What about the extinction of dinosaurs?

The debate about the extinction of dinosaurs, whether the evolution of organisms is gradual (such as evolution theory) or sudden (such as catastrophe theory), has been debated for a long time. One of the focuses of the debate between these two theories is why dinosaurs became extinct. There are many theories about the sudden extinction of dinosaurs. The main arguments are as follows:

Climate change theory: During the late Cretaceous orogeny, the climate changed greatly, many plants died, and herbivorous dinosaurs died, which affected the survival of carnivorous dinosaurs. Some people think that low temperature makes it difficult for dinosaur eggs to hatch, and even if they hatch, it is difficult to survive.

According to the theory of dinosaur fossil constipation and alkaloid poisoning, herbivorous dinosaurs ate plants such as cycads and ferns. Later, these plants became extinct, and dinosaurs planted willows and mulberries, which led to constipation, indigestion, mobility and death. Others believe that cycads and ferns contain a lot of alkaloids, and long-term consumption will cause poisoning and death.

Oxygen excess theory and volcanic eruption theory, as well as ethnic aging theory and mammalian competition theory: these theories mainly think that dinosaurs were replaced by latecomers in the competition for survival. Mammals not only compete with dinosaurs for food, but also eat dinosaur eggs clean and make them extinct.

Geomagnetic disappearance theory: after the disappearance of geomagnetism, the earth was intensified by external radiation, which had a great impact on the climate and made dinosaurs extinct.

Asteroids and comets explode: According to calculations, every 6,543.8 billion years, an asteroid hits the earth, and some people think it is hit by a comet. Asteroids and comets contain highly toxic cyanide, which pollutes the atmosphere and water and causes dinosaur poisoning. Scientists in China analyzed dinosaur fossils unearthed in Sichuan, and they did find that they contained high levels of arsenic (a highly toxic substance). According to the analysis of the crater, the content of iridium in the crater is too high, which supports the statement that the meteorite hit the earth and led to the extinction of dinosaurs. However, in the mid-1980s, American scientists discovered that iridium-rich strata may be the result of the interaction between volcanic ash and seawater. Even in some areas, there are six iridium-rich layers, but only one layer is related to dinosaurs. Therefore, it is not very reliable to judge the impact of meteorites on the earth according to the iridium-rich layer.

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 Mesozoic, the earth used to be a world dominated by dinosaurs, and dinosaurs could be seen everywhere, whether in plains, forests or swamps. They have lived on the earth for over 130 million years. However, 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 plummeted, the photosynthesis of plants stopped, plants withered, the "food chain" was interrupted, and dinosaurs died 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.

Interspecies competition and intraspecies competition of dinosaurs-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". Such as the competition between carnivores and herbivores. In the era of dinosaurs, carnivores with strong reproductive ability and developed brains appeared. They ate a lot of 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.