dinosaurs disappeared in the Cretaceous-Tertiary extinction event 65 million years ago. The usual explanation is that a huge meteorite hit the earth and caused extinction (first proposed by four scientists including Dr. Walter Alvarez of the University of California, Berkeley). But this theory is still controversial.

Generally speaking, after the meteorite hit the earth, a large number of dust storms flooded the earth and the atmosphere, resulting in the inability of sunlight to directly illuminate the earth's surface, and the temperature in various places gradually became cold. Dinosaurs died and became fossils because they could not survive and feed in the cold climate. There is another saying that at that time, due to the sharp change of temperature at the two poles of the earth, the sea level rose, resulting in a river barrier between the mainland and the mainland, which made it difficult for dinosaurs to feed and died.

asteroid (meteorite) impact theory

This is the most acceptable statement for everyone at present. An asteroid hit the earth, causing extinction, and nearly 9% of the life on the earth disappeared. In addition to the powerful explosive damage caused by the impact, it also caused a large amount of dust to cover the whole earth's atmosphere, the temperature gradually dropped, and sunlight could not penetrate into the earth, so that most plants disappeared because of the inability to photosynthesis, while herbivorous dinosaurs died because of lack of food, and carnivorous dinosaurs gradually disappeared because they did not eat herbivorous dinosaurs, and finally dinosaurs became extinct. The remaining 1% are small animals and a few plants.

The theory of comet impact

This theory is based on the fact that the extinction of paleontology almost happens every 26 million years, and astronomy believes that there is an Oort cloud around the solar system, and the comets in the Oort cloud periodically advance to the sun in the center of the solar system (for example, Halley's Comet and Hale's Popper Comet). The extinction of dinosaurs may have been caused by one of the comets hitting the earth.

Theory of orogeny

At the end of Cretaceous, the intense orogeny caused the crust to uplift, many shallow seas and lakes turned into land, and some dinosaurs and creatures that took water as their home gradually disappeared; The wet swamp also swelled and dried up, so many plants living in the swamp disappeared, and the herbivorous dinosaurs that ate swamp plants also died out, and the carnivorous dinosaurs also died out one after another.

theory of climate change

According to Wegener's theory of plate drift, the plate distribution at that time in Cretaceous had changed from Pangu, which was originally connected together, to five continents. Plate drift itself will cause climate change, for example, Antarctica is originally located in the middle latitude and has a warm climate. However, because of the plate drift, Antarctica entered the polar circle, causing the severe cold in Antarctica today. Because of the plate drift, ocean currents change and climate change, many places become cold, hot and dry, which is not suitable for dinosaurs and other creatures to live in. Dinosaurs gradually became extinct.

Volcanic eruption theory

Volcanoes erupted in large quantities and sharply, spewing out many greenhouse gases such as carbon dioxide and methane, which caused the greenhouse effect of the earth. As the temperature rises, many plants can't adapt to the temperature and die. Herbivorous dinosaurs die because of lack of food, and carnivorous dinosaurs die out one after another.

ocean ebb theory

when the situation like the ice age happened on the earth, the sea water decreased, and there was no barrier between the land and the land, forming a land bridge, and creatures would make a great migration at this time to promote biological communication and contact. According to Darwin's theory of "survival of the fittest and elimination of the unfit", the strong will bully the weak, and in the end the weak will be extinct. In addition, there are problems of bacteria, viruses and parasites.

Warm-blooded animals say

Some people think that dinosaurs are different from living reptiles, not cold-blooded animals but warm-blooded animals. But even if dinosaurs were warm-blooded animals, their body temperature was still not high, which might be similar to that of living sloths. To maintain such a body temperature, they could only grow in tropical climates. In addition, the dinosaur's respiratory system is not good, and it can't fully replenish oxygen; The body has no thick hair, and heat is easily lost from the tail, feet and other places; Coupled with the huge body, when the temperature plummeted, there was no way to hide in the cave to keep out the cold. Therefore, dinosaurs may not be able to withstand the sudden climate change in the late Cretaceous period and slowly freeze to death.

cannibalism theory

Some people think that the reason why dinosaurs really died was the result of cannibalism. When there are more and more carnivorous dinosaurs, more and more herbivorous dinosaurs are preyed on. When herbivorous dinosaurs become less and less, or even disappear and become extinct, carnivorous dinosaurs will begin to kill each other. And the dinosaurs were all extinct.

oppression theory

The number of dinosaurs increased rapidly, which led to the extinction of herbivorous dinosaurs under the condition of limited plants, and then carnivorous dinosaurs who lived on herbivorous dinosaurs died because of lack of food. Why dinosaurs suddenly increased after about 2 million years of ecological balance is an important key to the establishment of this theory, which directly caused many scholars to review the reasons for the abnormal increase in dinosaur production.

Mammalian prisoners said

In the second half of Mesozoic, there were ancestors of mammals. According to the records of fossils, the mammals at that time were very small and the number was very limited. It was not until the late Cretaceous that the number began to increase rapidly. It is speculated that they are omnivorous with insects as their staple food. After these small mammals found dinosaur eggs, they kept eating them. Is that really the case? If mammals beat dinosaurs, then with the increase of mammalian fossils, dinosaur fossils should be gradually reduced, but in fact there is no such phenomenon of fossil alternation. The real increase in mammalian fossils was after the end of the dinosaur era. Moreover, dinosaur fossils disappeared suddenly. Therefore, the theory that dinosaurs were wiped out by mammals cannot be established.

The theory of aging of species

holds that dinosaurs' bodies were too large because of their prosperity for hundreds of millions of years. Moreover, horns and other bones are also extremely developed, which causes great inconvenience in life and finally leads to extinction. Lei Long, the most representative dinosaur, was 25 meters long and weighed 3 tons. Because of his huge size, he lost his ability to live. In addition, Triceratops and others went to the road of self-destruction because of the constantly expanding three horns and the unusually developed bones to protect their heads. However, not all dinosaurs are so huge, and there are small dinosaurs with a body length of only about one meter. In addition, there are dinosaurs whose bones are like deer and can run briskly, but these dinosaurs have also become extinct. Moreover, in cold-blooded animals, abnormally developed bones and other parts are supposed to be able to absorb the outside temperature and release the heat in the body to adjust the body temperature, which has a very favorable function. It can be seen that dinosaurs lived for a long time, so from a long time ago, many people doubted that dinosaurs became extinct because of the aging of species.

Alkaloid theory

This theory holds that flowering plants began to appear in the last period of dinosaurs' existence, that is, Cretaceous, and some of them contained toxic alkaloids. Dinosaurs died of poisoning due to eating a lot. Because mammals can distinguish poisonous plants by taste and smell, but dinosaurs have no such ability. However, plants containing alkaloids did not suddenly appear in the late Cretaceous period, and they were already visible five million years before the extinction of dinosaurs. This theory does not explain why dinosaurs survived during this period.