Why was there mass extinction of many living beings on Earth in distant past? What was the reason behind it - a falling asteroid or volcanic activity? Paleontologist Kirill Yeskov believes that if asteroids and volcanoes had anything to do with these extinctions, they were only the last straw that broke the camel's back.
Usually the topic of mass extinctions that have occurred in the previous era pops up when a new potentially dangerous asteroid is found near the Earth or volcanoes are activated. This gives rise to speculations that such disasters may lead to the disappearance of the most of the living beings from the planet as it had happened in the distant past. An example of dinosaurs allegedly killed by a collision of giant asteroid with Earth is usually brought up.
There is no doubt that these "horror stories" are always popular with audiences of various scientific and popular media as for some reason people always like to fear something. This is precisely why the topic of impact extinctions (extinction due to an external factor) is often exploited by writers, directors and artists. What do scientists think of such hypotheses? Kirill Yeskov, a scientist paleontologist, an employee of the Paleontological Institute named after Borisyak RAS said that paleontologists were rather skeptical about such hypotheses.
"First of all, let's talk about the very asteroid and dinosaurs, to be precise, about the causes of extinction of many animals at the Cretaceous-Paleogene boundary (65 million years ago)," said Kirill. "I want to immediately note that the asteroid hypothesis was not the only catastrophic one. Alongside with it a "volcanic" theory has developed. There were reasons for it, as in these times there was a strong volcanic activity. For example, the Deccan Plateau in the Indian subcontinent has emerged as a direct result of these processes.
And so the asteroid hypothesis was born. In the 1960 the iridium anomaly was discovered, that is, high content of iridium metal in the Earth's rocks corresponding to the Cretaceous-Paleogene boundary. Iridium is rarely found on Earth as in the early stages of the development of our planet along with iron it went into the core. However, it is often found in meteorites and fragments of asteroids. Thus it was suggested that the iridium appeared in the tested layers as a result of the collision of Earth with a large celestial body.
This hypothesis was first suggested by a Nobel laureate, astrophysicist Luis Alvarez. He believed that the asteroid that brought iridium back to Earth was a fragment of a core of a large planet composed of iron and elements close to it. At the time not everyone agreed with this theory, and some scientists said that the iridium may have had a terrestrial origin and erupted from the depths of the planet with eruption of volcanoes. That is, this hypothesis had no advantage.
However, the asteroid hypothesis was "promoted" by NASA that at that time possessed enormous opportunities, both financial and informational. NASA began affecting grant policy, as well as the editorial boards of scientific journals, and the article about the asteroid hypothesis received support, while the articles about the volcanic hypothesis, on the contrary, were "swept under the rug." Following the positive feedback, and thanks to the efforts of NASA, the asteroid hypothesis has become "mainstream," which meant that grants were provided for its research. Of course, Hollywood has considerably contributed to the promotion of the asteroid hypothesis.
Behind all this it was somehow missed that the iridium anomaly was found increasingly more frequently, and sometimes it was found even in the sediments of the periods with no extinctions. This was a serious blow to the hypothesis delivered by geologists. Paleozoologists and paleobotanists from the onset were skeptical. Why so? Because according to the asteroid theory, the impact of a celestial body on the ground had to first form the cloud of dust that would arrange for an asteroid winter that led to the death of plants and the collapse of the entire ecosystems.
Only later, due to the inability of photosynthesis, problems began in the ocean. Plankton does not absorb CO2, the acidity of water is increased and, accordingly, calcium shells of marine animals are destroyed. This also brings down ecosystems, in this case, the marine ones.
That is, simply put, if we accept the "asteroid" scenario, the first mass extinction has to occur on the land, and only then in the sea, because the ocean is a fairly inert system. But the picture restored by paleontologists, based on their findings, looked completely different. Cretaceous-Paleogene extinction began in the sea and then came to land. There were very different scenarios. Entire taxa have completely disappeared from the oceans, or there was a strong reduction of their diversity, for example, of the fifty species only one has survived. There was nothing like this on land. Dinosaurs and pterosaurs became completely extinct, and at different times. Among such a large group of living beings like flowering plants, insects or mammals only single species were extinct.
All this means only one thing: the extinctions at the Cretaceous- Paleogene boundary in the oceans and continents were quite different in nature and, therefore, have been caused by different reasons. Incidentally, this makes us very skeptical about the volcanic theory as it also implies a catastrophic impact on the entire planet. However, massive release of gases from the crater of a fire-breathing giant had to change the composition of the atmosphere and first arrange a catastrophe on the land, and only then in the sea. In this case again the nature of the extinctions must be the same.
However, we have other, more compelling evidence that volcanic eruptions likely have not been involved in the Cretaceous-Paleogene mass extinction. In particular, in the Far East, an interesting layer of sedimentary was discovered (a basic unit of regional stratigraphic units composed of layers of sedimentary or igneous metamorphic rocks). This layer is interesting because it is located exactly on the border of the Cretaceous and Paleogene.
It was researched and a curious thing was discovered. Volcanism at this time in the Pacific has been quite active as evidenced by many traces of eruptions in the suite. Yet, there was no trace of extinction on land - animals, plants and other organisms lived their normal lives, that is, bloomed, bore fruit, hunted, and left traces. It turns out that volcanic eruptions right before the ecosystem has no serious impact on its life.
Incidentally, the same pattern is seen with another major extinction that occurred much earlier, at the border of the Paleozoic and Mesozoic era (Permian-Triassic). In that case there was no talk about an asteroid because the iridium anomaly has never been found, although it was long and purposefully looked for. Volcanism was suspected from the very beginning. In fact, it caused the formation of the Central Siberian Plateau. So, we investigated the deposits directly there, that is, at the epicenter of the volcanic activity, and the picture turned out to be the same. In this volcanic hell there were normal ecosystems with no trace of mass extinctions.
This means that if asteroids and volcanoes had to do with the mass extinctions, there only were the last straw that broke the camel's back, that is, they only accelerated these extinctions, but did not cause them. What are the real reasons? Now it is difficult to talk about some specific events that led to the extinctions, but one thing is clear - they are the result of the crisis of the ecosystems of that time. This crisis, unlike most of extinctions, in all cases lasted very long, and the extinction was just its "peak."
However, as is evident from the fossil remains, along with the extinction of some living beings others have also appeared and new ecosystems were formed. That is, it must be recognized that any known mass extinction is not the result of an accident, but just a link in the chain of events of legitimate evolution of ecosystems. Simply put, animals or plants die out when the conditions are changing around them so that they cannot exist any longer. For example, this is what had happened to dinosaurs.
In conclusion I would like to talk about the "alarming" statistics that non-specialists often mistake for evidence of a catastrophe, I would like to talk about statements according to which, for example, "during the Permian-Triassic extinction 90 percent of living creatures disappeared from the face of the Earth." In fact, most of the ninety percent are groups that have come and gone in the ecosystem crisis. This happens frequently - if the structure of ecosystems is broken, a rapid formation of new species begins, as if nature is "recruiting" in the ranks of the inhabitants of the future ecosystems.
The overwhelming majority of these "children of the crisis," are short-lived. As seen from the fossil material, they exist for a very short time from a geological point of view. When we sum up the findings from all the deposits of the period of extinction, it turns out that most of the extinct creatures are "fly by night." This is very similar to the situation observed by historians during the collapse of the Roman Empire and the Great Migration. Then, too, there were numerous barbarian kingdoms, most of which lasted only a few years. A large number of extinct groups of animals does not indicate that there was a catastrophic event, it says more about the acceleration of the process of speciation."
As you can see, our planet and everything that lives on it is the system very resistant to many external influences. One asteroid, even a very large one, and global volcanic eruptions cannot destroy everything that lives on Earth. If this has not happened in the past, there are no reasons to worry about it now.