A new study of an ancient period that is considered the closest natural analog to the era of modern human carbon emissions has found that massive volcanism sent great waves of carbon into the oceans over thousands of years—but that nature did not come close to matching what humans are doing today. The study estimates that humans are now introducing the element three to eight times faster, or possibly even more. The consequences for life both in the water and on land are potentially catastrophic. The findings appear this week in the journal Proceedings of the National Academy of Sciences.