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A plethora of hypotheses try to explain the disappearance of the dinosaurs, some of which are more far-fetched than others. If the meteorite thesis is the most popular, there is also that of the mega eruption. But scientists are not ruling out the theory of an epidemic or biological senescence.
65 million years ago, the impact of a huge meteorite would have put an end to the existence of dinosaurs. This catastrophe led to the disappearance of 75% of the life forms existing on Earth at that time. And to cause such damage, the celestial body was more than bulky: an estimated 11 to 81 kilometres in diameter. Even today you can still see the impact crater in Chicxulub Puerto, on the Yucatan Peninsula in Mexico. Looking at the dimensions of the crater, which is over 180 kilometres in diameter, it is clear that the force of the explosion must have been impressive. According to the scientists, the power generated would be equivalent to "several billion times that of the Hiroshima bomb", that is to say the damage! Following this cataclysm, the extinction of species on Earth was rapid.
It was certainly a day like any other, until a huge meteorite crashed to Earth. The power of the explosion was so powerful that gigantic flames set the vegetation ablaze for thousands of kilometres around. In just a few seconds, the collision created an impressive tsunami more than 1,500 metres high. And that's not all, a thick circle of smoke formed 40 metres above the giant crater.
The impact of the meteorite then led to a chain reaction and the formation of a very thick layer of smoke. The latter was composed of debris, carbon and above all sulphide from the evaporation of the rocks. At this stage, the amount of sulphide present in the air was equivalent to 325 gigatonnes, darkening the sky and blocking out the sun's rays. This led to unprecedented cooling, causing the oceans to lose 10°C and the continents to lose 28°C.To top it all off, the smoke in the form of mist turned into sulphuric acid, polluting and destroying plants and animals with acid rain. The planet remained in darkness for more than two years, leading to a near collapse of the food chain. As photosynthesis could no longer take place, dinosaurs and 80% of marine species had very little chance of surviving.
The exact reasons for the extinction of the dinosaurs continue to divide the scientific community. Many agree with the hypothesis that a mega-volcanic eruption caused a mass extinction. To support this hypothesis, researchers have focused on analyses of volcanic sediments on the east coast of India.In 2009, oil drilling off the Indian coast rekindled the hypothesis that a super volcano was responsible for the Cretaceous-Tertiary extinction. Sediments collected at the Trapps of the Deccan have uncovered a large number of fossils dating from this period. Based on these discoveries, scientists have found solidified lava containing many fossilised lime-shelled molluscs. Numerous animal fossils have also been discovered in these volcanic geological layers present over a very large surface area worldwide, which, according to dating, date back 65 million years. By grouping these data together, researchers have concluded that a super volcano would have been the cause of the extinction of the dinosaurs. Although the impact of the Chicxulub meteorite has been proven, it appears to be too small to have caused the total extinction of all these forms of life on Earth.
The famous Trapps de Deccan were formed following the eruptions of a super volcano under Reunion Island. For more than a thousand years, numerous eruptions caused a cataclysm on a planetary scale, followed by the formation of a thick sulphurous mist, permanent darkness and the absence of photosynthesis. It should be remembered that the Trapps of the Deccan were formed 65 million years ago, so it is quite possible that repeated volcanic eruptions put an end to the reign of the dinosaurs. To get an idea of the size of a super volcano, you should know that the surface area of the Trapps du Deccan is several times that of the California. Imagine lava flows 10 or even 150 metres thick. They can pile up to form mountains nearly 2,400 metres high! A large part of the Trapps du Deccan (i.e. 500,000 km²) constitutes an entire plateau of the igneous province. Similarly, these giant lava flows are at the origin of the formation of plains and mountains in the Kâthiâwar peninsula.
According to another theory, the impact of the meteorite would have created a huge crater, which would then have generated huge lava flows 65 million years ago. The lava was so large that it would have weakened the lithosphere, causing sulphide mists that would have resulted in years and years of darkness on Earth. Even if this hypothesis remains to be proven, it is possible that the cause-and-effect relationship is more or less plausible.
Marine regressions at the end of the Cretaceous period are also believed to have contributed to the disappearance of dinosaurs and many forms of life on Earth. This cataclysm would have modified the extent as well as the conformation of the coastal and benthic environments. We owe this hypothesis to a French paleontologist, L. Ginsburg. This illustrious figure put forward this theory in 1964, in which he argued that a considerable drop in sea and ocean levels had reduced the habitats of marine organisms. This marine regression would have had an impact on the climate in general, to such an extent that it would have caused the end of the dinosaurs.
Although there are many hypotheses concerning the extinction of dinosaurs, that of senescence deserves further investigation. According to experts, dinosaurs were doomed to extinction due to biological degeneration. In other words, the groups are getting older, and are unable to adapt to changes in their living conditions. And according to the theory, they would have become extinct because of genetic exhaustion and their gigantism. For yes, these giants probably suffered from hormonal disorders. Their eggs may have undergone abnormal development, as may their embryos, causing them to gradually disappear. According to these scientists, the horns, collars and other aberrant anatomical structures characteristic of some dinosaurs are also evidence of biological degeneration.
Among the least convincing hypotheses about the extinction of dinosaurs is the mass epidemic. Although epizootics could have wiped out groups, a total extinction of the dinosaurs seems unthinkable. For the time being, there is little or no evidence of a possible worldwide epidemic.Similarly, the hypothesis of massive poisoning has been put forward: flowering plants or angiosperms would have developed enormously at the end of the Cretaceous period. It was thought that vegetation became toxic to herbivorous dinosaurs, and that if mammals had survived, it was because they did not eat such plants.There is also the theory of the virulent virus, which caused the extinction of the dinosaurs, or the theory of ultraviolet radiation, which would have caused the degradation of the DNA of the dinosaurs.
While there are many theories on the extinction of dinosaurs, those of asteroids and volcanoes are the most plausible. Geophysicists at the University of Berkeley have even looked into the question and hypothesised that these events were linked. The story may have begun with the fall of the meteorite to Earth, and it was the impact that caused the eruptions that led to the Trapps eruptions of the Deccan.
The dinosaurs didn't stand a chance: their extinction was total. In any case, the Chicxulub crater, the gaping wound off the Yucatan, has not yet revealed all its secrets. Indeed, a violent impact could just as easily have caused a nuclear winter and led to the extinction of thousands of life forms on Earth... For their part, experts who have studied the Trapps of the Deccan state that, given their scale, the lava flows could have been particularly devastating, even harmful.
It is therefore no coincidence that this hypothesis is often cited when talking about the extinction of the dinosaurs. Indeed, the lava flows in very, very large quantities may have contributed to the formation of the famous sulphur mist that has been mentioned. In any case, the end of the dinosaurs allowed mammals (including the ancestors of human beings) to evolve and take their place on Earth. In other words, if the dinosaurs still existed, man might never have found his place...
This mass extinction was not the first that the Earth has faced. Traces have been found of other periods in history when species have become extinct in large numbers. But scientists, and mainly geophysicists, are continuing their research in order to detect the exact cause or causes of the extinction of the dinosaurs. What is clear is that drastic changes in the environment are at the root of the end of the reign of these giant animals. Moreover, the dating carried out has shown that the impact, the extinction of the Cretaceous-Tertiary and the impulse of volcanism are closely linked. In other words, hypotheses such as the epidemic, the virus or toxic plants must be forgotten. All that can be scientifically affirmed is the fact that the Trapps of the Deccan and the Yucatan crater were indeed formed 65 million years ago. Obviously, one or both of these cataclysms were responsible for the disappearance of the dinosaurs.
Several millennia were necessary for the Earth to recover from the Cretaceous-Tertiary extinction. It took more than half a million years for life to regain its rights and for species to reclaim the ecological niches left vacant. As for the first representatives of the human species, they appeared about 3 million years ago... well after the extinction of the dinosaurs. However, many people still wonder whether humans and dinosaurs could have lived together!
For the time being, scientists are concentrating on fossils that would allow them to affirm the causes of the end of the Cretaceous-Tertiary period.
Whatever the exact cause of the extinction of the dinosaurs, it is important to look at the world after them. Several million years have allowed the reconstitution of vegetation such as ferns. For their part, the mammals that survived also evolved, and some species of flying dinosaurs survived. Most of them developed and transformed into... birds. Scientists are fairly certain that small theropod-like dinosaurs are the ancestors of more than 8,000 species of birds today.
Paleontologists such as Thomas Huxley have also found many similarities between dinosaurs and birds. His colleague, J. Ostrom, stated in 1970 that theropods are indeed the ancestors of birds. To prove this, he studied the appearance of the archaeopterix, a flying reptile with teeth, a tail and claws. He concluded that this bird resembled the Compsognathus (a small theropod).
Tyler Lyson's team from the Denver Museum of Nature and Science also unearthed ancient bones east of Colorado Springs in the United States. They discovered several skulls of mammals that are believed to have lived in the first million years after the Cretaceous mass extinction. Even though they weighed less than half a kilogram, they may well have survived in a hostile environment.
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