2-billion-year-old carbon isotope signal may be local, not global, Caltech study suggests

A new Caltech-led study questions a long-held interpretation of a 2-billion-year-old carbon isotope anomaly in rocks from Karelia, Russia. The signal, part of the Shunga-Francevillian event, was often cited as evidence of a global disruption of Earth's carbon cycle after oxygen rose. The team analyzed gases trapped in fluid inclusions and found the anomaly can be explained by local magma heating, hydrocarbon generation, and methane-consuming microbes in a small sedimentary basin. This means the reference site may not represent a worldwide event, and the team will now test the same hypothesis on rocks from Gabon. For those tracking carbon cycle science, this matters because it refines how we interpret ancient carbon records used to model Earth's climate history. If the signal is local, then global carbon cycle models built on that assumption need adjustment. The study also shows how modern gas basin insights can be applied to ancient rocks, offering a new lens for reading old data. Published in Geology, the paper is a reminder that even well-established climate markers deserve re-examination when new techniques become available.