A seawater throttle on H <sub>2</sub> production in Precambrian serpentinizing systems
Benjamin M. Tutolo, William E. Seyfried, Nicholas J. Tosca
Abstract
Significance Our current understanding of the redox state of Earth’s ancient atmosphere is heavily dependent on the assumption that ancient low-temperature serpentinizing systems produced abundant H 2 , as they do today. Here, we examine this assumption using data that constrain Fe partitioning in serpentine minerals. We find that H 2 production is linked to a Si deficiency in the serpentine structure, which itself is caused by low SiO 2 (aq) concentrations in fluids derived from modern seawater. Calculations accounting for this dependence of H 2 production on seawater SiO 2 (aq) imply that Precambrian serpentinizing systems would have produced up to about two orders of magnitude less H 2 than today, prompting a reexamination of atmospheric redox state and H 2 -dependent origins of life scenarios on early Earth.