We are left with only 10 per cent of the animal species

The animal life on earth has seen at least five major mass extinctions in the millions of years of its existence. A noteworthy period  of  mass  extinctions  is  the  Permian-Triassic  extinction event that occurred about 252 million years ago. The event saw the extinction of about 96 per cent of the marine life and 70 per cent of the terrestrial life over a considerable period of time. It is estimated that five mass extinction events in the past 500 millions of years wiped out 90 per cent of the animal species from the face of the earth.