Hypotheses for the extinction of dinosaurs. How the dinosaurs disappeared. A – four-radial pelvis with free space below; B – triradiate pelvis with pubic bones directed forward

It has long been known: dinosaurs became extinct at the end of the Cretaceous period due to an asteroid falling on Earth. There is such a version. However, there is little evidence. Scientists are still speculating about the reasons for the extinction of lizards and building new hypotheses.

Asteroid

This is one of the most popular scientific theories . It was put forward by American physicist Luis Alvarez in 1980. It is believed that a huge asteroid fell on Earth 66 million years ago. The crash site is believed to be the Chicxulub crater on the Yucatan Peninsula in Mexico. The celestial body raised clouds of dust into the atmosphere, awakened dormant volcanoes, which caused an asteroid winter and led to the extinction of dinosaurs and some other animals. Opponents of the theory believe that the crater is too small; there are craters on Earth from more impressive celestial bodies (for example, Chesapeake or Popigai), and moreover, at the time when they fell, there were no serious changes in the fauna on Earth. Proponents of the theory counter this with the fact that reptiles became extinct as a result of the fall of several asteroids at once. After all, the death of dinosaurs occurred rather slowly, over hundreds of thousands of years. 2 Active volcanism Another hypothesis for the extinction of dinosaurs is a significant increase in the Earth’s volcanic activity. Most often, scientists refer to the Deccan Traps plateau, which is located in India and is covered with igneous basalt two kilometers thick. Its age is determined to be 60 - 68 million years. Proponents of the volcanism theory believe that volcanic activity went on for so long that the Earth's climate became colder, and the dinosaurs froze. Opponents of the theory assure opponents that with a long eruption, dinosaurs could adapt to the cold, as crocodiles did, and survive. 3 Climate change Under this hypothesis, it is believed that dinosaurs died due to changes in the Earth's climate caused by continental drift. The drift caused temperature changes, mass death of plants, changes in the food supply of lizards, and drying out of water bodies. There is also an assumption that due to temperature changes in dinosaurs, only females or only males began to hatch from eggs. This happened in exactly the same way as in modern crocodiles. And this led to the death of the species. There is a theory that when it got colder, the shells of dinosaur eggs became thicker or thinner than necessary. In the first case, the fully formed baby could not leave the shell and died, and in the second, it became a victim of predators or infection. This theory is opposed by research by climatologists who have already found that there were no significant climate changes on Earth 66.5 million years ago. The next serious cooling began at the end of the Eocene, that is, only 58 million years ago. 4 Change in the atmosphere This theory is due to the fact that as a result of cataclysms, the Earth’s atmosphere changed its composition so much that the huge lizards could not breathe and they died. Scientists name different reasons for this turn of events. Some still claim that asteroids are to blame, others point to volcanoes. The fact is that during the heyday of dinosaurs, the oxygen content in the atmosphere was 10-15%, and the carbon dioxide content was only a few percent. The change in air composition led to changes in plants, and made it possible for the development of new fauna.

Opponents of this hypothesis studied the composition of the air in the ancient atmosphere of the Earth in rocks and sediments and came to the conclusion that the composition of the air did not change significantly during the Cretaceous period. At the end of the Cretaceous, carbon dioxide levels were about the same as 100 million years earlier, in the mid-Jurassic period.

Dinosaurs are huge lizards, the height of which reached a 5-story building. Their remains are found deep in the earth, which is why scientists say that dinosaurs lived on Earth millions of years ago. The last dinosaurs went extinct about 65 million years ago. And they appeared 225 million years ago. Judging by the remains of the bones of these lizards, scientists conclude that there were more than 1000 varieties of such animals. Among them were large and medium-sized, bipedal and quadrupedal, as well as those that crawled, walked, ran, jumped or flew in the sky.

Why did these giant animals become extinct? There are several theories about their death.

Why dinosaurs became extinct: scientific research facts

Since the death of dinosaurs occurred a very long time ago, we can only build hypotheses based on known scientific facts:

The extinction of the dinosaurs proceeded very slowly and took millions of years. This period was called “glacial” by paleontologists.
Over the course of these millions of years, the climate has changed. In the previous era, there were no ice caps on Earth, and the water temperature at the ocean floor was +20ºC. Climate change has caused a decrease in overall temperature and the appearance of significant icing.
In addition to climate, the composition of the atmosphere changed. If at the beginning of the Cretaceous period the air contained 45% oxygen, then after 250 million years it was only 25%.
During this period of time, a planetary catastrophe occurred. It is confirmed by the presence of iridium, an element that is located deep in the earth’s core and is also found in asteroids and comets. Iridium is found in deep layers of soil throughout the planet.
There are indirect witnesses of the collision of the Earth with an asteroid - huge craters. The largest are in Mexico (80 km in diameter) and at the bottom of the Indian Ocean (40 km).
Along with dinosaurs, some species of lizards (sea and flying) became extinct.

When and how dinosaurs went extinct: theories of disaster

Habitat change

Our planet is changing very slowly but steadily. The climate is changing, new species of animals appear and old species disappear. They find themselves not adapted to life in new conditions.

Cold snap

The average air temperature dropped from 25ºC to +10ºC. The amount of precipitation has decreased. The climate has become colder and drier. Dinosaurs, like other lizards, were not adapted to life in cool conditions.

It is known that most lizards are cold-blooded. When the air temperature drops, they cool down and become numb. However, this theory cannot explain why those reptiles that were warm-blooded and could hibernate became extinct.

Another theory is more viable - as a result of climate change, there is less grass vegetation - ferns, which were eaten by non-predators. Judging by the size of dinosaurs, they needed substantial thickets of food to feed them. As a result of a decrease in the amount of food, gradual extinction began. Herbivores died because they lost food. And the predatory ones - because there were few herbivores (which they ate).

Planetary catastrophe: collision with an asteroid or explosion of a star

Traces of collision with celestial body discovered on the island of Yucatan - a huge crater covered with stones and soil. When the asteroid collided with the earth, a powerful explosion should have occurred, which would have lifted tons of soil, stone and dust into the air. The dense suspension blocked the sun for a long time and caused a cold snap. As a result, not only dinosaurs, but also a number of other reptiles became extinct. This theory is confirmed by the remains of iridium in the soil of the Cretaceous period.

The explosion of a star relatively close to our planet could be the cause of a significant increase in radiation. However, it is not clear why the colossal emissions of radiation left other animals alive. Why dinosaurs became extinct still remains a mystery that haunts the minds of scientists.

Despite many theories, scientists are making computer simulations and reconstructions of what happened many millions of years ago. This is what the film will talk about.

Dinosaurs are ancient creatures that appeared on the planet approximately 225 million years ago. For 160 million years, these animals dominated the planet. The period of extinction took about 5 million years, and for about 65 million years they have been absent from the animal kingdom. There are many hypotheses about why dinosaurs disappeared. We will tell you in our article how these animals became extinct and ceased to exist.

The emergence of dinosaurs

Planet Earth was inhabited different types plants and animals 3 billion years ago. In the process of evolution, plants and animals appear and disappear, and each such process has its own time period and period. Dinosaurs on the planet lived during the Mesozoic era - the Triassic, Jurassic and Cretaceous periods.

The first simple plants were seaweed, and the first animals were small sea mollusks. The appearance of fish occurred approximately 500 million years ago. About 370 million years ago, the first animals, amphibians, came onto land. Reptiles are a new group of animals that appeared approximately 300 million years ago. The animals had scaly skin, they could lay eggs and be constantly on land. Next in the chain of evolution were dinosaurs. An extinct species of animal gave impetus to the development of such a science as paleontology.

Description of dinosaurs

One of the amazing animals that lived on the planet are dinosaurs. How these large animals became extinct and how they lived can only be judged from their fossilized remains. From the fossil remains it can be concluded that they were reptiles like crocodiles, lizards, turtles and snakes. Dinosaurs range in size from tiny to giant. They had four limbs and a tail. Dinosaurs stood and moved on straight limbs, some on hind legs, others - on all four, others could move on both two and four limbs. Many dinosaurs had long necks and teeth. Their habitat was significant, but 65 thousand years ago they suddenly became extinct.

Dinosaurs are divided into two groups: saurischians and ornithischians. The difference between the groups is the structure of the pelvic bones. In lizard-hipped dinosaurs the structure of the pelvis is four-rayed, while in ornithischian dinosaurs it is three-rayed. Some species of ornithischians had horns, spines, and shells.

The emergence of interest in dinosaurs

In the 1930s, fossilized remains of dinosaurs were first discovered. Then archaeologists did not attach much importance to them, and only after some time it became clear that these fossils belonged to ancient animals. The very concept of “dinosaur” was introduced by the English zoologist Richard Owen in the mid-19th century. From Latin “dinosaur” is translated as “terrible”, “dangerous”, “terrible”, and from ancient Greek - “lizard”, “lizard”. Since then, interest in these animals has been constantly growing. How many years ago did dinosaurs go extinct? The answer to this question is given by the science of paleontology. Ancient animals are studied by scientists, filmed in films, and become heroes of books. And despite such interest, there is no exact answer to the question of why dinosaurs became extinct.

Age of Dinosaurs

At the end of the Permian period, the formation of a single continent - Pangea. A characteristic feature of this time was global volcanic activity and the disappearance of about 90% of animals. Reptiles adapted best to the new conditions. At the beginning of the Triassic, a group of reptiles called pelycosaurs appeared. By the middle of the Triassic period they were replaced by a group of reptiles called therapsids. In parallel with the therapsids, a new group of reptiles developed - archosaurs. This group of reptiles is the ancestor of all dinosaurs, pliosaurs, crocodylomorphs, ichthyosaurs, placodonts and pterosaurs. The next type of reptile was called thecodont and was adapted to life on land. And it was from them that dinosaurs developed. Extinct animals adapted well and took dominant positions on land, in water and in the air.

During the Triassic period, the following species existed: Coelophysis, Mussaurus and Procompsognathus. Plant dinosaurs developed and evolved.

The largest animals lived in the Jurassic period. In the Late Jurassic period, land animals began to appear - brachiosaurus, diplodocus, etc.

During the Cretaceous period, predatory reptiles began to dominate in the seas and oceans. New species of dinosaurs appear.

End of an era

The Cretaceous period is the heyday of giant lizards, aerial pterodactels and marine reptiles. At the end of the Cretaceous period, a split into Gondwana and Laurasia occurs. The climate on Earth is becoming much colder, and ice caps are forming at the poles. The number of insects appears and increases.

All this led to the extinction of many species of plants and animals, including dinosaurs. They did not die out overnight, but considering that their dominance lasted 160 million years, their disappearance occurred quite quickly. The causes of the disaster that occurred during the Cretaceous period are still unclear.

But did all dinosaurs go extinct? The descendants of ancient reptiles are the crocodiles, lizards and birds that exist today. The first birds appeared during the Cretaceous era, and by the end of the era they already had developed plumage. When the dinosaurs went extinct, birds took over the baton of evolution.

Astrophysical extinction hypotheses

The fall of an asteroid is one of the common versions. The time of its fall coincides with the formation of the Chicxulub crater (Mexico. These events occurred approximately 65 million years ago, during the period when the dinosaurs became extinct. Perhaps the fall of the asteroid led to destructive actions, as a result of which a mass extinction of all living things occurred.

The multiple impact hypothesis states that the asteroid fell several times. In addition to the Chicxulub crater, there is the Shiva crater in the Indian Ocean, which was formed around the same time. This hypothesis explains why the extinction occurred gradually.

There is also a version of a supernova explosion and a comet colliding with the Earth.

Geological and climatic extinction hypotheses

The planet was undergoing significant changes during the period when dinosaurs began to disappear. How animals became extinct is suggested by the theory of changes in average annual and seasonal temperatures. Large individuals need a warm and even climate. Volcanic activity could lead to changes in the composition of the atmosphere and cause a greenhouse effect. A large emission of volcanic ash could provoke a volcanic winter, thereby changing the illumination of the Earth. Significant drop in sea level, ocean cooling, change in composition sea water and a sharp jump in the Earth's magnetic field could also have contributed to the extinction of dinosaurs.

Evolutionary biological hypotheses of extinction

One of the hypotheses of this group adheres to the situation of a mass epidemic. It is possible that dinosaurs were unable to adapt to the changed vegetation, which resulted in poisoning. There is a high probability that the eggs and young will be destroyed by the first predatory mammals. There is also a version that females disappeared during the Ice Age. Scientists have proposed another version of the death of dinosaurs - suffocation: there was a sharp decrease in the amount of oxygen in the atmosphere.

Why did dinosaurs disappear?

Why did dinosaurs disappear? How these became extinct. Various theories and hypotheses provide answers to these questions, but none of them fully answers all the questions. It is known that the extinction of species began long before the moment of the catastrophe, and the astronomical hypothesis in this case is doubtful. Many theories lack actual data, such as the hypothesis of regression of the World Ocean or changes in the magnetic field. Also, the lack of completeness of paleontological data can give a distorted picture.

Combining hypotheses forms a more clear picture. Hypotheses, complementing each other, provide answers to more questions, and the picture of that time looks more drawn and detailed.

The process of evolution - the extinction of the old and the formation of the new - is consistent. And the process of evolution of dinosaurs until the end of the Cretaceous period occurred naturally. But for some reason, at the end of the Cretaceous period, the old species died out, and new ones did not appear, and, as a result, the complete extinction of this species occurred.

From a paleontological point of view

The great extinction version is based on the following facts:

The appearance of flowering plants.
Gradual climate change caused by continental drift.

According to the scientific world, the following picture was observed. The developed root system of flowering plants and their better adaptability to soils quickly replaced other types of vegetation. Insects that fed on flowering plants began to appear, and insects that had previously appeared began to disappear.

The root system of the flowering plants began to grow and impede the process. The land surface stopped eroding, and nutritional material stopped flowing into the oceans. This has led to the depletion of the ocean and the death of algae, which, in turn, are producers of biomass in the ocean. The ecosystem was disrupted in the water, which caused a mass extinction. It is believed that they are closely connected with the sea, so the chain of extinction spread to them. On land they tried to adapt to the green mass. Small mammals and small predators began to appear. This was a threat to the offspring of dinosaurs, since eggs and baby dinosaurs became food for the emerging predators. As a result, conditions were created that were negative for the emergence of new species.

It ended, and with it, active tectonic, climatic and evolutionary activity also ended.

Children and dinosaurs

Not only adults, but also children have an interest in ancient animals. Today the project “Why did dinosaurs become extinct?” included in the curriculum of kindergartens and primary schools. The uniqueness of such activities lies in the fact that the child independently develops, seeks answers to questions and gains new knowledge. The question of why dinosaurs became extinct is as curious for children as it is for scientists. The interest is primarily due to the fact that these animals are not on earth today and an exact answer to the question of the reasons for their disappearance has not yet been received.

And a lot of small algae. In total, 16% of marine animal families (47% of marine animal genera) and 18% of land vertebrate families died.

Presumably, some dinosaurs (triceratops, theropods, etc.) existed in western North America and India for several million years at the beginning of the Paleogene, after their extinction in other places.

The most famous versions of the extinction of dinosaurs

Astrophysical

Geophysical and climatic

Evolutionary-biological

The dinosaurs were unable to adapt to the change in vegetation type and were poisoned by alkaloids contained in the flowering plants that emerged.
Dinosaurs were exterminated by the first predatory mammals, destroying clutches of eggs and young.

Disadvantages of hypotheses

Speaking about the reasons for the extinction of dinosaurs themselves, it is necessary to note some important features of this extinction:

The extinction can only be described as “rapid” by geological standards, whereas most paleontologists believe that it actually took at least several hundred thousand years.
In general, talking about the “rapid extinction of dinosaurs” is not entirely correct. In any group of living beings, new species are constantly being formed and previously existing ones are dying out. These processes occur simultaneously, and if the rates of extinction and formation of new species are equal, the group exists. From this point of view, during the period of the “great extinction” the speed itself extinction dinosaurs (namely dinosaurs, the picture looks different with marine reptiles), that is, the disappearance of previously existing species does not exceed the rate of extinction in previous periods. But the extinct species of dinosaurs were not replaced by new ones, as a result of which the group eventually became completely extinct.

In fairness, it should be noted, however, that this point of view is not shared by all experts.

As a result of the above, the main problems of the listed versions are as follows:

The hypotheses focus specifically on extinction, which, according to some researchers, proceeded at the same pace as in the previous time.
Some hypotheses have insufficient factual evidence. Thus, no traces have been found that reversals of the Earth’s magnetic field affect the biosphere; there is no convincing evidence that the Maastrichtian regression of sea levels could have caused a mass extinction of such proportions; there is no evidence of sharp changes in ocean temperature during this period; It has also not been proven that the catastrophic volcanism that created the Deccan Traps was widespread, or that its intensity was sufficient to cause global changes in the climate and biosphere.
All impact hypotheses, including astronomical ones, do not explain the selectivity of extinction (why certain organisms survived when others died) and do not correspond to the expected duration of its period (many groups of animals began to die out long before the end of the Cretaceous). The transition of the same ammonites to heteromorphic forms also indicates some kind of instability. It may very well be that many species had already been undermined by some long-term processes and were on the path to extinction, and the catastrophe simply accelerated the process.

On the other hand, it should be borne in mind that the duration of the extinction period cannot be accurately estimated due to the Signor-Lipps effect, which is associated with incomplete paleontological data (the time of burial of the last found fossil may not correspond to the time of extinction of the taxon).

"Biosphere" version

In Russian paleontology, the biosphere version of the “great extinction” is popular, including the extinction of dinosaurs. According to it, the main initial factors that predetermined the extinction of dinosaurs were:

The appearance of flowering plants;
Gradual climate change caused by continental drift.

The sequence of events leading to extinction is as follows:

Flowering plants, which have a more developed root system and better use of soil fertility, quickly replaced other types of vegetation everywhere. At the same time, insects specialized in feeding on flowering plants appeared, and insects “attached” to pre-existing types of vegetation began to die out.
Flowering plants form turf, which is the best natural erosion suppressor. As a result of their spread, the erosion of the land surface and, accordingly, the flow of nutrients into the oceans have decreased. The “depletion” of the ocean in food led to the death of a significant part of the algae, which were the main primary producer of biomass in the ocean. Along the chain, this led to a complete disruption of the entire marine ecosystem and became the cause of mass extinctions at sea. The same extinction also affected large flying dinosaurs, which, according to existing ideas, were trophically connected with the sea. Some of the large marine reptiles, in addition, could not withstand competition with the modern type of sharks that appeared at this time.
On land, animals actively adapted to feeding on green matter (by the way, herbivorous dinosaurs too). Small phytophagous mammals (such as rats) appeared in the small size class. Their appearance led to the emergence of corresponding predators, which also became mammals. Small-sized mammalian predators were harmless to adult dinosaurs, but they fed on their eggs and young, creating additional difficulties for dinosaurs in reproduction. At the same time, protecting the offspring is practically impossible for a dinosaur due to the too large difference in the sizes of adults and young.
As a result of continental drift at the end of the Cretaceous period, the system of air and sea currents changed, which led to some cooling over a significant part of the land and an increase in the seasonal temperature gradient. Inertial homeothermy, which provided dinosaurs with an evolutionary advantage in previous periods, no longer had an effect under such conditions.

As a result of all these reasons, unfavorable conditions were created for dinosaurs, which led to the cessation of the emergence of new species. The “old” species of dinosaurs existed for some time, but gradually died out completely. Apparently, there was no severe direct competition between dinosaurs and mammals; they occupied different size classes, existing in parallel. Only after the disappearance of dinosaurs did mammals take over the vacated ecological niche, and even then not immediately.

Interestingly, the development of the first archosaurs in the Triassic period was accompanied by the gradual extinction of many therapsids. higher forms which were essentially primitive oviparous mammals.

Disadvantages of the biosphere version

In the above form, the version uses hypothetical ideas about the physiology and behavior of dinosaurs, does not compare all the changes in climate and currents that took place in the Mesozoic with those that took place at the end of the Cretaceous period, does not explain the simultaneous extinction of dinosaurs on continents isolated from each other, and does not explain the selectivity of the asserted effects of mammalian evolution on other vertebrates.

Sources and notes

Links

Impact theory of mass extinction The Impact Theory of Mass Extinction )
Reflections on the “rare event” and related ideas in geology

Evolutionary biology
Mechanisms and processes

Dinosaurs(Latin Dinosauria, from ancient Greek δεινός - terrible, terrible, dangerous and σαῦρος - lizard, lizard) - a superorder of terrestrial vertebrates that dominated the Earth in the Mesozoic era - for more than 160 million years, starting from the Upper Triassic period (approximately 225 million years ago) until the end of the Cretaceous period (66 million years ago), when most began to go extinct during a large-scale extinction of animals and many plant species in a relatively short geological period of history. Fossil remains of dinosaurs have been found on all continents of the planet. Nowadays, paleontologists have described more than 500 different genera and more than 1000 various types, which are clearly divided into two orders: ornithischians and lizards.

The most famous versions of the extinction of dinosaurs

Nobody knows the exact reason. But there are a great many theories about the death of dinosaurs. Most of them suggest that there were some strong changes in the climate of our planet, which damaged many living organisms, not just dinosaurs. The most popular theory claims that dinosaurs and other animal species became extinct due to one terrible universal catastrophe: 65 million years ago, the Earth collided with an asteroid, and a terrible explosion occurred. Interesting fact: In addition to dinosaurs, flying reptiles and a large number of marine inhabitants became extinct 65 million years ago.

Asteroid hypothesis

Story

By examining clay deposits in layers of the Earth's crust dated to have been deposited 65 million years ago, scientists have found high levels of iridium in these rocks. Iridium is rarely found on Earth, since during the formation of our planet, iridium, as a heavy element, sank deep underground and is found mainly near the earth's core. Iridium only reaches Earth from space when meteorites and asteroids fall from the sky. Scientists have found iridium in ancient clay deposits around the world. Here is their conclusion: the iridium fell from a cloud of dust that was thrown into the atmosphere when the asteroid collided with the Earth. Thus, the fall of an asteroid is one of the most common versions.

It is based mainly on the approximate timing of the formation of the Chicxulub crater (which is the impact of an asteroid of about 10 km in size about 65 million years ago) on the Yucatan Peninsula in Mexico and the time of extinction of most of the extinct dinosaur species. In addition, celestial-mechanical calculations show that asteroids larger than 10 km collide with the Earth on average about once every 100 million years, which in order of magnitude corresponds, on the one hand, to the dating of known craters left by such meteorites, and on the other – time intervals between the peaks of extinctions of biological species in the Phanerozoic.

Lack of theory

Many scientists, however, are skeptical about this theory. Why then, they ask, did birds, crocodiles, turtles, snakes and most mammals survive, as well as insects, shellfish, ocean fish, and many plants? This theory is also questionable because the extinction of dinosaurs occurred very slowly - over millions of years, and not during one gigantic cataclysm.

Advantage of theory

The only advantage of the asteroid theory is that it can be tested. Scientists were looking for a crater of suitable size. Looking at space photographs of Mexico, they discovered a semicircular chain of lakes. These lakes on the Yucatan Peninsula may border the edges of a giant crater buried under one and a half kilometers of rock. In 1992, scientists obtained rock samples from deep within the supposed crater while the Mexican National Oil Company was drilling at the site. After dating the samples, scientists determined that the crater is indeed about 65 million years old. At the same time, scientists examining leaf fossils from rock samples dating back 65 million years found that these leaves had been severely damaged by severe frost. The stage of leaf development showed that they froze in June. The leaf fossils provide further evidence that rock debris and dust thrown into the air by the big explosion may have suddenly cooled the air temperature. Scientists, however, argue that this event, even if it did occur, could have caused the extinction of the dinosaurs.

Supernova explosion or nearby gamma-ray burst

In 1971, physicist Wallace Tucker and paleontologist Dale Russell suggested that a supernova explosion located quite close to the solar system at the end of the Cretaceous period could have catastrophic consequences for life on Earth. As a result of such a supernova explosion, the upper layers of the planet's atmosphere were exposed to X-rays and other types of radiation, which caused rapid climate change, and the temperature on Earth began to drop rapidly, but no evidence of such an event was found.

Volcanic activity

Story

Increased volcanic activity, which is associated with a number of effects that could affect the biosphere: changes in the gas composition of the atmosphere; the greenhouse effect caused by the release of carbon dioxide during eruptions; changes in the Earth's illumination due to emissions of volcanic ash (volcanic winter). This hypothesis is supported by geological evidence of a gigantic outpouring of magma between 68 and 60 million years ago on the territory of Hindustan, as a result of which the Deccan Traps were formed.

Research

New data obtained by a group of international researchers from Princeton and the Massachusetts Institute of Technology (USA), the University of Lausanne (Switzerland) and the University of Amravati (India) suggests that - yes, volcanoes could literally drive dinosaurs to their graves. Michael Eddy and his colleagues were able to more or less accurately determine the age of geological formations in the Deccan Traps, one of the largest igneous formations on the planet, located on the Deccan Plateau in western and central India. (The term trap, which is used in geology to denote this type of relief, comes from the Swedish word trappa - ladder.) From such geological zones it is possible to determine the time and duration of large-scale volcanic "seasons" that occurred in the distant past.

Igneous rocks were dated using zircon, a uranium-bearing mineral that forms in magma shortly after an eruption, so it can be used to fairly accurately determine the age of sediments. The chemical “clocks” here are uranium isotopes. It was possible to find samples of zirconium corresponding to the beginning and end of the volcanic period. As the authors of the work write in Science Express, the eruptions began 250 thousand years before the fall of the alleged asteroid and continued for another 500 thousand years after, throwing out about 1.5 million square kilometers of lava.

Such prolonged volcanic activity could not but affect chemical composition atmosphere and the World Ocean: substances appeared in the air and water that ruined the lives of many organisms. One of the most abundant volcanic “gifts” could be carbon dioxide, which, once in the ocean, greatly acidified it, thereby killing some of the plankton. Which, of course, affected all food chains that started with marine plankton. Of course, no one says that external intervention in the form of an asteroid had no effect on the Earth’s biosphere. There was an asteroid, and it affected the biosphere, but the ecology was already largely shaken by internal reasons, so the collision could only accelerate what would have happened anyway.

Change in Earth's gravity

One of the most recent versions suggests that giant lizards disappeared due to an increase in the Earth's gravitational force. The theory is based on the fact that planets gradually increase in size. This means that their mass and force of attraction also increase. This circumstance could well have affected the mobility of dinosaurs, as well as other creatures. To understand why this happens, we can recall an example of such a phenomenon as complete weightlessness in outer space on ships. That is, the lower the force of gravity, the easier it is to move. The weight of the dinosaurs was too high, and their bodies might not actually be able to adapt to such changes. Every day it became harder and harder for them to move, which significantly hampered their search for food and their life processes in general.

Continental drift

Dinosaurs, according to scientists, lived in the Mesozoic era (248-65 million years ago). The Mesozoic, in turn, is divided into the Triassic, Jurassic and Cretaceous periods. Initially, all the continents made up a single giant continent called Pangea. During the Jurassic period, Pangea gradually “broke” in half, and land parts began to move away from each other. By the time of the extinction of the dinosaurs, the continents had moved even further apart. The contours of the continents began to resemble modern ones. Continental drift could have caused the extinction of dinosaurs, because their habitats changed dramatically, as did climatic conditions. The vegetation has changed, and it has become more difficult for herbivorous lizards to get food. With their numbers declining, hard times also came for the carnivorous dinosaurs.

Epidemic

Based on Charles Darwin's theory of evolution, bacteria and microbes appeared before all other forms of life on Earth. The processes of evolution did not bypass them, and these microorganisms mutated. Thanks to such statements, it was born new hypothesis about why giant lizards became extinct. Any living organism adapts to changing environmental conditions, but not all inhabitants of the Earth can live with different bacteria on the principles of mutualism (“mutually beneficial cohabitation”). Therefore, the version that the dinosaurs were destroyed by an epidemic has the right to life. It is quite possible that most of the epidemics that at one time destroyed a huge number of people also destroyed the dinosaurs millions of years ago. The proof of this theory can only be knowledge about some properties of microorganisms. The fact is that bacteria survive under a wide variety of environmental conditions. In severe frosts, they do not die, but simply curl up into a cyst. This shell allows microbes to live for a huge number of years in the so-called sleep mode. As soon as conditions again become suitable for the life of microorganisms, they “wake up” and begin to multiply.

Dinosaurs were exterminated by the first predatory mammals

The theory claims that mammals turned out to be more advanced in terms of survival, it is easier for them to get food and adapt to environment. The main advantage of mammals was the difference between their method of reproduction and the method of reproduction of dinosaurs. The latter laid eggs, which could not always be protected from the same small animals. In addition, the small dinosaur needed a huge amount of food to grow to the required size, and food became increasingly difficult to obtain. Mammals were carried in the womb, fed with mother's milk, and then did not need too much food. Moreover, there were always dinosaur eggs under our noses, which could be capitalized unnoticed.

From a paleontological point of view

The great extinction version is based on the following facts:

The appearance of flowering plants.
Gradual climate change caused by continental drift.

The root system of flowering plants began to grow and prevent the process of soil erosion. The land surface stopped eroding, and nutrient material stopped flowing into the oceans. This has led to the depletion of the ocean and the death of algae, which, in turn, are producers of biomass in the ocean. The ecosystem was disrupted in the water, which caused a mass extinction. It is believed that flying lizards are closely related to the sea, so the chain of extinction spread to them. On land they tried to adapt to the green mass. Small mammals and small predators began to appear. This was a threat to the offspring of dinosaurs, since eggs and baby dinosaurs became food for the emerging predators. As a result, conditions were created that were negative for the emergence of new species.

When the dinosaurs became extinct, the Mesozoic era ended, and with it, active tectonic, climatic and evolutionary activity also ended.

Combined theories

The above hypotheses can complement each other, which is used by some researchers to put forward various kinds of combined hypotheses. For example, the impact of a giant meteorite could provoke increased volcanic activity and the release of a large mass of dust and ash, which together could lead to climate change, and this, in turn, changes the type of vegetation and food chains, etc.; Climate change could also be caused by lowering sea levels. The Deccan volcanoes began to erupt even before the meteorite fell, but at a certain point, frequent and small eruptions (71 thousand cubic meters per year) gave way to rare and large-scale ones (900 million cubic meters per year). Scientists admit that a change in the type of eruptions could have occurred under the influence of a meteorite that fell at the same time (with an error of 50 thousand years).

It is known that in some reptiles the phenomenon of dependence of the sex of the offspring on the temperature of egg laying is observed. In 2004, a group of researchers from the British University of Leeds, led by David Miller, suggested that if a similar phenomenon was typical for dinosaurs, then climate change of just a few degrees could provoke the birth of individuals of only a certain sex (male, for example), and this, in turn, makes further reproduction impossible.

Disadvantages of hypotheses

None of these hypotheses can fully explain the entire complex of phenomena associated with the extinction of dinosaurs and other species at the end of the Cretaceous period.

The main problems of the listed versions are as follows:

The hypotheses focus specifically on extinction, which, according to some researchers, proceeded at the same pace as in the previous time (but at the same time, new species ceased to form within extinct groups).
All impact hypotheses (impact hypotheses), including astronomical ones, do not correspond to the expected duration of its period (many groups of animals began to die out long before the end of the Cretaceous). The transition of the same ammonites to heteromorphic forms also indicates some kind of instability. It may very well be that many species had already been undermined by some long-term processes and were on the path to extinction, and the catastrophe simply accelerated the process.
On the other hand, it should be borne in mind that the duration of the extinction period cannot be accurately estimated due to the Signor-Lipps effect associated with the incompleteness of paleontological data (the time of burial of the last found fossil may not correspond to the time of extinction of the taxon).
Some hypotheses have insufficient factual evidence. Thus, no traces have been found that reversals of the Earth’s magnetic field affect the biosphere; there is no convincing evidence that regression of sea levels could cause a mass extinction of such proportions; there is no evidence of sharp changes in ocean temperature during this period; It is also not proven that the catastrophic volcanism that resulted in the formation of the Deccan Traps was widespread, or that its intensity was sufficient to cause global changes in the climate and biosphere.

Conclusion

Answer the question: “Why did dinosaurs become extinct?” Today there is no certainty. All versions, in the absence of significant evidence, exist only at the level of assumptions. It is worth noting that dinosaurs, probably for the first time in millions of years, were influenced by several of these factors, as a result of which they gave way to mammals.

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Sources

http://www.voprosy-kak-i-pochemu.ru/pochemu-vymerli-dinozavry/ http://www.crimea.kp.ru/daily/26123.4/3015794/