Mantle data imply a decline of oxidizable volcanic gases could have triggered the Great Oxidation

Aerobic lifeforms, including humans, thrive because of abundant atmospheric O₂, but for much of Earth history O₂ levels were low. Even after evidence for oxygenic photosynthesis appeared, the atmosphere remained anoxic for hundreds of millions of years until the ~2.4 Ga Great Oxidation Event. The delay of atmospheric oxygenation and its timing remain poorly understood. Two recent studies reveal that the mantle gradually oxidized from the Archean onwards, leading to speculation that such oxidation enabled atmospheric oxygenation. But whether this mechanism works has not been quantitatively examined. Here, we show that these data imply that reducing Archean volcanic gases could have prevented atmospheric O₂ from accumulating until ~2.5 Ga with ≥95% probability. For two decades, mantle oxidation has been dismissed as a key driver of the evolution of O₂ and aerobic life. Our findings warrant a reconsideration for Earth and Earth-like exoplanets.