Ordovician-Silurian extinction event: occurred in the late Ordovician or the transitional period between Ordovician and Silurian. From 450 million years ago to 440 million years ago, about 27% families and 57% genera became extinct. The number of genera classified from extinct organisms was rated as the third among the five mass extinctions. The direct reason is that Gondwana mainland entered the Antarctic region, which affected the change of global circulation, led to the global cooling into the Andean-Saharan Ice Age, and the sea level dropped significantly.
Late Devonian extinction event: 375 million years ago to 360 million years ago, close to the transition period from Devonian to Carboniferous. This time, marine life was mainly extinct, and terrestrial life was not significantly affected. About 19% of families and 50% of genera are extinct. This mass extinction event lasted for nearly 20 million years, during which there were many extinction peaks. Reef-building organisms disappeared, and more than 65,438+00 families of Bambusoideae, brachiopods and radiant corals became extinct, which was called Keller-Vasseur event, also known as Frans-Famen event. Because the extinction event lasts for a long time, its root cause is difficult to identify. The possible biological reason is that a large number of terrestrial plants were bred before Devonian, which led to the increase of oxygen content in the earth's atmosphere and the sharp decrease of carbon dioxide, and the earth entered the Karoo Ice Age. Terrestrial plants evolved developed roots several meters below the surface soil, which accelerated the weathering of terrestrial rock soil, and a large number of elements such as iron were released into the surface water, leading to a large outbreak of eutrophication in the water system and a submarine hypoxia event. Rich organic deposits on the ocean surface make a large amount of atmospheric carbon dioxide enter the seabed sediments in the global carbon cycle, which also strengthens the cooling of the earth. Devonian is also a period when large coalfields were produced on land, which also intensified the solidification of carbon dioxide to the lithosphere.
Permian-Triassic extinction event: occurred in the Permian-Triassic transition period 25/kloc-0.0 million years ago. This is the biggest extinction event in the known geological history. The whole order or suborder of many animal classes were extinct in this extinction event. The once widely distributed ferns are almost extinct. All the trilobites that flourished in the early Paleozoic disappeared. ? There are more than 40 genera, which completely disappeared at the end of the world. There are 10 families extinct in ammonites; Brachiopods used to belong to the genus 140, and there are few left after this incident. About 57% families and 83% genera (53% families, 84% genera and 96% species of marine life), it is estimated that 70% of terrestrial life, including insects, has become extinct. The impact on plants is still unclear, but after this extinction, new plant groups began to dominate. There are few coalfields formed in the early Triassic in the world. The possible reasons for this mass extinction event include the melting of flammable ice in the nearby shallow sea caused by the large-scale basalt eruption in Siberia, which released a large amount of greenhouse gas methane, and the formation of Pangu continent changed the global circulation and ocean current system.
Triassic-Jurassic extinction event: Triassic-Jurassic transition period 200 million years ago. About 23% families and 48% genera have become extinct. The reason is still inconclusive.
Cretaceous-Tertiary extinction events (referred to as K-T extinction or K-T events): About 17% families, 50% genera and 75% species were extinct 65 million years ago. This extinction event was rated as the second of the five mass extinctions, second only to the Permian-Triassic extinction event. The reason is generally believed to be a meteorite impact in Mexico's Yucatan Peninsula.