Known Mass Extinction Events

1. Great Oxygenation Event (2.4 billion years ago) - The earliest mass death of which we know, caused by the significant change in global oxygen levels by the rise of photosynthetic life.

The Eurypterida of New York, Charles R Knight.

1. Ordovician–Silurian extinction event invertebrates died, including two-thirds of all brachiopod and bryozoan families. In all, it killed 27% of all families, 57% of all genera and 60% to 70% of all species. It was caused by the shift of Gondwana (the supercontinent formed by the union of South America, Africa, Australia, Antarctica, and India) to the South, which would have triggered global cooling and a decrease in sea level. The initial phase of the extinction was also helped by a hypernova (a supernova on steroids) 6000 light years from Earth whose radiation, in a matter of ten seconds, wiped out half of the Earth's ozone and allowed for a flood of solar, ultraviolet radiation onto the planet that devastated life.

2. Late Devonian extinction (360 million years ago) - Plants and insects now exist on land. 19% of all families and 50% of all genera went extinct. Causes include decrease in ocean oxygen levels by geologic activity and the massive expansion of plants on land, as they evolved seeding abilities and vascular systems.

1. Carboniferous rainforest collapse (305 m years ago) - Vertebrates (mainly water-based amphibians) now walk on land. The event affected mostly Euramerica (union of Europe and North America) and was caused by the rise of trees and ferns which altered the landscape, causing the continent-wide rainforests to shrink into separate islands of plant life.

2. Permian–Triassic extinction event (250 m years ago) - This was the largest mass death in world history. Just before the event, Pangaea exists, and mammal-like reptiles are now prominent on land, as are trilobites in the ocean. The results were incredible. 96% of marine species were lost, as were 70% of land-base vertebrates. Estimates show that it took as long as ten million years for life on Earth to reach pre-event levels. The event ended the trilobites in the ocean and paved the way for the rise of the archosaurs (dinosaurs and other non-mammal-like reptiles) after the recovery. The most likely cause was an asteroid impact. No crater to account for it exists, as ocean floors recycle themselves every 200 million years, meaning that this crater would be forever lost. The impact would have triggered possibly the largest mega-tsunamis the Earth has ever known. A cloud of dust may have covered the Earth for as long as a decade, inhibiting photosynthesis. Further, the rupture could have caused volcanic eruptions at various locations on the earth. The lack of evolutionary transition along with the mass extinctions also implies a sudden event to which life could not adapt, like an asteroid impact.

1. Triassic–Jurassic extinction event (200 m years ago) - 50% of the world's species were lost. Dinosaurs remained as the surviving archosaurs from this event, with crocodiles being a notable exception to non-dinosaur reptiles that survived. The cause is unidentified.

2. Cretaceous–Paleogene extinction event (65 m years ago) - 76% of the species on the planet were lost. Non-avian dinosaurs were completely eliminated. The death allowed for a leap in biodiversity. Birds emerged from the surviving dinosaurs. All major mammalian groups survived. The rodent-like mammals quickly transformed into hoofed creatures, whales, and more varied rodents.

National Science Foundation, Zina Deretsky