Scientists have proposed that a well-known 2-billion-year-old chemical signature, once interpreted as evidence of a global shift in Earth’s carbon cycle, might actually have a more localized origin. Researchers analyzed gases trapped in microscopic pockets within rocks from the Zaonega Formation in Karelia, Russia. They found that the unusual carbon-isotope signal could be explained by local processes: heat from a magma intrusion warmed organic-rich sediments, generating hydrocarbons (including methane), which were then consumed by near-seafloor microbes. These microbes produced biomass with a light carbon isotope signature. The team plans to test whether similar explanations apply to analogous rock samples from the Francevillian Basin in Gabon.
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