Extinctions in the history of our planet are somehow unevenly distributed, which has long made it possible to assume some connection between such events and extraterrestrial factors. In an attempt to figure out what that might be, scientists have superimposed extinctions on the trajectory of the solar system through the Milky Way.
The sun and its planets make a complete revolution around the center of the Galaxy every 200 million years. During the galactic year, the system passes through the spiral arms of the Milky Way. They have a much higher density of stars, and sometimes the density of interstellar gas.
Sometimes we are in one of the galactic arms, as, for example, now. And there is a suspicion that at such moments various troubles can happen to us. Let's say mass extinction. (Here and below illustrations by MD Filipović et al.)
Combining today's data on the speed of the system around the galactic core with the fossil record, specialists led by Miroslav Filipović from the University of Western Sydney (Australia) have obtained a funny result. Almost all intersections with spiral arms coincided with periods of severe extinction of species, including such monstrous events as the Cretaceous-Paleogene (66 million years ago), Triassic (200 million years ago), which cleared the way for dinosaurs, the Permian, Late Devonian, Late Ordovician and Late Cambrian extinctions, as well as five collisions of lesser intensity during the same period.
Since the Sun spent 60% of its time in the spiral arms of the Galaxy, the researchers tried to check whether the passage through the arms and the disappearance of species coincided. For this, the "null hypothesis" was applied, and the probability of coincidence of eleven events was combined with the finding of our planetary system in the arms.
The blue circles represent where the Earth was at the time of the mass extinctions. Orange - to the points where there was a less intense impoverishment of all living things, and yellow - this is the current position of the Sun.
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Such a coincidence could take place, the authors of the work believe, but only with a probability of 0.611 - that is, only 0.36%. Obviously there is something in the sleeves that doesn't work well with the existing species?
What could it be? The authors list a number of hypotheses in this regard known from the literature. So, passing through the arms dramatically increases the likelihood of a nearby supernova explosion - an event that, in principle, can destroy most living organisms in the shortest possible time. However, according to their own remarks, the available estimates of a nearby explosion of this kind, even for spiral arms, give too little probability. All eleven extinctions are difficult to explain by this accident.
The abundance of marine species, reflecting the degree of biodiversity. Blue and orange lines = circles from the previous illustration. Green and red show the moments when the planet is in the spiral arms according to the Filipovich model and one of the previous ones. It is clearly seen that Filipovich's model shows the passage along the spiral arm at the time of the Permian extinction, the worst in the last half a billion years.
Most of all Serbian scientists are attracted by another option: perturbations associated with the gravitational influence of the dense stellar environment disturbed the stability of the comet cloud at the periphery of the solar system, thereby provoking the entry of a large comet into our planet. In principle, this can also lead to unpleasant consequences. For example, in 1994, only one comet that fell on Jupiter caused an energy release of 6 million megatons (360 million Hiroshima) in its atmosphere, which is hundreds of times more powerful than the entire nuclear arsenal of the Earth and 12 million times more powerful than the explosion of the Chelyabinsk meteoroid.
Given that the comet was originally only 5 km in diameter, it can be assumed that more powerful cometary impacts have hit the Earth in the past, which makes the theory of periodic "stoning" of earthly life seem quite reliable.
Note, however, that these are far from all possible mechanisms of the destructive effect of spiral arms.
According to the theory of the Danish physicist Henrik Svensmark, a sharp increase in cosmic rays in the earth's atmosphere causes the most active cloud formation, an increase in albedo and a cooling of the planet, which in theory can lead to equally drastic climatic changes and associated extinction. At the same time, one cannot reject the possibility of the existence of other mechanisms, which have not yet come to the attention of astro-scientists.
Obviously, the scientific community will have to consider all other alternatives as well: you need to know what type of shelter is worth digging in the yard.