Permian–Triassic extinction event

Approximately 251.9 million years ago, the Permian–Triassic (P–T, P–Tr) extinction event (PTME; also known as the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying) forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is also the largest known mass extinction of insects. It is the largest of the "Big Five" mass extinctions of the Phanerozoic. There is evidence for one to three distinct pulses, or phases, of extinction.

The precise causes of the Great Dying remain unknown. The scientific consensus is that the main cause of extinction was the flood basalt volcanic eruptions that created the Siberian Traps, which released sulfur dioxide and carbon dioxide, resulting in euxinia, elevating global temperatures, and acidifying the oceans. The level of atmospheric carbon dioxide rose from around 400 ppm to 2,500 ppm with approximately 3,900 to 12,000 gigatonnes of carbon being added to the ocean-atmosphere system during this period. Important proposed contributing factors include the emission of much additional carbon dioxide from the thermal decomposition of hydrocarbon deposits, including oil and coal, triggered by the eruptions, emissions of methane from the gasification of methane clathrates, emissions of methane possibly by novel methanogenic microorganisms nourished by minerals dispersed in the eruptions, an extraterrestrial impact creating the Araguainha crater and consequent seismic release of methane, and the destruction of the ozone layer and increase in harmful solar radiation.