New research from Caltech challenges a long held reading of an ancient carbon isotope signal. The signal in rocks from Karelia, Russia, previously linked to a global disruption of Earth's carbon cycle, may actually come from local heating by magma intrusions. Gases trapped in microscopic pockets show temperatures near 350 degrees Celsius, suggesting hydrocarbons formed and fed seafloor microbes, producing the unusual isotope pattern. The finding raises questions about the Shunga-Francevillian event as a worldwide marker. The team plans to test the same explanation on similar rocks from Gabon using new drill cores. If the local explanation holds, scientists may need to reinterpret other ancient carbon isotope records.
