Now we know that dinosaurs died out 65 million years ago. Moreover, at that time, not only all kinds of dinosaurs that ruled the earth for more than 100 million years were extinct, but also the tragic fate came to many other creatures living on the earth's land, sea and sky. Also extinct in this disaster are marine reptiles such as plesiosaur, flying reptiles such as pterosaurs, relatives of terrestrial reptiles such as colorful lizards, and marine invertebrates such as ammonites and arrowheads. As for the micro-phytoplankton in the ocean, calcareous planktonic foraminifera and calcareous micro-phytoplankton have also been almost swept away. After this catastrophe, about 50% of the biological genera and almost 75% of the biological species on the earth disappeared from the earth forever.

This is really a mass extinction and catastrophe. Due to the extinction of species, the face of the biological world on earth changed fundamentally about 65 million years ago. This extinction marks the end of Mesozoic era, and the geological history of the earth has entered a new era-Cenozoic era.

Through unremitting efforts, scientists have analyzed and studied all the clues that can be found at present and put forward various theories to explain this extinction phenomenon. But so far, there is still no 100% correct answer about the cause of this extinction.

Perhaps, such an answer is waiting for you to find.

Since ancient times, there have been different opinions about the real cause of dinosaur extinction, but there is no definite statement, so it is still an unsolved mystery. Here are only some well-known statements as follows:

1. meteorite collision theory:

1980, American scientists found a high concentration of iridium in the stratum 65 million years ago, which was dozens or even hundreds of times higher than the normal content. Such a high concentration of iridium can be found in meteorites, so scientists associate it with the extinction of dinosaurs. According to the content of iridium, it is also calculated that the impact object is an asteroid with a diameter of 10 km. Such a large meteorite hit the earth. It's definitely an unparalleled blow. According to the earthquake intensity, it is about Richter scale 10, and the diameter of the crater produced by the impact will exceed 100 km. It took scientists 65,438+00 years and finally got the preliminary results. They found this crater in the stratum of Yucatan Peninsula in Central America. According to the calculation, the diameter of this crater is 65438+.

_ _ _ Scientists began to describe the heroic scene 65 million years ago for us. One day, dinosaurs were still eating and drinking carefree in paradise on earth. Suddenly, a dazzling white light appeared in the sky, and a boulder with a diameter of 10 km fell from the sky. It was an asteroid that fell into the sea at a speed of 40 kilometers per second and hit a huge one at the bottom of the sea. Steam sprayed tens of thousands of meters into the sky, and then the tsunami was as high as 5 kilometers and spread at an extremely fast speed. The turbulent sea swept everything that landed on land, and the turbulent waves swept the earth's surface, and then merged at the back end of the impact point. The huge sea power triggered a strong volcanic eruption in Deccan Plateau here, which changed the movement direction of the earth plate. What a terrible disaster this is. Meteorites hit the earth and produced a lot of dust. The polar snow melts, plants are destroyed and volcanic ash fills the sky. For a time, the sky was dark, the temperature plummeted, and it rained heavily. Mountain torrents and mudslides swept away the dinosaurs and buried them. In the next few months or even years, the sky is still dusty and overcast, and the earth enters a low temperature because it has not seen the sun all the year round, and the vast land is silent for a while. Therefore, an era in the history of biology is over.

2. Comet collision theory;

The "comet collision theory" is based on paleontologist David? Rapp and John? Sepkovsky's argument that "the extinction of paleontology occurs every 26 million years" is the beginning. Louis? Albalez gave this argument and his own theory to the astrophysicist-Charlie? Milla, later believed by Milla, periodically pushed comets to the earth because of the gravitational force of Nemesis, the half star of the sun.

3. Theory of orogeny;

At the end of Cretaceous, the swamp was dried up by orogeny, and many dinosaurs whose home was swamp could no longer survive. Because of the changes in the post-Qi Dynasty, plants also changed, and herbivorous dinosaurs could not adapt to new foods and died out one after another. The herbivorous dinosaurs became extinct, and the carnivorous dinosaurs also lost their dependence. As a result, they also became extinct. This extinction process lasted 65,438+0,000-20 million years. By the end of Cretaceous, it was extinct on the earth.

4. Climate change theory:

As a result of plate movement, ocean currents change, which leads to great changes in climate. The cold climate killed plants and dinosaurs died for lack of food.

5. Volcanic eruption theory:

Because the volcano erupts, it spews a lot of carbon dioxide, causing the global greenhouse effect and causing food death. Moreover, the volcano spewed fire, resulting in the release of a large amount of salt, the destruction of the ozone layer, harmful ultraviolet radiation on the surface, resulting in extinction.

Antonio Cikic, a famous Italian physicist, recently 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, and now 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.

The theory of ocean ebb tide with intransitive verb;

According to Barker, when the ocean ebbs and the land borders, creatures contact each other, which leads to the extinction of some species. Kangaroos, for example, can live in the island continent of Europe, but they will die if they meet other animals in South America. In addition to this relationship between eating and being eaten, there are also infectious problems such as diseases and parasites.

Seven. Warm-blooded animals say:

Some people think that dinosaurs were warm-blooded animals, so they could not bear the cold weather 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.

Eight. Fratricidal theory:

Because of the climate problem, a large number of flowers and plants are extinct, herbivores who live on grass are dying gradually, and carnivores are extinct because of lack of food.

Nine. 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. (Doubt: Why did dinosaurs suddenly increase after about 200 million years of ecological balance? The key to the establishment of this theory has also directly caused many scholars to review the reasons for the abnormal increase in dinosaur production. )

10. The mammalian prisoner said:

In the second half of Mesozoic, the ancestors of mammals existed. According to fossil records, 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 omnivores whose main food is insects. These small mammals have been eating dinosaur eggs since they found them.

1 1. The aging theory of species;

People think that the dinosaur's body was too big because it flourished for hundreds of millions of years. Moreover, bones such as horns are also extremely developed, which causes great inconvenience to life and eventually leads to extinction.

The most representative dinosaur brontosaurus is 25 meters long and weighs 30 tons. Because of his huge size, he lost his ability to survive. 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.

My opinion: not all dinosaurs are so huge, but there are also small dinosaurs with a body length of only about one meter. In addition, there are dinosaurs with bones like deer that can run briskly. But why did this dinosaur die out at the same time? Moreover, in cold-blooded animals, abnormally developed bones and other parts are considered to be able to absorb external temperature and release internal heat to regulate body temperature, which has very favorable functions. Therefore, I suspect that the extinction of dinosaurs was due to the aging of species. )

Twelve. Alkaloid theory:

According to this theory, flowering plants began to appear in the last period of dinosaur existence, that is, the Cretaceous period, and some of them contained toxic alkaloids. Dinosaurs died of poisoning because of eating a lot of food. 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.

In addition to the above twelve statements, there are other less well-known statements, such as "infectious diseases", "radiation from the universe or supernova explosion", "not taking Noah's Ark" and "vibration theory of the solar system". As for which is the best statement, it depends on everyone's thoughts, and there is no right or wrong. After all, the mystery of dinosaur extinction has not really been solved!

Asteroid impact theory

1980, at a scientific seminar, American geologist Alvarez and others vividly told a thrilling story that happened 65 million years ago according to their own research results: on a sunny afternoon, in the tropical bush under the scorching sun, many different kinds and shapes of dinosaurs walked quietly by the lake or foraged in the water as usual; On the edge of the forest, a newly hatched hadrosaur is pacing back and forth by the egg nest; In an open Yuan Ye, a Tyrannosaurus rex is preparing to pounce on a giant triceratops. ...

Suddenly, a loud noise that I had never heard before broke the quiet world. A meteor with a diameter of several kilometers hit the earth. The collision was terrible, and there was an explosion equivalent to tens of thousands of atomic bombs in an instant. This is an unexpected asteroid. After colliding with the earth, the impact force can reach 10 15 tons of TNT explosive. A huge mushroom cloud with dust rose rapidly, soared into the sky, then dispersed, and finally enveloped the whole earth. Soon, dinosaurs can't see each other, because dark clouds cover the sky and there is no sunshine during the day. This terrible situation lasted for a year or two. The photosynthesis of plants was interrupted, so a large number of plants withered and died. Vegetarian dinosaurs who ate plants died one after another. Later, carnivorous dinosaurs also became extinct because they lost food.

This story is the essence of the theory that asteroids hit the earth and led to the extinction of dinosaurs. Later, it received continuous support from many scientists. Some scientists even believe that during this period, the earth not only experienced a large planetary impact, but also suffered many smaller but still life-threatening asteroid impacts, among which the traces of planetary impacts found in the Caribbean and Iowa in the United States can be confirmed.

The evidence of this hypothesis also comes from an amino acid found in sediments around the world 65 million years ago. This amino acid contains a lot of iridium, which is abundant in some celestial bodies, but it should not exist on earth at all. This iridium-rich layer is found in many areas of North America, Europe and Australia, and it was also found in Gamba, Tibet a few years ago.

Some scientists think that the explosion wiped out all the dinosaurs. However, some scientists believe that only 70% of dinosaurs were extinct at that time, and other dinosaur species narrowly escaped the disaster, but gradually became extinct in the following millions of years. The latter statement makes sense, because some dinosaur bones were still found in the strata formed after this incident 65 million years ago. For example, dinosaur remains were found in the upper and lower floors of New Mexico 60 million years ago. Fossils of Triceratops were also found in Cenozoic tundra in Alaska. These phenomena seem to show that some dinosaurs still struggled for millions of years after the big bang caused by the asteroid hitting the earth, and eventually died out because they did not adapt to the new climate and environment.

Reproductive frustration theory

At present, egg fossils of ancient reptiles, especially dinosaurs, have been 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 electron microscope, X-ray diffractometer, polarizing microscope and CT scanner. In recent years, Chinese scientists used medical CT technology for the first time 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, there are fewer pores on the eggshells of dinosaur eggs near extinction than in other periods, which is probably related to the cold and dry climate.

Theory of atmospheric composition change

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, why did reptiles closely related to dinosaurs such as turtles, crocodiles and lizards escape the disaster and survive? 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 appearance of autotrophs, photosynthesis began to consume carbon dioxide and 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; On the contrary, 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, the content of carbon dioxide in the atmosphere was 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.

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.

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.

The latest report of the American Geological Society

The extinction of dinosaurs is a century mystery that scientists cannot solve. Many scientists speculate that the impact of cosmic matter on the earth many times is the reason for the extinction of dinosaurs. However, after analyzing the sedimentary rocks at the bottom of the Atlantic Ocean, a scientific research team in the United States believes that a single asteroid hitting the earth is the real reason.

This discovery was published in detail on the website of Bulletin of American Geological Society (165438+1October 30th).

■ discover

Research leader, geologist Ken of Missouri-Columbia University? Mcleod said: "Our findings strongly support the single-effect hypothesis."

Scientists discovered 26 years ago that iridium, a rare chemical element, existed on the earth during the Cretaceous period. Iridium is a common chemical component of asteroids, which led scientists to speculate that asteroids hit the earth during the Cretaceous period and brought iridium to the earth. Later, scientists identified that the Chickrobel crater with a diameter of about 180 km found in Mexico's Yucatan Peninsula was also formed in the Cretaceous period, which made scientists think that the crater was the product of an asteroid hitting the earth.

In order to obtain evidence, the researchers drilled five samples of sedimentary rocks from the De Melara Dome in the Atlantic Ocean about 2,800 miles (about 4,500 kilometers) from the impact point of Yucatan Peninsula for analysis.

For researchers, Mount De Melara is an ideal place because it is located at a moderate distance from the crater. If the sampling site is too close to the crater, the collected samples may not truly reflect the situation at that time due to tsunami, earthquake and landslide after impact. If the distance is too far, the rock will contain too little impact evidence.

According to the researchers, impact-related substances only existed in rock formations about 65 million years ago, but these substances did not exist in longer and lighter rock formations. This means that the asteroid only hit the earth once. Mcleod said: "This is a very obvious single impact event."

Researchers believe that at the end of Cretaceous 65.5 million years ago, an asteroid about 6 miles (about 10 km) hit the earth, forming the Chickroeber crater, which led to the extinction of dinosaurs.

■ explanation

Scientists have made the following explanations about how asteroids hit the earth and led to the extinction of dinosaurs.

Asteroids hit the earth quickly, causing drastic changes in the earth's environment. The huge impact throws a lot of rocks and dust into the air, which leads to frequent earthquakes, marine tsunamis and volcanic eruptions, and many forests are swallowed up by fires.

For decades, dust has been floating in the air, making it difficult for the earth to receive enough sunlight, so the number of plants has dropped sharply, leading to the collapse of the food chain from the bottom. At the same time, the weakening of sunlight makes the earth increasingly cold, and rainwater turns into hot acid rain mixed with volcanic eruption and falls to the surface, which leads to great challenges for the living environment of animals and plants.

Dinosaurs, which once ruled the earth for 65438+600 million years, could not adapt to the changes in the environment and were naturally eliminated. From black dragon and plesiosaurs living in the ocean, pterosaurs flying in the air to all kinds of dinosaurs living on land, no one was spared. In addition, many ancient creatures, including ammonites and marine plankton all over the ocean, were also extinct in this catastrophe.

Birds and mammals were badly hit, but they survived. Warm-blooded animals with long hair eventually replaced dinosaurs as masters of the earth, laying the foundation for the birth of mankind.

Supplement:

In the past, all scientists thought that dinosaurs were cold-blooded or warm-blooded like all 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. This is also reasonable from the point of view that carnivorous dinosaurs are far less than herbivorous dinosaurs. In addition, there are some smaller dinosaurs, who are likely to be 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.

In ancient times, there used to be a group of strange creatures-dinosaurs. They ruled the earth, lived for nearly 15 thousand years, and finally died out magically. Everything we know about dinosaurs today comes from dinosaur fossils.

There are many kinds of dinosaurs, and their shapes and habits are quite different. Among them, the big one can be as big as dozens of elephants combined; Small, but almost like a chicken. As far as food habits are concerned, dinosaurs have mild vegetarians and fierce carnivores, and there are omnivorous dinosaurs that eat both vegetarian and vegetarian foods.