Who knows why dinosaurs became extinct? ! ! !

One day 65 million years ago, the green jungle was bathed in the scorching sun and was peaceful. Some dinosaurs gathered near the jungle, some of them chased each other, some were quietly devouring fresh leaves, some triceratops snuggled together to rest, and two hadrosaurs walked around the nest, carefully guarding their unborn babies. In the shadow of the jungle not far away, there is a Tyrannosaurus Rex. Its fierce eyes stare at everything in front of it, looking for opportunities to pounce on the target it is interested in.

Suddenly, a dull thunder broke the peace of the jungle. Hadrosaurs first craned their necks warily, and their voices grew louder and louder. It shook the earth and brought an ominous omen. Triceratops jumped up quickly, but it was too late. The earth is shaking, like a mountain of boulders falling from the sky, surrounded by smoke, clouds of smoke rising from the ground. In an instant, the boundary between heaven and earth disappeared, darkness was everywhere, and the world seemed to come to an end. Within a few days, the earth's surface was completely covered with smoke and dust, covering the sky, the temperature plummeted and darkness enveloped the earth. Without sunshine, plants withered, a large number of dinosaurs suffocated and died, and those who survived by luck fell down one after another because there was no food to eat. The earth is full of dinosaur bodies and bones.

This is the story that scientists told us about the extinction of dinosaurs. At that time, many asteroids hit the earth. The strong impact not only left a crater with a diameter of about 200 kilometers on the earth's surface, but also caused the high temperature and high pressure generated during the impact to vaporize the material, thus making the earth's surface constantly full of dust, leading to a large number of animal and plant deaths and the disintegration of the biological chain. Dinosaurs died out after this sudden disaster. A few dinosaurs may have narrowly escaped a temporary disaster, but they won't last long, because the environment on which they live has been completely destroyed and it will take a long time to recover, and only death awaits them.

The theory that asteroids hit the earth is not a woven myth, and the enrichment of iridium in the stratum is an important scientific basis. It turns out that the content of iridium on the earth is very small, only concentrated in the depths of the core. Where does a small amount of iridium in the formation come from? Through in-depth study, scientists believe that these iridium should come from cosmic dust. In the late 1970s, a high concentration of iridium was found in the clay layer on the Cretaceous-Tertiary boundary in Italy, which coincided with the extinction time of dinosaurs. Subsequently, during this period, the iridium content in the strata was found to be abnormal in many parts of the world, so the hypothesis that whisperd hit the earth and made iridium exist in the strata was proved. According to this hypothesis, geologists began to look for iridium anomalies around the world, and more and more evidence supported this hypothesis. It has become an acceptable theory that asteroids hit the earth and led to the extinction of dinosaurs. Information from astronomical observations shows that more than 2,200 asteroids have been discovered and named in the solar system, and there is no doubt that they have the opportunity to "visit" the Earth. It is also calculated that when an asteroid falls to the earth, the energy released by the impact is equivalent to hundreds of atomic bombs and hydrogen bombs exploding at the same time, and hundreds of tons of soil and dust may be thrown into the air, leaving the earth in darkness and disorder for at least several months or even longer. It seems that the extinction of dinosaurs is an act of god.

There are many other hypotheses about the extinction of dinosaurs. For example, the "Nemesis Hypothesis", that is, the theory of comet impact. It is believed that when a comet in the solar system is disturbed by the gravity of a companion star, it will produce thousands of "storms", and some of these "storms" will spread to the earth, so that the earth will suffer a trauma every once in a while (about 26-30 million years), and dinosaurs will die because of this continuous blow. Related to the hypothesis that the universe brings disaster, there are supernova explosion theory and solar flare hypothesis. In recent years, some new hypotheses have emerged, such as the "canceration theory" that dinosaurs were caused by the penetration of neutrinos in outer space, and dinosaurs were probably collectively extinct after suffering from various cancers. All these hypotheses are dinosaur extinction theories that emphasize extraterrestrial factors, but the causes of dinosaur extinction can not be ignored. The earth entered the late Mesozoic, and the living environment changed greatly. The development of dinosaurs has reached its limit and it can't adapt well to new conditions. Although dinosaurs ruled for a while, with the arrival of a new era, they had to give way to emerging mammals.

In the Mesozoic era more than 200 million years ago, a large number of reptiles lived on land, so the Mesozoic era was also called the "reptile era", and the earth was widely occupied by vertebrates for the first time. At that time, the earth's climate was warm and there were dense forests everywhere. Reptiles have enough food, and gradually flourish, with more and more kinds. They constantly differentiate into various reptiles, some become turtles today, some become crocodiles today, some become snakes and lizards today, and some evolve into mammals all over the world today.

Dinosaurs are the largest reptiles. They are very suitable for living in swamps and shallow lakes. At that time, the air was warm and humid, and food was easy to find. So dinosaurs ruled the earth for tens of millions of years, but for some reason, they suddenly became extinct in a short time 65 million years ago. Today, people only see a large number of dinosaur fossils left at that time.

People are still studying the reasons for the extinction of dinosaurs. For a long time, the most authoritative view is that the extinction of dinosaurs was related to a big meteorite 65 million years ago. According to research, an asteroid with a diameter of 7- 10 km once fell on the earth's surface, causing a big explosion, throwing a lot of dust into the atmosphere, forming dust fog that covered the sun, leading to the temporary suspension of plant photosynthesis and the extinction of dinosaurs.

The asteroid impact theory quickly gained the support of many scientists. 199 1 year, a meteorite impact crater was discovered in Yucatan Peninsula, Mexico, which further confirmed this view. Today, this view seems to be conclusive.

However, many people are skeptical about this asteroid impact theory, because the fact is that frogs, crocodiles and many other temperature-sensitive animals survived the Cretaceous period. This theory can't explain why only dinosaurs died. So far, scientists have put forward more than a dozen hypotheses about the causes of dinosaur extinction, and the more exciting and dramatic "meteorite impact theory" is just one of them.

In addition to the "meteorite impact theory", the main viewpoints about the extinction of dinosaurs are:

First, the theory of climate change. 65 million years ago, the earth's climate changed suddenly and the temperature plummeted, which led to the decrease of oxygen content in the atmosphere and dinosaurs could not survive. Some people think that dinosaurs were cold-blooded, without hair and warm organs, unable to adapt to the decline of the earth's temperature, and all of them froze to death.

Second, the theory of species struggle. At the end of the dinosaur era, the first small mammals appeared. These animals are rodent carnivores and may feed on dinosaur eggs. Due to the lack of natural enemies, more and more small animals finally ate dinosaur eggs.

Third, the theory of continental drift. Geological research has proved that there was only one continent on the earth when dinosaurs lived, and that was Pangea. Due to the change of the crust, the Jurassic continent split and drifted, which eventually led to the change of environment and climate and the extinction of dinosaurs.

Fourth, the theory of geomagnetic variation. Modern biology has proved that the death of some creatures is related to magnetic fields. When the earth's magnetic field changes, creatures sensitive to the magnetic field may lead to extinction. It can be inferred that the extinction of dinosaurs may be related to the change of the earth's magnetic field.

Five, angiosperm poisoning theory. At the end of the dinosaur era, gymnosperms on the earth gradually became extinct, replaced by a large number of angiosperms, which contained toxins that gymnosperms did not have. Giant dinosaurs ate a lot, and a large number of angiosperms led to excessive accumulation of toxins in the body and finally poisoning.

Sixth, the theory of acid rain. There may have been strong acid rain at the end of Cretaceous, which dissolved trace elements including strontium in the soil. Dinosaurs ingested strontium directly or indirectly through drinking water and food, which led to acute or chronic poisoning and eventually died in batches.

There are many hypotheses about the extinction of dinosaurs. However, these hypotheses have more supporters in the scientific community. Of course, each of the above statements has some imperfections. For example, the "climate change theory" does not clarify the reasons for climate change. After investigation, it was found that some small osteophytes in dinosaurs could compete with early small mammals, so there were loopholes in the theory of species struggle. In modern geology, the "continental drift theory" itself is still a hypothesis. "Angiosperm poisoning theory" and "acid rain theory" also lack sufficient evidence. Therefore, the real reason for the extinction of dinosaurs remains to be further explored.

The eternal mystery of volcano-the extinction of dinosaurs

Mesozoic is the age of dinosaurs, when dinosaurs were almost all over the earth's ecological environment. But by the end of the Cretaceous period 65 million years ago, dinosaurs-whether huge or small; Smart or stupid; Agile or clumsy; Carnivorous or herbivorous animals-all extinct, no one survived. The giants who ruled the earth for 65438+ billion years and their close relatives quickly disappeared from the earth in such a short time. If they didn't leave many huge or strange bone fossils, people might never know about them. What caused their extinction?

1At the beginning of June, 980, Alvarez published an article entitled "The Extraterrestrial Causes of the Cretaceous-Tertiary Extinction" in the magazine Science, proposing that the culprit leading to the extinction of dinosaurs was a cosmic celestial body. He suggested that if a meteorite with a diameter of 10 km hit the earth 65 million years ago, a crater with a width of about 175 km would be dug up, and the rock fragments produced by the explosion would splash into the stratosphere in the form of dust and quickly spread to the whole earth, blocking most of the light that normally reaches the surface of the earth. In the darkness that followed, photosynthesis stopped, plants stopped growing, the foundation of the food chain was destroyed, and dinosaurs and many other animals became extinct. The evidence of this hypothesis is that a clay layer rich in iridium was found between Cretaceous and Tertiary strata, and the paleontological records in the strata reflect the high extinction rate of organisms. This assumption is the famous "collision theory".

However, 65 million years ago, dinosaurs were not all extinct in an instant. This phenomenon makes people doubt the correctness of the statement that disaster fell from the sky. The Institute of Geochemistry of Siberian Branch of the former Soviet Academy of Sciences studied five species of dinosaurs and some dinosaur egg in Mongolian Gobi Desert. The results show that the fossils contain phosphate containing carbonate. It is worth noting that fossils are rich in rare earth metals such as fluorine, sulfur, barium, lead and thorium, and the thorium content is as high as 0.37%, which is 80 times higher than the percentage of thorium in the crust. There is evidence that the tectonic movement at that time was violent. With the eruption of volcano, the landform and climatic conditions of biological existence have been changed, the geological and chemical environment has been affected, and food and water quality have been polluted. At that time, the content of rare earth elements in the ecological environment was saturated, and its concentration was close to or enough to kill animals and plants. So some people think that geochemical changes are an important reason for the extinction of dinosaurs.

Other scientists put forward the comet impact hypothesis. Comet is a kind of celestial body with small mass and special shape. It does harm to living things in two ways. First, when a comet approaches the earth, its toxic components, such as colorless gas cyanide, will pollute the earth's atmosphere. Second, when a comet meets the earth, if a big comet hits the earth's land, the splash it hits can be greater than the weight of the comet itself, which can cause serious disasters in geological structure, climate and biology, just like an asteroid hitting the earth's land. Global warming will kill land animals. The study on the oxidation potential of the transition layer from Cretaceous to Tertiary shows that the seawater temperature at that time increased by about 5℃. Therefore, some scholars believe that the extinct dinosaurs died of heart disease because of the hot weather.

What caused the extinction of dinosaurs? For years, people have been arguing endlessly. In addition to the above three hypotheses, there are supernova explosion hypothesis, solar superflare hypothesis and so on. All kinds of hypotheses have their reasons and limitations. With the development of science, the penetration of disciplines and the application of new ideas and technologies, scientists are still exploring and trying to find the most practical answers.

Dinosaurs, like all reptiles, are egg-laying animals. Oviposition and reproduction. Zhao, a scholar from China, studied dinosaur eggs unearthed in Nanxiong Basin, Guangdong Province, and found that the ultrastructure of dinosaur eggshells was generally abnormal under the electron microscope. After in-depth and meticulous research, they put forward a unique view on the extinction of dinosaurs. They believe that the extinction of dinosaurs in southern China at the end of Cretaceous began 200,000-300,000 years before the Cretaceous-Tertiary junction, and the extinction reason may be related to the environmental changes at that time, especially the enrichment of trace elements. They speculated that South China might have been polluted by trace elements at that time, and the climate was quite dry. On the one hand, through the operation of the food chain, a large number of trace elements gathered in dinosaurs, which destroyed the balance of trace elements in their physiological activities, and then affected the reproductive process of dinosaurs, forming eggshells with pathological structures, which were fragile and could not guarantee the normal development of embryos. On the other hand, the excessive enrichment of trace elements in eggs will greatly reduce the hatching rate of dinosaur eggs, which will make dinosaurs unable to reproduce normally and thus embark on the road of extinction.

dinosaur

Wikipedia, the encyclopedia of freedom

dinosaur

Scientific classification

Domain: Eukaryotic domain Eukaryote

Boundary: animals in the animal kingdom

Phylum: Vertebrate of Chordata phylum.

Class: Reptiles, Reptiles

Subclass: Porphyra

Objective: * sauropod, sauropod

Objective: * Birch order.

Dinosaurs are different from dragons. See the dragon (qi)

Dinosaurs are a general term for some prehistoric reptiles. It first appeared about 2 10/00000 years ago, lived in Triassic, Jurassic and Cretaceous and existed for1500000 years. Almost all kinds of dinosaurs died out in the late Cretaceous about 65 million years ago, but there is a view that modern birds are related to some dinosaurs.

The name dinosaur was first put forward by British scientist richard owen in 1842. It consists of the Greek words deinos (meaning "terrible" or "extremely huge") and sauros (meaning "lizard"). The word dinosaur was translated from Japanese and later quoted by China.

Dinosaurs vary greatly in size. The smallest known dinosaur is only as big as a chicken (Mussaurus, its larva is only 20 cm), but most of them are huge. The largest is the sauropod dinosaur (klamelisarusgobiens, with a body length of more than 30 meters and a height of 10 meter), which is the largest terrestrial creature in history, second only to whales among all creatures.

Many other kinds of reptiles lived at the same time as dinosaurs. Some species are also big and strange in appearance, but they are not dinosaurs. See plesiosaur.

Dinosaurs died out in the Cretaceous-Tertiary extinction event 65 million years ago. The usual explanation is that a huge meteorite hit the earth and caused extinction (first proposed by Walter Alvarez). But this theory is still controversial.

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Dinosaur classification

Dinosaurs are divided into two types: sauropods and ornithopods, which are distinguished by pelvic structure.

Sauropods

Theropoda

Ceratosauridae (coelomosaurus, Protognathus, Liang Long, Abelosaurus)

Spinosauridae (Spinosaurus)

Allosauridae (Allosaurus)

Osteoporosis

Tyrannosaurus rex (Tyrannosaurus rex, Albertosaurus)

Bird wing family (bird wing order, ostrich)

Egg stealing dragon (egg stealing dragon)

Ankylosauridae (Ankylosaurus, Ankylosaurus)

Odontosaurus (odontosaurus)

Ceratosauridae (Deinonychus, Raptors)

Sauropoda

Ceratopogonidae (Ban Long)

Sauropods

Diptera (Puzzled Dragon, Liang Long, Mamenxilong)

Brachiosauridae (Brachiosaurus)

Dipterocarpaceae (Saltarone)

ornithischia

Ankylosaurus was covered with shields.

Stegosaurus (stegosaurus)

Ankylosaurus (Ankylosaurus, Skull Dragon, Arthropod Dragon)

Hand-foot

Ornithopoda (Duckbilled Dragon, Parasaurolophus, Toothed Dragon, Iguanodon)

Pachycephalosaurus (pachycephalosaurus)

Ceratosaurus (Ceratosaurus, protoceratops, Triceratops)