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

At present, molecular hydrogen (H2) produced through Fe(II) oxidation during serpentinization of ultramafic rocks represents a small fraction of the global sink for O2 due to limited exposures of ultramafic rocks. In contrast, ultramafic rocks such as komatiites were much more common in the Early Earth and H2 production via serpentinization was a likely factor in maintaining an O2-free atmosphere throughout most of the Archean. Using thermodynamic simulations, this work quantifies the global O2 consumption attributed to serpentinization during the past 3.5 billion years. Results show that H2 generation is strongly dependent on rock compositions where serpentinization of more magnesian lithologies generated substantially higher amounts of H2. Consumption of >2 Tmole O2 yr-1 via low-temperature serpentinization of Archean continents and seafloor is possible. This O2 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.