Redox state of Earth’s magma ocean and its Venus-like early atmosphere
Sossi, P.A.; Burnham, A.D.; Badro, J.; Lanzirotti, A.; Newville, M.; O’Neill, H.S.C. (2020). Redox state of Earth’s magma ocean and its Venus-like early atmosphere. Science Advances 6(48): eabd1387. https://dx.doi.org/10.1126/sciadv.abd1387
In: Science Advances. AAAS: New York. ISSN 2375-2548; e-ISSN 2375-2548, more
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| Authors | | Top |
- Sossi, P.A.
- Burnham, A.D.
- Badro, J.
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- Lanzirotti, A.
- Newville, M.
- O’Neill, H.S.C.
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| Abstract |
Exchange between a magma ocean and vapor produced Earth’s earliest atmosphere. Its speciation depends on the oxygen fugacity (fO2) set by the Fe3+/Fe2+ ratio of the magma ocean at its surface. Here, we establish the relationship between fO2 and Fe3+/Fe2+ in quenched liquids of silicate Earth-like composition at 2173 K and 1 bar. Mantle-derived rocks have Fe3+/(Fe3++Fe2+) = 0.037 ± 0.005, at which the magma ocean defines an fO2 0.5 log units above the iron-wüstite buffer. At this fO2, the solubilities of H-C-N-O species in the magma ocean produce a CO-rich atmosphere. Cooling and condensation of H2O would have led to a prebiotic terrestrial atmosphere composed of CO2-N2, in proportions and at pressures akin to those observed on Venus. Present-day differences between Earth’s atmosphere and those of her planetary neighbors result from Earth’s heliocentric location and mass, which allowed geologically long-lived oceans, in-turn facilitating CO2 drawdown and, eventually, the development of life. |
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