Abstract Molecular hydrogen production occurs through the serpentinization of mantle peridotite exhumed at mid‐ocean ridges. Hydrogen is considered essential to sustain microbial life in the subsurface; however, estimates of hydrogen flux through geological time are unknown. Here we present a model of the primary, abiotic production of molecular hydrogen from the serpentinization of oceanic lithosphere using full‐plate tectonic reconstructions for the last 200 Ma. We find significant variability in hydrogen fluxes (1–70 • 10 16 mol/Ma or 0.2–14.1 • 10 5 Mt/Ma), which are a function of the sensitivity of evolving ocean basins to spreading rates and can be correlated with the opening of key ocean basins during the breakup of Pangea. We suggest that the primary driver of this hydrogen flux is the continental reconfiguration during Pangea breakup, as this produces ocean basins more conducive to exhuming and exposing mantle peridotite at slow and ultraslow spreading ridges. Consequently, present‐day flux estimates are ~7 • 10 17 mol/Ma (1.4 • 10 6 Mt/Ma), driven primarily by the slow and ultraslow spreading ridges in the Atlantic, Indian, and Arctic oceans. As methane has also been sampled alongside hydrogen at hydrothermal vents, we estimate the methane flux using methane‐to‐hydrogen ratios from present‐day hydrothermal vent fluids. These ratios suggest that methane flux ranges between 10 and 100% of the total hydrogen flux, although as the release of methane from these systems is still poorly understood, we suggest a lower estimate, equivalent to around 7–12 • 10 16 mol/Ma (1.1–1.9 • 10 6 Mt/Ma) of methane.
Abstract Serpentinization refers to the alteration of ultramafic rocks that produces serpentines and secondary (hydr)oxides under hydrothermal conditions. Serpentinization can generate H 2 , which in turn can potentially reduce CO/CO 2 and produce organic molecules via Fischer–Tropsch type (FTT) and Sabatier type reactions. Over the last two decades, serpentinization has been extensively studied in laboratories, mainly due to its potential applications in prebiotic chemistry, origin of life in extreme environments, development of carbon‐free energies and CO 2 sequestration. However, the production of H 2 and organics during experimental serpentinization is hugely variable from one publication to another. The experiments span over a large range of pressure and temperature conditions, and starting compositions of fluid and solid phases are also highly variable, which collectively adds up to more than a hundred variables and leads to controversial results. Therefore, it is extremely difficult to compare results between studies, explain their variability and identify key parameters controlling the reactions. To overcome these limitations, we collected and analysed 30 peer‐reviewed articles including over 100 experimental parameters and ca. 30 mineral and organic products, hence building up a database can be completed and implemented in future studies. We then extracted basic statistical information from this dataset and demonstrate how such a comprehensive dataset is essential to better interpret available data and discuss the key parameters controlling the effectiveness of H 2 , CH 4 and other organics production during experimental serpentinization. This is essential to guide the design of future experiments.
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