Introduction

Life on Earth arose about 3 billion years ago;

it began with tiny single-celled creatures, and about 225 million years ago, dinosaurs appeared on Earth in the process of evolution. They inhabited the Earth for approximately 160 million years, i.e. over a period 50 times longer than the period from the appearance of man to the present day. Not all types of dinosaurs existed at the same time: some species died out, others arose.

Dinosaurs were well adapted to their environment. Some of them were herbivores, others were carnivores, so there was enough food for everyone.

Dinosaurs had very tough skin, some species had huge massive bodies and long necks, while others were no larger than a turkey. Dinosaurs reproduced by laying eggs with a hard shell that well protected the embryo during development.

How did it happen that dinosaurs, which dominated the Earth for so long, suddenly disappeared 65 million years ago? The answer to this question interests many, which is why there are many hypotheses about the reasons for the mass extinction of dinosaurs. We'll look at some of them.

Searching for traces of the past

From the middle of the 19th century. Amateurs and professionals began searching for dinosaur remains all over the world. Violent passions flared up in the Far West of the United States between 1870 and 1890. The expeditions of two outstanding American paleontologists, Edward Cope and Othniel Marsh, discovered huge dinosaur cemeteries in the Rocky Mountains (Canada).

The most expensive expedition was organized by the Berlin Academy of Sciences to Tendaguru (Africa) in 1907. It cost 200 thousand German marks. Over 1,500 people discovered more than 250 tons of fossil remains over 3 years of work. During their study, scientists came to the conclusion that among the lizards there were small, medium, large and simply huge lizards. The body length of dinosaurs ranged from 20 cm to 30 m. In total, there are currently about 1 thousand species of dinosaurs.

The most ancient dinosaurs were land predators, then herbivores appeared.

Some of them switched to life in water. Ancient dinosaurs were bisexual, but scientists still do not know for sure how males differed from females. It is assumed that among horned dinosaurs, males had longer and more massive horns, which could be used as tournament weapons. Male duck-billed dinosaurs had a longer crest on their heads than females.

It is even assumed that some forms, differing in morphological characters and sizes and described as different species and genera, represent males and females belonging to the same species.

Dinosaur groups Based on the type of food they eat, dinosaurs are divided into predators that walked on two legs, herbivores and scavengers. They lived alone or in groups, in both warm and cold climates. Some hunted, which required not only muscular, but also intellectual effort. The anatomical features (massive hind limbs, huge body and vestigial forelimbs) of giant predatory dinosaurs created a serious problem: if they fell, they were not able to get back to their feet, because. they could neither lean on their weak forelimbs nor tuck their hind legs under their heavy body. (The distribution of dinosaurs into groups does not depend on their size, mode of movement and nutrition. Based on the structure of the pelvic bones, dinosaurs are divided into two orders: Lizard-pelvic (Saurischia). The differences between them are as follows. The pelvis of four-legged animals consists of three pairs of bones: the pubis, the ilium and the ischium. In lizard-pelvic dinosaurs, the ilia point upward where they connect to the sacrum, the ischia point downward and backward, and the pubis point forward and downward. In ornithischian dinosaurs, the ischial and ilium bones are arranged in the same way, and the pubic bones have two branches directed in different directions: one forward and the other backward, parallel to the ischial bones. The significance of these differences is not clear.

The differences between groups of dinosaurs in the structure of the jaws and teeth and the associated differences in nutrition are easier to explain. In lizard-hipped dinosaurs, the teeth were located along the edge of the jaw in one row, which reached the end of the muzzle. Each conical or chisel-shaped tooth sat in a separate cell. Ornithischian dinosaurs had a toothless predentary bone in the front part of the lower jaw; front teeth were often absent in the upper jaw. Many ornithischians had a horny beak, like turtles. In addition, the lateral teeth were moved inward from the edge of the jaw, and their arrangement was multi-rowed. This displacement of the teeth is due to the fact that the cheeks were located outside the jaws. This made it possible to hold food in the mouth while chewing.

Lizard-hipped dinosaurs did not chew.

All ornithischians were herbivores and walked on either two or four legs. Among the lizards there were both herbivores and predators, which, for the most part, were bipedal.

Another characteristic feature characteristic of dinosaurs was the structure of the pelvic girdle and the placement of the limbs, which ensured greater mobility of the animals. Unlike other archosaurs and most reptiles, dinosaurs' hind legs were straight and moved in a vertical plane when walking, like birds and mammals. Most other reptiles (for example, crocodiles, lizards, turtles) have paws widely spaced to the sides. In the pelvic girdle, dinosaurs had a complex sacrum of five fused vertebrae and a perforated acetabulum, into which the head of the femur entered. These anatomical features made dinosaurs the most mobile of the land inhabitants of the Mesozoic.

A – four-radial pelvis with free space below;
B – triradiate pelvis with pubic bones directed forward

One of the amazing features of some large herbivorous dinosaurs, both lizard-hipped (diplodocus, brachiosaurs) and ornithischians (stegosaurs, ankylosaurs), not present in any other animals, was the presence of a second brain (this is reflected in the generic name of one of them: "Diplodocus" translated from Greek means "two minds"). The volume of the brain inside the fused sacral vertebrae of the pelvic girdle was 10–100 times greater than the volume of the brain. The question arises, which brain, the hindbrain or the forebrain, was the main one? It is believed that the hindbrain coordinated the work of the limbs, the forebrain coordinated food activity and sensory organs.

This “decentralization” of brain functions, some researchers believe, was one of the reasons for the extinction of dinosaurs.

Hypotheses about the causes of the mass extinction of dinosaurs

From the Triassic to the Late Cretaceous, dinosaur diversity increased. It seemed that nothing foreshadowed their disappearance without a trace.

But at the end of the Cretaceous period, the entire prosperous group of planetary owners died out. The extinction of species is a natural evolutionary process. It usually occurs slowly and unevenly. But the speed with which the largest group of reptiles disappeared is amazing.
Hypotheses about how this happened can be divided into two groups:

– hypotheses explaining extinction by external, including extraterrestrial, causes;

The first group includes the hypothesis that on the territory of India, in the Deccan region, lava oozed abundantly from a giant fault 400 km long and there was unbearable heat. Volcanoes released huge amounts of carbon dioxide into the hot air. It was almost impossible to breathe such air. Clouds of ash and sulfur, escaping from the vents of volcanoes, rose high into the sky and enveloped the entire Earth. The atmosphere was poisoned by poisonous volcanic gases, and the soil by endless acid rain. Plants died from lack of light, followed by herbivores, and then predators. It started to get colder on Earth. Then the ash settled, and the cold was replaced by heat again. Carbon dioxide (then there was 10 times more of it in the atmosphere than today) created the “greenhouse effect”. Heat was retained near the surface of the Earth, and the air began to warm up, rains became rare, lakes and swamps dried up, and many rainforests were replaced by deserts.

The drying out of coastal shallow waters with their rich fauna and the increase in the overall salinity of the Ocean led to the extinction of 95% of marine animal species. And then a new emission of ash darkened the sky again, and the cold returned to the planet. Such sharp climate changes continued for more than 600 thousand years. As a result, only species less specialized than dinosaurs, such as mammals, survived.

Hypothesis 2

This hypothesis appeared in 1970. Its factual basis is evidence from the geological record: in many areas of the world, in marine and continental sediments, a small layer of clays with an unusually high content of platinum group elements was discovered, in particular iridium, rare in the earth's crust, but widespread in meteorites element.

Such a layer is believed to have formed only if the sediments were "diluted" by large amounts of meteorite material.

Having estimated how much such a meteorite could weigh, scientists turned their attention to an ancient crater near the village of Chicxulub. The time level of the layer exactly coincides with the time when the last dinosaurs, as well as other groups of terrestrial and marine animals and plants, disappeared.

The dust raised as a result of the explosion made the atmosphere almost opaque to sunlight for several years. The photosynthetic activity of green plants, which are the initial link in the food pyramid, has sharply decreased. Further, as if in a chain, the extinction of various groups of marine and terrestrial organisms occurred.

Hypothesis 3

It is believed that rapid climate change, which led to mass extinction of species, could be caused by continental drift and changes in the direction of winds and sea currents. On the continents, the change of seasons sharply became apparent: hot summers began to give way to cold winters, when herbivorous dinosaurs were deprived of green food. Dinosaurs were unable to adapt to seasonal temperature changes. However, there are no facts confirming such a catastrophic acceleration of the drift of continental plates.

Location and directions of continental drift during the Cretaceous period

Hypothesis 4

Recently, scientists have put forward a new hypothesis for the extinction of dinosaurs - at least some carnivorous species. Prehistoric lizards fell victim to the discrepancy between the energy needs of their gigantic organism and the objective possibilities of satisfying them. Experts from the British Zoological Society link this version with the answer to the question of why nature did not create, say, a lion or a tiger the size of an elephant.

Such a huge carnivorous creature would not be able to hunt fast enough to replenish its energy needs in time, they believe. According to scientists, evolution should ultimately lead to the fact that carnivores with a body weight of more than 1 ton, living on the surface of the Earth, will lose the right to exist due to energy deficiency.

However, it is doubtful that this shortage occurred suddenly and led to the extinction of all dinosaurs in a historically short time.

Hypothesis 6

Perhaps the dinosaurs lost the fight for survival with new, rapidly emerging species of mammals and birds. However, this hypothesis lacks factual material to substantiate.

Hypothesis 7

As a result of any catastrophe on a planetary scale, the destruction of the ozone layer could occur, and ultraviolet rays could cause a sharp increase in the rate of mutations in organisms.

Perhaps common parts of the dinosaur genomes were unstable to such mutations, which led to the rapid extinction of all their species. Species with stable genomes survived.

A proponent of the “meteorite” hypothesis, Dutchman Jan Smith, believes that Hertha Keller misinterpreted the results of samples taken in the crater. In his opinion, after the meteorite hit, the crash site was covered by a powerful tidal wave - a tsunami - and went under water, and it took only a few weeks for such a layer of sediment to form.

According to geologist Vincent Courtillot, the death of ancient lizards was not as catastrophic and fleeting as is usually imagined. The latest fossils from that time show that the giant reptiles died out gradually over hundreds of thousands of years.

And this is difficult to explain using the “meteorite” hypothesis. Over the past 260 million years, there have been four mass extinctions on Earth, each time preceded by unprecedented volcanic eruptions.

Not everyone agrees with this opinion. Geologist Eric Byufto is confident that for each case of animal extinction it is possible to select a suitable meteorite crater. Well, then, why should all such disasters on Earth have the same cause? Byufto does not argue with the fact that numerous species of animals became extinct regularly, and these dramas were not necessarily associated with sudden catastrophic changes.

However, the extinction of animals 65 million years ago was so massive that it is more correct to assume

that it was caused by some powerful and fleeting impact, for example, the fall of a large meteorite. Well, besides, says Byufto, it is difficult to imagine that dinosaurs, who inhabited the entire Earth from the equator to the poles, became victims of sharp climate fluctuations, but, for example, crocodiles calmly survived the boundary of the Cretaceous and Tertiary periods.

1. So, the time for the final verdict is postponed. Scientists still have to examine meteorite craters again and again, carefully study fossils and, finally, find out why crocodiles survived the dinosaurs... Literature

Laura Cambournac.

Dinosaurs and other extinct animals. – M.: Makhaon, 2006. – 123 p.

3. Illustrative encyclopedia: dinosaurs / D. Burney; Artist D. Sibbick; Per. from English I.N. Alcheeva, N.N. Nepomnyashchy. – M.: AST Publishing House LLC: Astrel Publishing House LLC, 2002. – 222 p.: ill.

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 different species, 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 the chemical composition of the atmosphere and the oceans: 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, a new hypothesis was born 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 states that mammals turned out to be more advanced in terms of survival, it is easier for them to obtain food and adapt to the 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:

1. The appearance of flowering plants.
2. 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 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.

Hypothesis 7

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.

Video

Sources

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

Modern science is at a high level of development. However, at the same time, there are still many topics that remain a mystery to her. One of the most important is the extinction of dinosaurs. Scientists are well aware that ancient lizards became extinct at the final stage of the Cretaceous period due to the fall of a huge asteroid on our planet. This version is one of the main ones, but there is very little evidence in its favor. There are still heated debates among experts regarding the causes of the death of dinosaurs, and more and more new versions are appearing.

Scientists are trying to understand why the ancient lizards, which dominated the Earth for millions of years, became extinct in a relatively short time. World science often tries to explain the death of lizards using so-called “catastrophic” hypotheses. Lizards, and along with them ammonites and marine reptiles, could have died as a result of volcanic activity, a drop in ocean water levels, a supernova outbreak in the vicinity of the solar system, or a meteorite impact.

The most popular version is that the lizards became extinct due to the fall of an asteroid. Its author is Luis Alvarez, an American physicist who claimed that approximately 66 million years ago a gigantic meteorite fell on the planet. The location of the disaster is the Yucatan Peninsula in Mexico. After the cataclysm, a lot of dust rose into the atmosphere, and previously dormant volcanoes became active. All this led to the astroid winter and, as a consequence, to the extinction of ancient reptiles and some other animal species. This version has opponents who claim that the Chicxulub crater is very small in size, and that there are much larger craters on the planet from larger celestial bodies, but during the period of time when these objects collided with our planet, there were no significant changes fauna did not occur. However, adherents of this theory argue that the death of the lizards was provoked by the fall of not one, but several asteroids at once, since dinosaurs died out over hundreds of thousands of years, that is, quite slowly.

Another version is quite popular - the so-called hypothesis of active volcanism. Proponents of this theory rely in their conclusions on the Deccan Traps (India) - a plateau covered with basalt eruptions, the thickness of which is about two kilometers. The age of the basalt is estimated at approximately 60-68 million years. According to supporters of this version, volcanic activity continued for a considerable time, as a result of which the earth’s climate became much colder, and the ancient lizards simply froze.

However, their opponents argue that if the process of eruption and cooling was long, then reptiles could well adapt to it and, therefore, survive.

This hypothesis suggests that the death of dinosaurs occurred as a result of changes in climatic conditions on the planet due to continental drift. The drift provoked temperature changes, the death of many plant species, drying out of water bodies and, as a result, a change in the food supply of reptiles.

In addition, there is a theory that temperature changes caused exclusively males or exclusively females to emerge from lizard eggs. Ultimately, this provoked the death of the species.

Another version says that due to cold weather, the shells of lizard eggs became thinner or thicker, therefore, the cubs either could not get out and died, or died from numerous infections or predators.

Opponents of this hypothesis are climatologists, whose research indicates that 66 million years ago there were no significant climate changes. The most recent cooling began 58 million years ago.

There is also a popular assumption among scientists that the cause of death of ancient lizards could have been a change in the atmosphere. According to this theory, the cataclysms entailed such large-scale atmospheric changes on the planet that the dinosaurs simply died from lack of air. According to scientists, the reasons for such changes may be different. Some researchers, again, talk about asteroids, others blame volcanoes.

As experts note, during the period of existence of ancient lizards on the planet, the oxygen content in the atmosphere was approximately 10-15 percent, and much less carbon dioxide. As a result of changes in the composition of the air, plants also changed, due to which new fauna began to develop.

However, opponents of this theory, after studying the composition of air in ancient sediments and rocks, stated that during the Cretaceous period no significant changes in the composition of air occurred.

The hypothesis about the appearance of flowering plants is related to changes in the food pyramid of ancient dinosaurs. It is generally accepted that during that period the vegetation on the planet was changing rapidly. Flowering plants, completely new to dinosaurs, began to appear. The reptiles were unable to adapt to the alkaloids present in the plants, so they died from poisoning.

And the mass extinction of herbivorous dinosaurs also led to the death of predators.

According to the hypothesis of competition with mammals, clumsy lizards of gigantic size could not compete with much smaller active warm-blooded mammals, which, among other things, also fed on lizard eggs.

Modern science adheres to the theory of the great extinction, the essence of which is that the main factors in the death of ancient dinosaurs are climate changes caused by continental drift, as well as the appearance of flowering plants.

At first, new plants gradually replaced horsetails and ferns. The developed root system of flowering plants significantly slowed down the flow of nutrients into the ocean, which led to the death of algae and, consequently, the extinction of sea lizards.

At the same time, land dinosaurs gradually adapted to new plant species. As a result of continental drift, sea and air currents changed, cooling began, which resulted in the cessation of the emergence of new species of lizards. Those species that existed up to this point lived for some time and then died out. Belemnites and ammonites, as well as small algae, died along with them. Crocodiles, turtles and snakes, birds, corals, as well as relatives of ammonites - nautiluses - survived. Mammals, which gradually evolved, did not immediately establish their dominance on land.

It should be noted that domestic and foreign paleontologists hold different points of view. Thus, domestic experts claim that ancient lizards disappeared gradually - as a result of climate cooling and the appearance of flowering plants. The development of plants led to the appearance of insects that small mammals fed on. They, quite obviously, could not compete with dinosaurs, but at the same time, predators fed on the eggs of dinosaurs. Thus, the viability of dinosaurs was weakened, despite the fact that there was no direct competition between them and mammals.

Western paleontologists are more inclined towards catastrophic hypotheses. The basis for this kind of view was the Chicxulub crater. The main argument in this theory was a thin layer of clay, in which experts discovered a high content of the metal iridium (probably of unearthly origin).

The weak point of catastrophic hypotheses is the fact that the extinction of dinosaurs lasted for millions of years, and it began much earlier than the fall of the asteroids. It is quite possible that before the asteroids fell, many species of dinosaurs suffered from some negative long-term processes, and the asteroid only accelerated their death.

However, why did the asteroid fall have such catastrophic consequences? How did the disaster affect the biosphere? And why was the death so selective - only the ancient lizards died out, but turtles, snakes and crocodiles remained.

To find answers to all these questions, a marine scientific expedition began last spring: researchers are trying to drill into the Chicxulub crater from a tower in the Gulf of Mexico. Scientists hope that rock samples extracted from there will help them clarify the situation.

Japanese experts, at the same time, put forward another hypothesis, according to which the cause of the death of the lizards was the soot that rose into the atmosphere after the fall of the asteroid. It should be noted that the generally accepted assumption is that the impact of the asteroid led to the filling of the atmosphere with aerosols of sulfuric acid, which reflected sunlight, as a result of which photosynthesis stopped, darkness set in, acid rain began and temperatures dropped. At the same time, this theory does not explain in any way why mammals, birds and crocodiles survived.

All this has led Japanese scientists to suggest that soot emissions are a more realistic scenario.

The final calculations confirmed that the probable soot emissions were about 1,500 teragrams. The moderate cooling and slowdown in photosynthesis in the ocean that followed the release led to the extinction of ammonites, but did not affect deep-sea organisms.

Geologists have found that a drop in temperature and drought triggered a destructive process: the drying out of plants triggered a drop in soil moisture. Those plants that managed to survive were eaten by herbivorous dinosaurs. The process of desertification began, which entailed the death of herbivorous reptiles, and, consequently, the predators that fed on them. Freshwater crocodiles survived because the basis of their food supply was plant detritus, which entered the water in sufficient quantities even during the critical years of the disaster.

Scientists say the asteroid impact was not as bad as commonly thought. At the same time, the extinction of the dinosaurs shows that even such a short-term catastrophe can lead to irreversible changes in the biosphere - and this is a valuable lesson in the age of global warming...

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There is still no consensus in the scientific community about what caused the extinction of dinosaurs. Several theories and hypotheses have been put forward by various scientists. Each of the hypotheses has a theoretical justification, but none of the theories has yet been 100% proven. We will not analyze exotic theories that do not have an evidence base. In this article we will examine in detail the main directions of scientific thought on this issue.

Main theories of dinosaur extinction

1. Catastrophic theory.

One of the theories that became most widespread in the 20th century. Its founder is a scientist from the USA Alvarez Luis. In 1980, he put forward a theory and provided scientific justification. According to his theory in the Cretaceous period, planet collided with an asteroid big size. The site of the collision is believed to be the Yutokan Peninsula on the coast of Mexico.

The result of the collision was a global release of fine radioactive particles into the atmosphere. The collision also caused movements of the lithospheric plates of the earth's crust, which led to the launch of active volcanic processes throughout the globe. Active volcanic processes are accompanied by the release of large amounts of carbon dioxide and dust into the atmosphere.

The planet experienced a rather dramatic change in the composition of the atmosphere with an increase in the amount of carbon dioxide and a decrease in oxygen. This led to change in flora composition, a sharp decrease in the food supply of dinosaurs, since they were mainly herbivores. There was also a sharp climate change towards cold snap.

Opponents of this scientific theory argue that the impact crater is too small to trigger such catastrophic changes in environmental conditions. But some supporters claim that several asteroid bodies are bombarding the earth.

1. Evolutionary theory.

According to this theory, in the Cretaceous period, the earth appeared on the planet due to the evolution of species. flower fauna, and also received widespread development mammal species. Because dinosaurs were mostly herbivores. Changes in the composition of the food supply, in particular the presence of alkaloids in flowering plants, led to a sharp population reduction these animals.

Their digestive system did not have time to evolve with the environment. After the decline in the population of herbivores, the population of predators began to decline, since herbivores were their food source. Also, the appearance of smaller warm-blooded mammals, according to some scientists, led to a reduction in the population of dinosaurs, and subsequently to their complete disappearance.

Dinosaurs could not compete with mammals. Warm-blooded animals were more mobile. The food supply of mammals included eggs and baby dinosaurs from predators. Which led to their gradual reduction, and subsequently to their complete disappearance.

1. Climate theory.

According to this hypothesis, it is believed that prehistoric dinosaurs became extinct due to climate change on the planet. During the Cretaceous period, active tectonic movements of lithospheric plates. The movement of the continental crust was accompanied by a change in current conditions in the world's oceans. Climate change has caused cold snap atmosphere. This caused a massive death of fauna on the planet and a change in its species composition.

Plants constituted the natural food supply of dinosaurs. The decrease in food supply has had a sharp negative impact on the numbers of these animals.

Some researchers suggest that when the environment cooled, dinosaurs began to predominate in the offspring of dinosaurs. babies of the same sex. These studies are based on the study of the processes of childbirth in modern crocodiles, since they are the closest species to dinosaurs that currently exist.

The future sex of crocodiles is determined not by genetics, but by external factors temperature around the eggs. In order to produce offspring of both sexes, it is necessary that the air in the clutch be heated from 30 to 34 degrees Celsius; at a cooler temperature, only girls will be obtained, and at a hotter temperature, only boys will be obtained.

Also, some scientists hypothesize that the cooling caused changes in egg shell structure lizards. The structure became either larger or thinner. In the first option, the offspring could not hatch, and in the second, they were susceptible to infections.

Some scientists who do not agree with this hypothesis argue that according to micropaleontological data, in particular the analysis of plant pollen, cooling began 58 million years ago, and the extinction of dinosaurs is dated to a later period.

Theories put forward by our scientists

• Space theory.

Nominated by a Soviet astrophysicist I.S. Shklovsky. According to his theory, the extinction of dinosaurs is explained supernova explosion in our galaxy. The appearance of the star is definitely based on the study of the Crab Nebula. These are remnants from a supernova. According to astronomers' calculations, cosmic radiation harmful to animals reached planet earth during a period coinciding with the extinction of dinosaurs.

The actual confirmation of this theory is the presence throughout the planet of a reference layer of radioactive isotopes in the sediments of the Cretaceous period. These isotopes are formed when exposed to radioactive radiation characteristic of the formation of a supernova.

Opponents of the theory argue that the force of radiation during the formation of cosmic bodies does not lead to such consequences, since throughout the history of planet earth there were still periods that did not cause the extinction of mammals.

• Coincidence theory.

This theory was put forward by Russian scientific geologists brothers Vladimir And Vadim Ryzhov. When analyzing the evidence-based factual material of the main theories of dinosaur extinction, they identified several coinciding factors.

According to their theory, the extinction of dinosaurs occurred due to the coincidence of external conditions and the evolution of species. During the Cretaceous period, the extinction of some species of oceanic mollusks was recorded. According to all theories, what happened on the planet changing of the climate and atmospheric composition. Theories differ on the factors causing these changes.

According to the theory of coincidences, active events occurred on planet earth during the Cretaceous period. tectonic changes, it coincided that in the same period there was supernova formation in the galaxy and hit by a large meteorite to the surface. Only the combination of all factors could cause a sharp change in climate and atmospheric composition. Which in turn launched evolutionary processes to change the species composition of flora and fauna on the planet.

Groups of scientists for each theory presented are finding factual material all over the globe, but a consensus has not yet been put forward in the scientific community. Most scientists are inclined to the Ryzhov theory of coincidences. The factual material indicates the correctness of this theory. After the Cretaceous period, 18% of land vertebrate families, 16% of marine fauna and 47% of marine flora disappeared on the planet. But this gave impetus to the active development of modern mammals.

Dinosaurs are an evolutionary miracle, representatives of which appeared on our planet 225 million years ago and ceased to exist 65.5 million years ago. They were very different: two-legged and four-legged, meat-eaters and vegetarians, small and huge, crawling, flying and running. Paleontologists around the world have found and are finding dinosaur fossils all over the planet, including Antarctica. Currently, more than 1000 species of ancient lizards have been found and classified, but every new day brings more and more new discoveries.

One of the most burning questions for paleontologists is: “Well, why did they go extinct?” Unfortunately, there is no clear answer to this question yet, but there are a sufficient number of hypotheses. Of course, the time period that has passed since the planetary death of ancient lizards makes it very difficult to find the true cause of this latest extinction due to its enormous distance from our days, but scientists still have facts in their arsenal that can be used when putting forward one or another scientific theory .

Scientists have proposed the term “glacial extinction.” In their opinion, this “glacial extinction” was a fairly slow process and approximately lasted for millions of years. It is clear that climatic conditions changed over this period of time. In the previous period, there were no ice caps at the earth's poles, and

the water temperature at the ocean bottom was +20ºC. After the appearance of the polar ice caps, the overall temperature on our planet dropped significantly and caused the appearance of new icing.

The Earth's atmosphere also underwent significant changes. It is reliably known that when the Cretaceous period just began, there was 45% oxygen in the lower layers of the atmosphere, and after 250 million years its amount decreased to 25%. Feel the difference!!!

65.5 million years ago, a planetary tragedy occurred on earth - a cosmic body fell to Earth. The craters found by scientists in the Gulf of Mexico (diameter 80 km) and in the Indian Ocean (diameter 40 km) are convincing facts proving that a catastrophe (certainly not an isolated one) definitely took place. And another ironclad argument is the presence of the chemical element iridium, which is located in the earth’s core and is also part of comets, asteroids and other celestial bodies.

When, after many years of research, geologists discovered this element in the deep soil of almost our entire planet, the scientific world accepted the theory of collisions of the Earth with other celestial bodies as an axiom.

When all the ancient lizards became extinct. Extinction theories. Change of habitat.

Everything flows - everything changes. Also, slowly and steadily, everything is changing on Earth. Any one large-scale change entails another, no less dramatic, and a dialectical chain of changes is born. The climate has changed, which means the atmosphere has changed, temperature indicators have changed and led to the extinction of animals and plants that did not have time to adapt to the new conditions.

Temperature change

During the cold snap, the temperature on Earth became on average 15 degrees lower (25ºC to +10ºC). Naturally, the climate became colder and drier (the amount of precipitation decreased significantly). The ancient lizards (alas!) were unable to rebuild and adapt to new, less comfortable living conditions. We know that almost all dinosaurs were cold-blooded animals, which means that when the temperature drops, they fall into a state of suspended animation: they experience a slowdown in all life processes, then numbness and cooling. The temperature on Earth did not rise for a long time, so the dinosaurs, which fell into suspended animation, exhausted all vital resources and became extinct. True, there is a weak point in this theory: why then did warm-blooded dinosaurs become extinct?

Here are some more theories