaissance missions to be followed by manned exploration missions. High performance leverage technologies will be required to reach Mars and return to <span class="hlt">earth</span>. This paper describes the mission concepts currently identified for these <span class="hlt">early</span> Mars missions. These concepts include requirements and capabilities for Mars and <span class="hlt">earth</span> aerocapture, Mars surface operations and ascent, and Mars and <span class="hlt">earth</span> rendezvous. Although the focus is on the unmanned missions, synergism with the manned missions is also discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20060015668&hterms=soup&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dsoup','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20060015668&hterms=soup&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dsoup"><span>Prebiotic materials from on and off the <span class="hlt">early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bernstein, Max</p> <p>2006-01-01</p> <p>One of the great puzzles of all time is how did life arise? It has been universally presumed that life arose in a soup rich in compounds made mostly of carbon, the kind of which we are currently composed. Where did these organic molecules come from? In this talk I will review proposed contributions to pre-biotic organic chemistry from both terrestrial processes (i.e., hydrothermal vents, Miller-Urey syntheses) and also from space. While the former is perhaps better known and more commonly taught in school, we now know that comet and asteroid dust deliver tons of organics to the <span class="hlt">Earth</span> every day, and there is a growing consensus among scientists that molecules from space played an important role in making the <span class="hlt">Earth</span> habitable, and perhaps even provided specific compounds that were directly related to the origin of life.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150023540','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150023540"><span>Environmental Consequences of Big Nasty Impacts on the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zahnle, Kevin</p> <p>2015-01-01</p> <p>The geological record of the Archean <span class="hlt">Earth</span> is spattered with impact spherules from a dozen or so major cosmic collisions involving <span class="hlt">Earth</span> and asteroids or comets (Lowe, Byerly 1986, 2015). Extrapolation of the documented deposits suggests that most of these impacts were as big or bigger than the Chicxulub event that famously ended the reign of the thunder lizards. As the Archean impacts were greater, the environmental effects were also greater. The number and magnitude of the impacts is bounded by the lunar record. There are no lunar craters bigger than Chicxulub that date to <span class="hlt">Earth</span>'s mid-to-late Archean. Chance dictates that <span class="hlt">Earth</span> experienced no more than approximately 10 impacts bigger than Chicxulub between 2.5 billion years and 3.5 billion years, the biggest of which were approximately 30-100 times more energetic, comparable to the Orientale impact on the Moon (1x10 (sup 26) joules). To quantify the thermal consequences of big impacts on old <span class="hlt">Earth</span>, we model the global flow of energy from the impact into the environment. The model presumes that a significant fraction of the impact energy goes into ejecta that interact with the atmosphere. Much of this energy is initially in rock vapor, melt, and high speed particles. (i) The upper atmosphere is heated by ejecta as they reenter the atmosphere. The mix of hot air, rock vapor, and hot silicates cools by thermal radiation. Rock raindrops fall out as the upper atmosphere cools. (ii) The energy balance of the lower atmosphere is set by radiative exchange with the upper atmosphere and with the surface, and by evaporation of seawater. Susequent cooling is governed by condensation of water vapor. (iii) The oceans are heated by thermal radiation and rock rain and cooled by evaporation. Surface waters become hot and salty; if a deep ocean remains it is relatively cool. Subsequently water vapor condenses to replenish the oceans with hot fresh water (how fresh depending on continental weathering, which might be rather rapid</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150023449','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150023449"><span>Environmental Consequences of Big Nasty Impacts on the <span class="hlt">Early</span> <span class="hlt">Earth</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zahnle, Kevin</p> <p>2015-01-01</p> <p>The geological record of the Archean <span class="hlt">Earth</span> is spattered with impact spherules from a dozen or so major cosmic collisions involving <span class="hlt">Earth</span> and asteroids or comets (Lowe, Byerly 198