What did our planet represent in the past. The past of the planet earth. The Arctic was green and full of life

The ideas of the ancients about the Earth were based primarily on mythological ideas.
Some peoples believed that the Earth is flat and rests on three whales that swim in the vast world ocean. Consequently, these whales were in their eyes the main foundations, the foot of the whole world.
The increase in geographical information is associated primarily with travel and navigation, as well as with the development of the simplest astronomical observations.

Ancient Greeks imagined the earth was flat. This opinion was held, for example, by the ancient Greek philosopher Thales of Miletus, who lived in the 6th century BC. He considered the Earth to be a flat disk surrounded by a sea inaccessible to man, from which stars come out every evening and into which stars set every morning. Every morning the sun god Helios (later identified with Apollo) rose from the eastern sea in a golden chariot and made his way across the sky.

The world in the view of the ancient Egyptians: below - the Earth, above it - the goddess of the sky; left and right - the ship of the sun god, showing the path of the sun across the sky from sunrise to sunset.

The ancient Indians imagined the Earth as a hemisphere held by four elephant . Elephants stand on a huge turtle, and the turtle is on a snake, which, curled up in a ring, closes the near-Earth space.

Babylonians represented the Earth in the form of a mountain, on the western slope of which Babylonia is located. They knew that there was a sea to the south of Babylon, and mountains to the east, which they did not dare to cross. Therefore, it seemed to them that Babylonia is located on the western slope of the "world" mountain. This mountain is surrounded by the sea, and on the sea, like an overturned bowl, the firm sky rests - the heavenly world, where, like on Earth, there is land, water and air. The heavenly land is the belt of the 12 constellations of the Zodiac: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces. In each of the constellations, the Sun visits each year for about a month. The Sun, Moon and five planets move along this belt of land. Under the Earth is an abyss - hell, where the souls of the dead descend. At night, the Sun passes through this dungeon from the western edge of the Earth to the eastern, in order to begin its daytime journey through the sky again in the morning. Watching the sunset over the sea horizon, people thought that it goes into the sea and also rises from the sea. Thus, the basis of the ideas of the ancient Babylonians about the Earth were observations of natural phenomena, but the limited knowledge did not allow them to be explained correctly.

Earth according to the ancient Babylonians.

When people began to make long journeys, evidence gradually began to accumulate that the Earth was not flat, but convex.


Great ancient Greek scientist Pythagoras Samos(in the VI century BC) for the first time suggested the sphericity of the Earth. Pythagoras was right. But to prove the Pythagorean hypothesis, and even more so to determine the radius of the globe, it was possible much later. It is believed that this idea Pythagoras borrowed from the Egyptian priests. When the Egyptian priests knew about this, one can only guess, since, unlike the Greeks, they hid their knowledge from the general public.
Pythagoras himself, perhaps, also relied on the evidence of a simple sailor, Skilak of Karyanda, who in 515 BC. made a description of his voyages in the Mediterranean.

famous ancient greek scientist Aristotle(IV century BCe.) He was the first to use observations of lunar eclipses to prove the sphericity of the Earth. Here are three facts:

1. the shadow from the earth falling on the full moon is always round. During eclipses, the Earth is turned to the Moon in different directions. But only the ball always casts a round shadow.
2. Ships, moving away from the observer into the sea, are not gradually lost from sight due to the long distance, but almost instantly, as it were, "sink", disappearing behind the horizon line.
3. some stars can only be seen from certain parts of the Earth, while for other observers they are never visible.

Claudius Ptolemy(2nd century AD) - ancient Greek astronomer, mathematician, optician, music theorist and geographer. In the period from 127 to 151 he lived in Alexandria, where he carried out astronomical observations. He continued the teachings of Aristotle regarding the sphericity of the Earth.
He created his own geocentric system of the universe and taught that all celestial bodies move around the Earth in an empty world space.
Subsequently, the Ptolemaic system was recognized by the Christian church.

The universe according to Ptolemy: the planets revolve in empty space.

Finally, the outstanding astronomer of the ancient world Aristarchus of Samos(late 4th - first half of the 3rd century BC) suggested that it is not the Sun, together with the planets, that moves around the Earth, but the Earth and all the planets revolve around the Sun. However, he had very little evidence at his disposal.
And it took about 1700 years before the Polish scientist managed to prove it. Copernicus.

Since the formation of the Earth as a planet was completed, a restructuring of both its internal structure and its external appearance began. But what processes are leading in this restructuring, there is no consensus to this day. From the time when the primordial Earth was represented as a cooling fiery-liquid body, the problem of its evolution was solved simply: the process of cooling began from the surface; first, the earth's crust was formed, which, as the volume of the cooling Earth decreased, cracked, crumpled into folds, its individual sections sank, and thus the planet's surface was divided into oceans and continents and mountains arose. In a still molten body, the substance, under the influence of gravity, was differentiated by specific gravity: heavy elements and compounds “sank”, light ones “floated up” and broke out to the surface in the form of lava flows.

In this or a slightly different modification in the field of cosmogony, this hypothesis dominated from the middle of the 18th century until the beginning of the Second World War. However, already from the end of the 19th century, facts began to accumulate that contradicted this scheme. Already in 1870, the Englishman R. Proctor published the idea of ​​the origin of the solar system from a cluster of meteorites. This idea was picked up by the English astronomers G. Lockyer, J. Darwin (son of Charles Darwin) and the Australian D. Multon. But D. Multon and the famous American astrophysicist T. Chamberlain believed that the solar system arose from a swarm of the smallest planetary bodies - planetesimals, rotating around the central nebula in a spiral, colliding with each other. The sun formed from the central nebula, and the planets from the planetesimals. Thus, the idea of ​​an originally cold Earth and other planets originated over 100 years ago. According to this hypothesis, the heating of the planets was presented at the stage of their formation as a result of the transition of motion energy into thermal energy, and then due to the energy of gravitational compression. In accordance with this, it was assumed that at first the diameter of the planet grew both due to the addition of planetesimals to it and due to heating. At later stages of development, the planets contracted pulsatingly: when they cooled, their diameter decreased, the surface gathered into mountain folds, and, contracting, the planets expanded again due to heating. It was assumed that there were several such stages.

Although the fiery-liquid Earth hypothesis remained dominant, the idea of ​​an originally cold Earth did not die; it was soon shown that the compression energy alone was not enough to heat up to existing temperatures. The situation changed in the 1920s, when the Englishman J. Jolie put forward the idea of ​​radioactive heating of the planets. And although J. Jolie himself proceeded from the original model of the fiery-liquid Earth, the idea of ​​radioactive heating played a big role in the formation of the theory of the cold origin of the planets. In the 1930s, the pulsation hypothesis of D. Multon and T. Chamberlain was revived on the basis of ideas about the radioactive heating of the Earth. Radioactive heat periodically accumulated, then in the process of expansion, when cracks revived and volcanism and tectonic processes sharply intensified, excess heat was consumed, and the compression stage began.

In this form, the history of the Earth after its origin was imagined by most geologists until about the middle of the 20th century. Of the well-known Soviet scientists, this concept was supported by V. A. Obruchev, M. M. Tetyaev and further developed by V. V. Belousov, A. V. Khabakov. It explains well many facts of the tectonic history of the Earth and some morphological features of its surface.

In 1910, A. Bem put forward the rotational hypothesis of the evolution of the globe. This hypothesis in the USSR was especially supported and developed since 1931 by B. L. Lichkov, and since 1951 by M. V. Stovas. Supporters of this hypothesis believe that the axial rotation of the Earth, its own gravitational field, as well as the gravitational interaction of the Earth, the Moon and the Sun are factors that largely determine the history of the development of our planet. It is known that tidal friction gradually slows down the rotation of the Earth. Any redistribution of masses inside the Earth immediately responds to its axial rotation. With the concentration of masses near the axis of rotation, its speed increases, otherwise, on the contrary, it decreases. These transitions often occur abruptly, abruptly, and although fluctuations in the Earth's axial velocity are negligible, they can cause significant stresses in the solid body of the Earth, which leads to ruptures and displacements of individual sections of the earth's crust.

The hypothesis developed in the USSR since 1954 by VV Belousov assigns the decisive role of the evolution of the Earth to the process of deep differentiation of the material composing the Earth. In fact, the Earth, which was initially homogeneous in general, over several billion years of its existence, stratified into geospheres and acquired two more shells that the primordial planet did not have - the hydrosphere and the atmosphere. It is obvious that the differentiation of terrestrial matter continues, the stratification of the most ancient geospheres - the core and the mantle - is still taking place. Differentiation is accompanied by the movement of huge masses of matter, the emergence of convective currents, the redistribution of heating sources - radioactive elements, now concentrated in the upper layers of the Earth. The result of differentiation is the lithosphere with its relief, although the process of formation of the main forms of relief - oceanic depressions and continental protrusions, and most importantly, their distribution on the surface cannot be considered complete. The consequence of the differentiation of matter was the convective currents of matter in the shells of the Earth, to which many researchers attached great importance, especially in the 30s of our century.

All three hypotheses developed separately, although they did not exclude each other. However, as the Soviet geologist G. N. Katterfeld rightly noted, not only is a reasonable synthesis of all three hypotheses possible, but also necessary, and therefore, in his opinion, the most methodologically correct and scientifically most promising is the generalized rotational-pulsation hypothesis based on on the dialectical unity of pulsations of the volume and shape of the earth's ellipsoid and taking into account the processes of deep differentiation of the Earth's matter.

It was from such generalized positions that G. N. Katterfeld expounded the hypothetical history of the Earth - a controversial history, not sufficiently substantiated in everything, but certainly interesting. The author believes that some of its provisions deserve attention, so let's dwell on it in more detail. Let us only note the main thing in this scheme, referring those interested in details to the books of G. N. Katterfeld and A. M. Ryabchikov.

It has long been known that the northern and southern hemispheres of our planet are not symmetrical. In the northern hemisphere, continental masses are mainly concentrated, in the southern - the water mass of the oceans. We can assume that one hemisphere is like a mirror image of the other. Is it by chance?

If the Earth were to acquire its current shape under the influence of only gravitational and centrifugal forces, this shape would not be asymmetric. Therefore, G. N. Katterfeld believes that in this case special "asymmetric" forces of an unknown nature manifested themselves. Note that the difference between the radii directed from the center of the Earth to the north and south poles is only 100 m. But this difference was recorded by measurements from artificial satellites of the Earth, it is real, and therefore must be somehow explained. The claim that the Earth's asymmetry is caused by "asymmetric" forces is, of course, no more than a tautology. As is known, in 1958, Professor N. A. Kozyrev tried to explain the asymmetry of the Earth by the action of forces born by the “course of time” itself. However, this unusual idea, which formed the basis of the "causal mechanics" of N. A. Kozyrev, later received neither recognition nor sufficient justification. In a word, the riddle of the asymmetry of the Earth still remains unresolved.

Direct measurements using ultra-precise quartz clocks have shown that the Earth's rotation is uneven. For example, a day in March is 0.0025 seconds longer than in August, which means that every year the Earth's rotation speeds up by August and slows down by March. This is partly due to seasonal changes in atmospheric circulation, and partly to other causes. In general, changes in the speed of the Earth's axial rotation are caused by various reasons: tides, uneven compression of the Earth's outer geospheres, redistribution of masses in it, the impact of solar corpuscular flows, and a number of other, sometimes not yet fully understood, physical processes. All this does not pass without a trace for the Earth. According to G. N. Katterfeld, if we analyzed all those small pulsating and rotational effects that have accumulated over a long geological history and have been inconspicuously imprinted on the face of the Earth as a result of constant and seemingly insignificant interactions, we would be amazed at their significance. Let's try to concretely imagine (according to G. N. Katterfeld) how fluctuations in the volume and speed of rotation of the Earth affected its appearance.

The radius of the Earth, according to G. N. Katterfeld, decreases on average by 5 cm per century (According to P. N. Kropotkin, by 3 mm.). This gravitational contraction (consider the size of the Earth) releases huge energy - 17x10 23 J! Since only part of this energy is dissipated into the world space, the Earth heats up, which means that each time the contraction is temporarily replaced by a much smaller expansion of the warming Earth. This is the physical background of the intermittent, pulsating contraction of the Earth's radius. The same part of the thermal energy that is not radiated by the Earth into the world space becomes the latent heat of physical and chemical transformations in the bowels of the Earth. These transformations, ultimately, contribute to the compaction of the internal parts of the Earth and, therefore, to a decrease in its volume.

Calculations show that under the influence of tidal braking, the rate of the Earth's axial rotation slows down and, as a result, the polar compression of the Earth decreases. It would seem that this process should be expressed in the subsidence of the equatorial "tumor" of the Earth and the uplift of the polar regions. As a result of such a process, the distribution of land and water on Earth should have turned out to be very peculiar: the equator is surrounded by a continuous water strip of the ocean, and two huge antipodal continents occupy the space from the poles to temperate latitudes. If, on the contrary, the polar compression were to increase for a long time, the equatorial zone would eventually be filled by a continuous continental belt, and oceans would extend from temperate latitudes to the poles.

Rice. 10. Evolution of continents according to A. Wegener. a - 200 million years ago; b - 60 million years ago; c - 1 million years ago (about the reasons for the drift of the continents)

In fact, there is neither one nor the other. But it is remarkable that the first of these theoretical schemes (prolonged decrease in polar compression) corresponds to the northern hemisphere, and the second to the southern hemisphere. This, apparently, can be explained by the fact that in the process of a general very slow decrease in the Earth's compression, the northern hemisphere is ahead of the southern one. This means that here, too, an asymmetric process is observed, caused by some unknown forces. But this hypothetical asymmetry well explains the most common feature of the face of the Earth - the uneven distribution of water and land. Of course, the scheme of the evolution of the Earth's surface, proposed by G. N. Katterfeld, is nothing more than a hypothesis. It does not take into account the differentiation of its substance and other factors that have continued throughout the history of the Earth, and therefore cannot be considered as something proven and final.

At one time, a sensation was caused by the hypothesis of continental drift, proposed in 1912 by the German scientist A. Wegener (Fig. 10). A. Wegener himself stubbornly defended this idea, although his hypothesis seemed absurd to the usual way of thinking of geologists. After the death of her main, and then almost the only, protector, they forgot about her, and it seemed that nothing was able to resurrect her. However, only in the 1950s, in connection with new works on paleomagnetism, the ideas of A. Wegener seemed to have received experimental confirmation. Recently, many works have appeared that promote the hypothesis of continental drift. Perhaps, indeed, A. Wegener's hypothesis deserves serious scientific analysis?

A. Wegener drew attention to the seemingly random features of the coastlines of some continents. The eastern, "Brazilian" ledge of the South American mainland fits tightly into the depression of the Gulf of Guinea. The docking turns out to be especially dense if instead of the coastline we take the outline of the shelf - the continental shelf.

In 1970, American researchers using electronic computers studied the "combination" of some continents over tens of thousands of kilometers. The result was amazing: in general, more than 93% of the shelf boundaries, i.e., the marginal part of the continents, were well combined. Africa and South America, Antarctica and Africa joined best of all, Hindustan, Australia and Antarctica adjoined each other somewhat worse. It seemed that once Africa and America were a single whole. Then, for some unclear reason, the primary continent split into two parts, and these parts, spreading apart, formed modern Africa and South America, as well as the Atlantic Ocean that separated them.

A. Wegener himself went further. He assumed that once all the current land was a single and only mainland - Pangea. From all sides it was washed by the boundless World Ocean, named by A. Wegener Panthalasse. Under the influence of some forces, possibly related to the rotation of the Earth, about 200 million years ago, Pangea split into several parts, like a gigantic ice floe. Its fragments - the current continents - have dispersed in different directions and continue their extremely slow drift to this day. Drifting to the west, the American continent, on its front, western edge, experienced the resistance of the underlying layer of the Earth, along which the continents float. Naturally, he crumpled and formed the gigantic mountain ranges of the Cordillera and the Andes. On the rear side, small pieces, for example, the Antilles, separated from the floating mainland, lagging behind. Some fragments of Pangea floated, turning like ice floes in a turbulent stream. This seems to be how Japan behaved.

The followers of A. Wegener (Du Toit, 1937, and others) believed that initially there were two continents - Laurasia, which split into North America and Eurasia, and Gondwana, which broke up into South America, Africa, Australia and Antarctica. Supporters of this version of A. Wegener's hypothesis cite many facts that seem to confirm the reality of Laurasia and Gondwana. In particular, they refer to the similarity of the geological structures of different continents, the commonality of their flora and fauna.

In recent years, the hypothesis of the expansion of the ocean floor has come to the aid of the continental drift hypothesis. In it, the most important role was assigned to rifts - giant planetary faults confined to the axial parts of the mid-ocean ridges. It is assumed that the material of the upper mantle is squeezed out from the depths through the rifts, which in the process of physicochemical differentiation turns into basaltic lavas. Each new portion of this substance presses on the rocks that arose earlier and pushes them away from the rift. This pressure is transmitted further, and thus, the ocean floor gradually expands, pushing the continents apart. Supporters of this hypothesis suggested that chronological facts should also correspond to this point of view: the youngest rocks should be confined to rift zones, and with distance from the rifts to the sides at points located on the same line perpendicular to the axis of the rifts and at equal distances, the rocks must be older and of the same age.

Initially, this seemed to be the case, but on one of its voyages, the American research vessel Glomar Challenger discovered between Newfoundland and the Bay of Biscay that at such conjugated points west of the mid-Atlantic rift, the age of bottom rocks is 155 million years. years, and to the east - 110 million years. Samples aged 200 million years were taken in the rift itself. Other contradictions in this hypothesis were also pointed out. If the continents move apart as a result of the expansion of the seabed, then, for example, the action of the mid-Atlantic rift should push Africa to the east, and the material coming from the Indian Ocean's median rift to the west. The question is: where will poor Africa go? But in the same position are all the continents. And further. There are ore-forming zones on the globe, for example, along the eastern margin of Asia. Such zones develop over hundreds of millions - up to a billion years. Their geochemistry remains unchanged. And this means that for the entire period of existence of these zones, they had the same source of matter, which could not be if the continents moved.

Later, the modern concept of mobilism was developed. According to this concept, the earth's crust is divided into large plates. These plates can cover areas of both continental and oceanic crust, but there are also entirely "oceanic" plates. Such slabs build up along the rift at one end, and sink under the edge of the neighboring slab along the other end. For example, the African-Indian plate, located between the mid-ridges of the Atlantic and Indian oceans, is constantly growing in the west, while plunging under the Indian Ocean plate in the east.

Rice. 11. Lithospheric plates

The long disputes between the mobilists and their opponents, the "fixists", ended in the end with the victory of the former. In the 60s of the current century, the dynamics of the lithosphere became clear to everyone. Huge lithospheric plates are in extremely slow but constant motion. Rising from the mantle in the zones of mid-ocean ridges, they sink back into the mantle in the zones of deep-sea trenches. The earth's continents are, as it were, soldered into the creeping plates of the oceanic crust and move along with them. This set of lithospheric plates “floating” along the mantle, in fact, constitutes the lithosphere. The main strength of the moving plate is the ongoing process of differentiation of the stratification of the earth's interior. There are several lithospheric plates (Fig. 11). The arrows indicate the directions of their movements. No matter how small the speed of movement of lithospheric plates (centimeters per year), over long periods of time, the appearance of the Earth changes unrecognizably. Modern geographic globes record what is today, but will never be repeated in the future.



The theme of the "end of the world", some kind of global catastrophe on a planetary scale that will destroy humanity, constantly excites the minds of people. True, throughout the known history of mankind, all forecasts of the “end of the world” turned out to be simple horror stories, which gives reason for some to smile condescendingly when they hear about the threat of a global catastrophe and be sure that this time everything will work out. But can a catastrophe of such a magnitude actually occur that will destroy humanity? Unfortunately, perhaps, and confirmation of this is the history of our planet. This post is about the most grandiose cataclysms that befell our planet in the past.

1. Collision of Earth and Theia

As you know, the Earth has a rather large satellite - the Moon, and for many years astronomers have tried to explain its origin. After expeditions to the Moon and analysis of the lunar soil, it was found that the composition of the lunar rocks is very close to that of the earth, which means that once the Moon and the Earth were probably one. How then could the moon have arisen? At the moment, scientists consider the only plausible hypothesis to be the collision of the Earth with another planet, as a result of which part of the earth's rock was thrown into orbit and served as material for the formation of the moon. This event occurred, according to calculations, in the initial period of the existence of the solar system, about 4.5 billion years ago, and the planet itself that collided with the Earth (it was given the name Theia) should have been no smaller than Mars in size. As a result of this long-standing catastrophe, no one was hurt, because the Earth was still lifeless, but if a cataclysm of this magnitude were repeated today, humanity would have absolutely no chance of salvation.

2. Global glaciation

Today there is a lot of talk about the dangers of global climate change, but if you look into the past of the Earth, the changes that the climate underwent were really catastrophic. So, according to modern concepts, in the history of the Earth there were several global glaciations, when glaciers covered almost the entire surface of the planet, up to the equator. One of the geological periods in the history of the Earth even received the name "cryogeny". It lasted about 215 million years, starting 850 million years ago and ending about 635 million years ago.

The reasons for the onset of global glaciation are unclear. It could be provoked, for example, by the entry of the solar system into a dust cloud, a decrease in the amount of greenhouse gases in the atmosphere, etc. But, as computer models show, if glaciers capture too much territory, descending to the tropics, the further glaciation process becomes self-sustaining. This happens because snow and ice absorb heat very poorly, reflecting most of the sun's rays, which means that the more territory is covered with ice, the colder the climate becomes.

At the peak of global glaciation, the thickness of glaciers on land reached 6 km, and the ocean level fell by 1 km. It was as cold at the equator as it is now in Antarctica. It was a very severe test for life. Most organisms died out, but some were able to adapt. Today, while exploring Antarctica and the Arctic, scientists are discovering amazing life forms that exist in very cold climates. For example, numerous microscopic algae and invertebrate animals—worms, crustaceans, etc.—live in the Arctic and Antarctic ice. Life has also been discovered in the subglacial lakes of Antarctica, which are isolated from the surface by a layer of ice hundreds of meters thick.

It is believed that sharply increased volcanic activity was able to interrupt the long global glaciation. Awakened volcanoes released a huge amount of greenhouse gases into the atmosphere and covered the ice with a layer of black ash. As a result, the Earth became warmer and the global glaciation ended.

3. Great Permian extinction

The mass extinction of living organisms that occurred at the end of the Permian period (about 250 million years ago) was called great for a reason. Indeed, at this time, in a very short period of time - some tens of thousands of years, 95% of all types of living organisms disappeared! The mass extinction affected everyone - both terrestrial inhabitants, and marine, and animals, and plants, and vertebrates, and insects. The scale of the disaster was truly monstrous. But what happened?

The reason for this was an unprecedented increase in geological activity. Today, earthquakes and volcanic eruptions can cause significant damage and claim thousands of lives, but no one perceives them as a global threat. But 250 million years ago, something incredible began. As a result of powerful tectonic processes, faults in the earth's crust occurred, from which a huge amount of lava began to flow. The scale of the eruptions can be judged by the fact that most of the territory of Siberia - millions of square kilometers - was filled with lava!

Siberian traps - formed by flowing lava

Massive eruptions released into the atmosphere a huge amount of greenhouse and acidic (i.e., forming acids in combination with water) gases. The result was, firstly, dramatic global warming, and secondly, acid rain. Much of the landmass has turned into deserts, while the oceans have become acidic, heated, and depleted of much of their oxygen. Entire classes of living organisms died out from the consequences of the catastrophe, and it took about 30 million years to restore the biosphere.

Trilobites and pareiasaurs - these animals that once inhabited the Earth, one of many that completely died out during the great Permian extinction

4 Dinosaur Extinction

The extinction of dinosaurs, which occurred about 65 million years ago, is not the largest, but the most famous mass extinction of species. It completely changed the face of the animal world of the planet.

There are many hypotheses about the extinction of dinosaurs, the most popular of which connects this extinction with the fall of a large asteroid or comet (about 5-10 km in diameter), the crater from which was found on the Yucatan Peninsula and coincides in age with the extinction. True, not all scientists believe that it was the fall of the asteroid that was the only reason for the extinction of the dinosaurs, but there were others, but, one way or another, the fall of a large asteroid clearly could not but harm large reptiles.

The release of a large amount of dust into the atmosphere, to which smoke from fires was added, closed the surface of the Earth from the sun's rays for quite a considerable time and led to a sharp cooling. It would be extremely problematic for giant cold-blooded animals to survive in such conditions, but small warm-blooded mammals living in burrows, in large numbers, were able to survive the cataclysm.

The future generation will consider the 80-90s of the last century as the period that determined the development of astronomy in the 21st century. This is true, because it was in those years that scientific results were obtained, which, in terms of significance, are difficult to find analogues in the history of astronomy of the 20th century. That period is also significant in that astronomers began to seriously raise the question of the future of our Earth, not only in epistemological terms, but also to ensure the safety of all mankind. Unfortunately, the range of opinions, especially in the mass media, about the possible danger is very wide - from frankly panicky to completely ignoring the problem. Therefore, we will try to give a brief summary of the actual state of affairs.

GENERAL CONCEPTS OF THE ORIGIN OF THE EARTH AND THE SUN

Astronomers have not yet developed a final opinion on the detailed processes of the formation of the solar system, since none of the hypotheses is able to explain many of its features. But what almost all astronomers are unanimous about is that a star and its planetary system are formed from a single gas and dust cloud, and this process can be explained by the known laws of physics. It is assumed that this cloud had rotation. In the center of such a cloud, 4.7 billion years ago, a condensation formed, which, due to the law of universal gravitation, began to contract and attract surrounding particles to itself. When this condensation reaches a certain mass, high temperatures and pressures are created in the center, which leads to the release of enormous energy due to thermonuclear reactions of the conversion of four protons into a helium atom 4H + He. At this moment, the object enters a responsible stage of its life - the stage of a star.

The rotation of the cloud leads to the appearance of a rotating disk around the star. In those areas where the average distance between the particles of the disk is small, they collide, which causes the formation of so-called planetesimals about 1 km in size, and then planets around the star. The formation of the Earth took about 50 million years. Part of the non-condensed matter of the disk (solid and ice particles) could fall onto the surface of the planets during movement. For the Earth, this process lasted approximately 700 thousand years. As a result, the mass of the Earth constantly increased and, most importantly, was replenished with water and organic compounds. About 2 billion years ago, primitive plants began to appear, and 1 billion years later, the current nitrogen-oxygen atmosphere formed. About 200 million years ago, the simplest mammals appeared, 4 million years ago, Australopithecus stood on its feet, and 35 thousand years ago, the direct ancestor of Homo sapiens appeared.

For us, the main thing is the following: can the described scheme be refuted or confirmed by observations, if we check, in particular, such consequences of it:
a) protoplanetary disks should be found near young stars;
b) near stars that are at a later stage of development, it is necessary to detect planetary systems;
c) since not all the matter of the protoplanetary disk condenses into large bodies, especially at the periphery of the disk, there must be remnants of such matter in the solar system.
If this article had been written 30 years ago, it would have been difficult for the author to find such confirmation, since the telescopes and receiving equipment that existed at that time could not register the objects mentioned above because of their low brightness. And only in the last decade, thanks to the use of space telescopes, increasing the accuracy of astronomical measurements, most of the predictions of the theory have been fully confirmed.

protoplanetary disks. Since there is dust in such disks, an infrared excess of color should be observed in the radiation of the disk and the star. Such excesses have been found in several stars, in particular, in the bright star of the northern hemisphere, Vega. For some stars, the Space Telescope. E. Hubble obtained images of such disks, for example, for many stars in the Orion Nebula. The number of discovered disks around stars is constantly growing.

Planets around stars. To observe planets near stars by traditional methods, it is necessary to create telescopes of very large diameters - about a hundred meters. The creation of such telescopes is a completely hopeless business, both from a technical and financial point of view. Therefore, astronomers found a way out by developing indirect methods for detecting planets. It is known that two gravitationally bound bodies (a star and a planet) revolve around a common center of gravity. Such a motion of the star can only be established on the basis of extremely precise methods of observation. Such methods based on modern technology have been developed in the most recent years, and for acquaintance with them we refer the reader to the article by A.M. Cherepashchuk.

About 700 stars were immediately observed using these methods. The result exceeded the best expectations. By the end of January 2001, 63 planets around 50 stars had been discovered. Basic information about the planets can be found in the article.

Discovery of transplutonian comets. In 1993, objects 1992QB and 1993FW were discovered, located outside the orbit of Pluto. This discovery could have big implications, as it confirmed the existence of the far periphery of our solar system at a distance of more than 50 AU. the so-called Kuiper belt and further the Oort clouds, where hundreds of millions of comets have been concentrated, preserved for 4.5 billion years and are the remnants of that substance that could not condense into planets.

EARTH'S ASTRONOMIC PAST

After its formation, the Earth has come a long way of development. It was found that the natural course of its development was disturbed due to certain geological, climatic or biological reasons, leading to the disappearance of vegetation and wildlife. The causes of most of these crises are explained by scientists as oceanic phenomena (decrease in the salinity of the oceans, a change in the chemical composition towards an increase in toxic elements in the ocean waters, etc.) and terrestrial phenomena (greenhouse effect, volcanic activity, etc.). In the 50s of the XX century, attempts were made to explain some crises by astronomical factors - on the basis of many astronomical phenomena recorded by observers and described in historical documents. It should be noted that over a period of 2000 years (from 200 BC to 1800 AD), 1124 important astronomical facts were recorded in various sources, some of which can be associated with crisis phenomena.

Currently, there is an opinion that the crisis that took place 65 million years ago, when reef corals disappeared and dinosaurs died out, was caused by the collision of a large celestial body (asteroid) with the Earth. For a long time, astronomers and geologists have been looking for confirmation of this phenomenon, until they discovered a large crater on the Yucatan Peninsula in Mexico with a diameter of 300 km. Calculations showed that to create such a crater, an explosion equivalent to 50 million tons of TNT was needed (or 2500 atomic bombs that fell on Hiroshima; an explosion of 1 ton of TNT corresponds to the release of energy of 4 "1016 erg). Such energy could be released in a collision with an asteroid 10 km in size and having a speed of 15 km / s. This explosion raised dust into the atmosphere, which completely eclipsed the Sun, which led to a decrease in the temperature of the Earth, followed by the extinction of life. Estimation of the age of this crater led to a figure of 65 million years, which coincides with the moment of one of the biotic crises in the development of the Earth.

Further, in 1994, astronomers theoretically predicted, and then observed, the collision of the comet Shoemaker-Levy with Jupiter. Have there been similar collisions of comets with the Earth? According to the American scientist Masse, there have been similar collisions over the past 6 thousand years. Especially catastrophic was the fall of a comet into the ocean near Antarctica in 2802 BC.

Thus, all of the above leads to the following conclusions:
* astronomers have reliable confirmation of existing ideas about the past development of the solar system;
* this allows us to quite definitely judge the future of the solar system. In particular, some of the described phenomena raise a serious question: does the Cosmos pose a danger to the future of our Earth?

EARTH'S ASTRONOMIC FUTURE

It is clear from the foregoing that the greatest troubles for humanity can be caused by moving small celestial bodies. Consider how big the chance of a collision is.

Asteroids (or minor planets). The main characteristics of these objects are as follows: masses 1 g-1023 g, dimensions 1 cm-1000 km, average speeds when approaching the Earth 10 km/s, kinetic energy of objects 5 "109-5" 1030 erg.

Astronomers have found that in the solar system the number of asteroids with a diameter of more than 1 km is about 30 thousand, smaller asteroids are much larger - about a hundred million. Most of the asteroids rotate in orbits located between the orbits of Mars and Jupiter, forming the so-called asteroid belt. These asteroids, of course, do not carry the danger of a collision with the Earth.

But several thousand asteroids with a diameter of more than 1 km have orbits that cross the Earth's orbit (Fig. 2). Astronomers explain the appearance of such asteroids by the formation of instability zones in the asteroid belt. Let's give some examples.

The asteroid Icarus in 1968 approached the Earth at a distance of 6.36 million km. If Icarus had collided with the Earth, then there would have been an explosion equivalent to the explosion of 100 Mt of TNT, or the explosion of several atomic bombs. Another asteroid - 1991BA with a diameter of 9 m passed on January 17, 1991 at a distance of only 170 thousand km from the Earth. It is easy to calculate that the time difference between the Earth and the asteroid passing the intersection point is only 1.5 hours. Asteroid 1994XM1 on December 9, 1994 flew over the territory of Russia at a distance of only 105 thousand km.

There are also examples of asteroids falling to the Earth's surface. There is a certain opinion that in 1908 in Siberia there was a collision of an asteroid with a diameter of 90 m, followed by an explosion equivalent to an explosion of about 20 Mt of TNT. If this body had fallen three hours later, it would have destroyed Moscow.

Using data on impact craters on the surface of the Earth, planets and their satellites, astronomers came up with the following estimates:
* collisions with large asteroids, which can lead to global catastrophes in the development of the Earth, occur approximately once every 500 thousand years;
* collisions with small asteroids occur more often (every 300 years), but the consequences of collisions are only local.

Based on the orbits of already studied asteroids, astronomers have compiled a list of potentially dangerous known asteroids that will orbit at a critical distance from Earth before the end of the 21st century. This list includes about 300 objects whose orbits intersect the Earth's orbit. The closest passage at a distance of 880 thousand km is expected near the asteroid Hathor in October 2086.

In general, astronomers believe that the number of dangerous and yet undiscovered dangerous asteroids is approximately 2500. It is these mysterious wanderers that will constitute the main danger to the future of the Earth.

Comets. Their typical characteristics are as follows: mass 1014-1019 g, core size 10 km, tail size 10 million km, speed 10 km/s, kinetic energy 1023-1028 erg.

Comets differ from asteroids in their structure: if asteroids are solid blocks, then comet nuclei are accumulations of "dirty ice". In addition, comets, unlike asteroids, have extended gaseous tails. But the passage of the Earth through such tails does not pose any danger due to their low density. For example, during the passage of the Earth through the tail of Halley's comet on May 18, 1910, no anomalies were noticed on the Earth's surface.

But the problem of the danger of a collision with the nucleus of a comet became very relevant after 1994 in connection with the fall of various parts of the comet Shoemaker-Levy on the surface of Jupiter. The resulting explosions were estimated to be equivalent to the explosion of 60,000 Mt of TNT, which is equal to the explosion of several million atomic bombs dropped on Hiroshima.

Astronomers have calculated that comets pass between the Earth and the Moon every 100 years, and some fall to Earth about once every 100,000 years. It has also been estimated that during the average human lifetime the probability of hitting a comet is 1/10,000.

Studies by astronomers have shown that over the past 2400 years there have been 20 close (less than 15 million km) passages of 18 comets. Comet Lexel's closest passage at a distance of 2.3 million km was in July 1770. It is estimated that three comets studied will have close passages in the next 30 years. But, fortunately, the minimum distances will not be so dangerous - more than 9 million km.

It should be borne in mind that so far we have been talking about known comets. It was said above about the discovery of transplutonian comets. These comets can fly into the inner regions of the solar system, in particular, intersecting with the Earth's orbit. It is possible that these not yet discovered comets can carry danger.

ASTROPHYSICAL HAZARD

But, alas, not only collisions carry global consequences for the Earth. Let us briefly mention only two possible dangers emanating from deep space.

The future life of the Sun. Astrophysicists can calculate all the stages of a star's life. According to calculations, for example, in 7.9 billion years the Sun will turn into a red supergiant, increasing its size by 170 times, while absorbing Mercury. It is easy to calculate that in our sky the Sun will look like a red ball, occupying half of the celestial sphere. As a result, the temperature on the Earth will rise, intense evaporation of the oceans will begin, which will increase the opacity of the atmosphere, which will cause the so-called greenhouse effect: the Earth will become very hot.

Further inflation of the Sun will lead to the fact that the Earth will actually rotate inside the Sun. According to this scenario, the Earth is destined for a not very pleasant fate. The friction of the Earth and the Sun's gas particles will decrease the Earth's orbital velocity, causing the Earth to spiral down toward the central regions of the Sun. This will lead to the fact that the Sun will heat the Earth to extremely high temperatures, turning it into red-hot rocks with no signs of water in the oceans and, of course, life.

Supernova explosions. Other stars, which have more mass than the Sun, live a little differently. At a certain stage, they can explode, releasing monstrous energy in the process (astronomers call this process a supernova explosion). It was found that there are two reasons for such outbreaks.

At the last stage of a star's life, nuclear reactions stop and it turns into a dense object - a white dwarf (WD). But if there is a neighboring star near the BC, then the matter of this star can flow onto the BC. At the same time, thermonuclear reactions begin again on the surface of the BC, releasing enormous energy. This flare mechanism works for SNI-type supernovae.

Another type of supernovae (SNII) is explained by the evolution of a star with a mass of more than ten solar masses. Thermonuclear reactions are accompanied by the transformation of hydrogen into heavier elements. At each stage, energy is released that heats the star. The theory predicts that when the formation of iron is reached, the sequence of reactions stops. The inner part of the iron core is compressed within a second. As the interior of the star reaches nuclear densities, it bounces off the center, colliding with the still-collapsed outer core. The resulting shock wave carries the entire star. The energy released in 1 second will be monstrous, equal to the energy emitted by 100 suns in 109 years.

Some astronomers (I.S. Shklovsky and F.N. Krasovsky) believed that such an explosion could have occurred near a star close to the Sun 65 million years ago. According to the scenario described by these authors, the ejected matter after the explosion reached the Earth after several thousand years. It contained relativistic particles, which, when entering the Earth's atmosphere, caused an intense stream of secondary cosmic particles, which, upon reaching the Earth's surface, increased radioactivity by 100 times. This would inevitably lead to mutations in living organisms with their subsequent disappearance.

The probability of the global influence of such an explosion on the Earth in the future depends, firstly, on how often supernova explosions occur in our Galaxy, and, secondly, on the critical distance r to the star. Based on the observed data, the well-known stellar statistician S. Van der Berg came to the conclusion that for every 1 billion years in the volume of our Galaxy of 1 kpc3, an average of 150,000 supernova explosions occur. If we take r = 10 light-years as the critical distance to the star, then it is easy to obtain that in order for one flash to occur in a volume of such a radius, a time of 60 billion years is needed. This value is much greater than the age of the Earth. Thus, it is unlikely that biotic crises can be explained by the outbreak phenomenon. In the future, such an outbreak is also not very likely. However, it should still be noted that the above reasoning is based on average estimates. For example, we note that the star Betelgeuse in the constellation Orion can flare up in several thousand years. Another star - h Car will erupt in 10,000 years. Fortunately, the distances to them are quite large - 650 and 10,000 light years.

Gamma flares. About 30 years ago, using satellite observations, astronomers established that at various points in the celestial sphere, objects are observed that flare in the gamma range (Fig. 3) with a flare duration from fractions of a second to several minutes. The latest estimates of the distances to these objects indicate that they are located far beyond our Galaxy. This means that the radiation energy in the gamma range of these objects is fantastically high - about 1050-1052 erg.

The most common hypothesis about the flare mechanism proposed by S.I. Blinnikov et al., is a hypothesis about the merger of two neutron stars - the last stage in the life of a binary system consisting of two massive stars. Calculations by astrophysicists have shown that such a merger releases energy equivalent to the radiation energy of a billion galaxies like ours. You can read more about these objects in .

But such pairs of neutron stars can exist not only at a cosmological distance, but also inside our Galaxy. Astrophysicists have calculated that in our galaxy, one pair merger occurs every 2-3 million years. The presence of three such pairs has now been reliably established. If one of them (PSR B2127 + 11C) starts to merge, then the consequences for the Earth will be very serious, however, in more than 220 million years. First of all, strong gamma radiation will destroy the ozone layer of the Earth's atmosphere. But the main thing is that during the flash, energetic cosmic particles are formed, which, having reached the Earth's atmosphere, will create secondary cosmic particles. These particles will reach the surface of the Earth and even deeper, turning it into a radioactive graveyard.

All the above facts raise the main question.

WHAT TO DO?

The answer to this question in relation to small bodies of the solar system should contain two aspects:
astronomical - it is necessary to discover in advance unknown and potentially dangerous objects at the greatest possible distance from the Earth, calculate their exact orbits and predict the moment of possible danger;
technical - it is necessary to make decisions and implement them in order to avoid a possible collision.

To solve the astronomical part, a network of telescopes with a diameter of about 2 m is currently being created. This will make it possible to detect approximately 90% of dangerous asteroids at a distance of up to 200 million km and 35% of dangerous comets at a distance of up to 500 million km. Since the speed of movement of objects is about 10 km/s, this will allow us to have a reserve of several months for making a decision.

The accuracy of theoretical calculations of the orbits and moments of collisions is primarily determined by the number of established positions in the sky of dangerous objects. This problem can be solved using the above network of telescopes. Further, when calculating the orbits, it is necessary to carefully take into account the perturbations in the motion of celestial bodies caused by the influence of all the planets of the solar system. This problem has already been solved by astronomers with high accuracy.

The most difficult thing to take into account are non-gravitational forces that affect the movement of objects. These forces are due to many reasons. Asteroids and comets move in the material environment (interplanetary plasma, electromagnetic field), while experiencing resistance. They are also affected by light pressure forces from the Sun. As a result, bodies can deviate from a purely Keplerian orbit, that is, calculated taking into account only the gravitational interaction of the body with the Sun (and planets).

The technical aspect of the problem is more complex, and there are essentially three options so far. One involves the destruction of a dangerous object by sending a missile with a nuclear bomb at it. Calculations have shown that an explosion of 4 "1019 ergs is needed to destroy an asteroid with a diameter of 1 km. But this project can bring unpredictable environmental consequences associated with the clogging of space with nuclear waste.

There is a variant of an attempt to deviate the movement of an object from its natural orbit by giving it an additional impulse, say, by landing a rocket with a powerful power plant on its surface. Today, both such projects are still difficult to implement: for this it is necessary to have rockets with larger masses and higher speeds than are currently available. But in principle, this is not at all a hopeless case for the technology of the 21st century.

The third option is based on the use of non-gravitational effects in the motion of celestial bodies. For example, comet nuclei can be deflected from their original orbit using the sublimation method, the essence of which is as follows. The orbit of a comet is to some extent determined by the forces of light pressure from the Sun, which causes the formation of a tail. If the dust surface of the core is destroyed or weakened, then
the increased outflow of matter from the nucleus can give the comet an impulse in the right direction.

Although the astrophysical danger awaits the Earth in the distant future, there are already quite interesting ideas to avoid it. Some of them even seem fantastic. In one version, it is proposed to create a shield around the Earth using the substance of asteroids or the Moon. For example, the mass of the asteroid Ceres is quite sufficient to create a disk about the Earth with a thickness of 1 km. It may well shield particle flows and radiation from supernovae and gamma-ray bursts.

In conclusion, we note that there are no grounds for apocalyptic fatalism. Humanity has already reached a sufficiently high level of science and technology to foresee danger. Moreover, it is already on the verge of creating an effective defense system. One can only hope that humanity, realizing the impending danger, will make efforts to further develop science and the necessary technology, instead of resolving internal conflicts, thoughtlessly spending their intelligence and financial resources.

LITERATURE
1. Surdin V.G. Birth of stars. M.: URSS, 1997. 207 p.
2. Cherepashchuk A.M. Planets in the Universe // Soros Educational Journal. 2001. No. 4. S. 76-82.
3. Kippenhan R. 100 Billion Suns: Birth, Life and Death of Stars. M.: Mir, 1990. 293 p.
4. Lipunov V.M. "Military secret" of astrophysics // Soros Educational Journal. 1998. No. 5. S. 83-89.
5. Kurt V.G. Experimental methods for studying cosmic gamma-ray bursts // Ibid. 1998. No. 6. S. 71-76.
6. Near-Earth astronomy (space debris). M.: Kosmosinform, 1998. 277 p.
Reviewer of the article A.M. Cherepashchuk

* * *
Nail Abdullovich Sakhibullin, Doctor of Physical and Mathematical Sciences, Professor, Head. Department of Astronomy, Kazan State University, Director of the Astronomical Observatory named after A.I. V.P. Engelhardt. RAS Prize Winner. Active member of the Academy of Sciences of Tatarstan. Area of ​​scientific interests - astrophysics, physics of stellar atmospheres. Author of 80 scientific publications and one monograph.

In science fiction, alien planets are inhabited by bizarre creatures that live in unusual and strange environments. Compared to the fantasies of science fiction, the old Earth looks boring and modest. But if we look into the past, we will see that our beloved planet was once no less bizarre.

Before there were forests of trees, there were forests of mushrooms

400 million years ago, you would not have seen the forests familiar to us on Earth, but this does not mean that no one occupied this niche. Before the appearance of trees, the Earth was covered with "forests" of 8-meter mushrooms.

In 1859, scientists in Canada began digging up fossils that they initially thought were ancient tree trunks, but it wasn't until 2007 that the "trees" were actually mushrooms. The organisms, called prototaxites, grew up to 8 meters in height and made the landscape look more like a picture from the video game "Super Mario" than modern Earth.

The habitats of prototaxites are not limited to Canada. Fossil hunters have found giant mushrooms all over the world, suggesting that it was probably the largest form of life on earth at a time when the entire animal kingdom consisted only of worms and microbes.

Later, plants appeared that began to develop and consume the same resources that were necessary for the growth of prototaxites. The plants won the resource contest and the fungi shrunk to a size that allowed them to live off the remains of rotting plants.

The ancient world was inhabited by giant insects

If you're dreaming of traveling to the Carboniferous, about 358 million years ago, you'd better stock up on a flamethrower and a few cyanide tablets (just in case the flamethrower runs out of gas).

At that time, thanks to the explosive growth of plant life, the oxygen content in the atmosphere was 15 percent higher than it is now. And this had an incredible impact on some species of the animal world, which began to develop rapidly.

Today's insects are only limited in size by the amount of oxygen they can take in. Atmospheric oxygen levels of 20 to 21 percent means we jump on the table at the sight of a 4cm cockroach. In the Carboniferous, you'd have to contend with dog-sized scorpions, anaconda-sized caterpillars, and dragonflies that might eat an albatross for dinner.

Combined with the fact that predators such as birds and reptiles appeared millions of years later, environmental conditions allowed insects to grow to fantastic sizes. But a world with such a high oxygen content has another side effect - constant fires.

If the environment is warm and there is a lot of oxygen, as it was in the Carboniferous period, even a spark is not needed to start a fire. As a result, fires were a constant occurrence on Earth, and there is speculation that the skies were constantly misty brown with smoke and flames. Try to imagine it: a bunch of giant flaming insects are rushing right at you from a blinding fog. It looks like the Resident Evil movie was historically accurate.

The planet was purple

If during a flight into space you are sucked into a black hole and thrown back 3-4 billion years ago, you will see a fabulous sight. One hypothesis says that the planet was then purple.

The reason land on Earth looks green from above is our plants, which are green because of the chlorophyll they contain. But plants didn't always use chlorophyll. In the earliest stages of life, they used various chemical compounds based on retinol, which has a purple color.

Scientists believe that for some time there were so many purple organisms on Earth that from space it seemed not green, but purple.

Earth had two moons

Can you imagine that two moons revolve around the Earth? I cant. This is one of the craziest theories that scientists consider quite possible. Scientists, one day, looked at the moon and realized that it has two sides: the light side, which we see, and the dark side, which no one from Earth can see. The crust on the dark side is much thicker and has a more varied landscape.

For a long time, scientists have wondered how the two halves could be so different in geology. One theory suggests that at one time, in the distant past, for about 80 million years, the Earth had two satellites. Gravity then brought them closer together and they crashed into each other (apparently while intoxicated).

Due to the fall of huge asteroids, there were iron rains

Hollywood films about the end of the world have convinced us that an asteroid impact can put an end to all of humanity. But life is much stronger than some space rocks. In fact, there was a time on our planet when ancient life forms were daily attacked by meteorites, and not just large ones, but huge ones - more than the one that later killed out the dinosaurs. About 4.5 - 3.5 billion years ago, the Earth was young and was constantly bombarded with stones, some of which were comparable in size to minor planets. Planet-changing events occurred with the regularity of rain.

And the rains, at that time, were from molten iron.

Due to the constant meteorite impacts, enough heat was released to vaporize metals such as iron, gold, platinum and they rose into the atmosphere as metal vapors. But everything that went up had to come down later, and therefore the young Earth knew well what a metallic rain was.

However, the primary forms of life treated these disasters as if they were a daily occurrence. You wake up, have breakfast, wander around for a while, go down to the bunker to survive another global catastrophe, then have dinner and go to bed. This partly helps to look at human problems from a completely different point of view.

It is possible that life originated on Mars

Many people ask: “Why do scientists spend so much money looking for life on Mars instead of creating sex robots or hoverboards for us, or better, sex robots on hoverboards?” One of the reasons for this is that of everything we know about life, it seems most likely that it originated on Mars and not on Earth.

Billions of years ago, the environment on Mars was much more favorable than on Earth. Life requires a large amount of oxygen, but on Earth it was relatively scarce. But on Mars it was in abundance. In addition, life required the presence of such elements as molybdenum and boron, which are still very abundant on Mars.

Therefore, some scientists believe that life first originated on Mars, and then some very nimble microorganisms left the Martian surface and hitchhiked on meteorites to the Earth.
So we could all be aliens from Mars.