Redox state of Earth's magma ocean and its Venus-like early atmosphere
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Open Access
- 1 November 2020
- journal article
- research article
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 6 (48), eabd1387
- https://doi.org/10.1126/sciadv.abd1387
Abstract
Exchange between a magma ocean and vapor produced Earth's earliest atmosphere. Its speciation depends on the oxygen fugacity (fO(2)) set by the Fe3+/Fe2+ ratio of the magma ocean at its surface. Here, we establish the relationship between fO(2) 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 fO(2) 0.5 log units above the iron-wiistite buffer. At this fO(2), 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-N-2, 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.Funding Information
- Australian Research Council (FL130100066)
- Schweizerischer Nationalfonds (180025)
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