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Zhang F, Stagno V, Zhang L, Chen C, Liu H, Li C, Sun W. The constant oxidation state of Earth's mantle since the Hadean. Nat Commun 2024; 15:6521. [PMID: 39127717 DOI: 10.1038/s41467-024-50778-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Accepted: 07/19/2024] [Indexed: 08/12/2024] Open
Abstract
Determining the evolutionary history of mantle oxygen fugacity (fo2) is crucial, as it controls the fo2 of mantle-derived melts and regulates atmospheric composition through volcanic outgassing. However, the evolution of mantle fo2 remains controversial. Here, we present a comprehensive dataset of plume-derived komatiites, picrites, and ambient mantle-derived (meta)basalts, spanning from ~3.8 Ga to the present, to investigate mantle thermal and redox states evolution. Our results indicate that fo2 of both mantle plume-derived and ambient mantle-derived melts was lower during the Archean compared to the post-Archean period. This increase in the fo2 of mantle-derived melts over time correlates with decreases in mantle potential temperature and melting depth. By normalizing fo2 to a constant reference pressure (potential oxygen fugacity), we show that the fo2 of both the mantle plume and ambient upper mantle has remained constant since the Hadean. These findings suggest that secular mantle cooling reduced melting depth, increasing the fo2 of mantle-derived melts and contributing to atmospheric oxygenation.
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Affiliation(s)
- Fangyi Zhang
- Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China.
| | - Vincenzo Stagno
- Department of Earth Sciences, Sapienza University of Rome, Rome, Italy
| | - Lipeng Zhang
- Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
- Laoshan Laboratory, Qingdao, 266237, China
| | - Chen Chen
- Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
| | - Haiyang Liu
- Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
| | - Congying Li
- Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
- Laoshan Laboratory, Qingdao, 266237, China
| | - Weidong Sun
- Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China.
- Laoshan Laboratory, Qingdao, 266237, China.
- University of the Chinese Academy of Sciences, Beijing, 100049, China.
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Birner SK, Cottrell E, Davis FA, Warren JM. Deep, hot, ancient melting recorded by ultralow oxygen fugacity in peridotites. Nature 2024; 631:801-807. [PMID: 39048684 DOI: 10.1038/s41586-024-07603-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 05/23/2024] [Indexed: 07/27/2024]
Abstract
The oxygen fugacity (fO2) of convecting upper mantle recorded by ridge peridotites varies by more than four orders of magnitude1-3. Although much attention has been given to mechanisms that drive variations in mantle fO2 between tectonic settings1,3,4 and to comparisons of fO2 between modern rocks and ancient-mantle-derived rocks5-10, comparatively little has been done to understand the origins of the high variability in fO2 recorded by peridotites from modern mid-ocean ridge settings. Here we report the petrography and geochemistry of peridotites from the Gakkel Ridge and East Pacific Rise (EPR), including 16 new high-precision determinations of fO2. Refractory peridotites from the Gakkel Ridge record fO2 more than four orders of magnitude below the mantle average. With thermodynamic and mineral partitioning modelling, we show that excursions to ultralow fO2 can be produced by large degrees of melting at high potential temperature (Tp), beginning in the garnet field and continuing into the spinel field-conditions met during the generation of ancient komatiites but not modern basalts. This does not mean that ambient convecting upper mantle had a lower ferric to ferrous ratio in Archaean times than today nor that modern melting in the garnet field at hotspots produce reduced magmas. Instead, it implies that rafts of ancient, refractory, ultrareduced mantle continue to circulate in the modern mantle while contributing little to modern ridge volcanism.
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Affiliation(s)
- Suzanne K Birner
- Division of Natural Sciences, Nursing, and Mathematics, Berea College, Berea, KY, USA.
| | - Elizabeth Cottrell
- National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
| | - Fred A Davis
- Department of Earth and Environmental Sciences, University of Minnesota Duluth, Duluth, MN, USA
| | - Jessica M Warren
- Department of Earth Sciences, University of Delaware, Newark, DE, USA
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3
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Korenaga J, Marchi S. Vestiges of impact-driven three-phase mixing in the chemistry and structure of Earth's mantle. Proc Natl Acad Sci U S A 2023; 120:e2309181120. [PMID: 37812730 PMCID: PMC10614616 DOI: 10.1073/pnas.2309181120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 08/22/2023] [Indexed: 10/11/2023] Open
Abstract
Highly siderophile elements (HSEs; namely Ru, Rh, Pd, Re, Os, Ir, Pt, and Au) in Earth's mantle require the addition of metals after the formation of Earth's core. Early, large collisions have the potential to deliver metals, but the details of their mixing with Earth's mantle remain unresolved. As a large projectile disrupts and penetrates Earth's mantle, a fraction of its metallic core may directly merge with Earth's core. Ensuing gravitational instabilities remove the remaining projectile's core stranded in Earth's mantle, leaving the latter deprived of HSEs. Here, we propose a framework that can efficiently retain the metallic components during large impacts. The mechanism is based on the ubiquitous presence of a partially molten region in the mantle beneath an impact-generated magma ocean, and it involves rapid three-phase flow with solid silicate, molten silicate, and liquid metal as well as long-term mixing by mantle convection. In addition, large low-shear-velocity provinces in the lower mantle may originate from compositional heterogeneities resulting from the proposed three-phase flow during high-energy collisions.
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Affiliation(s)
- Jun Korenaga
- Department of Earth and Planetary Sciences, Yale University, New Haven, CT06520
| | - Simone Marchi
- Department of Space Studies, Southwest Research Institute, Boulder, CO80302
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4
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Warren AO, Kite ES. Narrow range of early habitable Venus scenarios permitted by modeling of oxygen loss and radiogenic argon degassing. Proc Natl Acad Sci U S A 2023; 120:e2209751120. [PMID: 36877840 PMCID: PMC10089166 DOI: 10.1073/pnas.2209751120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Accepted: 01/13/2023] [Indexed: 03/08/2023] Open
Abstract
Whether Venus was ever habitable is a key question driving missions to Earth's sister planet in the next decade. Venus today has a dry, O2-poor atmosphere, but recent work has proposed that early Venus may have had liquid water [J. Krissansen-Totton, J. J. Fortney, F. Nimmo, Planet. Sci. J. 2, 216 (2021)] and reflective clouds that could have sustained habitable conditions until 0.7 Ga [J. Yang, G. Boué, D. C. Fabrycky, D. S. Abbot, Astrophys. J. 787, L2 (2014), M. J. Way, A. D. Del Genio, J. Geophys. Res.: Planets 125, e2019JE006276 (2020)]. Water present at the end of a habitable era must since have been lost by photodissociation and H escape, causing buildup of atmospheric oxygen [F. Tian, Earth Planet. Sci. Lett. 432, 126-132 (2015)]. We present a time-dependent model of Venus's atmospheric composition starting from the end of a hypothetical habitable era with surface liquid water. We find that O2 loss to space, oxidation of reduced atmospheric species, oxidation of lava, and oxidation of a surface magma layer formed in a runaway greenhouse climate can remove O2 from up to 500 m global equivalent layer (GEL) (30% of an Earth ocean), unless melts on Venus had a much lower oxygen fugacity than Mid Ocean Ridge melts on Earth, which increases the upper limit twofold. Volcanism is required to supply oxidizable fresh basalt and reduced gases to the atmosphere but also contributes 40Ar. Consistency with Venus's modern atmospheric composition occurs in less than 0.4% of runs, in a narrow parameter range where the reducing power introduced by O2 loss processes can balance O2 introduced by H escape. Our models favor hypothetical habitable eras ending before 3 Ga and very reduced melt oxygen fugacities three log units below the fayalite-magnetite-quartz buffer (fO2< FMQ-3), among other constraints.
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Affiliation(s)
| | - Edwin S. Kite
- Department of Geophysical Sciences, University of Chicago, Chicago, IL60637
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Nitrogen isotope evidence for Earth's heterogeneous accretion of volatiles. Nat Commun 2022; 13:4769. [PMID: 35970934 PMCID: PMC9378614 DOI: 10.1038/s41467-022-32516-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 07/28/2022] [Indexed: 11/08/2022] Open
Abstract
The origin of major volatiles nitrogen, carbon, hydrogen, and sulfur in planets is critical for understanding planetary accretion, differentiation, and habitability. However, the detailed process for the origin of Earth's major volatiles remains unresolved. Nitrogen shows large isotopic fractionations among geochemical and cosmochemical reservoirs, which could be used to place tight constraints on Earth's volatile accretion process. Here we experimentally determine N-partitioning and -isotopic fractionation between planetary cores and silicate mantles. We show that the core/mantle N-isotopic fractionation factors, ranging from -4‰ to +10‰, are strongly controlled by oxygen fugacity, and the core/mantle N-partitioning is a multi-function of oxygen fugacity, temperature, pressure, and compositions of the core and mantle. After applying N-partitioning and -isotopic fractionation in a planetary accretion and core-mantle differentiation model, we find that the N-budget and -isotopic composition of Earth's crust plus atmosphere, silicate mantle, and the mantle source of oceanic island basalts are best explained by Earth's early accretion of enstatite chondrite-like impactors, followed by accretion of increasingly oxidized impactors and minimal CI chondrite-like materials before and during the Moon-forming giant impact. Such a heterogeneous accretion process can also explain the carbon-hydrogen-sulfur budget in the bulk silicate Earth. The Earth may thus have acquired its major volatile inventory heterogeneously during the main accretion phase.
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Miyazaki Y, Korenaga J. Inefficient Water Degassing Inhibits Ocean Formation on Rocky Planets: An Insight from Self-Consistent Mantle Degassing Models. ASTROBIOLOGY 2022; 22:713-734. [PMID: 35235378 DOI: 10.1089/ast.2021.0126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
A sufficient amount of water is required at the surface to develop water oceans. A significant fraction of water, however, remains in the mantle during magma ocean solidification, and thus the existence of water oceans is not guaranteed even for exoplanets located in the habitable zone. To discuss the likelihood of ocean formation, we built two models to predict the rate of mantle degassing during the magma ocean stage and the subsequent solid-state convection stage. We find that planets with low H2O/CO2 ratios would not have a sufficient amount of surface water to develop water oceans immediately after magma ocean solidification, and the majority of the water inventory would be retained in the mantle during their subsequent evolution regardless of planetary size. This is because oceanless planets are likely to operate under stagnant lid convection, and for such planets, dehydration stiffening of the depleted lithospheric mantle would limit the rate of mantle degassing. In contrast, a significant fraction of CO2 would already be degassed during magma ocean solidification. With a strong greenhouse effect, all surface water would exist as vapor, and water oceans may be absent throughout planetary evolution. Volatile concentrations in the bulk silicate Earth are close to the threshold amount for ocean formation, so if Venus shared similar concentrations, small differences in solar radiation may explain the divergent evolutionary paths of Earth and Venus.
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Affiliation(s)
- Yoshinori Miyazaki
- Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
| | - Jun Korenaga
- Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA
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Miyazaki Y, Korenaga J. A wet heterogeneous mantle creates a habitable world in the Hadean. Nature 2022; 603:86-90. [PMID: 35236974 DOI: 10.1038/s41586-021-04371-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Accepted: 12/20/2021] [Indexed: 11/09/2022]
Abstract
The Hadean eon, following the global-scale melting of the mantle1-3, is expected to be a dynamic period, during which Earth experienced vastly different conditions. Geologic records, however, suggest that the surface environment of Earth was already similar to the present by the middle of the Hadean4,5. Under what conditions a harsh surface environment could turn into a habitable one remains uncertain6. Here we show that a hydrated mantle with small-scale chemical heterogeneity, created as a result of magma ocean solidification, is the key to ocean formation, the onset of plate tectonics and the rapid removal of greenhouse gases, which are all essential to create a habitable environment on terrestrial planets. When the mantle is wet and dominated by high-magnesium pyroxenites, the removal of carbon dioxide from the atmosphere is expected to be more than ten times faster than the case of a pyrolitic homogeneous mantle and could be completed within 160 million years. Such a chemically heterogeneous mantle would also produce oceanic crust rich in olivine, which is reactive with ocean water and promotes serpentinization. Therefore, conditions similar to the Lost City hydrothermal field7-9 may have existed globally in the Hadean seafloor.
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Affiliation(s)
- Yoshinori Miyazaki
- Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA. .,Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
| | - Jun Korenaga
- Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA
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8
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Oxygen controls on magmatism in rocky exoplanets. Proc Natl Acad Sci U S A 2021; 118:2110427118. [PMID: 34725159 PMCID: PMC8609297 DOI: 10.1073/pnas.2110427118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Accepted: 09/23/2021] [Indexed: 11/18/2022] Open
Abstract
Refractory oxygen bound to cations is a key component of the interior of rocky exoplanets. Its abundance controls planetary properties including metallic core fraction, core composition, and mantle and crust mineralogy. Interior oxygen abundance, quantified with the oxygen fugacity (fO2), also determines the speciation of volatile species during planetary outgassing, affecting the composition of the atmosphere. Although melting drives planetary differentiation into core, mantle, crust, and atmosphere, the effect of fO2 on rock melting has not been studied directly to date, with prior efforts focusing on fO2-induced changes in the valence ratio of transition metals (particularly iron) in minerals and magma. Here, melting experiments were performed using a synthetic iron-free basalt at oxygen levels representing reducing (log fO2 = -11.5 and -7) and oxidizing (log fO2 = -0.7) interior conditions observed in our solar system. Results show that the liquidus of iron-free basalt at a pressure of 1 atm is lowered by 105 ± 10 °C over an 11 log fO2 units increase in oxygen abundance. This effect is comparable in size to the well-known enhanced melting of rocks by the addition of H2O or CO2 This implies that refractory oxygen abundance can directly control exoplanetary differentiation dynamics by affecting the conditions under which magmatism occurs, even in the absence of iron or volatiles. Exoplanets with a high refractory oxygen abundance exhibit more extensive and longer duration magmatic activity, leading to more efficient and more massive volcanic outgassing of more oxidized gas species than comparable exoplanets with a lower rock fO2.
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Barth P, Carone L, Barnes R, Noack L, Mollière P, Henning T. Magma Ocean Evolution of the TRAPPIST-1 Planets. ASTROBIOLOGY 2021; 21:1325-1349. [PMID: 34314604 DOI: 10.1089/ast.2020.2277] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Recent observations of the potentially habitable planets TRAPPIST-1 e, f, and g suggest that they possess large water mass fractions of possibly several tens of weight percent of water, even though the host star's activity should drive rapid atmospheric escape. These processes can photolyze water, generating free oxygen and possibly desiccating the planet. After the planets formed, their mantles were likely completely molten with volatiles dissolving and exsolving from the melt. To understand these planets and prepare for future observations, the magma ocean phase of these worlds must be understood. To simulate these planets, we have combined existing models of stellar evolution, atmospheric escape, tidal heating, radiogenic heating, magma-ocean cooling, planetary radiation, and water-oxygen-iron geochemistry. We present MagmOc, a versatile magma-ocean evolution model, validated against the rocky super-Earth GJ 1132b and early Earth. We simulate the coupled magma-ocean atmospheric evolution of TRAPPIST-1 e, f, and g for a range of tidal and radiogenic heating rates, as well as initial water contents between 1 and 100 Earth oceans. We also reanalyze the structures of these planets and find they have water mass fractions of 0-0.23, 0.01-0.21, and 0.11-0.24 for planets e, f, and g, respectively. Our model does not make a strong prediction about the water and oxygen content of the atmosphere of TRAPPIST-1 e at the time of mantle solidification. In contrast, the model predicts that TRAPPIST-1 f and g would have a thick steam atmosphere with a small amount of oxygen at that stage. For all planets that we investigated, we find that only 3-5% of the initial water will be locked in the mantle after the magma ocean solidified.
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Affiliation(s)
- Patrick Barth
- Centre for Exoplanet Science, University of St Andrews, St Andrews, UK
- SUPA, School of Physics & Astronomy, University of St Andrews, St Andrews, UK
- Max Planck Institute for Astronomy, Heidelberg, Germany
| | | | - Rory Barnes
- Astronomy Department, University of Washington, Seattle, Washington, USA
- NASA Virtual Planetary Laboratory Lead Team, USA
| | - Lena Noack
- Freie Universität Berlin, Institute of Geological Sciences, Berlin, Germany
| | - Paul Mollière
- Max Planck Institute for Astronomy, Heidelberg, Germany
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Russell MJ. The "Water Problem"( sic), the Illusory Pond and Life's Submarine Emergence-A Review. Life (Basel) 2021; 11:429. [PMID: 34068713 PMCID: PMC8151828 DOI: 10.3390/life11050429] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 04/30/2021] [Accepted: 05/01/2021] [Indexed: 01/10/2023] Open
Abstract
The assumption that there was a "water problem" at the emergence of life-that the Hadean Ocean was simply too wet and salty for life to have emerged in it-is here subjected to geological and experimental reality checks. The "warm little pond" that would take the place of the submarine alkaline vent theory (AVT), as recently extolled in the journal Nature, flies in the face of decades of geological, microbiological and evolutionary research and reasoning. To the present author, the evidence refuting the warm little pond scheme is overwhelming given the facts that (i) the early Earth was a water world, (ii) its all-enveloping ocean was never less than 4 km deep, (iii) there were no figurative "Icelands" or "Hawaiis", nor even an "Ontong Java" then because (iv) the solidifying magma ocean beneath was still too mushy to support such salient loadings on the oceanic crust. In place of the supposed warm little pond, we offer a well-protected mineral mound precipitated at a submarine alkaline vent as life's womb: in place of lipid membranes, we suggest peptides; we replace poisonous cyanide with ammonium and hydrazine; instead of deleterious radiation we have the appropriate life-giving redox and pH disequilibria; and in place of messy chemistry we offer the potential for life's emergence from the simplest of geochemically available molecules and ions focused at a submarine alkaline vent in the Hadean-specifically within the nano-confined flexible and redox active interlayer walls of the mixed-valent double layer oxyhydroxide mineral, fougerite/green rust comprising much of that mound.
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Affiliation(s)
- Michael J Russell
- Dipartimento di Chimica, Università degli Studi di Torino, via P. Giuria 7, 10125 Turin, Italy
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11
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Lichtenberg T, Bower DJ, Hammond M, Boukrouche R, Sanan P, Tsai S, Pierrehumbert RT. Vertically Resolved Magma Ocean-Protoatmosphere Evolution: H 2, H 2O, CO 2, CH 4, CO, O 2, and N 2 as Primary Absorbers. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2021; 126:e2020JE006711. [PMID: 33777608 PMCID: PMC7988593 DOI: 10.1029/2020je006711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 01/05/2021] [Accepted: 01/08/2021] [Indexed: 06/12/2023]
Abstract
The earliest atmospheres of rocky planets originate from extensive volatile release during magma ocean epochs that occur during assembly of the planet. These establish the initial distribution of the major volatile elements between different chemical reservoirs that subsequently evolve via geological cycles. Current theoretical techniques are limited in exploring the anticipated range of compositional and thermal scenarios of early planetary evolution, even though these are of prime importance to aid astronomical inferences on the environmental context and geological history of extrasolar planets. Here, we present a coupled numerical framework that links an evolutionary, vertically resolved model of the planetary silicate mantle with a radiative-convective model of the atmosphere. Using this method, we investigate the early evolution of idealized Earth-sized rocky planets with end-member, clear-sky atmospheres dominated by either H2, H2O, CO2, CH4, CO, O2, or N2. We find central metrics of early planetary evolution, such as energy gradient, sequence of mantle solidification, surface pressure, or vertical stratification of the atmosphere, to be intimately controlled by the dominant volatile and outgassing history of the planet. Thermal sequences fall into three general classes with increasing cooling timescale: CO, N2, and O2 with minimal effect, H2O, CO2, and CH4 with intermediate influence, and H2 with several orders of magnitude increase in solidification time and atmosphere vertical stratification. Our numerical experiments exemplify the capabilities of the presented modeling framework and link the interior and atmospheric evolution of rocky exoplanets with multiwavelength astronomical observations.
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Affiliation(s)
- Tim Lichtenberg
- Atmospheric, Oceanic and Planetary Physics, Department of PhysicsUniversity of OxfordOxfordUK
| | - Dan J. Bower
- Center for Space and HabitabilityUniversity of BernBernSwitzerland
| | - Mark Hammond
- Department of the Geophysical SciencesUniversity of ChicagoChicagoILUSA
| | - Ryan Boukrouche
- Atmospheric, Oceanic and Planetary Physics, Department of PhysicsUniversity of OxfordOxfordUK
| | - Patrick Sanan
- Institute of Geophysics, Department of Earth SciencesETH ZurichZurichSwitzerland
| | - Shang‐Min Tsai
- Atmospheric, Oceanic and Planetary Physics, Department of PhysicsUniversity of OxfordOxfordUK
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Russell MJ, Ponce A. Six 'Must-Have' Minerals for Life's Emergence: Olivine, Pyrrhotite, Bridgmanite, Serpentine, Fougerite and Mackinawite. Life (Basel) 2020; 10:E291. [PMID: 33228029 PMCID: PMC7699418 DOI: 10.3390/life10110291] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 11/13/2020] [Accepted: 11/14/2020] [Indexed: 12/25/2022] Open
Abstract
Life cannot emerge on a planet or moon without the appropriate electrochemical disequilibria and the minerals that mediate energy-dissipative processes. Here, it is argued that four minerals, olivine ([Mg>Fe]2SiO4), bridgmanite ([Mg,Fe]SiO3), serpentine ([Mg,Fe,]2-3Si2O5[OH)]4), and pyrrhotite (Fe(1-x)S), are an essential requirement in planetary bodies to produce such disequilibria and, thereby, life. Yet only two minerals, fougerite ([Fe2+6xFe3+6(x-1)O12H2(7-3x)]2+·[(CO2-)·3H2O]2-) and mackinawite (Fe[Ni]S), are vital-comprising precipitate membranes-as initial "free energy" conductors and converters of such disequilibria, i.e., as the initiators of a CO2-reducing metabolism. The fact that wet and rocky bodies in the solar system much smaller than Earth or Venus do not reach the internal pressure (≥23 GPa) requirements in their mantles sufficient for producing bridgmanite and, therefore, are too reduced to stabilize and emit CO2-the staple of life-may explain the apparent absence or negligible concentrations of that gas on these bodies, and thereby serves as a constraint in the search for extraterrestrial life. The astrobiological challenge then is to search for worlds that (i) are large enough to generate internal pressures such as to produce bridgmanite or (ii) boast electron acceptors, including imported CO2, from extraterrestrial sources in their hydrospheres.
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Affiliation(s)
- Michael J. Russell
- Dipartimento di Chimica, Università degli Studi di Torino, via P. Giuria 7, 10125 Turin, Italy
| | - Adrian Ponce
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA;
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