<Li> Ordovician--Silurian extinction events (End Ordovician or O--S): 450--440 Ma (million years ago) at the Ordovician--Silurian transition . Two events occurred that killed off 27% of all families, 57% of all genera and 60% to 70% of all species . Together they are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of genera that became extinct . </Li> <Li> Late Devonian extinction: 375--360 Ma near the Devonian--Carboniferous transition . At the end of the Frasnian Age in the later part (s) of the Devonian Period, a prolonged series of extinctions eliminated about 19% of all families, 50% of all genera and at least 70% of all species . This extinction event lasted perhaps as long as 20 million years, and there is evidence for a series of extinction pulses within this period . </Li> <Li> Permian--Triassic extinction event (End Permian): 252 Ma at the Permian--Triassic transition . Earth's largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species (53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species, including insects). The highly successful marine arthropod, the trilobite, became extinct . The evidence regarding plants is less clear, but new taxa became dominant after the extinction . The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of mammal - like reptiles . The recovery of vertebrates took 30 million years, but the vacant niches created the opportunity for archosaurs to become ascendant . In the seas, the percentage of animals that were sessile dropped from 67% to 50% . The whole late Permian was a difficult time for at least marine life, even before the "Great Dying". </Li> <Li> Triassic--Jurassic extinction event (End Triassic): 201.3 Ma at the Triassic--Jurassic transition . About 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species became extinct . Most non-dinosaurian archosaurs, most therapsids, and most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition . Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments . The Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia (e.g., Koolasuchus). </Li>

What was the biggest mass extinction in geologic time