Methane from microbial hydrogenolysis of sediment organic matter

Methane, along with other short-chain alkanes from some Archean metasedimentary rocks, has unique isotopic signatures that possibly reflect the generation of atmospheric greenhouse gas on early Earth. We find that alkane gases from the Kidd Creek mines in the Canadian Shield are microbial products in a Neoarchean ecosystem. The widely varied hydrogen and relatively uniform carbon isotopic compositions in the alkanes infer that the alkanes result from the biodegradation of sediment organic matter with serpentinization-derived hydrogen gas.

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FIG: Distinct geochemical signatures of the Kidd Creek gas: a δ13C versus δD. b Distribution of alkane abundances (relative to CH4). cδD against the reciprocal of hydrogen number of alkanes. Blue lines—Kidd Creek gas (depth > 2500 m); violet—hydrothermal field gas data from the Lost City of Mid-Atlantic Ridge, black, grey, and white triangles stand for methane, ethane, and propane, respectively; pink—thermogenic gas data from NW Australia Shelf; red—thermogenic gas data from NW Sichuan Basin, China; black dashed lines—linear trend lines of the Kidd Creek gas.

This proposed process is supported by published geochemical data on the Kidd Creek gas, including the distribution of alkane abundances, stable isotope variations in alkanes, and CH2D2 signatures in methane. The recognition of Archean microbial methane in this work reveals a biochemical process of greenhouse gas generation before the Great Oxidation Event and improves the understanding of the carbon and hydrogen geochemical cycles.

Xia, X., Gao, Y. Methane from microbial hydrogenolysis of sediment organic matter before the Great Oxidation Event. Nat Commun 12,5032 (2021). https://doi.org/10.1038/s41467-021-25336-6

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