Modern science is at a high level of development. However, at the same time, there are many more topics that remain a mystery to her. One of the most important is the extinction of the dinosaurs. Scientists are well aware that the 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. Until now, there are heated debates among experts regarding the causes of the death of dinosaurs, and more and more new versions appear.
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 the so-called "catastrophic" hypotheses. Lizards, and with them the ammonites and marine reptiles, could die 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 from the fall of an asteroid. Its author is Luis Alvarez, an American physicist who claimed that about 66 million years ago, a giant meteorite fell on the planet. The crash site is the Yucatan Peninsula in Mexico. After the cataclysm, a lot of dust rose into the atmosphere, volcanoes that had been dormant were activated. All this led to astroid winter and, as a result, to the extinction of ancient reptiles and some other animal species. This version has opponents who argue that Chicxulub crater is very small in size, and that there are much larger craters from large celestial bodies on the planet, however, 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 the dinosaurs died out over hundreds of thousands of years, that is, rather slowly.
Another version is quite popular - the so-called active volcanism hypothesis. The adherents of this theory in their conclusions rely on the Deccan traps (India) - a plateau covered with basalt eruptions, the thickness of which is about two kilometers. The basalt is estimated to be around 60-68 million years old. According to the 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 prolonged, then the reptiles could well adapt to it and, therefore, survive.
This hypothesis assumes 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, the drying up of water bodies and, as a result, a change in the food supply of reptiles.
In addition, there is a theory that temperature changes were the reason that exclusively males or exclusively females began to emerge from the eggs of the lizards. Ultimately, this provoked the death of the species.
Another version says that due to the cold snap, the lizard's eggshell became thinner or thicker, therefore, the cubs either could not get out and died, or died from numerous infections or predators.
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The opponents of this hypothesis are climatologists, whose studies indicate that 66 million years ago there were no significant climatic changes. The closest cooling began 58 million years ago.
There is also a popular assumption among scientists that the cause of death of the ancient dinosaurs could be a change in the atmosphere. According to this theory, cataclysms caused such large-scale atmospheric changes on the planet that dinosaurs simply died from lack of air. According to scientists, the reasons for these changes can be different. Some researchers, again, talk about asteroids, others blame volcanoes.
According to experts, during the existence of ancient lizards on the planet, the oxygen content in the atmosphere was about 10-15 percent, and carbon dioxide - much less. As a result of changes in the composition of the air, plants also changed, due to which a new fauna began to develop.
However, opponents of this theory, after studying the composition of the air in ancient sediments and rocks, stated that during the Cretaceous period no significant changes in the composition of the air took place.
The hypothesis of the emergence of flowering plants is related to changes in the food pyramid of ancient dinosaurs. It is generally accepted that during this period the vegetation on the planet was rapidly changing. Flowering plants began to appear, completely new to the dinosaurs. The reptiles could not adapt to the alkaloids in the plants, so they died from poisoning.
And the mass extinction of herbivorous dinosaurs led to the death of predators.
According to the hypothesis of competition with mammals, hulking lizards of gigantic size could not compete with much smaller mobile 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 lizards are climatic 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 the continental drift, sea and air currents changed, a cooling began, which entailed the cessation of the appearance of new species of lizards. Those species that existed before this moment lived for some time, and then became extinct. Belemnites and ammonites, as well as small algae, died along with them. Survived by crocodiles, turtles and snakes, birds, corals, as well as relatives of the ammonites - nautilus. Mammals, which gradually evolved, did not immediately establish their dominance on land.
It should be noted that domestic and foreign paleontologists have different points of view. Thus, domestic experts claim that ancient lizards disappeared gradually as a result of the cooling of the climate and the appearance of flowering plants. The development of plants led to the appearance of insects, which fed on small mammals. They, quite obviously, could not compete with dinosaurs, but at the same time - predators fed on lizard eggs. 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 Chicxulub crater served as the basis for such views. The main argument in this theory was a thin layer of clay, in which experts found a high content of the metal iridium (probably of unearthly origin).
The weak point of catastrophic hypotheses is the fact that the extinction of the dinosaurs lasted for millions of years, and it began much earlier than the fall of asteroids. It is quite possible that until the moment of the fall of the asteroids, many types of dinosaurs suffered from some negative long-term processes, and the asteroid only accelerated their death.
However, why was the fall of the asteroid so disastrous? How did the disaster affect the biosphere? And why the death was so selective - only the ancient lizards died out, but turtles, snakes and crocodiles remained.
To find the answers to all these questions, a marine scientific expedition began last spring: researchers are trying to drill 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 asteroid fell. It should be noted that the generally accepted assumption is that the fall of the asteroid led to the filling of the atmosphere with sulfuric acid aerosols, reflecting sunlight, as a result of which photosynthesis stopped, darkness fell, acid rains began and the temperature dropped. At the same time, this theory does not explain in any way why mammals, birds and crocodiles survived.
All of this led Japanese scientists to speculate that soot emissions are a more realistic scenario.
The final calculation confirmed that the likely soot emissions were around 1,500 teragrams. Moderate cooling and the slowing down of photosynthesis in the ocean, which followed the release, led to the extinction of ammonites, but did not affect deep-sea organisms.
Geologists found that the drop in temperature and drought triggered a destructive process: the drying out of plants provoked a drop in soil moisture. Those plants that managed to survive were eaten by herbivorous dinosaurs. The process of desertification began, which led to the death of herbivorous reptiles, and, consequently, the predators that fed on them. Freshwater crocodiles survived, since the basis of the food supply was plant detritus, which entered the water in sufficient quantities even in the critical years of the disaster.
Scientists say that the fall of the asteroid was not as bad as people think. At the same time, the extinction of dinosaurs indicates 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 …