113-million-year-old fossils reveal how volcanic CO2 caused plankton extinction

Tiny fossils have helped scientists crack a Cretaceous cold case. Using chemical signals preserved in microscopic shells, Northwestern University researchers found strong evidence that ocean acidification helped trigger one of the biggest extinction events in the history of planktic foraminifera, small shell-building organisms that are essential to Earth’s carbon cycle.The extinction happened around 113 million years ago, during the Early Cretaceous, and appears to have been driven by massive volcanic eruptions from the Kerguelen Plateau in the southern Indian Ocean. Those eruptions released huge amounts of carbon dioxide into the atmosphere, which then dissolved into the sea and made surface waters more acidic. That chemical shift made it much harder for marine organisms to build and maintain their shells.What the fossils revealedThe study focused on planktic foraminifera, tiny organisms that live near the ocean surface and build shells out of calcium carbonate.