mass extinction

Scientific  

1. The extinction of a large number of species within a relatively short period of geological time, thought to be due to factors such as a catastrophic global event or widespread environmental change that occurs too rapidly for most species to adapt. At least five mass extinctions have been identified in the fossil record, coming at or toward the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous Periods. The Permian extinction, which took place 245 million years ago, is the largest known mass extinction in the Earth's history, resulting in the extinction of an estimated 90 percent of marine species. In the Cretaceous extinction, 65 million years ago, an estimated 75 percent of species, including the dinosaurs, became extinct, possibly as the result of an asteroid colliding with the Earth.

2. Compare background extinction

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mass extinction Cultural  

1. Any of several events in the Earth's past in which large numbers of species (in some cases, up to eighty percent) became extinct.

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Discover More

The most famous mass extinction included the destruction of the dinosaurs sixty-five million years ago. (See Alvarez hypothesis.)

Example Sentences

It also helps scientists better understand ecosystems that existed just before the Triassic-Jurassic mass extinction, a major event linked to increased volcanic activity and climate disruption.

From Science Daily • Mar. 21, 2026

These animals are considered distant ancestors of modern birds and were the only dinosaur lineage to survive the mass extinction at the end of the Mesozoic era 66 million years ago.

From Science Daily • Mar. 18, 2026

Bodenham's discovery adds another piece to the growing diversity of animals living in this region during the Late Triassic before the Triassic–Jurassic mass extinction event caused by an increase in volcanic activity altering the climate.

From BBC • Feb. 17, 2026

This mass extinction, known as the Sinsk event, is thought to have been caused by declining oxygen levels.

From Barron's • Jan. 28, 2026

Researchers had previously noted the temporal coincidence between the paleo-Indians’ arrival and the mass extinction, but they didn’t believe that small bands of hunters could wreak such ecological havoc.

From "1491" by Charles C. Mann