The five mass extinction episodes occurred because of major changes in the prevailing ecological conditions brought about by climate change, cataclysmic volcanic eruptions, or collisions with giant meteors.
|Millions of Years Ago||Name of Extinction Episode||Percent of Families That Died Out|
440Late Ordovician20 - 50 %Tropical areas are hit hardest. No terrestrial vertebrates have evolved yet.360Late Devonian 20 - 30 %Many fish and marine invertebrates die out.250End of Permian 50 %Greatest mass extinction ever.213Late Triassic20 - 35 %Dinosaurs and mammals had just recently evolved; both live through this extinction.66Late Cretaceous15 %Dinosaurs become extinct, possibly caused by a metorite colliding with the Earth. Mammals and fishes begin to proliferate. 65 million of years after this mass extinction, early humans evolve.