<P> The Permian--Triassic (P--Tr or P--T) extinction event, colloquially known as the Great Dying, the End - Permian Extinction or the Great Permian Extinction, occurred about 252 Ma (million years) ago, forming the boundary between the Permian and Triassic geologic periods, as well as between the Paleozoic and Mesozoic eras . It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct . It is the only known mass extinction of insects . Some 57% of all biological families and 83% of all genera became extinct . Because so much biodiversity was lost, the recovery of land - dwelling life took significantly longer than after any other extinction event, possibly up to 10 million years . Studies in Bear Lake County near Paris, Idaho showed a relatively quick rebound in a localized marine ecosystem, taking around 2 million years to recover, suggesting that the impact of the extinction may have been felt less severely in some areas than others . </P> <P> There is evidence for one to three distinct pulses, or phases, of extinction . Suggested mechanisms for the latter include one or more large meteor impact events, massive volcanism such as that of the Siberian Traps, and the ensuing coal or gas fires and explosions, and a runaway greenhouse effect triggered by sudden release of methane from the sea floor due to methane clathrate dissociation according to the clathrate gun hypothesis or methane - producing microbes known as methanogens . Possible contributing gradual changes include sea - level change, increasing anoxia, increasing aridity, and a shift in ocean circulation driven by climate change . </P>

The permian period ended in the greatest extinction of the
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