A little over 250 million years ago, our planet experienced a mass extinction the likes of which have never been seen before or since. About 90% of all species were suddenly wiped out. And new study suggests it wasn't caused by an asteroid or super-volcano — but rather methane-spewing microbes.
It's known as the Permian-Triassic Extinction Event. By the time it ended, some 96% of all marine animals were gone, and about 70% of terrestrial vertebrates. It's also the only known mass extinction of insects, in which some 57% of all families and 83% of all genera disappeared.