The dinosaur extinction wasn't the worst mass extinction, it was the middle one. The Permian-Triassic event 244 million years ago wiped out 90 to 95 percent of all life on Earth, terrestrial and marine. Nearly everything died, and we're still arguing about what caused it. The leading possibility is a combination of extraterrestrial impact and extreme volcanism, but there's no definitive answer for the most catastrophic event in the history of life on this planet. | The Randall Carlson

The K-PG Boundary and Dinosaur Extinction (aka "K-T Boundary")