Suppose, by some miracle, mankind will manage to avoid a nuclear war, the fall of a huge asteroid, atmospheric intrigues of supervolcanoes and deadly radiation from supernovae that exploded nearby. We have about 6 billion years before the day when the Sun swells up according to the precepts of red gigantism and engulfs our planet, melting everything to hell. This is only at first glance a long time - the apocalypse will not keep itself waiting so long and will come much earlier, astrophysicists Michael Khan and Daniel Wolf Savin from Columbia University in New York (USA) predict in an article in the popular edition of Nautilus.
The bleak future of our planet. Photo: Mark Garlick.
To begin with, the Earth is very lucky to rotate in that elite range of orbital distances, within which liquid water (a necessary condition for life in our usual version) and a sufficient amount of carbon dioxide for photosynthesis can exist. According to the calculations of some scientists, the inner boundary of such a "photosynthetic habitable zone" lies in only 7.5 million km from us - this is about 5% of the distance from the Earth to the Sun. And this border is gradually shifting outward, in our direction.
Our star is a massive ball of gas, held within its own gravity. In the center of it, under conditions of colossal pressure and the highest temperature, hydrogen nuclei merge in four and form helium nuclei, which logically leads to a decrease in the total number of nuclei and a decrease in the external pressure of the solar core (it is proportional to the number of nuclei per unit volume). As a result, the outer layers press more and more on the core of the star, as a result, inside it, the pressure and temperature rise even more, as well as the rate of nuclear fusion, which leads to an increase in the brightness of the Sun by 10% every billion years.
In response to the rising heat, the earth is gradually throwing off its greenhouse coat of carbon dioxide: the rise in temperature accelerates chemical reactions between water and silicate rocks, during which CO2 is sorbed from the atmosphere. Eventually, there will be so little of it that the plants will start to die out.
First, those that practice C3 photosynthesis will disappear - and there are most of them, including among the most important crops (wheat, rice, barley, oats, soybeans, potatoes, peanuts, coconut, banana, cotton, most trees). This will happen in about 200 million years, when the CO2 concentration drops to 150 ppm (for comparison: today it is more than 400 ppm). As they become extinct, they will gradually be replaced by plants with C4 photosynthesis, which some believe have evolved in response to carbon dioxide depletion. They use CO2 more efficiently - they account for a quarter of all terrestrial photosynthesis, despite the fact that they are only 3% of the total plant species (these include corn, sorghum, millet, sugar cane, some weeds). But C4 plants, alas, will also die out 300 million years after C3 plants,when the CO2 is less than 10 ppm.
Along with plants and other photosynthetic organisms, animals will begin to die out, because there are no non-biological sources of oxygen on Earth. Large animals will suffocate first, followed by small and microscopic ones. Even if someone manages to survive in an oxygen-free atmosphere (say, worms), in a billion years the average temperature on the planet's surface will exceed + 45 ° C (now + 17 ° C) - and the most important biochemical processes in such conditions simply stop working. You can try to look for salvation at the poles, but even there it will soon become too hot. Ultimately, only chemosynthetic microbes will remain, which do not need carbon dioxide and oxygen for metabolism, but rely, for example, on sulfates or iron.
Too hot. Illustration: Ron Miller.
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And what about people? They cannot enter chemosynthesis. So in the next half a billion years, they urgently need to get rid of Zemlyashka. However, during this time, conditions on other planets or satellites of the solar system will hardly become so acceptable for living, and flying beyond its limits is a rather unpromising idea. "If we are talking about exoplanets, then it is worth clarifying: we will never move there," said the other day Swiss astrophysicist Michel Mayor, a freshly baked Nobel Prize winner for the discovery in 1995 of the first exoplanet near a sun-like star (together with Didier Kelo). "Even in a very optimistic case - if a planet suitable for life is not very far away, say, a few tens of light years, which is not much, literally in the neighborhood - it will take a lot of time to fly there." Hundreds of millions of days with state-of-the-art technology.“This is complete madness,” added the professor. Well, he knows better.
One can try to delay the climatic execution by shifting the earth's orbit, as Khan and Savin suggest. For example, if you destroy an asteroid 100 km, which flies near the Earth every five thousand years, then as a result of gravitational changes, our orbit will slowly move away from the Sun at a respectable distance - the main thing is not to accidentally destroy the Earth at the same time. Or you should build a giant solar sail on gravitational tethers so that the solar wind, with its photonic breeze, pushes the planet a little further into the habitable zone - it will be possible to inhabit there until the final swelling of our reddening star. Such a sail should be 20 times the diameter of the Earth, but not more than a trillion tons in mass - this is about 2% of Everest. By the way, if some alien civilization has already built such a sail,then it is quite possible to detect it using the same methods that are used to detect exoplanets.
Another way to survive will require a high level of development of artificial intelligence technologies. Generally speaking, in the future our planet will become much more favorable for non-biological life. First, due to the increased brightness of the Sun, which powers the robots' batteries. Secondly, space weather will improve: if today the Sun is spinning with a frantic dynamo, turning around its axis in 24 Earth days, and regularly causing magnetic storms on our planet, which often disable communications, power systems and orbital satellites, then by old age its rotation will slow down and the magnetic storms will stop. Robots will not need to worry about their exquisite microcircuits, and people with a light heart will be able to load their minds into them in order to continue to drag out an earthly existence with relative comfort in openly inhuman conditions.
Possible perspective. Illustration: Sophia Foster-Dimino.
However, all these terrible space challenges are still quite far away - there are tens of millions of years left to figure out how to resist them. On the nose are much more pressing problems of a planetary nature - if they are not solved, humanity will not have a chance to live even ten thousand years. “We must take care of our planet,” Professor Michel Mayor rightly edifies. "She is very beautiful and still absolutely fit for life."
Author: Viktor Kovylin