scholarly journals A mushy Earth's mantle for more than 500 Myr after the magma ocean solidification

2020 ◽  
Vol 221 (2) ◽  
pp. 1165-1181
Author(s):  
J Monteux ◽  
D Andrault ◽  
M Guitreau ◽  
H Samuel ◽  
S Demouchy
Keyword(s):  
Thermal Evolution ◽  
Numerical Models ◽  
Spherical Geometry ◽  
Magma Ocean ◽  
Mantle Dynamics ◽  
Mineral Physics ◽  
The Earth ◽  
Complete Melting ◽  
Metal Silicate ◽  
Impact Heating

SUMMARY In its early evolution, the Earth mantle likely experienced several episodes of complete melting enhanced by giant impact heating, short-lived radionuclides heating and viscous dissipation during the metal/silicate separation. After a first stage of rapid and significant crystallization (Magma Ocean stage), the mantle cooling is slowed down due to the rheological transition, which occurs at a critical melt fraction of 40–50%. This transition first occurs in the lowermost mantle, before the mushy zone migrates toward the Earth's surface with further mantle cooling. Thick thermal boundary layers form above and below this reservoir. We have developed numerical models to monitor the thermal evolution of a cooling and crystallizing deep mushy mantle. For this purpose, we use a 1-D approach in spherical geometry accounting for turbulent convective heat transfer and integrating recent and solid experimental constraints from mineral physics. Our results show that the last stages of the mushy mantle solidification occur in two separate mantle layers. The lifetime and depth of each layer are strongly dependent on the considered viscosity model and in particular on the viscosity contrast between the solid upper and lower mantle. In any case, the full solidification should occur at the Hadean–Eoarchean boundary 500–800 Myr after Earth's formation. The persistence of molten reservoirs during the Hadean may favor the absence of early reliefs at that time and maintain isolation of the early crust from the underlying mantle dynamics.

Isotopes as clues to the origin and earliest differentiation history of the Earth

2008 ◽  
Vol 366 (1883) ◽  
pp. 4129-4162 ◽  
Author(s):  
Stein B Jacobsen ◽  
Michael C Ranen ◽  
Michael I Petaev ◽  
John L Remo ◽  
Richard J O'Connell ◽  
...  
Keyword(s):  
Time Scale ◽  
Magma Ocean ◽  
Crust Formation ◽  
Early Atmosphere ◽  
The Earth ◽  
Metal Silicate ◽  
Deep Earth ◽  
History Of ◽  
Mean Time ◽  
Late Veneer

Measurable variations in 182 W/ 183 W, 142 Nd/ 144 Nd, 129 Xe/ 130 Xe and 136 Xe Pu / 130 Xe in the Earth and meteorites provide a record of accretion and formation of the core, early crust and atmosphere. These variations are due to the decay of the now extinct nuclides 182 Hf, 146 Sm, 129 I and 244 Pu. The l82 Hf– 182 W system is the best accretion and core-formation chronometer, which yields a mean time of Earth's formation of 10 Myr, and a total time scale of 30 Myr. New laser shock data at conditions comparable with those in the Earth's deep mantle subsequent to the giant Moon-forming impact suggest that metal–silicate equilibration was rapid enough for the Hf–W chronometer to reliably record this time scale. The coupled 146 Sm– 147 Sm chronometer is the best system for determining the initial silicate differentiation (magma ocean crystallization and proto-crust formation), which took place at ca 4.47 Ga or perhaps even earlier. The presence of a large 129 Xe excess in the deep Earth is consistent with a very early atmosphere formation (as early as 30 Myr); however, the interpretation is complicated by the fact that most of the atmospheric Xe may be from a volatile-rich late veneer.

Accretion and core formation: constraints from metal–silicate partitioning

2008 ◽  
Vol 366 (1883) ◽  
pp. 4339-4355 ◽  
Author(s):  
Bernard J Wood
Keyword(s):  
Oxidation State ◽  
Maximum Pressure ◽  
Magma Ocean ◽  
Core Formation ◽  
The Core ◽  
Refractory Elements ◽  
The Earth ◽  
Metal Silicate ◽  
Restricted Volume ◽  
Si Content

Experimental metal–silicate partitioning data for Ni, Co, V, Cr, Nb, Mn, Si and W were used to investigate the geochemical consequences of a range of models for accretion and core formation on Earth. The starting assumptions were chondritic ratios of refractory elements in the Earth and the segregation of metal at the bottom of a magma ocean, which deepened as the planet grew and which had, at its base, a temperature close to the liquidus of the silicate. The models examined were as follows. (i) Continuous segregation from a mantle which is chemically homogeneous and which has a fixed oxidation state, corresponding to 6.26 per cent oxidized Fe. Although Ni, Co and W partitioning is consistent with chondritic ratios, the current V content of the silicate Earth cannot be reconciled with core segregation under these conditions of fixed oxidation state. (ii) Continuous segregation from a mantle which is chemically homogeneous but in which the Earth became more oxidized as it grew. In this case, the Ni, Co, W, V, Cr and Nb contents of core and mantle are easily matched to those calculated from the chondritic ratios of refractory elements. The magma ocean is calculated to maintain a thickness approximately 35 per cent of the depth to the core–mantle boundary in the accreting Earth, yielding a maximum pressure of 44 GPa. This model yields a Si content of the core of 5.7 per cent, in good agreement with cosmochemical estimates and with recent isotopic data. (iii) Continuous segregation from a mantle which is not homogeneous and in which the core equilibrates with a restricted volume of mantle at the base of the magma ocean. This is found to increase depth of the magma ocean by approximately 50 per cent. All of the other elements (except Mn) have partitioning consistent with chondritic abundances in the Earth, provided the Earth became, as before, progressively oxidized during accretion. (iv) Continuous segregation of metal from a crystal-melt mush. In this case, pressures decrease to a maximum of 31 GPa and it is extremely difficult to match the calculated mantle contents of the highly incompatible elements Nb and W to those observed. Progressive oxidation is required to fit the observed mantle contents of vanadium. All of the scenarios discussed above point to progressive oxidation having occurred as the Earth grew. The Earth appears to be depleted in Mn relative to the chondritic reference.

Thermal evolution of the Earth

2014 ◽  
pp. 300-316 ◽  
Author(s):  
Claude Jaupart ◽  
Jean-Claude Mareschal
Keyword(s):  
Thermal Evolution ◽  
The Earth

scholarly journals Variability of the adiabatic parameter in monoatomic thermal and non-thermal plasmas

2018 ◽  
Vol 616 ◽  
pp. A58 ◽  
Author(s):  
Miguel A. de Avillez ◽  
Gervásio J. Anela ◽  
Dieter Breitschwerdt
Keyword(s):  
Internal Energy ◽  
Impact Ionization ◽  
Thermal Evolution ◽  
Numerical Models ◽  
Linear Equations ◽  
Thermal Plasmas ◽  
Specific Heats ◽  
Partial Pivoting ◽  
Electron Distributions ◽  
Collisional Ionization

Context. Numerical models of the evolution of interstellar and integalactic plasmas often assume that the adiabatic parameter γ (the ratio of the specific heats) is constant (5/3 in monoatomic plasmas). However, γ is determined by the total internal energy of the plasma, which depends on the ionic and excitation state of the plasma. Hence, the adiabatic parameter may not be constant across the range of temperatures available in the interstellar medium. Aims. We aim to carry out detailed simulations of the thermal evolution of plasmas with Maxwell–Boltzmann and non-thermal (κ and n) electron distributions in order to determine the temperature variability of the total internal energy and of the adiabatic parameter. Methods. The plasma, composed of H, He, C, N, O, Ne, Mg, Si, S, and Fe atoms and ions, evolves under collisional ionization equilibrium conditions, from an initial temperature of 109 K. The calculations include electron impact ionization, radiative and dielectronic recombinations and line excitation. The ionization structure was calculated solving a system of 112 linear equations using the Gauss elimination method with scaled partial pivoting. Numerical integrations used in the calculation of ionization and excitation rates are carried out using the double-exponential over a semi-finite interval method. In both methods a precision of 10−15 is adopted. Results. The total internal energy of the plasma is mainly dominated by the ionization energy for temperatures lower than 8 × 104 K with the excitation energy having a contribution of less than one percent. In thermal and non-thermal plasmas composed of H, He, and metals, the adiabatic parameter evolution is determined by the H and He ionizations leading to a profile in general having three transitions. However, for κ distributed plasmas these three transitions are not observed for κ < 15 and for κ < 5 there are no transitions. In general, γ varies from 1.01 to 5/3. Lookup tables of the γ parameter are presented as supplementary material.

scholarly journals Atmospheric speciation of rocky planets from magma ocean outgassing

2020 ◽  
Author(s):  
Tim Lichtenberg ◽  
Dan J. Bower ◽  
Mark Hammond ◽  
Ryan Boukrouche ◽  
Shang-Min Tsai ◽  
...  
Keyword(s):  
Coupled Model ◽  
Initial Distribution ◽  
Occurrence Rate ◽  
Magma Ocean ◽  
Mantle Dynamics ◽  
Mantle Geochemistry ◽  
Prebiotic Chemical ◽  
History Of ◽  
Climatic History ◽  
Rocky Planets

&lt;p&gt;The earliest atmospheres of rocky planets originate from extensive volatile release during one or more magma ocean epochs that occur during primary and late-stage assembly of the planet (1). These epochs represent the most extreme cycling of volatiles between the interior and atmosphere in the history of a planet, and establish the initial distribution of the major volatile elements (C, H, N, O, S) between different chemical reservoirs that subsequently evolve via geological cycles. Crucially, the erosion or recycling of primary atmospheres bear upon the nature of the long-lived secondary atmospheres that will be probed with current and future observing facilities (2). Furthermore, the chemical speciation of the atmosphere arising from magma ocean processes can potentially be probed with present-day observations of tidally-locked rocky super-Earths (3). The speciation in turn strongly influences the climatic history of rocky planets, for instance the occurrence rate of planets that are locked in long-term runaway greenhouse states (4). We will present an integrated framework to model the build-up of the earliest atmospheres from magma ocean outgassing using a coupled model of mantle dynamics and atmospheric evolution. We consider the diversity of atmospheres that can arise for a range of initial planetary bulk compositions, and show how even small variations in volatile abundances can result in dramatically different atmospheric compositions and affect earliest mantle geochemistry and atmospheric speciation relevant for surficial prebiotic chemical environments (5). Only through the lense of coupled evolutionary models of terrestrial interiors and atmospheres can we begin to deconvolve the imprint of formation from that of evolution, with consequences for how we interpret the diversity revealed by astrophysical observables, and their relation to the earliest planetary conditions of our home world.&lt;/p&gt; &lt;div class=&quot;&quot;&gt;&lt;em&gt;References&lt;/em&gt;&lt;/div&gt; &lt;ol&gt; &lt;li&gt;Bower, D. J., Kitzmann, D., Wolf, A. S., et al. (2019). Astron. Astrophys. 631, A103.&lt;/li&gt; &lt;li&gt;Bonati, I., Lichtenberg, T., Bower, D. J., et al. (2019). Astron. Astrophys. 621, A125.&lt;/li&gt; &lt;li&gt;Kreidberg, L., Koll, D. D., Morley, C., et al. (2019). Nature 573, 87-90.&lt;/li&gt; &lt;li&gt;Hamano, K., Abe, Y., Genda, H. (2013). Nature 497, 607-610.&lt;/li&gt; &lt;li&gt;Sasselov, D. D., Grotzinger, J. P., Sutherland, J. D. (2020). Sci. Adv. 6, eaax3419.&lt;/li&gt; &lt;/ol&gt;

Effect of H2O on metal–silicate partitioning of Ni, Co, V, Cr, Mn and Fe: Implications for the oxidation state of the Earth and Mars

2016 ◽  
Vol 192 ◽  
pp. 97-121 ◽  
Author(s):  
V. Clesi ◽  
M.A. Bouhifd ◽  
N. Bolfan-Casanova ◽  
G. Manthilake ◽  
A. Fabbrizio ◽  
...  
Keyword(s):  
Oxidation State ◽  
The Earth ◽  
Metal Silicate
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