Extinction has happened many times.
Extinction is a normal part of evolution.
There is a normal background rate of extinction, punctuated by mass extinctions. Extinctions are always happening. The normal rate of extinctions is called the background rate . This rate is about two to five families of marine invertebrates and vertebrates per million years. Punctuating this normal background are mass extinctions which result in the extinction of a large number of families, genera, and species.