6. Late Permian, 260 million to 251 million years ago
The Late Permian was a rough time to be alive, especially if you were an ocean dweller. About 252 million years ago, the largest mass extinction in Earth’s history occurred, wiping out 96% of all marine life and about two-thirds of large life on land. Recent research has indicated the “Great Dying,” as the extinction event is known, was caused by a global warming that prevented oceans from holding enough oxygen for sea creatures to breathe. The oceans may have become so acidic thanks to a huge amount of volcanic activity. Whatever the cause, we lost a great many species, including the iconic trilobites that had persevered for so long on seafloors.
