So far, our planet has seen five mass extinction events. The first wiped out the trilobites -- a species so ubiquitous in Earth's oceans you probably have one of their fossils on your bookshelf. The Permian extinction event wiped out 96 percent of the species on the planet.
The last of the five killed off the dinosaurs.
Many believe that we are currently in the middle of the sixth -- the Anthropocene extinction