Geochemical and petrological evidence demonstrates that the early Earth possessed a defined atmospheric and mantle oxidation state, which governed volatile outgassing and early biochemical evolution.
Multiple studies examine the geochemical proxies, magma ocean oxidation states, mantle outgassing models, and sulfur-cycling enzymes of the Hadean and Archean eons. These lines of evidence directly support the claim that empirical data indicate the oxidation state of the early Earth's atmosphere and interior.