The existing continents are moving towards merging into one - it's only a matter of time, according to most researchers. A group of scientists decided to find out what will happen to the habitability of the Earth after this merger is completed. As it turned out, the temperature on the planet will rise significantly in any outcome. But if one of two possible supercontinents forms on land, it will get much colder. If a second supercontinent arises, the proportion of habitable solid surface, on the contrary, will increase. Why does this happen and what follows from this?
Scientists led by Michael Way from the Goddard Institute for Space Research (USA) have checked how habitable our planet will be in 200-250 million years. As it turned out, in the case of the formation of the supercontinent Amazia (America plus Asia) in high latitudes, the climate will be noticeably colder than when the formation of Aumerica (Australia plus America) at the equator. The planet's suitability for habitation in the event of the "victory" of Amazia will be much lower. Modern agriculture in its conditions is becoming largely impossible. The new work will also make it possible to more accurately assess the habitability of terrestrial exoplanets.
In the 21st century, the need to assess the habitability of other potentially habitable planets forced researchers to develop a scale of “climatic habitability”. According to her, zones with an average temperature below zero Celsius are either uninhabited or limited inhabited.
At first glance, it is strange, since modern Russia in this case lies mainly outside the habitable zone. However, the classification makes sense: modern complex life is based on autotrophs-plants, and in zones where the temperature is below zero, plants practically do not photosynthesize. In other words, all these zones are temporarily inhabited or inhabited only when the temperature there is positive. Scientists call this "partial habitability." From this point of view, modern Earth has 85% habitability. Arctic and Antarctic deserts are almost completely excluded from this figure, but not the Sahara and other non-arctic deserts.
Aumerica or Amasia? Any option for Earth's future will end in a supercontinent
The authors of the new work, published in Geochemistry, Geophysics, Geosystems, have calculated the climate for two main scenarios of geography of the distant future. The first of them is the formation of the supercontinent Amasia as a result of the merger of America and Eurasia, moving northward (and then merging with the rest of the continents). An approximate predicted route of this process can be seen in the video below:
The second scenario is the formation of Aurica, a continent stretched along the equator (it is better to look at twice the speed):
Today, the scientific understanding of plate tectonics is not advanced enough to accurately predict which of the two supercontinents will form in practice: the current speeds and directions of movement of lithospheric plates are in principle compatible with both options. However, as the authors of the new work note, the very formation of the future supercontinent around this time frame raises few doubts.
From the geological history of the planet, it is known that supercontinents form and disintegrate on it cyclically, every 400-600 million years. The last time the supercontinent was formed 330 million years ago and was called Pangea. About 180 million years ago, during the Jurassic period, it disintegrated. From this it is quite obvious that now the Earth is in the middle of the formation cycle of the next supercontinent, and in 200-250 million years its appearance would be quite expected.
Supercontinent at the pole and at the equator: two different planets
In the event of the formation of the Amazia, its main part will be concentrated around the North Pole. The inland seas - the remnants of the Arctic Ocean - will be reliably isolated from warm currents such as the Gulf Stream, which will give them a stable ice cover. The ice sheet will inevitably cover most of the land. In this scenario, Antarctica will remain unattached to the supercontinent and will also be covered in ice.
Despite this, the average temperature of the planet will be much higher than today (when it is plus 15) and will become approximately equal to the Mikulino interglacial, reaching plus 17, 2. The reason is the increase in the luminosity of the Sun by 1.9%. Astronomers have established quite a long time ago that the brightness of stars increases with age, and for a star of our class, the growth rate is determined so accurately that it can be predicted hundreds of millions or even several billion years ahead.
However, a higher planetary temperature on average does not mean higher habitability. After all, almost all of the land will lie in high latitudes, and the level of its habitability will drop to 58% - from 85% today. This is a serious drop in habitable area, up to 30%. Moreover: in today's world, more than 90% of species exist outside the temperate zones, and on the Amazia there will be few areas warmer than the modern temperate climate. Therefore, the actual biodiversity in such a future of the planet should fall by many tens of percent.
The Earth will be fundamentally different in the event of the formation of Aumerica. As you can easily see above, this continent will even include Antarctica. That is, almost all of the land will be concentrated in low latitudes. And there ice and snow can exist only on the tops of the highest mountains. Only a small fraction of the sun's rays will be reflected back into space by ice. As a result, the average temperature on the planet will become plus 20, 7 - almost like in the Mesozoic. Therefore, the share of inhabited land in the "Amerian" future will be 99.8% - much higher than today, and two-thirds higher than in the Amasia scenario.
It should be noted that almost all of this land will have an equatorial and tropical climate. Obviously, the biodiversity on it in this regard will become extremely high. From the point of view of agricultural suitability of the modern type of Avmeric, again, it is better than the current Earth and incomparably better than the Amazia variant.
What does this mean for the future
At first glance, given the current level of understanding of plate tectonics, it is a little too early to predict what the earth's land will be like in a quarter of a billion years. But the authors of the new work are right in the sense that the formation of a supercontinent still cannot be avoided. Taking Amasia (“all land at the poles”) and Aumerica (“all land at the equator”) as reference points, they outlined the boundaries of the Earth's climate variability in any possible scenario for the future of the planet.
Even more important is that with numbers in hand it was possible to show that the habitability of a terrestrial planet depends in the most serious way on the location of the continents, especially the supercontinents. The difference between 58% and 99.8% habitability for the scenarios studied is colossal and means that any future analysis of the habitability of exoplanets must take into account the location of the continents on them.
This is important: in the coming decades (and even the coming years), large telescopes will receive data on the location of the continents on the planets closest to us, available for the transit method of observation. In other words, on those planets that pass between the disk of their star and us.Today, dozens of such planets are known with dimensions close to the Earth.
But the new work is important not only because it allows you to separate the potentially less habitable planets (with the Amazians) from the potentially more habitable ones (with the Aumeriks). The fact is that, as other research groups have already noted more than once, if extraterrestrial civilizations exist, they will inevitably have a serious impact on the climate of their planet - either unintentionally, like people today, or deliberately, as the Soviet climatologist Mikhail Budyko suggested in last century (to make the northern parts of the USSR fully inhabited).
If our telescopes spot terrestrial planets near stars like the Sun, which have circumpolar supercontinents (like Amazia) and receive as much heat from their star as the Earth, but at the same time are devoid of ice cover, this can become a serious argument in favor of careful further analysis. … After all, such an anomaly can indicate the existence of extraterrestrial civilizations.
True, most of the terrestrial planets in the Universe revolve around completely different stars - red dwarfs. Since three-quarters of all existing luminaries belong to them, at least three-quarters of the earth-like planets should also be there. In red dwarfs, the location of the supercontinent means slightly less habitability than on Earth. 95% of the radiation of such stars is in the infrared range, and ice cannot reflect such rays into space. Accordingly, even on the circumpolar continents of the planet, there will be no stable ice caps in the habitable zone.
Nevertheless, tracking the positions of supercontinents will also be important for planets under red suns. Recall: in order to be inhabited, they need to receive a sufficient amount of radiation from the star. Since the luminosity of red dwarfs is tens or more times lower than that of the Sun, this is possible only if the planet is much closer to its star. But starting from a certain distance, the star slows down the rotation of the planet around its axis so much that the exoplanet begins to look at its star all the time with one side. Each of us has seen an example of such "synchronization" many times: the Moon looks at the Earth in this way.
In this scenario, the presence of a supercontinent on the illuminated side of the planet - and terrestrial astronomers with new telescopes will be able to detect it - will be even more important than when studying systems like the Sun. If a red dwarf has a supercontinent on the eternally illuminated side of the planet, it means that both terrestrial plants and complex land life are possible there. If there are no supercontinents and all of them are concentrated on the eternally shadow side of the planet, there is very little room for land life there. It is clear that a detailed study of such planets is less promising than those where the continents are on the "bright side".
It is not yet completely clear to science whether red dwarfs have plate tectonics on the planets - whether tidal capture prevents such tectonics. If tectonics do exist, every movement of the supercontinent from the illuminated side to the dark will mean the destruction of complex land life. Indeed, without light, plants will not be able to photosynthesize, and after their death, both herbivores and predators will disappear.
In the absence of tectonics, the planet of the red dwarf plays a kind of lottery. In the case of a "win", part of its continents (or even a supercontinent) is once and for all on the illuminated side, and then the exoplanet is ideal for life. If it loses, its supercontinent will be on the shady side, and only seas and oceans will remain for life. Judging by the experience of the terrestrial biosphere, the total biomass in the oceans is ten times lower than on land, although the oceans are much larger in area. That is, biologically, the oceans are extremely deserted in comparison with land. It is doubtful that the chances of intelligent life on worlds without illuminated land can be really high.