It takes about 10 million years for the living world to recover from large-scale extinctions and produce mature ecosystems, according to a study published in today’s issue of the journal Nature. “When we got that result, I was just stunned,” said study coauthor James Kirchner of the University of California at Berkeley. Many biologists say that humans are driving species extinct at an accelerating rate that if unchecked will result in one of the biggest extinctions in history, and we may already have destroyed enough species that it will require a full 10 million years for the planet to recover — 20 times as long as humans have existed.