Abstract
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.
Highlights
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
Microbial methane was an important source of greenhouse gases that kept the early Earth warm before the Great Oxidation Event (GOE, 2.4 Ga) under the faint Sun[1]
We present the evidence that the Kidd Creek gas is a microbial product in a Neoarchaean ecosystem
Summary
The linear trends with high coefficients of determination in the Kidd Creek gas (Fig. 1b, c) indicate that the interference from other reactions is minimal These reactions, including the thermal cracking of kerogen, oxidation of methane, and hydrogenolysis of non-alkyl organic precursors (e.g. carbohydrates, which are abundant in living organic matter), yield neither an exponential distribution of short-chain alkane abundance nor the above hydrogen isotope distribution. (1) All previously reported hydrocarbon gas samples with the above alkyl hydrogenolysis features (a widely varied δD accompanied by relatively uniform δ13C in alkanes, and a deuterium-depleted H2 source as indicated by the δD versus reciprocal hydrogen number correlation line) were obtained from the sites with both pre-GOE serpentinization and preGOE organic matter sedimentation (Fig. 4).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
