, Volume 31, Issue 4-5, pp 311-341

Redox History of the Earth's Interior since ∼3900 Ma: Implications for Prebiotic Molecules

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Abstract

The history of the oxidation state in the Earth's mantle has beenconstrained using (a) the whole-rock abundances of Cr and V inancient volcanics, and (b) the composition of Cr-rich spinels in ancient volcanics. Results indicate that the Earth's mantle hasbeen at-or-near its current oxidation state (±0.5 log-unitfO2) since at least 3600 Ma, and probably since at least 3960 Ma. Volatiles released into the Earth's atmosphere by high-temperature (T ≥ 1300 K) volcanism during this time have been dominated by H2O, CO2, and SO2. This blend ofvolatiles is known to provide smaller yields of prebiotic, organic molecules by atmospheric and surface processes than gasmixtures containing higher concentrations of reduced species suchas H2, CO, and H2S (e.g., Miller, 1998; Zolotov and Shock, 2000). The results discussed in this article independentlysupport the conclusion of Canil (1997, 1999). f the atmosphere was reducing (e.g., CH4, H2, H2S, NH3, CO) at any time during the last ∼3900 Ma,high-temperature volcanic outgassing was not the cause of it.