Mass Extinction

Earth has undergone several mass extinctions during its history. There are three extinctions you should pay the most attention to:

Permian - Triassic (250 million years ago):
Massive volcanoes, the Siberian Traps, spewed large amounts of carbon dioxide, smoke, ash, and other gases into the atmosphere. Ash and smoke would have covered up the sunlight, initially causing global temperatures to drop. However, carbon dioxide (a greenhouse gas) stays in the atmosphere longer, intensifying Earth's greenhouse effect and raising global temperatures over the long term. Scientists also believe that the formation of Pangaea at the end of the Permian may have altered weather and climate patterns, contributing to the extinction of so many species. Alternating patterns of warming and cooling temperatures happening on Earth at this time may have prevented species from adapting.

Cretaceous - Tertiary (KT) (65 million years ago):
Some of the reasons for this extinction include: an asteroid impact, volcanism, competition from mammals, and continental drift. Scientists do not know if only one of these events triggered a mass extinction, or if was a combination of several causes.

Pleistocene (11,000 years ago):
There are three theories for this extinction event. One is that humans over-hunted key species. Another theory is that the climate changed as the Earth began to warm up, and the third theory is that a "hyper-disease" triggered this mass extinction.