Depletion of dissolved oxygen in our oceans, which can cause dead zones, is occurring much faster than expected, a new study finds. And by combining oxygen loss with ever-worsening ocean warming and acidification, humans are re-creating the conditions that led to the worst-ever extinction, which killed over 90 percent of marine life 252 million years ago. Researchers at Georgia Institute of Technology reviewed ocean data going back to 1958 and “found that oxygen levels started dropping in the 1980s as ocean temperatures began to climb.”