Long recovery from mass extinction seen

It took 10 million years for Earth to recover from the greatest mass extinction ever when life was nearly wiped out 250 million years ago, researchers say. With only 10 percent of plants and animals surviving the extinction event triggered by global warming, acid rain, ocean acidification and ocean anoxia, there has been a longstanding debate about how long it took life on Earth to recover from the cataclysm, scientists said. Researchers from the China University of Geosciences in Wuhan and the University of Bristol in Britain say evidence shows the bounce-back took 10 million years because of the sheer intensity of the crisis and ongoing grim condition on Earth following the first wave of extinction. Those grim conditions existed in bursts for some 5 million to 6 million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects, researchers said. While some groups of animals in the oceans and on land did recover quickly, they suffered repeated setbacks because conditions were not conducive to establishing permanent ecosystems, they said. "Life seemed to be getting back to normal when another crisis hit and set it back again," Bristol paleontologist Michael Benton said in a university release. "The carbon crises were repeated many times, and then finally conditions became normal again after 5 million years or so. "We often see mass extinctions as entirely negative, but in this most devastating case, life did recover, after many millions of years, and new groups emerged," he said. "The event had reset evolution."