Redox state of earth's magma ocean and its venus-like early atmosphere

Paolo A. Sossi, Antony D. Burnham, James Badro, Antonio Lanzirotti, Matt Newville, Hugh St C. O'Neill

Research output: Contribution to journalArticleResearchpeer-review

70 Citations (Scopus)


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.

Original languageEnglish
Article numberabd1387
Number of pages8
JournalScience Advances
Issue number48
Publication statusPublished - 25 Nov 2020
Externally publishedYes

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