How did dinosaurs die out?

There are many kinds of reptiles in Mesozoic in the history of the earth, and the most famous one may be dinosaurs. Hundreds of dinosaur fossils have been found in the world, and such a huge animal group that ruled the earth for10.6 billion years suddenly collapsed at the end of Cretaceous. It has written a puzzling chapter in the history of biology. What people see today is only a large number of dinosaur fossils left at that time. Li Yang, a paleontologist and physicist from China, published a paper in Yale University in 2009, which caused a sensation in the field of international paleontology. He and his team from China discovered a high concentration of iridium in the stratum of K-T line in chicxulub crater 65.3483 million years ago, which was 232 times higher than the normal content. Such a high concentration of iridium can only be found in meteorites in space, and the earth itself cannot exist. According to the accurate determination of iridium content around the Gulf of Mexico, at that time, an asteroid equivalent to Mount Everest not only hit the Central American region of the earth, but also broke the crust, so the earth stopped rotating for 0.2 milliseconds, and then a major earthquake never happened on the earth. The impact caused the molten slurry to be thrown into the air for thousands of meters, followed by flashover for dozens of days. High temperature may not be the most deadly. In the next month, tens of millions of tons of dust and toxic substances spread all over the world. In the next four months, the sun was just a vague shadow, plants stopped growing, herbivores decreased greatly, polluted air, food shortage, and wanton diseases, all of which devastated the surviving dinosaurs. Covered with dust, the earth is facing a cold invasion. It seems that cold is not the most serious problem, but please remember that the sex of some animals is determined by temperature, and dinosaurs are one of them. Led to this mass extinction. In the past, the academic circles discussed the collision theory of alien objects and the volcanic eruption theory respectively, but both of them had considerable defects. Alien objects say that the single impact is not so serious, so long and so far away (global), while volcanoes say that the volcanic activity on the earth itself is very intense, but it is not enough to cause such a large extinction, including the Yellowstone super volcano. The demonstration direction and evidence provided by China scholar Li Yang perfectly answered the international paleontology community.

Recent theory

German scientists recently suggested that the extinction of dinosaurs was caused by the bad "space weather" at that time, that is, the strong particle flow from the universe broke into the earth's atmosphere, causing drastic changes in the earth's climate and leading to the extinction of dinosaurs. 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 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. So far, all kinds of explanations about the extinction of dinosaurs can't be justified. In recent years, the hypothesis that asteroids hit the earth put forward by American physicist Luis Alvarez has attracted much attention. He found that the content of trace element jujube iridium in the upper stratum of the late Cretaceous in gubbio suddenly increased by more than 30- 160 times compared with other strata, and then people came to the same conclusion from sampling tests all over the world, and the abnormal increase of iridium in the late Cretaceous strata was indeed universal. So Alvarez thinks that an asteroid with a diameter of about 10 km hit the earth at the end of Cretaceous, and the dust produced covered the sky. It caused great changes in the surface climate environment and led to the extinction of dinosaurs. However, there are many doubts about explaining the increase of iridium content in rock formations and the extinction of dinosaurs caused by the impact of asteroids on the earth. 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? As we know, thermonuclear reactions inside the earth will continuously accumulate enormous energy. Once the crust can't bear it, the internal pressure will break through the crust and suddenly release to form a big explosion. Iridium date, an element mainly existing in the core of the earth, was brought to the surface of the earth's crust by lava eruption during the Big Bang. It is recognized that the clay layer at the end of Cretaceous was formed by a large amount of volcanic dust accumulation. Therefore, the general increase of iridium content in the strata at the end of Cretaceous proves that the crust erupted violently at that time. Fossil archives tell us that most dinosaurs died and most dinosaur eggs were produced at the end of Cretaceous, and all the dinosaurs and dinosaur eggs found were preserved in the stratum under the thin clay layer rich in iridium, which is consistent with the time of a series of global crustal structural changes such as large-scale orogeny at the end of Cretaceous recognized by geologists. In recent years, hundreds of protoceratops and Ankylosaurus fossils were unearthed in Bayin Mandu Lake stratum in Inner Mongolia at the end of Cretaceous, and a large number of complete dinosaur bones were piled up in groups. Judging from the burial posture of the remains, they died in extreme pain, including the bones of a whole group of baby dinosaurs. This scene shows that they are catastrophic collective deaths, and the bodies are quickly buried in situ after death (many dinosaur fossils in other parts of the world also have similar death characteristics). At the same time, it is found that the local fossil-bearing rock stratum is brick red silty rock stratum, which is the best environment for fossil formation. It can be speculated that the process of environmental upheaval is quite sudden and short-lived. Because, if the earth's environment changed gradually over a long period of time and the dinosaur population gradually died out, they would not have left such a large number of dinosaur eggs and the whole group of dinosaur larvae fossils with relatively concentrated burial time. Therefore, most dinosaurs should have died in large numbers because of sudden devastating disasters when their living environment was basically normal. 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 were much higher than now, the surface was relatively flat, and the world was in 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 relatively cold and dry gas asteroids with different seasons.

Continue to be born in the environment. So the extinction of most dinosaurs is natural. There are also some surviving dinosaurs (mostly small in size) and some animals that evolved into primitive birds and mammals as early as Jurassic following the law 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. The biological remains in the earth's rock strata reveal that in the history of biological evolution, there will be a mass extinction every once in a while. The extinction of dinosaurs at the end of Cretaceous is not the only disaster in the history of biological evolution. In an earlier era, there was a "Cambrian Big Bang" phenomenon in which most invertebrates suddenly appeared in a short time. Just like the evolution of organisms from single cell to multi-cell, reptiles to mammals, it needs an evolutionary process (such as 1984, the discovery of Chengjiang Fossil Group in China). So far, there is no obvious evidence that the extinction of dinosaurs was caused by asteroid impact. However, the fact that the geological structure of the earth continues to change frequently shows that the environmental "catastrophe" caused by periodic crustal structure changes has always played a leading role in the process of biological evolution. Of course, the gradual evolution of small-scale species also runs through the whole process of life evolution. Periodic celestial explosion (such as nova explosion) is an indispensable link in the evolution of all planets, including the earth. Marine fossils and seabed minerals in those mountains are the best explanation for the end of the dinosaur era caused by the drastic changes in the earth's crust.

Extinction at the end of Mesozoic

Now we know that the extinction time of dinosaurs was about 65 million years ago, and the geological age was the end of Cretaceous in Mesozoic or the beginning of Tertiary in Cenozoic. Moreover, at that time, not only all kinds of dinosaurs that ruled the earth for more than 654.38 billion years were extinct, but also the tragic fate befell many other creatures on the earth. Other marine reptiles such as ichthyosaurs and plesiosaurs, flying reptiles such as pterosaurs, terrestrial reptile relatives of dinosaurs such as colorful lizards, marine invertebrates such as ammonites and arrow stones, micro-zooplankton in the ocean, calcareous planktonic foraminifera and calcareous micro-phytoplankton were 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, the face of the biological world on earth changed fundamentally 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 great extinction phenomenon. But so far, the scientific community has not found a completely correct answer about the cause of this extinction. Perhaps, such an answer is waiting for us to find. Here, only some familiar sayings are described as follows: starving to death, being killed by the other side, etc. But now there are more and more such claims, but scientists in China have verified that dinosaurs survived for about 2 million years after being hit by meteorites.

Meteorite collision theory

1980, American scientists affret and his son discovered 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 inferred that the impact object is an asteroid with a diameter of about 10 km. The impact of such a large meteorite on the earth is absolutely unparalleled. 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 10 years to finally get the preliminary results. They found this crater in the strata of Yucatan Peninsula in Central America and Mexico. It is estimated that the diameter of this pit is between 180 km and 300 km. Now, scientists are still doing further research on this pit. Scientists began to paint us a heroic picture 65 million years ago. 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 equivalent to the size of a medium-sized city fell from the sky. It was an asteroid, which fell into the sea at a speed of 40 kilometers per second and fell into a huge pit on the bottom of the sea. Seawater is rapidly gasified, and steam is sprayed into the sky for tens of thousands of meters. Then the tsunami was as high as 5 kilometers, spreading at an extremely fast speed, and the turbulent sea water swept everything in the landing area. After the turbulent waves swept the earth's surface, they met at the back end of the impact point. The huge seawater power triggered a strong volcanic eruption on the Deccan Plateau here, and the movement direction of the earth plates occurred simultaneously. This is a terrible disaster. Meteorites hit the earth and produced a lot of dust, polar snow melted, plants were destroyed and volcanic ash filled the sky. For a time, the sky was dark, the temperature plummeted, and the dinosaurs were swept away and buried by heavy rains, flash floods and mudslides. In the next few months or even years, the sky is still dusty and covered with dark clouds, and the earth enters a low temperature because it has not seen sunlight all the year round, and the vast land is silent for a while. An era of biological history (dinosaurs) and geological history (Mesozoic) ended in this way. Now that this crater has been discovered, and scientists have mastered some relevant evidence, it seems that the mystery of dinosaur extinction can be settled. However, if meteorites really caused the extinction of dinosaurs, why did birds escape the disaster and survive? This has prompted people to look for other ideas to analyze the reasons for the extinction of dinosaurs.

Climate change theory

Due to plate movement, ocean currents change, which leads to great changes in climate. The cold and dry climate killed plants and dinosaurs died for lack of food. It may also be that climate change directly led to the extinction of dinosaurs due to hunger and thirst.

Ocean ebb tide theory

According to Robert Barker, when the ocean ebbs and the land borders each other, creatures touch 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.

Volcanic eruption theory

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. But this theory has a premise, that is, large-scale volcanic eruption. 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.

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 are so huge, and not all dinosaurs can't hide in caves to take refuge, so this theory also has some imperfections that need to be corrected.

Fratricidal theory

Because of the climate problem, a large number of plants are extinct, so that herbivores who eat plants are gradually extinct, and carnivores become crazy and kill each other because they have no food.

Mammalian evolutionary theory

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. After these small mammals found dinosaur eggs, they kept eating them, which eventually led to the birth crisis and extinction of dinosaurs.

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 brings 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. (Doubt: 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. )

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 tunneling microscope, X-ray diffractometer, polarizing microscope and CT scanner. In recent years, Chinese scientists used CT technology to study the internal structural characteristics of dinosaur eggs unearthed in Laiyang, Shandong Province for the first time, and found that some dinosaur eggs in Laiyang, Shandong Province contained dinosaur embryos that could not be observed by other methods. Some scientists believe that. The deformation and dislocation of dinosaur embryos may cause dinosaur eggs to fail to hatch normally, thus weakening dinosaurs and eventually becoming extinct.

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, then why did birds 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; 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, 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. 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, and the other is that every living thing needs a suitable atmospheric environment to survive. 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 for the extinction of dinosaurs, asteroid impact may have played a role, 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. But no matter what happened, there is no doubt that dinosaurs could not adapt to the influence or change brought about by what happened.

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