Hydrogen isotopic evidence for early oxidation of silicate Earth

Pahlevan, Kaveh; Schaefer, Laura; Hirschmann, M. M.

doi:10.31219/osf.io/2wc98

Cited by 4 publications

(6 citation statements)

References 68 publications

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“…6). Such a low value lies within the error bars of the D/H seawater-carbonaceous chondrite "match" which is ≈ 10 -20% (Pahlevan et al, 2019; and references therein).…”

Section: Containing Early Earth's Accretion From D/hsupporting

confidence: 71%

Formation of Venus, Earth and Mars: Constrained by Isotopes

et al. 2020

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Here we discuss the current state of knowledge of terrestrial planet formation from the aspects of different planet formation models and isotopic data from 182 Hf-182 W, U-Pb, lithophile-siderophile elements, 48 Ca/ 44 Ca isotope samples from planetary building blocks, recent reproduction attempts from 36 Ar/ 38 Ar, 20 Ne/ 22 Ne, 36 Ar/ 22 Ne isotope ratios in Venus' and Earth's atmospheres, the expected solar 3 He abundance in Earth's deep mantle and Earth's D/H sea water ratios that shed light on the accretion time of the early protoplanets. Accretion scenarios that can explain the different isotope ratios, including a Moon-forming event ca. 50 Myr after the formation of the Solar System, support the theory that the bulk of Earth's mass (≥ 80 %) most likely accreted within 10-30 Myr. From a combined analysis of the before mentioned isotopes, one finds that proto-Earth accreted a mass of 0.5-0.6 MEarth within the first ≈ 4-5 Myr, the approximate lifetime of the protoplanetary disk. For Venus, the available atmospheric noble gas data are too uncertain for constraining the planet's accretion scenario accurately. However, from the available imprecise Ar and Ne isotope measurements, one finds that proto-Venus could have grown to a mass of 0.85-1.0 MVenus before the disk dissipated. Classical terrestrial planet formation models have struggled to grow large planetary embryos, or even cores of giant planets, quickly from the tiniest materials within the typical lifetime of protoplanetary disks. Pebble accretion could solve this long-standing time scale controversy. Pebble accretion and streaming instabilities produce large planetesimals that grow into Marssized and larger planetary embryos during this early accretion phase. The later stage of accretion can be explained well with the Grand-Tack model as well as the annulus and depleted disk models. The relative roles of pebble accretion and planetesimal accretion/giant impacts are poorly understood and should be investigated with N-body simulations that include pebbles and multiple protoplanets. To summarise, different isotopic dating methods and the latest terrestrial planet formation models indicate that the accretion process from dust settling, planetesimal formation, and growth to large planetary embryos and protoplanets is a fast process that occurred to a great extent in the Solar System within the lifetime of the protoplanetary disk.

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“…6). Such a low value lies within the error bars of the D/H seawater-carbonaceous chondrite "match" which is ≈ 10 -20% (Pahlevan et al, 2019; and references therein).…”

Section: Containing Early Earth's Accretion From D/hsupporting

confidence: 71%

Formation of Venus, Earth and Mars: Constrained by Isotopes

et al. 2020

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“…This suggests that the MO ferric iron content was in the range 3-10% relative iron (Fe 3+ /Fetot =0.03-0.1). Such an oxidized MO would be broadly consistent with conditions required to prevent hydrogen escape (Pahlevan et al, 2019).…”

Section: General Framework and Assumptionssupporting

confidence: 57%

“…1), is still under debate (eg. Pahlevan et al, 2019;Armstrong et al, 2019;Keppler and Gobalek, 2019;Sossi et al, 2020):…”

Section: General Framework and Assumptionsmentioning

confidence: 99%

“…Although no rock specimens have survived from the Hadean eon, some zircon crystals indicate that an early atmosphere, crust, oceans, and possibly life, were most likely established within the first 100 million years of the Earth's history (Catling and Zahnle, 2020). Consistent with such an early evolution, geochemical surveys indicate that most of the CHONS elements were delivered during accretion (Marty et al, 2016;Sarafian et al, 2014;Greenwood et al, 2018;Piani et al, 2020) and were thus processed by the various differentiation events, in particular the magma ocean stages (Pahlevan et al, 2019;Grewal et al, 2020;Sossi et al, 2020) (see Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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Redox controls during magma ocean degassing

Gaillard

Bernadou

Roskosz

et al. 2022

Earth and Planetary Science Letters

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Nitrogen, carbon, hydrogen and sulfur are essential elements for life and comprise about 1 % of terrestrial planet masses. These elements dominate planetary surfaces due to their volatile nature, but the Earth's interior also constitutes a major C-H-N-S reservoir. Resolving the origin of the surficial versus deep volatile reservoirs requires the past 4.5 Giga-years of mantle outgassing and ingassing processes to be reconstructed, involving many unknowns. As an alternative, we propose to define the primordial distribution of volatiles resulting from degassing of the Earth's magma ocean (MO). The equilibrium partitioning of C-H-O-N-S elements between the MO and its atmosphere is calculated by means of solubility laws, extrapolated to high temperatures and over a large range of redox conditions. Depending on the redox conditions, the amount of volatiles, and the size of the MO considered, we show that the last MO episode may have degassed 40-220 bar atmospheres, whereas hundreds to thousands of ppm of C-H-O-N-S can be retained in the magma. Two contrasting scenarios are investigated: reduced vs. oxidized MO. For reduced cases (IW+2) would be dry and C-N-S-rich. An intermediate redox state produces a C-N atmosphere. In many cases, the present-day surficial abundances (atmosphere+ocean+crust) of C and N, the most volatile elements, are very close to the calculated primordial MO -atmosphere distribution. This probably means that lithospheric recycling and post-magma ocean degassing only moderately alter the surficial abundances of these elements. Sulfur, in contrast, must have been mostly outgassed by post-MO events. Changes in redox conditions during magma ocean degassing played a first order role in the composition of the primordial atmosphere of planets. We suggest that the more oxidized conditions on Venus due to H-loss may have played a role in the growth of a dry MO atmosphere on this planet compared to an H-bearing one on Earth. To verify these first order assertions, constraints on volatile behaviour under extreme magma ocean conditions and upon magma ocean solidification are urgently needed.

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“…Jacobson et al 2014;Bottke et al 2015). The closeto-chondritic D/H ratio of sea water provides evidence that the oxidation of silicate Earth occurred during or before the crystallization of the final global-scale magma ocean (Pahlevan et al 2019, see Fig. 1).…”

Section: From Magma To a Water Oceanmentioning

confidence: 94%

Mission to Planet Earth: The First Two Billion Years

et al. 2020

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Solar radiation and geological processes over the first few million years of Earth’s history, followed soon thereafter by the origin of life, steered our planet towards an evolutionary trajectory of long-lived habitability that ultimately enabled the emergence of complex life. We review the most important conditions and feedbacks over the first 2 billion years of this trajectory, which perhaps represent the best analogue for other habitable worlds in the galaxy. Crucial aspects included: (1) the redox state and volatile content of Earth’s building blocks, which determined the longevity of the magma ocean and its ability to degas H2O and other greenhouse gases, in particular CO2, allowing the condensation of a water ocean; (2) the chemical properties of the resulting degassed mantle, including oxygen fugacity, which would have not only affected its physical properties and thus its ability to recycle volatiles and nutrients via plate tectonics, but also contributed to the timescale of atmospheric oxygenation; (3) the emergence of life, in particular the origin of autotrophy, biological N2 fixation, and oxygenic photosynthesis, which accelerated sluggish abiotic processes of transferring some volatiles back into the lithosphere; (4) strong stellar UV radiation on the early Earth, which may have eroded significant amounts of atmospheric volatiles, depending on atmospheric CO2/N2 ratios and thus impacted the redox state of the mantle as well as the timing of life’s origin; and (5) evidence of strong photochemical effects on Earth’s sulfur cycle, preserved in the form of mass-independent sulfur isotope fractionation, and potentially linked to fractionation in organic carbon isotopes. The early Earth presents itself as an exoplanet analogue that can be explored through the existing rock record, allowing us to identify atmospheric signatures diagnostic of biological metabolisms that may be detectable on other inhabited planets with next-generation telescopes. We conclude that investigating the development of habitable conditions on terrestrial planets, an inherently complex problem, requires multi-disciplinary collaboration and creative solutions.

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Hydrogen isotopic evidence for early oxidation of silicate Earth

Cited by 4 publications

References 68 publications

Formation of Venus, Earth and Mars: Constrained by Isotopes

Formation of Venus, Earth and Mars: Constrained by Isotopes

Redox controls during magma ocean degassing

Mission to Planet Earth: The First Two Billion Years

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