Once every 27 million years, a mass extinction of species occurs on Earth, associated with an external cause, about which practically nothing is known. This is not fiction, but a recent discovery made by astronomers
One of the hypotheses of cyclic extinction was associated with comets, but in the end it was not confirmed - now astronomers can only guess or write off everything as an accident.
Two researchers from the University of Kansas and the National Museum of Natural History have taken a close look at the history of mass extinctions on Earth over the past half a billion years. Using the paleontological data accumulated over several centuries, they were able to prove that extinctions occur cyclically, with a period of 27 million years.
The authors of the article, which has already been accepted for publication by the Monthly Notices of the Royal Astronomical Society, immediately tested the hypothesis that the cycle is a consequence of the fact that the vicinity of the solar system is visited by some foreign celestial body moving in an extremely elongated orbit. And the results of this test turned out to be even more surprising - the existence of such an object does not fit into the laws of celestial mechanics!
When?
It's too early to dig a shelter in the country and buy stewed meat. The last species-event that led to extinction, whatever it was, took place 11 million years ago and is ahead of another 16 million years. To scale, let us point out that a few million years ago the most highly developed creature on the planet was Australopithecus, and only about 35-40 thousand years ago, people began to create the first figurines from clay and stone. If during this time the path from cave dwellings to orbital stations was covered, then 16 million years is quite enough for preparation.
Doomsday Celestial Mechanics
About the "hypothesis of Nemesis", which later was not confirmed by calculations, it is worth telling in more detail. It was not invented by the authors of a recent study - several scientists back in 1984 suggested, although they could not then prove that mass extinctions of animals on Earth could be cyclical, and put forward a hypothesis that a certain celestial body revolves around the Sun at a very great distance. the code name "Nemesis" in honor of the Greek goddess of vengeance.
Nemesis, which could be a brown dwarf, passes at a noticeable distance from the planets. Therefore, there is no talk of any collision even with Neptune or Pluto, just as serious distortions of planetary orbits should not be considered seriously. The nemesis in the scientists' model only influenced bodies in the Oort cloud, a giant sphere around our system.
But this turned out to be enough for serious troubles - the gravity of the "dark satellite of the Sun" changes the orbits of comets, which are located at great distances from the Sun most of the time. Comets begin to move along trajectories that intersect the orbits of the inner planets … and where there is an intersection, there may well be a collision.
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A direct hit of a comet means an explosion comparable to the explosion of the entire nuclear arsenal of the Earth, followed by the onset of a "nuclear winter" - the dust raised into the sky blocks the sun's rays for several months, or even years, causing a drop in temperature.
Atmospheric issues
Why does dust lower the temperature, increase carbon dioxide, and reduce the ozone layer forced the world to stop using freon aerosols? Dust reflects the sun's rays into space and works like an umbrella from the sun, but carbon dioxide reflects heat down, but freely lets the sun's rays inward, behaving like a greenhouse glass. As for ozone, its role is not so much in regulating temperature (although it is also a greenhouse gas), but in protecting against ultraviolet radiation, the excess of which can cause skin cancer.
The risk of the Earth hitting anything is now very low. Even the asteroid Apophis, which for a long time was considered the most dangerous, in 2036 can collide with the Earth only with a probability of 1: 250,000, which, in general, is very small against the background of all other threats (the H1N1 / 09 influenza pandemic frightened WHO with exactly what could turn into a repeat of the "Spanish flu" with tens of millions of victims. No one will give guarantees that the next flu will end up being as "mild" as H1N1 / 09). But if we assume that many comets fly to the inner planets every 27 million years, the situation can change dramatically, and not for the better.
Scientists' problems
The fact that the process is stretched out in time, and comets can both collide with the Earth and fly by, seriously complicated the work of scientists. If every 27 million years, exactly on schedule, something fell on our planet, and in between everything would be calm, then, of course, the pattern described now would have been found much earlier.
But in fact, mass extinctions also happened for other reasons - in the solar system itself there are enough asteroids for at least one of them to arrive in half a billion years. And also supervolcanoes, climatic cycles, acidification of seawater, depletion of reserves of phosphorus or other important elements that are buried at the bottom of the oceans - and all this against the backdrop of a chronic lack of data.
Having collected enough information and used mathematical methods from the arsenal of statisticians, scientists nevertheless identified a cycle of 27 million years, and even showed that with an extremely small (less than a percent) probability it could turn out to be a random coincidence of unrelated events. The loop was found and the second problem immediately arose.
The cycle was too precise. For a celestial body that moves away from the Earth for several light years and passes by other stars, this is impossible. Comets that go so far from their star risk simply moving to other stellar systems, but there is no need to talk about the constancy of the orbit. If the mysterious object were a brown dwarf or something similar, it would not have been able to withstand the precision that the researchers noted!
What then? Unlike the sensational publications, the study authors are reserved. They do not say anything about what could provide the cycle they found - in the "discussion" section, only the hypothesis about the passage of the Earth through the Galaxy disk is mentioned. It also had to be discarded, since in this case it is extremely difficult to get exactly the period that the statistical analysis of extinctions shows. It is possible that there is no cycle at all, but there are coincidences, but again statistics indicate a low probability of such a combination of circumstances.