In the Mesozoic era more than 200 million years ago, a large number of reptiles lived on land, so the Mesozoic era was also called the "reptile era", and the earth was widely occupied by vertebrates for the first time. At that time, the earth's climate was warm and there were dense forests everywhere. Reptiles have enough food, and gradually flourish, with more and more kinds. They constantly differentiate into various reptiles, some become turtles today, some become crocodiles today, some become snakes and lizards today, and some evolve into mammals all over the world today.

Dinosaurs are the largest reptiles. They are very suitable for living in swamps and shallow lakes. At that time, the air was warm and humid, and food was easy to find. So dinosaurs ruled the earth for tens of millions of years, but for some reason, they suddenly became extinct in a short time 65 million years ago. Today, people only see a large number of dinosaur fossils left at that time.

People are still studying the reasons for the extinction of dinosaurs. For a long time, the most authoritative view is that the extinction of dinosaurs was related to a big meteorite 65 million years ago. According to research, an asteroid with a diameter of 7- 10 km once fell on the earth's surface, causing a big explosion, throwing a lot of dust into the atmosphere, forming dust fog that covered the sun, leading to the temporary suspension of plant photosynthesis and the extinction of dinosaurs.

The asteroid impact theory quickly gained the support of many scientists. 199 1 year, a meteorite impact crater was discovered in Yucatan Peninsula, Mexico, which further confirmed this view. Today, this view seems to be conclusive.

However, many people are skeptical about this asteroid impact theory, because the fact is that frogs, crocodiles and many other temperature-sensitive animals survived the Cretaceous period. This theory can't explain why only dinosaurs died. So far, scientists have put forward more than a dozen hypotheses about the causes of dinosaur extinction, and the more exciting and dramatic "meteorite impact theory" is just one of them.

In addition to the "meteorite impact theory", the main viewpoints about the extinction of dinosaurs are:

First, the theory of climate change. 65 million years ago, the earth's climate changed suddenly and the temperature plummeted, which led to the decrease of oxygen content in the atmosphere and dinosaurs could not survive. Some people think that dinosaurs were cold-blooded, without hair and warm organs, unable to adapt to the decline of the earth's temperature, and all of them froze to death.

Second, the theory of species struggle. At the end of the dinosaur era, the first small mammals appeared. These animals are rodent carnivores and may feed on dinosaur eggs. Due to the lack of natural enemies, more and more small animals finally ate dinosaur eggs.

Third, the theory of continental drift. Geological research has proved that there was only one continent on the earth when dinosaurs lived, and that was Pangea. Due to the change of the crust, the Jurassic continent split and drifted, which eventually led to the change of environment and climate and the extinction of dinosaurs.

Fourth, the theory of geomagnetic variation. Modern biology has proved that the death of some creatures is related to magnetic fields. When the earth's magnetic field changes, creatures sensitive to the magnetic field may lead to extinction. It can be inferred that the extinction of dinosaurs may be related to the change of the earth's magnetic field.

Five, angiosperm poisoning theory. At the end of the dinosaur era, gymnosperms on the earth gradually became extinct, replaced by a large number of angiosperms, which contained toxins that gymnosperms did not have. Giant dinosaurs ate a lot, and a large number of angiosperms led to excessive accumulation of toxins in the body and finally poisoning.

Sixth, the theory of acid rain. There may have been strong acid rain at the end of Cretaceous, which dissolved trace elements including strontium in the soil. Dinosaurs ingested strontium directly or indirectly through drinking water and food, which led to acute or chronic poisoning and eventually died in batches.

There are many hypotheses about the extinction of dinosaurs. However, these hypotheses have more supporters in the scientific community. Of course, each of the above statements has some imperfections. For example, the "climate change theory" does not clarify the reasons for climate change. After investigation, it was found that some small osteophytes in dinosaurs could compete with early small mammals, so there were loopholes in the theory of species struggle. In modern geology, the "continental drift theory" itself is still a hypothesis. "Angiosperm poisoning theory" and "acid rain theory" also lack sufficient evidence. Therefore, the real reason for the extinction of dinosaurs remains to be further explored.

However, "the Hiksulubo impact occurred in an era of intense volcanic activity and global warming." Keller said. Now Deccan in India was formed by lava eruption near the core 65 million years ago. Volcanic eruption brings a lot of carbon dioxide gas to the earth's surface, causing greenhouse effect and eventually leading to the extinction of a large number of animals and plants.

But it's up to you. What do you believe?