Redox states of Archean surficial environments: The importance of H-2,H-g instead of O-2,O-g for weathering reactions

Redox states of the Archean Eon have been constrained by various lines of evidence, including atmospheric, photochemical, and ecological models, mass-independent fractionations of sulfur isotopes, Fe-depletion of paleosols, and preservation of diagnostic detrital minerals. Although these lines of evidence present seemingly consistent upper limits on pO(2,g), they are conceptually contradictory about the redox state of Archean surficial environments. Atmospheric, photochemical, and ecological modeling studies suggest weakly reducing environments under redox states represented by moderate H-2,H-g levels. However, current interpretations of Fedepletion in paleosols and the preservation of detrital minerals are based on low O-2,O-g levels at which the reducing detrital minerals are thermodynamically unstable and survive because of slow kinetics of oxidative weathering.