Mass extinction (80-90%) of living species. This is the End-Ordovician Extinction, the First Mass Extinction. The Second Extinction is the Late Devonian, 375 million years ago, when 75% of living species became extinct. The Third is the End-Permian, 251 million years ago, when 96% of species became extinct; the Fourth is the End-Triassic, 200 million years ago, with the extinction of 80% of species. The Fifth is the KT Boundary, or End-Cretaceous, 66 million years ago, with the extinction of 76% of species, including ammonites and non-avian dinosaurs. The Sixth is the current extinction, caused by Homo sapiens since prehistoric times.
