Short, Rachel A. Department of Ecology and Conservation Biology, Texas A&M University, College Station, Texas.
Last reviewed:October 2021
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- Past mass extinctions
- Late Ordovician
- Late Devonian
- Sixth mass extinction
- Related Primary Literature
- Additional Reading
The widespread, catastrophic loss of many species in a relatively short period of geological time. Earth has supported life for approximately 3.5 billion years, and it is normal for species to become extinct and for new species to arise through evolution. However, a mass extinction happens when there is a loss of approximately 75% or more of the species on Earth in a short amount of geological time, usually two million years, instead of a gradual loss. Mass extinctions often mark the transition between two geologic time periods and are often associated with global environmental change. Scientists study mass extinctions by using the geological record and the fossils found within rocks from before and after extinction events. The sizable loss of biodiversity during a mass extinction opens ecosystems to new types of biodiversity. Only five, possibly six, instances have met the requirements of being called a mass extinction (see illustration). See also: Background extinction; Biodiversity; Evolution; Extinction; Extinction and the fossil record; Extinction (paleontology); Fossil; Geologic time scale; Paleobiodiversity; Paleontology; Speciation
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