科学美国人60秒 SSS 2014-2-24（在线收听）

 It was the largest of the five major mass extinctions in earth's history, well before the dinosaur killer 66 million years ago. What's called the end Permian extinction 252 million years ago, wiped out 96% of aquatic species and 70% of species on land. Scientists have been trying to gauge the time of the extinction and they hope to determine its causes. Now researchers say it's the fastest mass extinction known. Using new tools and models, including a fresh analysis of reference in China, the researchers determined that the extinction took only about 60,000 years. That's incredibly quick by geological standards, and it's more than ten times faster than previous estimates. The report is the preceding of the national academy sciences. Study author Simuel Aron from MIT says they can't yet compare the speed of the previous extinction to the extinction rates raised by human activities today. But he says there are researchers studying to help reveal how past environmental changes that influence extinctions, such as levels of carbon dioxide in the atmosphere, compare to the changes in those levels seen today in the midst of what many called the sixth extinction.