was caused by global warming that left ocean animals unable to breathe. The largest extinction in Earth's history marked the end of the Permian period, some 252 million years ago
Although the best-known cause of a mass extinction is the asteroid impact that killed off the non-avian dinosaurs, in fact, volcanic activity seems to have wreaked much more havoc on Earth's biota. Volcanic activity is implicated in at least four mass extinctions, while an asteroid is a suspect in just one.
