The team revealed that the answer may be a large decrease in ocean calcium levels. When these levels were high, the oceans behaved differently, storing less carbon in seawater and releasing more carbon dioxide into the atmosphere. The team used tiny fossil sea creatures, named foraminifera, from seafloor sediments to create the most detailed ocean-chemistry record to date. Using computer models, the team discovered that high levels of calcium change how much carbon can be ‘fixed’ by marine life, said Dr Evans. This would remove carbon from the atmosphere and the ocean and store it in ocean-floor sediments.