End Permian - 251 million years ago
The End Permian mass extinction was the largest ever to have occurred on Earth, much larger than the better-known extinction that wiped out the dinosaurs (the End Cretaceous extinction). The End Permian extinction is sometimes called the “Great Dying.” Some groups of organisms that survived the extinction were so decimated by it anyway that they eventually went extinct later on.
Cause:		This extinction lasted less than a million years, and extinction rates were the same world-wide. Many causes have been postulated for it, and it was likely a combination that brought the extinction about. They include: impact event, continental drift, global warming that led to lack of oxygen in the oceans, supernova that destroyed the ozone layer, massive volcanic event.
Result:		About 96% of marine and 70% of terrestrial vertebrate species went extinct. Affected marine species included corals, fish, and trilobites (the two remaining genera went extinct). On land, many plants and reptiles were affected.