Why did dinosaurs become extinct?

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.

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.

Continental drift theory

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.

Geomagnetic variation theory

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.

Plant 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 the intake of angiosperms led to excessive accumulation of toxins in the body and finally poisoning. Carnivores are poisoned after eating poisonous meat.

Acid rain theory

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.

Meteorite impact theory

There is a chicxulub crater on Mexican Yucatan Peninsula. What does it have to do with the extinction of dinosaurs 65 million years ago? The answer lies in this white rock.

This layer of rock is called the K-T boundary by geologists, which means the marker line of the Cretaceous-Tertiary boundary. The lower rocks are rich in dinosaur fossils, but above the K-T boundary, dinosaurs disappeared.

The rocks at the K-T boundary contain iridium, which is a rare metal with an average content of only one billionth in the earth. However, the iridium content in this rock layer is 200 times higher than the normal content. Where else can I find so much iridium? In space.

The content of iridium in space is 1000 times higher than that of the earth. People also found evidence of shocked quartz in this layer of white rock, and only asteroids will leave such traces. High concentrations of iridium and shocked quartz occur in tertiary boundary rocks in many parts of the earth. This global trace can only come from the most violent impact. The impact site was in Mexico's Yucatan Peninsula.

The impact 65 million years ago was so violent that nothing in human history could compare with it. The asteroid or comet that hit the earth at that time was about 6 miles wide. It rushed to the surface of the earth at a speed of more than 40 times the speed of sound. It is so huge that when it hits the earth, its front end has touched the ground, but its tail is still at an altitude of 35,000 feet, which is equivalent to the flying height of a jet airliner. What hit the earth was a boulder the size of a mountain.

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. There are many doubts about the explanation that the impact of asteroids on the earth led to the increase of iridium content in rock formations and the extinction of dinosaurs.

1. Asteroids are generally composed of silicon and iron, so it is impossible for such a huge asteroid to fall to the surface of the earth even after a long time, and such a large meteorite has never been found on the earth;

2. At the end of Cretaceous, most rock formations were igneous rocks formed by lava cooling, and sedimentary rocks formed by dust accumulation only occupied a small part of the surface. Can the dust raised by the asteroid impact bury most of the animals and plants on the earth in rocks thousands of meters deep?

3. Can iridium contained in asteroids be evenly distributed and cover the whole earth's surface? Iridium also exists deep in the earth. Why only speculate that iridium comes from outside the earth and not from inside it? So the real cause of dinosaur extinction needs further exploration, but a dinosaur fossil has been unearthed. According to foreign media reports, the end of the "dinosaur era" on earth is a great species "change" in history. Some scientists say that climate change caused the extinction of dinosaurs, but there is not enough evidence to prove this speculation. Scientists have discovered the last batch of dinosaur horn fossils on the earth, which is expected to find the main reason for the extinction of dinosaurs.

It is reported that this brown "dinosaur horn fossil" is about 45 cm long and belongs to the family of herbivorous dinosaurs, including the famous Triceratops. Scientists found this horn fossil in a wasteland called "Hell Creek Stratum" in southeastern Montana, USA. Many other dinosaur fossils have been found here, so it is also a geological place. What makes scientists feel special about this dinosaur horn fossil is that it was found at 13 cm below the rock layer, and the location of the fossil also means the place where the dinosaur died at that time, which can fully explain that this brown-horned herbivorous dinosaur lived in the Cretaceous Tertiary, or was on the verge of "K-T" extinction. This also fully shows that the brown-horned dinosaur is the last group of dinosaurs, and it became extinct after all its kind disappeared. But scientists believe that the reason why dinosaurs suddenly disappeared was not that they died out slowly, but because of a sudden planetary collision.

Scientists speculate that 65 million years ago, at the end of Cretaceous, a huge asteroid or comet collided violently with the earth off the coast of Mexico, which may be the main reason for the large-scale death of dinosaurs. However, some skeptics have repeatedly pointed out that the lack of dinosaur fossils 3 million years ago before the "big impact" is enough as evidence that dinosaurs were already extinct when the atmospheric phenomenon "attacked". It is understood that among the rock formations below the extinction edge of "K-T", the rock formations within ten feet are very close to this dinosaur fossil, and some people call this area "three meters blank". The theory of "three meters blank" also triggered a debate about what happened to dinosaurs. Some people still believe that dinosaurs did not become extinct, but eventually evolved into "the ancestors of birds". Some scientists believe that dinosaurs may eventually become extinct slowly.

In any case, this horn fossil seems to be very close to the "three-meter blank", and this discovery has also made scientists pay attention to the theory that "destructive asteroids led to the extinction of dinosaurs". At the same time, Dr. Tyler Lyson of Yale University also said that the discovery of this dinosaur horn fossil fully shows that dinosaurs did not die out slowly before the atmospheric phenomenon hit the earth. Judging from the geographical location of this fossil, it is enough to show that at least some dinosaurs survived before the asteroid hit the earth. At the same time, it also shows that there are no non-bird dinosaur fossils in the "three-meter blank", which contradicts the theory of non-bird dinosaur extinction before the "K-T" extinction.

Theory of orogeny

At the end of Cretaceous, the swamp was dried up by the orogeny, so many dinosaurs that used the swamp as their home could no longer survive. Because of climate change, plants have also changed, and herbivorous dinosaurs were unable to adapt to new foods and died out one after another. The extinction of herbivorous dinosaurs made carnivorous dinosaurs lose their dependence and became extinct. This extinction process lasted 1000 to 20 million years. By the end of Cretaceous, it was extinct on the earth.

Volcanic eruption theory

Volcanic eruption

Because of the eruption of the volcano, a large amount of carbon dioxide is ejected, which causes the greenhouse effect of the earth and leads to the death of plants. Moreover, the volcanic eruption released a lot of salt, which broke the ozone layer, and harmful ultraviolet rays irradiated the earth's surface, causing extinction.

Antonio Cikic, a famous Italian physicist, suggested that the extinction of dinosaurs was probably caused by a large-scale submarine volcanic eruption.

Professor Qi Jichi believes that at the end of Cretaceous, a series of large-scale volcanic eruptions occurred on the earth under the ocean, which affected the thermal balance of seawater, and then caused the change of land climate, thus affecting the survival of dinosaurs and other animals that needed a lot of food to survive. His reason is that the impact of modern submarine volcanic eruption on the ocean and atmosphere is well known, but its impact is far less than that of submarine volcanic eruption 65 million years ago.

Professor Qi Jichi believes that in the past, the scientific community knew very little about submarine volcanic eruption, so it is necessary to conduct in-depth research on this phenomenon that seriously affects the earth's environment. For example, he said that Greenland once had dense vegetation, but when the global ocean water temperature balance changed, the cold ocean current changed direction and crossed Greenland, thus turning this big island into a land covered with snow and ice. This is a typical example that the change of ocean water temperature balance has a great influence on climate. Submarine volcanic activity is an important factor affecting the balance change of ocean water temperature. Therefore, Professor Zichichi believes that the change of ocean water temperature balance caused by large-scale eruption of submarine volcano should be taken as an important reference factor for studying dinosaur extinction.

Ocean ebb tide theory

According to Robert Barker, when the ocean ebbs and the land borders each other, the creatures touch or influence each other, which leads to the extinction of some species. Kangaroos, for example, can live on the island continent of Oceania, but they will die if they meet other animals on the South American continent. In addition to this relationship between eating and being eaten, there are also problems of infection and spread of diseases and parasites, and dinosaurs may become extinct.

Theory of warm-blooded animals

In the past, all scientists thought that dinosaurs were cold-blooded or warm-blooded like other reptiles, but with the increasing number of fossil data, people's understanding has also changed. Some people think that some dinosaurs may be warm-blooded animals. First of all, they think that some dinosaurs are extremely agile, and they don't crawl on the ground like snakes, but run on the ground with two hind legs, which can reach 20 to 90 kilometers per hour. This requires a strong heart and a high metabolism, which is obviously impossible for cold-blooded animals. Secondly, dinosaurs ate a lot. It is speculated that a 30-ton sauropod dinosaur may eat nearly 2 tons of food every day, and only warm-blooded animals need so much energy. From the point of view that carnivorous dinosaurs are far less than herbivorous dinosaurs, this is also reasonable. In addition, there are some smaller dinosaurs whose bodies are covered with a layer of feathers or hair, which is also to prevent the loss of body temperature. Other aspects, such as the study of bones, also preliminarily show that some dinosaurs were warm-blooded animals. As soon as the theory of warm-blooded dinosaurs was put forward, it was strongly criticized, but it is still difficult to reach a conclusion.

Some people think that dinosaurs were warm-blooded animals, so they could not bear the cold climate in the late Cretaceous and could not survive. Because even if dinosaurs were warm-blooded, their body temperature was still not high, probably similar to that of living sloths, and to maintain such a body temperature, they could only live in a tropical climate. At the same time, the dinosaur's respiratory organs were not perfect and could not fully supplement oxygen. They don't have thick hair to avoid hypothermia, but they easily lose a lot of heat from their long tails and feet. The difference between warm-blooded animals and cold-blooded animals is that if the body temperature drops below a certain range, it will consume physical energy to raise the body temperature and the body will soon become weak. They are too big to go into caves to avoid the cold, so if the cold days last for a few days, they may freeze to death because of exhaustion. But there is a doubt in this theory, that is, not all dinosaurs were so huge, and not all of them could hide in caves to take refuge, so this theory is not perfect.

Fratricidal theory

Because of the climate problem, a large number of plants became extinct, which led to the gradual extinction of plant-eating herbivores.

Mishandle with each other, incompatible.

Death, and meat eaters, because there is no food, become crazy, kill each other and become extinct.

Oppression theory

The rapid increase in the number of dinosaurs led to the extinction of herbivorous dinosaurs with limited plants, and then carnivorous dinosaurs that ate herbivorous dinosaurs died because of lack of food.

Male and female temperature theory

According to the current situation of crocodiles, the sex of crocodiles depends on the temperature during the egg period. When the temperature is high, the crocodile is male, and when the temperature is low, the crocodile is female. Because crocodiles keep the original form of dinosaurs, the sex problem of eggs is likely to be similar to that of dinosaurs. Because the earth's climate changed suddenly 65 million years ago, the temperature rose sharply, and almost all dinosaur eggs became male, so male dinosaurs appeared.

Theory of species aging

People think that the meat of dinosaurs was too big because it flourished for more than 65.438+0.6 billion years. Moreover, bones such as horns are also extremely developed, which causes great inconvenience to life and eventually leads to extinction.

The most representative confusing dragon among dinosaurs, with a body length of 25 meters and a weight of 30 tons, lost its viability because of its huge size. In addition, Triceratops and others also went to the road of self-destruction because of their expanding three horns and unusually developed bones to protect their heads.

Alkaloid theory

According to this theory, flowering plants appeared in the last period of dinosaur prosperity, that is, the Cretaceous period, and some of them contained toxic alkaloids. Dinosaurs died of poisoning from eating too much. Because mammals can distinguish poisonous plants through taste and smell, but dinosaurs don't have this ability.

However, plants containing alkaloids did not suddenly appear in the late Cretaceous, but were already visible five million years before the extinction of dinosaurs. This theory can't explain why dinosaurs survived during this period. So this statement cannot be established alone.

Reproductive frustration theory

Before 20 13, egg fossils of ancient reptiles, especially dinosaurs, were found in many parts of the world. According to the morphological structure, dinosaur eggs can be divided into short round eggs, oval eggs and long eggs. The size of dinosaur eggs varies greatly, including the eggshell thickness, internal and external "ornamentation", eggshell structure and the proportion of cone layer and columnar layer in its shell. In order to further study the internal characteristics of dinosaur eggs, scientists have adopted many new technologies and methods, such as scanning tunneling microscope, X-ray diffractometer, polarizing microscope and CT scanner. For the first time, Chinese scientists used CT technology to study the internal structural characteristics of dinosaur eggs unearthed in Laiyang, Shandong Province, and found that some dinosaur eggs in Laiyang, Shandong Province contained dinosaur embryos that could not be observed by other methods.

Climate catastrophe theory

According to the data obtained from deep-sea geological drilling, some scientists believe that the climate on the earth changed abnormally 65 million years ago and the temperature suddenly rose. This change makes the temperature-changing animals with weak heat dissipation ability, such as dinosaurs, unable to adapt to the environment well, resulting in the disorder of endocrine system in their bodies, especially causing serious damage to the reproductive system of male individuals. As a result, dinosaurs could not reproduce and eventually went extinct.

There is also a theory that although sudden climate change led to the extinction of dinosaurs, the process of speculation is different. Scholars of this school believe that about 70 million years ago, the Arctic Ocean was completely separated from other oceans by land. In the last days, due to various factors, salty seawater gradually turned into fresh water. By 65 million years ago, the "bank" separating the Arctic Ocean from other oceans suddenly burst. A large amount of seawater from the Arctic Ocean is lightened by seawater desalination and flows into other oceans. Because the water temperature in the Arctic Ocean is very low, these "overflowing" cold water forms a layer of cold flow, which makes the seawater temperature in the oceans of the earth drop rapidly by about 20 degrees. The drop of ocean temperature has seriously affected the climate of the mainland, making the air over the mainland cold. At the same time, the water vapor content in the air has also decreased rapidly, resulting in a large area of drought on land. The comprehensive structure produced by these climate changes on land is the extinction of dinosaurs.

One possible way for climate change to lead to dinosaur extinction is to seriously affect dinosaur eggs. Some scientists found that at the end of Cretaceous before the extinction of dinosaurs, the eggshells of dinosaur eggs became thinner, indicating that there was a role caused by rapid climate change before the extinction of dinosaurs. Some paleontologists in China have also found that among the dinosaur eggs produced in some fossil sites, those near extinction have fewer pores on their eggshells than those in other periods, which is probably related to the cold and dry climate.

Atmospheric change theory

The extinction of dinosaurs at the end of Cretaceous is an eternal mystery in biological history. Scientists have put forward one theory after another to try to explain the reasons, but so far there is no acceptable conclusion. The popular saying is that the disaster caused by the asteroid hitting the earth led to the extinction of dinosaurs, but this theory is not perfect. Because dinosaurs were the most successful animals on earth at that time, their rich diversity was manifested in different sizes, shapes and lifestyles. If the disaster caused by asteroid impact led to the extinction of dinosaurs, then why did birds survive the disaster? This has prompted people to look for other ideas to analyze the reasons for the extinction of dinosaurs.

Modern scientific analysis tells us that in the distant age when the earth was just formed, there was basically no oxygen in the air, but the content of carbon dioxide was very high. Later, with the emergence of autotrophs, photosynthesis began the process of consuming carbon dioxide to produce oxygen, thus changing the atmospheric environment on the earth. At the same time, on the one hand, carbon dioxide is deposited in the stratum in the form of coal and oil through biological fixation, and on the other hand, it is deposited in the form of various carbonates through organic or inorganic processes. This kind of evidence collection has been going on.

There is evidence that the concentration of carbon dioxide in Mesozoic era in which dinosaurs lived was very high, but the concentration of carbon dioxide in Cenozoic era after that was very low. Is this change in atmospheric composition related to the extinction of dinosaurs?

As we all know, every living thing needs a suitable environment to survive normally, and environmental changes can often lead to the rise and fall of a species. When the environment is beneficial to this species, it will flourish; Otherwise, it will decline or even become extinct. Environmental factors include temperature, water and other factors, as well as atmospheric composition. So, will the change of atmospheric composition affect the life span of living things? The answer is yes. For example, people's lives are in danger in an environment with high carbon dioxide concentration, and some animals are even more sensitive to the change of carbon dioxide concentration than people.

In Mesozoic, when dinosaurs lived, the content of carbon dioxide in the atmosphere was relatively high, indicating that dinosaurs adapted well to the atmospheric environment with high carbon dioxide concentration. Perhaps only in such an atmospheric environment can they live well. At that time, although mammals had appeared, they had not developed greatly. Perhaps because the environment such as atmospheric composition was not favorable to them, they were in a weak position and developed slowly in Mesozoic. With the passage of time, at the end of Cretaceous, the atmospheric environment changed greatly, the content of carbon dioxide decreased and the content of oxygen increased. This unfavorable environment may be reflected in two aspects: 1, the dinosaur's body became uncomfortable, and it was easy to get sick in the new environment, and the disease would spread like a plague. 2. The new atmospheric environment is more suitable for the survival of mammals, and mammals have become more advanced and adaptable competitors. Under the action of these two factors, dinosaurs finally became extinct. And those reptiles that are left behind are a few reptile species that can adapt to both the old environment and the new environment.

The theory that the change of atmospheric composition led to the extinction of dinosaurs has two starting points. One is that the atmospheric composition of Mesozoic is different from that of modern times. Modern science has proved this. The other is that every living thing needs a suitable atmospheric environment to survive. Modern science is not difficult to verify this.

There was almost no oxygen in the ancient atmosphere, but the content of carbon dioxide was high. Later, due to the appearance of organisms, the process of carbon dioxide content gradually decreasing and oxygen content gradually increasing in the atmosphere under photosynthesis may explain many phenomena in the history of biological evolution. For example, the explosion of life in CAMBRIAN is also a mystery in evolutionary history. The change of atmospheric composition can also explain this, because animals can't directly use inorganic substances for photosynthesis, and its origin lags behind that of plants, and it will only happen when the oxygen content in the atmosphere reaches a certain level. Therefore, the outbreak of CAMBRIAN life must be guaranteed by the fact that the oxygen content in the atmosphere reaches a certain level, which has been proved by science.

So the impact of asteroids may have played a role in the extinction of dinosaurs, but it does not seem to be the most critical factor.

In addition to the above 22 famous sayings, there are many little-known sayings (such as sunspot eruption, electromagnetic disturbance, changes in the direction and intensity of the earth's magnetic field). As for which is the best, it depends on everyone's ideas, and there is no right or wrong. After all, the mystery of dinosaur extinction has not really been solved!

Comprehensive cause theory

Because the extinction of dinosaurs will only happen under the combined action of various internal and external factors, this theory holds that the extinction of dinosaurs is a complex process, and it is difficult to lead to the extinction of dinosaurs for a single reason, and the extinction of dinosaurs is caused by many reasons.

But no matter what happened at that time, at least one thing is undeniable, that is, dinosaurs could not adapt or change what happened. If they can adapt to or change the environment, will they become extinct mysteriously?

Dinosaurs are ancient reptiles, with various kinds and shapes. The small ones are less than one meter long, and the big ones are dozens of meters long and weigh forty or fifty tons. There are carnivores and vegetarians They lived near the land or swamp on the earth and once ruled the earth for a period of time.

Other guesses

According to the German magazine Science Illustrated, Joerg Farr, a professor from the Institute of Astrophysics in Bonn, said that the earth fell into a strong cosmic particle flow "storm" 60 million years ago. When encountering such a storm, various particles entering the earth's atmosphere at high speed will reach hundreds of times as usual, tearing the molecules in the atmosphere into condensation nuclei necessary for the formation of rain, which will eventually lead to the thickening of clouds in the earth's atmosphere, frequent rainfall and a sudden drop in temperature.

Scientists believe that the explosion of cosmic particle flow led to the drastic change of the earth's climate conditions, and dinosaurs that could not adapt to this climate change became extinct in a short time.

A large number of animals and plants reflecting the characteristics of the earth's environment at that time showed that before the end of Cretaceous, the density and thickness of the earth's atmosphere far exceeded that of modern times, the surface was relatively flat, and the whole world had a very warm and humid climate. At that time, the temperature difference between the polar regions and the equator was very small. In the 1980s, Canadian geologists discovered a fossil forest in ellesmere island, which was dominated by water jackets, and there were animal fossils such as crocodiles in the forest, indicating that the polar regions used to have a tropical climate. The natural environment is the main factor that determines the existence form of life. After the Big Bang, when the hot and humid environment on which giant dinosaurs lived no longer existed, even if some of them survived, they could not adapt to the different relatively cold and dry climates in cold and warm seasons and continue to survive. So the extinction of most dinosaurs is natural.

There are also some surviving dinosaurs (mostly smaller) and some animals that have evolved into primitive birds and mammals as early as Jurassic, following the laws of natural selection and survival of the fittest. In a relatively harsh environment, after 70 million years of continuous evolution, most species have changed their original forms, from cold-blooded animals to cold-tolerant warm-blooded animals (birds, mammals and humans). Of course, after every large-scale species evolution, some species will remain intact. For example, after fish evolved into amphibians, fish continued to survive, and very few reptiles (crocodiles, scorpions, etc. ) still maintains the original form of dinosaurs 70 million years ago.

There are also "infectious diseases", "cosmic radiation or supernova explosion", "not taking Noah's Ark" and "solar system vibration theory".

63 million years ago, the extinction of dinosaurs that lived on the earth for 65.438+0.6 billion years became the biggest mystery in the history of biology. According to the discovery of dinosaur fossils in Antarctica, the hypothesis of continental drift is proved. Through the reflection on "broken sand", it is proved that the impact of aliens led to the extinction of dinosaurs.

Theory of meteor hitting the earth

65 million years ago, an asteroid hit the earth, leading to the extinction of dinosaurs.

According to foreign media reports, the latest findings of scientists show that large-scale meteor impact or the culprit leading to the extinction of dinosaurs.

The dinosaur horn was discovered in the stratum of Hell Creek in Montana, USA, and many dinosaur fossils have been unearthed here. The location of the fossil is under the stratum of the Cretaceous-Tertiary (K-T) boundary 13 cm, which is the key point of dinosaur death in the fossil record. Scientists believe that these dinosaurs disappeared after a sudden global catastrophe, rather than a slow extinction as previously claimed.

At the end of Cretaceous 65 million years ago, an asteroid or comet hit the coast of Mexico, killing all the dinosaurs. Some skeptics pointed out that there were no dinosaur fossils for 3 million years, which made the impact a new evidence that all dinosaurs disappeared overnight. There are obviously no fossils at 10 feet underground in the rock stratum at the K-T boundary. This area is commonly known as the "three-meter-long gap".

The theory of "three-meter-long gap" caused controversy about dinosaurs. Some people think that they evolved into birds, while some scientists think that dinosaurs died slowly. However, the discovery of the dinosaur horn gradually filled this "blank", and to some extent supported the view that the devastating asteroid destroyed the dinosaurs.

Dr Taylor Marie Laure Gigon of Yale University said: "This shows that at least some dinosaurs were fine before the asteroid impact. These gaps indicating the lack of non-bird (bird) dinosaur fossils do not exist, which is inconsistent with the previous assumption that non-bird dinosaurs were extinct before the K-T boundary collision event. " Scientists pointed out that the 125 cm rock formation formed after the impact had no fossils at all. [3]

Due to meteorite impact: the earth entered the nuclear winter.

Dinosaurs once ruled the earth, but the reason why they disappeared is still controversial. It is said that a huge meteorite hit 66 million years ago, causing the earth to enter a "nuclear winter", and dinosaurs eventually died in a harsh environment. Scientists have recently found a lot of evidence to confirm this statement.

Scientists pointed out that 66 million years ago, a huge meteorite with a diameter of 10 km hit the earth, raising a lot of smoke and dust to cover the sky, and the earth's environment entered a "nuclear winter." The sun was covered, which caused the temperature to be cold, and plants could not carry out photosynthesis, so lack of oxygen made dinosaurs, which once dominated the earth, decline.

This theory comes from scientists' prediction that nuclear war will lead to climate disaster. Nuclear weapons attacking cities will let a lot of smoke and dust into the earth's atmosphere, which may lead to very cold weather.

A study published in the Proceedings of the National Academy of Sciences pointed out that after a meteorite hit the chicxulub crater about 65 million years ago, the global temperature suddenly dropped, and the sea surface temperature dropped to 7 degrees Celsius.

The evidence is hidden in brazos river, Texas, and the analysis shows that the stones produced by the sediments are the same age as those in the impact crater. Wei Leku, a scientist at Utrecht University in the Netherlands, said, "Meteorite impact has disrupted the relatively stable and warm climate, which may bring great pressure to life on earth."

This winter is said to last no more than 20 to 30 years, but it is enough to destroy all kinds of life on land, sea and air, as well as many other life forms, scientists said.

From the computer simulation of "nuclear winter", it can be seen that earthquakes, tsunamis and fires occurred on the earth a few hours after the impact. Then dust and sulfur liquid gather in the air, blocking the sunlight. Finally, the sunlight on the earth is only 20% of the original normal level.