1. During the Ordovician, shallow seas were widely distributed on the earth, and the climate was very suitable for biological growth. There were many marine life in this period, such as trilobites, sea lilies, corals, nautilus and so on. However, during the two million years from 4.46 million BC to 4.44 million BC (that is, the end of Ordovician), the first large-scale extinction event occurred on the earth. This extinction led to the extinction of about 85% species on the earth, also known as the Ordovician extinction.
Paleontologists believe that this extinction was caused by global climate cooling. At that time, the earth was going through the Andean-Saharan Ice Age. Large glaciers have cooled ocean currents and atmospheric circulation, and the global temperature has dropped. Glaciers are locked in the water, causing the sea level to drop. These changes have changed the living environment of living things, and the coastal biosphere has been seriously damaged, eventually leading to the extinction of a large number of species.
2. When the earth was in Devonian, ferns flourished, insects and amphibians rose, vertebrates entered a period of rapid development, the number and species of fish animals increased, and modern fish began to appear, so Devonian was often called? Fish age? .
However, from 375 million BC to 360 million BC, that is, the transition period from Devonian to Carboniferous, there was also a mass extinction, which lasted about 6.5438+0.5 million years. At that time, 82% of the world's marine species were extinct, almost all corals in shallow waters were extinct, and deep-sea corals were also partially extinct. This extinction is also due to global cooling, that is, the earth entered the Karoo Ice Age.
Three. During the transition period from Permian to Triassic 250 million BC, the largest known species extinction occurred on the earth, with about 57% of families, 83% of genera, 96% of marine species and 70% of terrestrial species extinct.
The main culprit of this extinction was large-scale volcanic activity at that time, which led to the release of a large number of greenhouse gases on the surface, and the greenhouse effect was rapid. The global average temperature was 25 degrees before extinction and 33 degrees after extinction.
Four. The Fourth Great Extinction During the transition period from Triassic to Jurassic 208 million BC, the fourth great extinction event occurred on the earth, which affected land and sea, resulting in the extinction of about 23% families and 48% genera in the world.
The extinction event lasted for a short time, less than 1 ten thousand years. The reason is still inconclusive, and scientists speculate that it is caused by meteorite impact. It was this great extinction that left a vast living space for dinosaurs.
Verb (abbreviation for verb) The fifth extinction occurred at the end of Cretaceous 65 million years ago. At that time, the overlord of the earth was dinosaurs, and this extinction was called dinosaur extinction. The cause of this mass extinction has not yet been determined, and most people think that it was caused by an asteroid hitting the earth.