Decreasing extents of Archean serpentinization contributed to the rise of an oxidized atmosphere

At present, molecular hydrogen (H 2 ) produced through Fe(II) oxidation during serpentinization of ultramafic rocks represents a small fraction of the global sink for O 2 due to limited exposures of ultramafic rocks. In contrast, ultramafic rocks such as komatiites were much more common in the Early Earth and H 2 production via serpentinization was a likely factor in maintaining an O 2 -free atmosphere throughout most of the Archean. Using thermodynamic simulations, this work quantifies the global O 2 consumption attributed to serpentinization during the past 3.5 billion years. Results show that H 2 generation is strongly dependent on rock compositions where serpentinization of more magnesian lithologies generated substantially higher amounts of H 2 . Consumption of >2 Tmole O 2 yr −1 via low-temperature serpentinization of Archean continents and seafloor is possible. This O 2 sink diminished greatly towards the end of the Archean as ultramafic rocks became less common and helped set the stage for the Great Oxidation Event. Throughout the Archean, H 2 generation via low-temperature ultramafic serpentinization likely helped prevent atmospheric O 2 accumulation and continued until the abundance of ultramafic rocks diminished setting the stage for the Great Oxidation Event.