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Nimmo F, Kleine T, Morbidelli A. Tidally driven remelting around 4.35 billion years ago indicates the Moon is old. Nature 2024; 636:598-602. [PMID: 39695207 DOI: 10.1038/s41586-024-08231-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2024] [Accepted: 10/16/2024] [Indexed: 12/20/2024]
Abstract
The last giant impact on Earth is thought to have formed the Moon1. The timing of this event can be determined by dating the different rocks assumed to have crystallized from the lunar magma ocean (LMO). This has led to a wide range of estimates for the age of the Moon between 4.35 and 4.51 billion years ago (Ga), depending on whether ages for lunar whole-rock samples2-4 or individual zircon grains5-7 are used. Here we argue that the frequent occurrence of approximately 4.35-Ga ages among lunar rocks and a spike in zircon ages at about the same time8 is indicative of a remelting event driven by the Moon's orbital evolution rather than the original crystallization of the LMO. We show that during passage through the Laplace plane transition9, the Moon experienced sufficient tidal heating and melting to reset the formation ages of most lunar samples, while retaining an earlier frozen-in shape10 and rare, earlier-formed zircons. This paradigm reconciles existing discrepancies in estimates for the crystallization time of the LMO, and permits formation of the Moon within a few tens of million years of Solar System formation, consistent with dynamical models of terrestrial planet formation11. Remelting of the Moon also explains the lower number of lunar impact basins than expected12,13, and allows metal from planetesimals accreted to the Moon after its formation to be removed to the lunar core, explaining the apparent deficit of such materials in the Moon compared with Earth14.
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Affiliation(s)
- Francis Nimmo
- Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USA.
| | - Thorsten Kleine
- Max Planck Institute for Solar System Research, Göttingen, Germany
| | - Alessandro Morbidelli
- Collège de France, CNRS, PSL University, Sorbonne University, Paris, France
- Laboratoire Lagrange, Université Cote d'Azur, CNRS, Observatoire de la Côte d'Azur, Boulevard de l'Observatoire, Nice, France
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2
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Wogan NF, Catling DC, Zahnle KJ. Timing and Likelihood of the Origin of Life Derived from Post-Impact Highly Reducing Atmospheres. ASTROBIOLOGY 2024; 24:881-891. [PMID: 39344973 DOI: 10.1089/ast.2023.0128] [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: 10/01/2024]
Abstract
Big impacts on the early Earth would have created highly reducing atmospheres that generated molecules needed for the origin of life, such as nitriles. However, such impactors could have been followed by collisions that were sufficiently big to vaporize the ocean and destroy any pre-existing life. Thus, a post-impact-reducing atmosphere that gives rise to life needs to be followed by a lack of subsequent sterilizing impacts for life to persist. We assume that prebiotic chemistry required a post-impact-reducing atmosphere. Then, using statistics for the impact history on Earth and the minimum impact mass needed to generate post-impact highly reducing atmospheres, we show that the median timing of impact-driven biopoiesis is favored early in the Hadean, ∼4.35 Ga. However, uncertainties are large because impact bombardment is stochastic, and so biopoiesis could have occurred between 4.45 and 3.9 Ga within 95% uncertainty. In an optimistic scenario for biopoiesis from post-impact-reducing atmospheres, we find that the origin of life is favorable in ∼90% of stochastic impact realizations. In our most pessimistic case, biopoiesis is still fairly likely (∼20% chance). This potentially bodes well for life on rocky exoplanets that have experienced an early episode of impact bombardment given how planets form.
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Affiliation(s)
- Nicholas F Wogan
- Space Science Division, NASA Ames Research Center, Moffett Field, California, USA
| | - David C Catling
- Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
| | - Kevin J Zahnle
- Space Science Division, NASA Ames Research Center, Moffett Field, California, USA
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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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Cornish-Bowden A, Cárdenas ML. The essence of life revisited: how theories can shed light on it. Theory Biosci 2022; 141:105-123. [PMID: 33956294 PMCID: PMC8101340 DOI: 10.1007/s12064-021-00342-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Accepted: 03/23/2021] [Indexed: 12/12/2022]
Abstract
Disagreement over whether life is inevitable when the conditions can support life remains unresolved, but calculations show that self-organization can arise naturally from purely random effects. Closure to efficient causation, or the need for all specific catalysts used by an organism to be produced internally, implies that a true model of an organism cannot exist, though this does not exclude the possibility that some characteristics can be simulated. Such simulations indicate that there is a limit to how small a self-organizing system can be: much smaller than a bacterial cell, but around the size of a typical virus particle. All current theories of life incorporate, at least implicitly, the idea of catalysis, but they largely ignore the need for metabolic regulation.
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Abstract
Due to active plate tectonics, there are no direct rock archives covering the first ca. 500 million y of Earth’s history. Therefore, insights into Hadean geodynamics rely on indirect observations from geochemistry. We present a high-precision 182W dataset for rocks from the Kaapvaal Craton, southern Africa, revealing the presence of Hadean protocrustal remnants in Earth’s mantle. This has broad implications for geochemists, geophysicists, and modelers, as it bridges contrasting 182W isotope patterns in Archean and modern mantle-derived rocks. The data reveal the origin of seismically and isotopically anomalous domains in the deep mantle and also provide firm evidence for the operation of silicate differentiation processes during the first 60 million y of Earth’s history. With plate tectonics operating on Earth, the preservation potential for mantle reservoirs from the Hadean Eon (>4.0 Ga) has been regarded as very small. The quest for such early remnants has been spurred by the observation that many Archean rocks exhibit excesses of 182W, the decay product of short-lived 182Hf. However, it remains speculative whether Archean 182W anomalies and also 182W deficits found in many young ocean island basalts (OIBs) mirror primordial Hadean mantle differentiation or merely variable contributions from older meteorite building blocks delivered to the growing Earth. Here, we present a high-precision 182W isotope dataset for 3.22- to 3.55-Ga-old rocks from the Kaapvaal Craton, southern Africa. In expanding previous work, our study reveals widespread 182W deficits in different rock units from the Kaapvaal Craton and also the discovery of a negative covariation between short-lived 182W and long-lived 176Hf–143Nd–138Ce patterns, a trend of global significance. Among different models, these distinct patterns can be best explained by the presence of recycled mafic restites from Hadean protocrust in the ancient mantle beneath the Kaapvaal Craton. Further, the data provide unambiguous evidence for the operation of silicate differentiation processes on Earth during the lifetime of 182Hf, that is, the first 60 million y after solar system formation. The striking isotopic similarity between recycled protocrust and the low-182W endmember of modern OIBs might also constitute the missing link bridging 182W isotope systematics in Archean and young mantle-derived rocks.
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Was There Land on the Early Earth? Life (Basel) 2021; 11:life11111142. [PMID: 34833018 PMCID: PMC8623345 DOI: 10.3390/life11111142] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Revised: 10/22/2021] [Accepted: 10/25/2021] [Indexed: 11/17/2022] Open
Abstract
The presence of exposed land on the early Earth is a prerequisite for a certain type of prebiotic chemical evolution in which the oscillating activity of water, driven by short-term, day–night, and seasonal cycles, facilitates the synthesis of proto-biopolymers. Exposed land is, however, not guaranteed to exist on the early Earth, which is likely to have been drastically different from the modern Earth. This mini-review attempts to provide an up-to-date account on the possibility of exposed land on the early Earth by integrating recent geological and geophysical findings. Owing to the competing effects of the growing ocean and continents in the Hadean, a substantial expanse of the Earth’s surface (∼20% or more) could have been covered by exposed continents in the mid-Hadean. In contrast, exposed land may have been limited to isolated ocean islands in the late Hadean and early Archean. The importance of exposed land during the origins of life remains an open question.
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Sakuraba H, Kurokawa H, Genda H, Ohta K. Numerous chondritic impactors and oxidized magma ocean set Earth's volatile depletion. Sci Rep 2021; 11:20894. [PMID: 34686749 PMCID: PMC8536732 DOI: 10.1038/s41598-021-99240-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 09/22/2021] [Indexed: 11/22/2022] Open
Abstract
Earth’s surface environment is largely influenced by its budget of major volatile elements: carbon (C), nitrogen (N), and hydrogen (H). Although the volatiles on Earth are thought to have been delivered by chondritic materials, the elemental composition of the bulk silicate Earth (BSE) shows depletion in the order of N, C, and H. Previous studies have concluded that non-chondritic materials are needed for this depletion pattern. Here, we model the evolution of the volatile abundances in the atmosphere, oceans, crust, mantle, and core through the accretion history by considering elemental partitioning and impact erosion. We show that the BSE depletion pattern can be reproduced from continuous accretion of chondritic bodies by the partitioning of C into the core and H storage in the magma ocean in the main accretion stage and atmospheric erosion of N in the late accretion stage. This scenario requires a relatively oxidized magma ocean (\documentclass[12pt]{minimal}
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\begin{document}$$f_{{\mathrm{O}}_2}$$\end{document}fO2 at the iron-wüstite buffer), the dominance of small impactors in the late accretion, and the storage of H and C in oceanic water and carbonate rocks in the late accretion stage, all of which are naturally expected from the formation of an Earth-sized planet in the habitable zone.
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Affiliation(s)
- Haruka Sakuraba
- Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8551, Japan.
| | - Hiroyuki Kurokawa
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
| | - Hidenori Genda
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
| | - Kenji Ohta
- Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
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Abstract
Globally distributed kimberlites with broadly chondritic initial 143Nd-176Hf isotopic systematics may be derived from a chemically homogenous, relatively primitive mantle source that remained isolated from the convecting mantle for much of the Earth's history. To assess whether this putative reservoir may have preserved remnants of an early Earth process, we report 182W/184W and 142Nd/144Nd data for "primitive" kimberlites from 10 localities worldwide, ranging in age from 1,153 to 89 Ma. Most are characterized by homogeneous μ182W and μ142Nd values averaging -5.9 ± 3.6 ppm (2SD, n = 13) and +2.7 ± 2.9 ppm (2SD, n = 6), respectively. The remarkably uniform yet modestly negative μ182W values, coupled with chondritic to slightly suprachondritic initial 143Nd/144Nd and 176Hf/177Hf ratios over a span of nearly 1,000 Mya, provides permissive evidence that these kimberlites were derived from one or more long-lived, early formed mantle reservoirs. Possible causes for negative μ182W values among these kimberlites include the transfer of W with low μ182W from the core to the mantle source reservoir(s), creation of the source reservoir(s) as a result of early silicate fractionation, or an overabundance of late-accreted materials in the source reservoir(s). By contrast, two younger kimberlites emplaced at 72 and 52 Ma and characterized by distinctly subchondritic initial 176Hf/177Hf and 143Nd/144Nd have μ182W values consistent with the modern upper mantle. These isotopic compositions may reflect contamination of the ancient kimberlite source by recycled crustal components with μ182W ≥ 0.
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9
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Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion. Proc Natl Acad Sci U S A 2020; 117:13997-14004. [PMID: 32513744 PMCID: PMC7322010 DOI: 10.1073/pnas.2003907117] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Volatile elements play a critical role in the evolution of Earth. Nevertheless, the mechanism(s) by which Earth acquired, and was able to preserve its volatile budget throughout its violent accretionary history, remains uncertain. In this study, we analyzed noble gas isotopes in volcanic gases from the Yellowstone mantle plume, thought to sample the deep primordial mantle, to determine the origin of volatiles on Earth. We find that Kr and Xe isotopes within the deep mantle have a similar chondritic origin to those found previously in the upper mantle. This suggests that the Earth has retained chondritic volatiles throughout the accretion and, therefore, terrestrial volatiles cannot not solely be the result of late additions following the Moon-forming impact. Identifying the origin of noble gases in Earth’s mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of 129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth’s history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth’s volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.
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10
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Bekaert DV, Broadley MW, Marty B. The origin and fate of volatile elements on Earth revisited in light of noble gas data obtained from comet 67P/Churyumov-Gerasimenko. Sci Rep 2020; 10:5796. [PMID: 32242104 PMCID: PMC7118078 DOI: 10.1038/s41598-020-62650-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Accepted: 03/17/2020] [Indexed: 11/25/2022] Open
Abstract
The origin of terrestrial volatiles remains one of the most puzzling questions in planetary sciences. The timing and composition of chondritic and cometary deliveries to Earth has remained enigmatic due to the paucity of reliable measurements of cometary material. This work uses recently measured volatile elemental ratios and noble gas isotope data from comet 67P/Churyumov-Gerasimenko (67P/C-G), in combination with chondritic data from the literature, to reconstruct the composition of Earth’s ancient atmosphere. Comets are found to have contributed ~20% of atmospheric heavy noble gases (i.e., Kr and Xe) but limited amounts of other volatile elements (water, halogens and likely organic materials) to Earth. These cometary noble gases were likely mixed with chondritic - and not solar - sources to form the atmosphere. We show that an ancient atmosphere composed of chondritic and cometary volatiles is more enriched in Xe relative to the modern atmosphere, requiring that 8–12 times the present-day inventory of Xe was lost to space. This potentially resolves the long-standing mystery of Earth’s “missing xenon”, with regards to both Xe elemental depletion and isotopic fractionation in the atmosphere. The inferred Kr/H2O and Xe/H2O of the initial atmosphere suggest that Earth’s surface volatiles might not have been fully delivered by the late accretion of volatile-rich carbonaceous chondrites. Instead, “dry” materials akin to enstatite chondrites potentially constituted a significant source of chondritic volatiles now residing on the Earth’s surface. We outline the working hypotheses, implications and limitations of this model in the last section of this contribution.
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Affiliation(s)
- David V Bekaert
- Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 CNRS - Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, 54501, Vandoeuvre-lès-Nancy, France.
| | - Michael W Broadley
- Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 CNRS - Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, 54501, Vandoeuvre-lès-Nancy, France.
| | - Bernard Marty
- Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 CNRS - Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, 54501, Vandoeuvre-lès-Nancy, France
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11
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Ruthenium isotope vestige of Earth's pre-late-veneer mantle preserved in Archaean rocks. Nature 2020; 579:240-244. [PMID: 32161386 PMCID: PMC7212018 DOI: 10.1038/s41586-020-2069-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 01/15/2020] [Indexed: 12/03/2022]
Abstract
The accretion of volatile-rich material from the outer solar system represents a crucial prerequisite for Earth developing oceans and becoming a habitable planet1–4. However, the timing of this accretion remains controversial5–8. It was proposed that volatile elements were added to Earth by late accretion of a late veneer consisting of carbonaceous chondrite-like material after core formation had ceased6,9,10. This view, however, could not be reconciled with the distinct ruthenium (Ru) isotope composition of carbonaceous chondrites5,11 compared to the modern mantle12, and in fact also not with any known meteorite group5. As a possible solution, Earth’s pre-late veneer mantle could already have contained a significant amount of Ru that was not fully extracted by core formation13. The presence of such pre-late veneer Ru could only be proven if its isotope composition would be distinct from that of the modern mantle. Here we report the first high-precision mass-independent Ru isotope compositions for Eoarchean ultramafic rocks from SW Greenland, which display a relative 100Ru excess of +22 parts per million compared to the modern mantle value. This 100Ru excess indicates that the source of the Eoarchean rocks already contained a significant fraction of Ru prior to the late veneer. By 3.7 Gyr the mantle beneath the SW Greenland rocks had not yet fully equilibrated with late accreted material. Otherwise, no Ru isotopic difference relative to the modern mantle would be observed. By considering constraints from other highly siderophile elements beyond Ru14, the composition of the modern mantle can only be reconciled if the late veneer contained significant portions of carbonaceous chondrite-like materials with their characteristic 100Ru deficits. These data therefore relax previous constraints on the late veneer and now permit that volatile-rich material from the outer solar system was delivered to Earth during late accretion.
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12
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Cornish-Bowden A, Cárdenas ML. Contrasting theories of life: Historical context, current theories. In search of an ideal theory. Biosystems 2020; 188:104063. [DOI: 10.1016/j.biosystems.2019.104063] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 10/10/2019] [Accepted: 10/10/2019] [Indexed: 12/18/2022]
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13
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Marchi S, Walker RJ, Canup RM. A compositionally heterogeneous martian mantle due to late accretion. SCIENCE ADVANCES 2020; 6:eaay2338. [PMID: 32095525 PMCID: PMC7015684 DOI: 10.1126/sciadv.aay2338] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 11/26/2019] [Indexed: 06/10/2023]
Abstract
The approximately chondritic estimated relative abundances of highly siderophile elements (HSE) in the bulk martian mantle suggest that these elements were added after Mars' core formed. The shergottite-nakhlite-chassigny (SNC) meteorites imply an average mantle Pt abundance of ≈3 to 5 parts per billion, which requires the addition of 1.6 × 1021 kilograms of chondritic material, or 0.25% martian masses, to the silicate Mars. Here, we present smoothed particle hydro-dynamics impact simulations that show that Mars' HSE abundances imply one to three late collisions by large differentiated projectiles. We show that these collisions would produce a compositionally heterogeneous martian mantle. Based mainly on W isotopes, it has been argued that Mars grew rapidly in only about 2 to 4 million years (Ma). However, we find that impact generation of mantle domains with variably fractionated Hf/W and diverse 182W could imply a Mars formation time scale up to 15 Ma.
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Affiliation(s)
| | - Richard J. Walker
- Department of Geology, University of Maryland, College Park, MD, USA
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14
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Pahlevan K, Schaefer L, Hirschmann MM. Hydrogen isotopic evidence for early oxidation of silicate Earth. EARTH AND PLANETARY SCIENCE LETTERS 2019; 526:115770. [PMID: 33688096 PMCID: PMC7939044 DOI: 10.1016/j.epsl.2019.115770] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The Moon-forming giant impact extensively melts and partially vaporizes the silicate Earth and delivers a substantial mass of metal to Earth's core. The subsequent evolution of the magma ocean and overlying atmosphere has been described by theoretical models but observable constraints on this epoch have proved elusive. Here, we report thermodynamic and climate calculations of the primordial atmosphere during the magma ocean and water ocean epochs respectively and forge new links with observations to gain insight into the behavior of volatiles on the Hadean Earth. As accretion wanes, Earth's magma ocean crystallizes, outgassing the bulk of its volatiles into the primordial atmosphere. The redox state of the magma ocean controls both the chemical composition of the outgassed volatiles and the hydrogen isotopic composition of water oceans that remain after hydrogen escape from the primordial atmosphere. The climate modeling indicates that multi-bar H2-rich atmospheres generate sufficient greenhouse warming and rapid kinetics resulting in ocean-atmosphere H2O-H2 isotopic equilibration. Whereas water condenses and is mostly retained, molecular hydrogen does not condense and can escape, allowing large quantities (~102 bars) of hydrogen - if present - to be lost from the Earth in this epoch. Because the escaping inventory of H can be comparable to the hydrogen inventory in primordial water oceans, equilibrium deuterium enrichment can be large with a magnitude that depends on the initial atmospheric H2 inventory. Under equilibrium partitioning, the water molecule concentrates deuterium and, to the extent that hydrogen in other forms (e.g., H2) are significant species in the outgassed atmosphere, pronounced D/H enrichments (~1.5-2x) in the oceans are expected from equilibrium partitioning in this epoch. By contrast, the common view that terrestrial water has a carbonaceous chondritic source requires the oceans to preserve the isotopic composition of that source, undergoing minimal D-enrichment via equilibration with H2 followed by hydrodynamic escape. Such minimal enrichment places upper limits on the amount of primordial atmospheric H2 in contact with Hadean water oceans and implies oxidizing conditions (logfO2>IW+1, H2/H2O<0.3) for outgassing from the magma ocean. Preservation of an approximate carbonaceous chondrite D/H signature in the oceans thus provides evidence that the observed oxidation of silicate Earth occurred before crystallization of the final magma ocean, yielding a new constraint on the timing of this critical event in Earth history. The seawater-carbonaceous chondrite "match" in D/H (to ~10-20%) further constrains the prior existence of an atmospheric H2 inventory - of any origin - on post-giant-impact Earth to <20 bars, and suggests that the terrestrial mantle supplied the oxidant for the chemical resorption of metals during terrestrial late accretion.
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Affiliation(s)
- Kaveh Pahlevan
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287, USA
| | - Laura Schaefer
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287, USA
| | - Marc M. Hirschmann
- Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA
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15
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Zube NG, Nimmo F, Fischer RA, Jacobson SA. Constraints on terrestrial planet formation timescales and equilibration processes in the Grand Tack scenario from Hf-W isotopic evolution. EARTH AND PLANETARY SCIENCE LETTERS 2019; 522:210-218. [PMID: 32636530 PMCID: PMC7339907 DOI: 10.1016/j.epsl.2019.07.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We examine 141 N-body simulations of terrestrial planet late-stage accretion that use the Grand Tack scenario, coupling the collisional results with a hafnium-tungsten (Hf-W) isotopic evolution model. Accretion in the Grand Tack scenario results in faster planet formation than classical accretion models because of higher planetesimal surface density induced by a migrating Jupiter. Planetary embryos which grow rapidly experience radiogenic ingrowth of mantle tungsten which is inconsistent with the measured terrestrial value, unless much of the tungsten is removed by an impactor core that mixes thoroughly with the target mantle. For physically Earth-like surviving planets, we find that the fraction of equilibrating impactor core kcore ≥ 0.6 is required to produce results agreeing with observed terrestrial tungsten anomalies (assuming equilibration with relatively large volumes of target mantle material; smaller equilibrating mantle volumes would require even larger kcore ). This requirement of substantial core re-equilibration may be difficult to reconcile with fluid dynamical predictions and hydrocode simulations of mixing during large impacts, and hence this result disfavors the rapid planet building of Grand Tack accretion.
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Affiliation(s)
- Nicholas G. Zube
- University of California Santa Cruz, Dept. of Earth and Planetary Sciences, 1156 High St., Santa Cruz, CA 95064, USA
| | - Francis Nimmo
- University of California Santa Cruz, Dept. of Earth and Planetary Sciences, 1156 High St., Santa Cruz, CA 95064, USA
| | - Rebecca A. Fischer
- Harvard University, Dept. Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138, USA
| | - Seth A. Jacobson
- Northwestern University, Dept. Earth and Planetary Sciences, 2145 Sheridan Road, Evanston, IL 60208, USA
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16
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Recreating ancient metabolic pathways before enzymes. Bioorg Med Chem 2019; 27:2292-2297. [DOI: 10.1016/j.bmc.2019.03.012] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 03/02/2019] [Accepted: 03/06/2019] [Indexed: 12/12/2022]
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17
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Grewal DS, Dasgupta R, Sun C, Tsuno K, Costin G. Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact. SCIENCE ADVANCES 2019; 5:eaau3669. [PMID: 30746449 PMCID: PMC6357864 DOI: 10.1126/sciadv.aau3669] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 12/10/2018] [Indexed: 05/31/2023]
Abstract
Earth's status as the only life-sustaining planet is a result of the timing and delivery mechanism of carbon (C), nitrogen (N), sulfur (S), and hydrogen (H). On the basis of their isotopic signatures, terrestrial volatiles are thought to have derived from carbonaceous chondrites, while the isotopic compositions of nonvolatile major and trace elements suggest that enstatite chondrite-like materials are the primary building blocks of Earth. However, the C/N ratio of the bulk silicate Earth (BSE) is superchondritic, which rules out volatile delivery by a chondritic late veneer. In addition, if delivered during the main phase of Earth's accretion, then, owing to the greater siderophile (metal loving) nature of C relative to N, core formation should have left behind a subchondritic C/N ratio in the BSE. Here, we present high pressure-temperature experiments to constrain the fate of mixed C-N-S volatiles during core-mantle segregation in the planetary embryo magma oceans and show that C becomes much less siderophile in N-bearing and S-rich alloys, while the siderophile character of N remains largely unaffected in the presence of S. Using the new data and inverse Monte Carlo simulations, we show that the impact of a Mars-sized planet, having minimal contributions from carbonaceous chondrite-like material and coinciding with the Moon-forming event, can be the source of major volatiles in the BSE.
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Affiliation(s)
- Damanveer S. Grewal
- Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
| | | | - Chenguang Sun
- Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
| | - Kyusei Tsuno
- Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
| | - Gelu Costin
- Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
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