List of extinction events

An extinction event is a relatively fast drop in the number of species living on Earth. It occurs when the rate of extinction increases more than the rate of speciation. This is a list of the largest. Major extinction events are important to both geology and evolution.
The Phanerozoic.
There are five major extinction events in the Phanerozoic eon, and many smaller events. In order of time, latest first:
1. K/T extinction event. The Cretaceous/Tertiary extinction event ended the Mesozoic era and started the Cainozoic era.
2. End–Triassic extinction event or events.
3. P/Tr extinction event. The Permian/Triassic extinction event ended the Palaeozoic era and started the Mesozoic era.
4. Late Devonian extinctions, at the Frasnian/Famennian junction.
5. End–Ordovician extinction event. After a series of lesser events, the end-Ordovician extinction resulted in an estimated 84% species loss.
Other extinction events in the Phanerozoic had significant impact on the evolution of the biota. Overall, it seems that climate changes caused some extinctions, and hits by asteroids sometimes caused extinctions. 
Before the Phanerozoic eon, there were even larger extinction events, which are often forgotten: