Some 250 million years ago, the earth suffered the greatest biological crisis in its history. Around 95 percent of all living species died out--a global catastrophe far greater than the dinosaurs' demise 185 million years later. How this happened remains a mystery. But there are many competing theories. Some blame huge volcanic eruptions that covered an area as large as the continental United States; others argue for sudden changes in ocean levels and chemistry, including burps of methane gas; and still others cite the impact of an extraterrestrial object, similar to what caused the...
Some 250 million years ago, the earth suffered the greatest biological crisis in its history. Around 95 percent of all living species died out--a g...
