We humans have lived on the earth for two or three million years, and this history should be said to be not short. But compared with the life span of dinosaurs, it was only a moment.
In the Mesozoic era, the earth was once a world dominated by dinosaurs, and dinosaurs could be found everywhere in both plain forests and swamps. They lived on the earth for1.300 million years, but somehow, the dinosaurs became extinct, and they all disappeared from the earth forever. This is really an eternal mystery.
For more than a hundred years, I don't know how many scientists have tried to uncover the secret of dinosaur childlessness, but they have never been able to justify themselves. With the mutual penetration of natural sciences, some new theories about dinosaur extinction have appeared in recent years.
Some scientists believe that the extinction of dinosaurs was due to the cold climate. At the end of the Cretaceous period 65 million years ago, the world was cold on a large scale, the daily temperature difference increased, and the hot and cold seasons alternated obviously. Dinosaurs used to living in tropical environment could not hibernate like snakes and lizards, nor could they hide in caves to avoid the cold like fur animals. Dinosaurs are warm-blooded animals. They have no appearance and physiological function to resist cold, and they can't resist and adapt to cold attacks. Finally, they are ruthlessly eliminated by nature.
Some scientists assert that the extinction of dinosaurs was the result of crustal movement. About 70 million years ago, there was a strong crustal movement on the earth, which caused some basins to rise and shallow hills to appear, thus causing water and forests to dry up. At the same time, the seabed changed, the sea level dropped by more than 300 meters, the land between Asia and North America began to connect, a large number of animals moved to dinosaur habitats, and food supply was difficult, which made dinosaurs in a state of "food shortage" and gradually died of severe hunger.
Some scientists also suggested that the extinction of dinosaurs was caused by the collision and explosion of stars. In the late Cretaceous, an asteroid with a diameter of about 10 km collided violently with the earth. The impact speed is about 6.5438+10,000 kilometers per hour. During the impact, amazing dust was raised. Dust floats in the atmosphere, even blocking sunlight, making the earth dark for a period of time, the temperature drops, the photosynthesis of plants stops, plants wither, the "food chain" is interrupted, and dinosaurs die one after another.
Other scientists speculate that dinosaurs were poisoned by flowering plants and died out. Dinosaurs lived in Mesozoic, and gymnosperms such as ferns, cycads, ginkgo biloba and conifers dominated the plant kingdom. There are many tannins in these plants, which are harmless to dinosaurs. However, the earliest flowering plants appeared1.200 million years ago. These flowering plants often contain strong alkaloids, which adversely affect the physiology of dinosaurs. Some alkaloids, such as brucine, are very toxic. Dinosaurs swallowed a lot of alkaloids, and the toxin reaction led to serious physiological disorders and death.
The extinction of dinosaurs was due to interspecific competition and intraspecific competition-this is the understanding of other scientists. The activities of one organism often directly or indirectly endanger the survival of another organism, so there is direct or indirect competition, which is called "interspecific competition". For example, meat, competition between animals and herbivores, and competition between animals. In the age of dinosaurs, carnivores with strong reproductive ability and developed brains appeared. They ate many eggs laid by dinosaurs, which led to the death of dinosaurs. Dinosaur eggs were found in Inner Mongolia, Shandong and Guangdong. In particular, Shixing County in northern Guangdong Province found the largest and best preserved dinosaur eggs in the world, with 34 and 35 eggs in a nest respectively, and found the existing dinosaur fossils. In order to survive, creatures of the same species attack each other and devour each other, which is called "intraspecific competition". Tyrannosaurus rex, for example, is a Tyrannosaurus rex in the dinosaur family. Its head is 1.5 meters long, and its jaw has sharp teeth, so it can devour other herbivorous dinosaurs at will. Dinosaurs can be divided into herbivores and carnivores, and they are very long, both of which are more than 20 meters. For example, dinosaurs found in the United States were 27 meters long, and Mamenxilong found in Sichuan, China was 22 meters long and weighed 40 to 50 tons. Dinosaurs about the size of roosters were found in Luban, China, but they were counted as two. This phenomenon of "everything has its vanquisher, the law of the jungle" led to the final extinction of dinosaurs.
Although all the above statements have some truth, each statement can't be justified and can't be fully affirmed by the scientific community. For example, "dinosaurs ate flowering plants and became extinct", then pterosaurs in the air and ichthyosaurs in the water didn't eat flowering plants on land at all, so why did they become extinct at the same time as other dinosaurs? But hadrosaurs, ceratosaurus and other groups are more prosperous after flowering plants appear? In a word, the mysteries in the evolutionary history of these creatures have not been completely uncovered so far.
Interviewee: lycol- Manager Level 4 8-3 22:40
It is said that an asteroid hit the earth, which led to the change of the earth's environment, which made the dinosaurs unable to adapt and became extinct.
Answer: Zeus in the Wind-Apprentice Wizard Level 2 8-3 22:43
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 textual 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.