Earth s largest mass extinction occurred some 252 million years ago, wiping out more than 96 percent of marine species and 70 percent of life on land, including the largest insects known to have inhabited the Earth.
Professor Emeritus Frederick Frey, a leader in the field of geochemistry, dies at 83 mit.edu - get the latest breaking news, showbiz & celebrity photos, sport news & rumours, viral videos and top stories from mit.edu Daily Mail and Mail on Sunday newspapers.