Permian–Triassic extinction event

The Permian–Triassic (P–Tr) extinction event, colloquially known as the Great Dying, the End Permian or the Great Permian Extinction,^[3][4] occurred about 252 Ma (million years) ago,^[5] forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with up to 96% of all marine species^[6][7] and 70% of terrestrial vertebrate species becoming extinct.^[8] It is the only known mass extinction of insects.^[9][10] Some 57% of all families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event,^[6] possibly up to 10 million years,^[11] although recent studies in Bear Lake County near the Idaho city of Paris showed a quick and dynamic rebound in a marine ecosystem, illustrating the remarkable resiliency of life.^[12]

• http://en.wikipedia.org/wiki/Permian–Triassic extinction event
• Page 75 - Hagadorn, J. W., et al., 2016, The Permian-Triassic transition in Colrado: Geol. Soc. Am. Field Guide 44, P. 73-92.