General, Research, Technology

When will mass extinction await us?

65 million years ago, a massive asteroid,five to ten kilometers across, hit the Earth at speeds exceeding 30,000 kilometers per hour. As a result of this catastrophic collision, giant creatures known to us as dinosaurs that ruled the Earth for more than 100 million years were destroyed. It is noteworthy that about 30% of all species now existing on Earth were destroyed at that time. That time was far from the first when a catastrophic object hits the Earth, and certainly did not become the last. It is believed that such events occur on a periodic basis due to the movement of the sun across the galaxy. If so, we should be able to predict when the next such event is coming and whether we should worry about our own fate.

The history of falls in our solar systemliterally painted on the faces of worlds like the moon. The lunar highlands - light spots - show us the history of the heavy bombardment of the times of the young solar system more than 4 billion years ago. There are many large craters with smaller craters inside, which indicates an extremely high level of activity in those days. However, if you look at dark areas (moonlit seas), you will not see many craters inside. Radiometric dating indicates that most of these zones are 3 to 3.5 billion years old. The youngest areas found in the largest sea of ​​the Moon Oceanus Procellarum are only 1.2 billion years old and relatively recently created.

Based on these data, we can concludethe fact that the asteroid belt will decrease over time and the rate of crater formation will drop. It is believed that we are far from this, but in the next several billion years the Earth will receive the last serious blow of the asteroid, and if it still has life, mass extinction is inevitable. Today, the asteroid belt is less threatening than in the past.

But the Oort cloud and the Kuiper belt are completely different stories.

Beyond Neptune, in the Outer Solarsystem, there is a deep threat. Hundreds of thousands - if not millions - of large blocks of ice and stone float in sparse orbits around the Sun, in anticipation of perturbations caused by the passage of large masses. Violation of the orbit can lead to different outcomes, among them the sending of an object to the inner solar system, where it will arrive as a brilliant comet and, possibly, will encounter something.

Interactions with Neptune or other objectsKuiper belts and Oort clouds are random and independent of the processes of our galaxy, but it is possible that passing through a region rich in stars - such as a galactic disk or one of the spiral arms - can increase the chances of comet rain and comet impact on Earth. As the sun moves through the Milky Way, once every 31 million years, it passes through the galactic plane. This is purely orbital mechanics, because the Sun and all stars move along elliptical roads around the center of the galaxy. But some people claimed that periodic extinctions occurred exactly at the same frequency. That is, these extinctions could be caused by comet rain, which happens every 31 million years.

Is it possible? The answer can be found in the data. We can consider major events of extinction on Earth as marks in the fossil record. We can calculate the number of genera (this is slightly higher than the “species” in our classification of living things; the human race is homo in homo sapiens) that existed at a particular time. We can do this by returning 500 million years ago in time, thanks to discoveries made in sedimentary rocks.

We can look for patterns in these events.extinction. The easiest way to do this quantitatively is the Fourier transform followed by a search for patterns. If we see events of mass extinction every 100 million years, for example, with a large disappearance of the number of species after a certain period of time, the Fourier transform will show a large burst with a frequency of 1 / (100 million years). What do extinction data show?

Measuring biodiversity, as well as changes in the number of births, at a given point in time, revealing most of the major extinction events over the past 500 million years.

There are several relatively weakevidence for a frequency of 140 million years and even more powerful - for jumps every 62 million years. Where the orange arrow is, you see a frequency of 31 million years. These two leaps seem huge, but only relative to other leaps, which are completely insignificant. How strong, objectively, are these two leaps that demonstrate periodicity?

This figure shows the Fourier transform for extinction events over the past 500 million years. The orange arrow shows where the frequency of 31 million years would fit.

In just 500 million years you can placethree possible mass extinctions with a period of 140 million years and eight with a period of 62 million years. What we see does not fit into such periods with such events; rather, if such an event was in the past, there is an increased chance that this will happen in 62 or 140 million years. However, the periodicity of 26-30 million as such is not observed.

If we begin to study craters on Earth andthe geological composition of sedimentary rocks, this idea crashes completely. Of all the craters that formed on Earth as a result of falls, less than a quarter are formed by objects from the Oort cloud. Moreover, the boundaries between the geological periods (Triassic / Jurassic, Jurassic / Cretaceous, Cretaceous / Paleogene) and geological records that correspond to extinction events show that only extinction 65 million years ago has a layer of dust and ash that we could associate with a big blow.

The boundary layer of the Cretaceous and Paleogeneperiods characteristically stands out in sedimentary rock, but is represented by a thin layer of ash, and its composition tells us about the extraterrestrial origin of the body, which led to mass extinction.

The idea that mass extinctions are occurring onperiodically interesting and convincing, but she simply does not have convincing evidence. The idea that the passage of the Sun through the galactic plane leads to periodic extinctions is also interesting, but unproven. We know that every half a million years, within the reach of the Oort cloud, stars pass, but at present we are far from these events. In the near foreseeable future, the Earth is not threatened by the natural cataclysm caused by the Universe. On the contrary, we ourselves pose the greatest threat to us.

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