End-Ordovician - about 444 million years ago
This ranks second in severity among the Big Five mass extinctions and is estimated to have eliminated about 85 percent of species. It likely followed rapid glaciation, sea-level fall, and then warming, which disrupted shallow marine habitats where life was most abundant. Recovery was slow and uneven in marine habitats because the extinction was tied to severe glaciation, sea-level fall and then warming and ocean chemistry changes. But eventually a huge variety of new species emerged, including marine groups such as corals and trilobites.
Late Devonian - roughly 383 to 359 million years ago
This mass extinction is generally fourth in severity and likely removed about 75 percent of species in multiple pulses spanning 24 million years. Its exact trigger is still debated, but likely contributors include major climate swings, sea-level change, ocean oxygen loss and ecological disruption linked to land-plant expansion. Recovery appears to have taken many millions of years, and completely reshaped ocean life, clearing the way for new groups such as early ammonites, ray-finned fish and the ancestors of land animals to thrive.
End-Permian - about 252 million years ago
This ranks first and is estimated to have killed about 96 percent of marine species and around 70 percent of terrestrial species. The leading explanation is massive volcanism in Siberia, which drove extreme warming, ocean acidification, acid rain, and toxic changes in ocean and land chemistry. Recovery was the slowest of the Big Five: marine ecosystems took roughly 4 to 8 million years to rebound, forests did not return in force for about 10 million years and broader terrestrial diversity may have taken around 30 million years to fully recover. Subsequently, major lineages such as archosaurs (the evolutionary group encompassing crocodilians, pterosaurs and dinosaurs) expanded, along with the later rise of modern mammal ancestors.
End-Triassic - around 201 million years ago
This extinction is usually ranked third in terms of estimated species loss, at about 80 percent. It is most often linked to enormous volcanic activity associated with the Central Atlantic Magmatic Province, which raised greenhouse gases, warmed the planet and altered ocean chemistry. Recovery took millions of years, but it cleared ecological space for the rapid diversification of dinosaurs, as well as the broader success of modern-style reef communities and other Mesozoic marine and terrestrial groups.
End-Cretaceous - about 66 million years ago
This ranks fifth, with roughly 76 to 78 percent of species lost, including all non-avian dinosaurs. The best-known cause is the asteroid impact at Chicxulub in present-day Mexico, likely amplified by ongoing volcanism and other environmental stresses. Recovery was much faster than after the end-Permian event, with some studies placing fuller biodiversity recovery on the order of about 10 million years. The big winners afterward were mammals and birds, which diversified dramatically, alongside flowering plants and many modern marine groups.
Holocene/Anthropocene - currently occurring
This is the ongoing human-driven extinction, sometimes called the sixth mass extinction, and it is already eliminating species and even whole genera at unusually high rates. Scientists caution that a true mass extinction threshold is usually defined by roughly 75 percent species loss over a geologically short interval, and current losses have not yet reached that benchmark globally, so there is no "recovery time" to report yet. If the biodiversity collapse continues, the eventual rebound could take tens of millions of years, but the exact outcome depends on future human action.