The history of life on Earth shows five mass extinctions, the results of natural disasters. Biologists refer to this time the occurrence of a sixth wave of extinction, the result of human action.
Taxonomists have already described nearly two million species. In fact, their number varies, estimated to 5 100 to millions. 90 to 99% of species have existed on earth are extinct. The vast majority has gone through a normal process of extinction of species due to the limited duration of the biological existence thereof. This period varies from one million years in mammals, eleven million years in the case of some marine invertebrates. Beyond the usual background extinction, the fauna experienced five mass extinctions, during which at 50 95% of existing species disappeared then in a historically short period of time.
According to many experts, a sixth wave of extinction is underway, under the effect of climate and environmental change as well as the disappearance of local habitats. Based on the current average extinction rate of species 40 daily, 16.000 years 96% disappear contemporary animal species, just as much as during the period of disastrous Permian extinction. Scientists estimate that the life of the species among contemporary mammals and birds is now at 100 1000 times lower than that of fossil forms: it would now 10.000 years. And if housing continued to be destroyed at the same rate, the life of these species would be more than 200 400 in years.