Mass extinctions of living beings in the history of evolution of Earth. How many they were? Scientists divideIn the history of development of life on Earth 6 (six!) mass extinctions of animals.
Silurian extinction happened near 440 million years ago , then still land life was not, but about 65% of the beings living in the sea died.
The bulk of scientists as the reason of extinction assumes sharp change of climate - after greenhouse conditions the great and long freezing suddenly began. On the southern and northern poles huge ice caps were formed, ocean level sharply went down, the beings living then were not ready to such changes, and their considerable share just died out.
Near 364 million years ago Devonian extinction happened, the quantity of marine animals was cut by half.
By this time on the land already too there was life, it was inhabited by plants, insects and Amphibia. In the rivers and oceans there was a lot of fish (and with dynamite or networks there was nobody to hunt it). Suddenly again the climate sharply changed, the content of oxygen strongly fell in water - and not managed to adapt died out. Trilobita, the whole classes of fishes disappeared...
Scientists assume that sudden climate change was caused by falling of an asteroid, on it specifies sharp increase in content of iridium in layers of deposits, appropriate time of mass extinction, and existence in these layers of a large number of the microspheres (which are melted off in small balls of pieces of strong breed). But other scientists do not consider such proofs sufficient.
Near 250 million years ago the Perm extinction happened. It call great because 95% of types of all living beings died out. Sharp climate change. Sharp cold snap. Many scientists consider as the extinction reason falling to Earth near Wilkes Land (it in Antarctica) an asteroid more than 10 kilometers in the diameter, on this place remained 500 - a kilometer crater. Collision caused huge waves of a tsunami on all ocean, the sharp, explosive growth of volcanic activity. Ocean currents changed, water level sharply fell in oceans, the climate became much more the land, the composition of sea water changed and the amount of oxygen in it decreased. Very many fishes and arthropods died out, but the possibility of development for early species of dinosaurs opened. And they did not miss such opportunities.
During Triassic extinction, 200 million years ago , about a half of all beings living then on Earth died. As the reason volcanic activity is supposed. After this mass extinction in life of Earth dinosaurs began to dominate.
It is best-known for chalk - paleogenovy extinction , it occurred approximately 65 million years ago . Then dinosaurs died.
The most popular version among scientists about the extinction reason - falling of an asteroid or asteroids, caused sharp strengthening of volcanic activity. All this became the reason of sudden climate change - and the reason of extinction of dinosaurs.
Though among theories there is also biological: the bred predatory mammals attacked layings of dinosaurs, eating their eggs, as was the reason of extinction of dinosaurs...
And, at last, approximately 34 million years ago occurred the Eocene - oligotsenovy extinction . It, among other, mass extinctions, even as if - not extinction, died out only several percent (from 3% to 4%) all living beings.
Scientists consider as the reason of mass death of animals during this period whether a volcanic eruption, whether collision with a large asteroid... Are uniform only that during that era on Earth the climate sharply exchanged, as became the reason of mass death of animals.
Six mass extinctions. From several percent of all living beings to 95% of life on Earth. And the last of them was already very long ago. And, according to assumptions of scientists, every time - either volcanoes, or asteroids. Let`s wait? Or we will try to make something?