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Extinction refers to the complete elimination of a given species. Extinctions may have various causes, including over-hunting, loss of habitat, climate change, competition from other species, obliteration due to local or global catastrophes, plague, gradual evolution, many other factors or combinations of factors.
- Main article: Extinction level event
Species become extinct all the time (an estimated 99% of all identified species are extinct). However, there have been times in geologic history called "mass extinction events" when large numbers of species vanish forever over a relatively short (geologically speaking) time. The most famous of these is the Cretaceous-Tertiary extinction, often known as the "wiping out (most) dinosaurs". The largest extinction was the Permian Mass Extinction event, which eliminated 96% of marine species and 70% of land species.
Extinction level events, in the past, could have any number of causes, from giant meteor impacts to oxygenation of the atmosphere. However, it is very likely that the rise of modern Homo sapiens has precipitated a mass extinction that we are still in the middle of. It is impossible to accurately estimate the rate of disappearing species, with some estimates ranging up to over 100,000 a year. This is roughly 100 times the "normal" background level of extinction.