Extinctions are a natural part of evolution, which occur when particular plants or animal species die-out. Sometimes extinctions can occur at much faster rates than normal causing entire species to disappear with just one disturbance. Five mass extinctions can be distinguished from the fossil record, with the most severe being the Permian extinction, occurring approximately 266 million years ago eliminating almost all marine species and three-quarters of all land species. Of the five mass extinctions, Cretaceous is the most well known across the globe. It occurred approximately 66 million years ago and different theories have been proposed stating why this extinction occurred, ranging from asteroids and comets to climate change and volcanic
