Accretion of these bodies introduces a considerable degree of stochasticity into the planetary inventories of these elements ( 4, 5) and, importantly, into planetary oxidation states. A small fraction of these embryos may have been sourced from the outer solar system and are expected to have been richer in atmophile elements such as H, C, and N. Models of their accretion suggest that the inner planets formed through an evolving hierarchy of solid-body size distributions, the terminal stages of which saw giant collisions between roughly Mars-sized planetary embryos ( 3).
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 CO 2 drawdown and, eventually, the development of life.Įarth’s present-day N 2-O 2 atmosphere differs markedly from those of her planetary neighbors, Venus and Mars, which both have CO 2-rich atmospheres with minor N 2 ( 1, 2). Cooling and condensation of H 2O would have led to a prebiotic terrestrial atmosphere composed of CO 2-N 2, in proportions and at pressures akin to those observed on Venus. At this fO 2, the solubilities of H-C-N-O species in the magma ocean produce a CO-rich atmosphere. Mantle-derived rocks have Fe 3+/(Fe 3++Fe 2+) = 0.037 ± 0.005, at which the magma ocean defines an fO 2 0.5 log units above the iron-wüstite buffer. Here, we establish the relationship between fO 2 and Fe 3+/Fe 2+ in quenched liquids of silicate Earth-like composition at 2173 K and 1 bar. Its speciation depends on the oxygen fugacity ( fO 2) set by the Fe 3+/Fe 2+ ratio of the magma ocean at its surface. Exchange between a magma ocean and vapor produced Earth’s earliest atmosphere.
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