Warming did it. Cooling did it.

“The Earth has known several mass extinctions over the course of its history. One of the most important happened at the Permian-Triassic boundary 250 million years ago. Over 95% of marine species disappeared and, up until now, scientists have linked this extinction to a significant rise in Earth temperatures. But researchers have now discovered that this extinction took place during a short ice age which preceded the global climate warming.”