The Great Dying wiped out about 81 percent of marine species
Around 252 million years ago, at the close of the Permian, life suffered its worst known catastrophe. Roughly four in five marine species and an estimated 70 percent of land vertebrate species vanished. Yet that emptied world gave dinosaur and crocodile relatives the opening they needed to flourish.
A mass extinction is a sharp, widespread drop in the diversity and abundance of multicellular life, when species disappear far faster than the normal background rate. How many major ones have happened in the last 540 million years is disputed, with estimates from five to more than twenty, depending on what counts as major and which data are used. In a landmark 1982 paper, Jack Sepkoski and David Raup picked out five intervals of exceptional loss, now called the Big Five. Even earlier, the Great Oxidation Event probably devastated microbial life far more widely.
The first of the five struck at the end of the Ordovician, about 445 million years ago, in two pulses that together erased around 85 percent of species. The first pulse matched a cooling and a great southern glaciation, the second the thaw; studies in 2020 blamed volcanic warming and oxygen loss instead, a view that clashes with much earlier work. The Late Devonian brought two blows, the Kellwasser and Hangenberg events, linked to oceans starved of oxygen, which flattened coral reefs and ended the armoured placoderm fish.
The Permian-Triassic event was the largest. It cut short many lines of mammal relatives, and vertebrate recovery took some 30 million years. Its effect on land may have been gentler than once thought: pollen and spores suggest some plant communities barely stumbled, and a 2025 study in China found a thriving ecosystem just 75,000 years afterwards. An earlier End-Capitanian crisis may have been a separate disaster.
The End Triassic extinction, about 201 million years ago, removed 70 to 75 percent of species, including the last conodonts. Then, 66 million years ago, the Cretaceous-Paleogene event, formerly called K-T, took roughly three quarters of species. Ammonites, plesiosaurs and mosasaurs disappeared from the seas, and every known non-avian dinosaur died out.
Source: Extinction event
