There have been five species extinctions on the earth. What is the reason?

The first extinction occurred at the end of Ordovician 440 million years ago, also known as the Ordovician extinction, which led to the extinction of about 85% species. It is easy to understand that marine life is very prosperous at this time. You know, water is the source of life. The earliest life on earth was born in the ocean, and terrestrial life evolved from marine life.

So what is the cause of this mass extinction? Paleontologists believe that this is due to the global climate cooling. About 440 million years ago, the Sahara desert is now located in the South Pole. When it is near the South Pole, it is easy to form a thick ice layer, just like during the Ordovician period. Large glaciers cool ocean currents and atmospheric circulation. The temperature of the whole earth has dropped, glaciers have locked in water, and the sea level has also dropped.

This situation is what we now call the Ice Age, which is also the Great Ice Age. The duration of the Little Ice Age is often only a few decades, and its impact is limited. But the Great Ice Age was different. It cooled the earth's temperature for a long time, possibly for thousands of years. Therefore, every time the Great Ice Age happened, it was a time when creatures faced great disasters.

The second extinction occurred in the late Devonian 365 million years ago, also known as the Devonian extinction. During this period, the land area began to expand, and a large number of terrestrial organisms began to evolve and develop, especially vertebrates ushered in a period of rapid development, and reptiles began to appear. This extinction event led to the extinction of 70% species on the earth.

The second extinction event still mainly affected marine life, but the impact of animals and plants on land was much smaller. After this extinction event, life on earth really ushered in a period of rapid development. The cause of this extinction is not clear. Some scientists believe that it is caused by the rapid change of global climate, and some scientists believe that it is caused by the impact of asteroids.

The third extinction occurred at the end of Permian 250 million years ago, also known as the Permian extinction, which was the most serious extinction event in history. If you want to ask which of the five mass extinctions was the most serious, it must be the third time. According to statistics, this extinction event reduced the number of biological families by 52% and the number of species by more than 90%. It has the greatest impact on marine life, and 96% of marine species are extinct, resulting in the reduction and disappearance of major organisms, including trilobites, which have occupied the ocean for nearly 300 million years.

On land, more than three-quarters of vertebrates have disappeared, and lizards, amphibians and theropods have decreased dramatically. Scientists believe that the reason for this extinction may be that the earth has experienced sea level decline and continental drift. At this time, all continents converge into a united ancient land, many creatures lose their living space, and the oxygen in the atmosphere is also drastically reduced. Plate movement causes climate change, which leads to the expansion of desert area and large-scale volcanic eruption.

Some scientists also believe that this mass extinction may be related to the gamma-ray bursts produced by supernova explosions illuminating the earth. For example, the decrease of ozone and oxygen in the atmosphere during this period is probably caused by cosmic ray irradiation. Although the third extinction was very serious, it almost wiped out all the creatures on the earth, but after the disaster, it ushered in the spring of reptiles, and there appeared huge creatures that ruled the earth for 65.438+0.6 billion years. That's a dinosaur.

The fourth mass extinction occurred in the late Triassic period 208 million years ago, also known as the Triassic mass extinction. The scale of this extinction is relatively small, with only 25% of species on the verge of extinction, mainly marine life. This small extinction also created many favorable conditions for the rule of dinosaurs, and dinosaurs began their long journey to rule the earth. Scientists believe that this extinction may be related to the impact of asteroids on the earth and the eruption of super volcanoes.

Everyone is familiar with the fifth extinction, which happened in the Cretaceous period 65 million years ago. This mass extinction event caused the overall extinction of the dinosaur family, and about 80% of the species on the earth became extinct.

There are various explanations for this disaster, one of which is generally accepted by the scientific community is asteroid impact. At the end of Cretaceous, one or more meteor showers led to the collapse of the global ecosystem. Exposure to a large amount of gas and dust enters the atmosphere, so the sun can't penetrate, the global temperature drops sharply, dark clouds cover the earth for several years, plants can't get energy from the sun, algae and terrestrial forests die gradually, the basic link of the food chain is destruction, and many animals starve to death, including dinosaurs.

After the fifth extinction, the rule of dinosaurs came to an end, which also opened the door for the emergence of mammals and humans. Since then, mammals have ushered in great development, and the primitive life of human beings has also appeared. Many people may think that human beings were born millions of years ago, but they are not. Millions of years actually refers to the time when human beings began to evolve wisdom.

The earliest forms of human life may have appeared tens of millions of years ago, shortly after the fifth extinction. At that time, the earliest life form of human beings appeared, and finally, through gradual evolution, it embarked on the road of intelligent evolution, and modern human beings gradually appeared. No life can appear out of thin air. There must be roots, and so does human nature.

Through five mass extinctions in the history of the earth, we seem to find that each mass extinction is a sublimation of life, and the purpose may be to finally give birth to intelligent life human beings. Now that human beings are born, will there be a sixth mass extinction in the future? It's hard to say, and I'm sure scientists can't predict it.

The occurrence of mass extinction is basically due to some factors leading to drastic changes in the earth's ecological environment. Some people think that if the sixth mass extinction event happens in the future, it may be caused by human beings themselves. The reason is that the rapid development of human science and technology has not protected the earth, making the earth environment worse and worse, and the carrying capacity of the earth ecosystem must have a limit. Once this limit is exceeded, the ecosystem will collapse completely, and the earth will once again usher in a mass extinction event.

Of course, if the sixth mass extinction really happens in the future, most of the creatures on the earth may become extinct, but human beings may survive. The reason is that human science and technology may have been very developed at that time, and interstellar migration has also been realized. When the earth can't survive, we can go to other planets to survive without worrying about the disappearance of human beings.