Scientists may have misread a 2-billion-year-old clue about Earth

Scientists have found that a famous 2-billion-year-old chemical signature, once thought to record a massive global change in Earth’s carbon cycle, may instead have been produced by local magma, hydrocarbons, and methane-eating microbes. The discovery raises new questions about what was really happening as oxygen transformed the young planet. Scientists may have misread a 2-billion-year-old clue about Earth.

5 to 2 billion years ago, Earth underwent the largest chemical transformation ever recorded at its surface. Oxygen began accumulating in the atmosphere, setting in motion changes that eventually helped make possible the rise of complex organisms such as plants and animals about half a billion years ago. As oxygen levels increased for the first time, enormous amounts of microbial material were buried beneath the seafloor.

That burial trapped carbon in rocks and left behind an unusual isotopic signature. For decades, many scientists have interpreted that signature as evidence that Earth’s carbon cycle became dramatically unbalanced on a global scale. A Famous Signal From Early Earth Evidence supporting that interpretation has come from drill cores — long cylinders of solid rock pulled from deep underground — recovered from ancient marine sediments in Karelia, Russia, and the Francevillian Basin in Gabon.