Extirpation

In biology and ecology, extinction is the cessation of existence of a species or group of taxa, reducing biodiversity. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point; see population bottleneck). Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "re-appears" (typically in the fossil record) after a period of apparent absence.

Through evolution, new species are created by speciation — where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche — and species become extinct when they are no longer able to survive in changing conditions or against superior competition. A typical species becomes extinct within 10 million years of its first appearance,[2] although some species, called living fossils, survive virtually unchanged for hundreds of millions of years. Only one in a thousand species that have existed remain today.[2]

Prior to the dispersion of humans across the earth, extinction was a purely natural phenomenon that generally occurred at a continuous low rate (mass extinctions being relatively rare events). Starting approximately 100,000 years ago, and coinciding with an increase in the numbers and range of humans, species extinctions have increased to a rate unprecedented[3] since the Cretaceous-Tertiary extinction event. This is known as the Holocene extinction event and is at least the sixth such extinction event. Some experts have estimated that up to half of presently existing species may become extinct by 2100.[4]