The earth has experienced five mass extinctions in which over 75% of all species rapidly and suddenly disappeared.
Caused by a devastatingly long ice age, the 1st Extinction, or Ordovician-Silurian, brought about the death of 85% of all marine species over a period of 10 million years.
A lack of environmental oxygen (anoxia) caused the 2nd Extinction, or Late Devonian. More than 75% of both marine and terrestrial species disappeared. This mass extinction lasted over 25 million years.
The 3rd Extinction, or Permian-Triasic, eliminated 95% of species. A combination of anoxia, volcanic activity and one or more asteroid impacts precipitated this mass extinction. . The Permian-Triasic extinction is often referred to as the Great Dying and lasted only 100,000 years.
During the the 4th Extinction, or Triassic-Jurassic, 90% of all species died within just 10,000 years. Like the 3rd Extinction, the 4th Extinction was caused by massive volcanic activity, asteroid impacts and severe climate change.
Most well-know, the 5th Extinction, or Cretaceous-Tertiary, ended the age of the dinosaurs and caused the death 85% of all species around 65 million years ago. This mass extinction is widely accepted to have caused by major asteroid impacts.
Won’t new animals evolve?
By wiping the earth of species, a mass extinction event actually opens ecological spaces and opportunities for new species. But the flowering of new life forms is a very slow process. The filling of these ecological niches usually takes about 10 million years. Thus, the fifth extinction, which ended the reign of the dinosaurs, opened up ecological niches for mammals, paving the way for the Great Age of the Mammal, known as the Pleistocene. But these mammals did not begin to flourish until many millions of years after the demise of the dinosaurs.