Methane from microbial hydrogenolysis of sediment organic matter before the Great Oxidation Event

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. 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. Microbial CH4 kept the early Earth warm under the faint young sun, but clear records are lacking. Here the authors present isotopic evidence that CH4 seepage in the Canadian shield is from hydrogen biodegradation in a Neoarchean ecosystem rather than an abiotic synthesis product.

Automated summary

The study suggests that the alkane gases in the Kidd Creek mines in Canada are microbial products in a Neoarchean ecosystem, created through the biodegradation of sediment organic matter by serpentinization-derived hydrogen gas. This process is supported by geochemical data on the Kidd Creek gas, indicating a biochemical process of greenhouse gas generation before the Great Oxidation Event.