One of the mysteries of the Earth, along with the emergence of Life on it and the extinction of dinosaurs at the end of the Cretaceous period, is - Great Glaciations.
It is believed that glaciations are repeated on Earth regularly every 180-200 million years. Traces of glaciation are known in deposits that are billions and hundreds of millions of years ago - in the Cambrian, in the Carboniferous, in the Triassic-Permian. The fact that they could be, "say" the so-called tillites, breeds very similar to moraine last one, to be exact. last glaciations. These are the remains of ancient deposits of glaciers, consisting of a clay mass with inclusions of large and small boulders scratched during movement (hatched).
Separate layers tillites, found even in equatorial Africa, can reach power of tens and even hundreds of meters!
Signs of glaciation have been found on different continents - in Australia, South America, Africa and India which is used by scientists to reconstruction of paleocontinents and are often cited as evidence theories of plate tectonics.
Traces of ancient glaciations indicate that continental-scale glaciations- this is not at all a random phenomenon, it is a natural phenomenon that occurs under certain conditions.
The last of the ice ages began almost a million years ago, in the Quaternary time, or the Quaternary period, the Pleistocene was marked by the extensive distribution of glaciers - Great Glaciation of the Earth.
Under thick, many kilometers of ice covers were the northern part of the North American continent - the North American ice sheet, reaching a thickness of up to 3.5 km and extending to about 38 ° north latitude and a significant part of Europe, on which (ice cover up to 2.5-3 km thick) . On the territory of Russia, the glacier descended in two huge tongues along the ancient valleys of the Dnieper and Don.Partially, the glaciation also covered Siberia - there was mainly the so-called "mountain-valley glaciation", when glaciers did not cover the entire space with a powerful cover, but were only in the mountains and foothill valleys, which is associated with a sharply continental climate and low temperatures in Eastern Siberia . But almost all Western Siberia, due to the fact that the damming of the rivers took place, and their flow into the Arctic Ocean stopped, it turned out to be under water, and was a huge sea-lake.
In the Southern Hemisphere, under the ice, as now, was the entire Antarctic continent.
During the period of maximum distribution of Quaternary glaciation, glaciers covered over 40 million km 2–about a quarter of the entire surface of the continents.
Having reached the greatest development about 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually decrease, as the glacial period was not continuous throughout the Quaternary period.
There are geological, paleobotanical and other evidence that glaciers disappeared several times, replaced by epochs. interglacial when the climate was even warmer than today. However, the warm epochs were replaced by cold spells, and the glaciers spread again.
Now we live, apparently, at the end of the fourth epoch of the Quaternary glaciation.
But in Antarctica, glaciation arose millions of years before the time when glaciers appeared in North America and Europe. In addition to climatic conditions, this was facilitated by the high mainland that existed here for a long time. By the way, now, due to the fact that the thickness of the glacier of Antarctica is huge, the continental bed of the "ice continent" is in some places below sea level ...
Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and reappeared, the Antarctic ice sheet has changed little in its size. The maximum glaciation of Antarctica was only one and a half times greater than the modern one in terms of volume, and not much more in area.
Now about the hypotheses ... There are hundreds, if not thousands, of hypotheses why glaciations occur, and whether they were at all!
Usually put forward the following main scientific hypotheses:
- Volcanic eruptions, leading to a decrease in the transparency of the atmosphere and cooling throughout the Earth;
- Epochs of orogeny (mountain building);
- Reducing the amount of carbon dioxide in the atmosphere, which reduces the "greenhouse effect" and leads to cooling;
- The cyclical activity of the Sun;
- Changes in the position of the Earth relative to the Sun.
But, nevertheless, the causes of glaciation have not been finally clarified!
It is assumed, for example, that glaciation begins when, with an increase in the distance between the Earth and the Sun, around which it rotates in a slightly elongated orbit, the number of solar heat received by our planet, i.e. Glaciation occurs when the Earth passes the point in its orbit that is farthest from the Sun.
However, astronomers believe that changes in the number of solar radiation falling on Earth is not enough to start an ice age. Apparently, fluctuations in the activity of the Sun itself also matter, which is a periodic, cyclic process, and changes every 11-12 years, with a cycle of 2-3 years and 5-6 years. And the largest cycles of activity, as established by the Soviet geographer A.V. Shnitnikov - approximately 1800-2000 years.
There is also a hypothesis that the emergence of glaciers is associated with certain parts of the Universe through which our solar system passes, moving with the entire Galaxy, either filled with gas, or “clouds” of cosmic dust. And it is likely that "space winter" on Earth occurs when the globe is at the point furthest from the center of our Galaxy, where there are accumulations of "cosmic dust" and gas.
It should be noted that usually periods of warming always “go” before cooling epochs, and there is, for example, a hypothesis that the Arctic Ocean, due to warming, is sometimes completely freed from ice (by the way, this is happening now), increased evaporation from the surface of the ocean , currents of humid air are directed to the polar regions of America and Eurasia, and snow falls over the cold surface of the Earth, which does not have time to melt in a short and cold summer. This is how ice sheets form on the continents.
But when, as a result of the transformation of part of the water into ice, the level of the World Ocean drops by tens of meters, warm Atlantic Ocean ceases to communicate with the Arctic Ocean, and it is again gradually covered with ice, evaporation from its surface abruptly stops, there is less and less snow on the continents, the “feeding” of glaciers is deteriorating, and the ice sheets begin to melt, and the level of the World Ocean rises again. And again the Arctic Ocean connects with the Atlantic, and again the ice cover began to gradually disappear, i.e. the cycle of development of the next glaciation begins anew.
Yes, all these hypotheses quite possible, but so far none of them can be confirmed by serious scientific facts.
Therefore, one of the main, fundamental hypotheses is climate change on the Earth itself, which is associated with the above hypotheses.
But it is quite possible that the processes of glaciation are associated with the combined impact of various natural factors, which could act jointly and replace each other, and it is important that, having begun, glaciations, like “wound clocks”, are already developing independently, according to their own laws, sometimes even “ignoring” some climatic conditions and patterns.
And the ice age that began in the Northern Hemisphere about 1 million years back, not finished yet, and we, as already mentioned, live in a warmer period of time, in interglacial.
Throughout the epoch of the Great Glaciations of the Earth, the ice either receded or advanced again. On the territory of both America and Europe, there were, apparently, four global ice ages, between which there were relatively warm periods.
But the complete retreat of the ice occurred only about 20 - 25 thousand years ago, but in some areas the ice lingered even longer. The glacier retreated from the area of modern St. Petersburg only 16 thousand years ago, and in some places in the North small remnants of the ancient glaciation have survived to this day.
Note that modern glaciers cannot be compared with the ancient glaciation of our planet - they occupy only about 15 million square meters. km, i.e. less than one thirtieth earth's surface.
How can you determine whether there was a glaciation in a given place on the Earth or not? This is usually quite easy to determine by the peculiar forms of geographical relief and rocks.
Large accumulations of huge boulders, pebbles, boulders, sands and clays are often found in the fields and forests of Russia. They usually lie directly on the surface, but they can also be seen in the cliffs of ravines and in the slopes of river valleys.
By the way, one of the first who tried to explain how these deposits were formed was the outstanding geographer and anarchist theorist, Prince Peter Alekseevich Kropotkin. In his work "Investigations on the Ice Age" (1876), he argued that the territory of Russia was once covered by huge ice fields.
If we look at the physical and geographical map of European Russia, then in the location of hills, hills, basins and valleys of large rivers, we can notice some patterns. So, for example, Leningrad and Novgorod region from the south and east, as it were, limited Valdai Upland, which has the form of an arc. This is exactly the line where, in the distant past, a huge glacier, advancing from the north, stopped.
To the southeast of the Valdai Upland is the slightly winding Smolensk-Moscow Upland, stretching from Smolensk to Pereslavl-Zalessky. This is another of the boundaries of the distribution of sheet glaciers.
On the West Siberian Plain numerous hilly winding uplands are also visible - "manes", also evidence of the activity of ancient glaciers, more precisely glacial waters. Many traces of stops of moving glaciers flowing down the mountain slopes into large basins have been found in Central and Eastern Siberia.
It is difficult to imagine ice several kilometers thick on the site of the current cities, rivers and lakes, but, nevertheless, the glacial plateaus were not inferior in height to the Urals, the Carpathians or the Scandinavian mountains. These gigantic and, moreover, mobile masses of ice influenced the entire natural environment - relief, landscapes, river flow, soils, vegetation and wildlife.
It should be noted that in Europe and the European part of Russia from the geological epochs preceding the Quaternary period - the Paleogene (66-25 million years) and the Neogene (25-1.8 million years) practically no rocks were preserved, they were completely eroded and redeposited during the Quaternary, or as it is often called, Pleistocene.
Glaciers originated and moved from Scandinavia, the Kola Peninsula, the Polar Urals (Pai-Khoi) and the islands of the Arctic Ocean. And almost all the geological deposits that we see on the territory of Moscow are moraine, more precisely moraine loams, sands of various origins (water-glacial, lake, river), huge boulders, as well as cover loams - all this is evidence of the powerful impact of the glacier.
On the territory of Moscow, traces of three glaciations can be distinguished (although there are many more of them - different researchers distinguish from 5 to several dozen periods of ice advances and retreats):
- Okskoe (about 1 million years ago),
- Dnieper (about 300 thousand years ago),
- Moscow (about 150 thousand years ago).
Valdai the glacier (disappeared only 10-12 thousand years ago) “did not reach Moscow”, and the deposits of this period are characterized by water-glacial (fluvio-glacial) deposits - mainly the sands of the Meshcherskaya lowland.
And the names of the glaciers themselves correspond to the names of those places to which the glaciers reached - to the Oka, the Dnieper and the Don, the Moscow River, Valdai, etc.
Since the thickness of the glaciers reached almost 3 km, one can imagine what a colossal work he did! Some elevations and hills on the territory of Moscow and the Moscow region are powerful (up to 100 meters!) Deposits that the glacier “brought”.
The best known, for example Klinsko-Dmitrovskaya moraine ridge, separate hills on the territory of Moscow ( Vorobyovy Gory and Teplostan Upland). Huge boulders weighing up to several tons (for example, the Maiden's Stone in Kolomenskoye) are also the result of the work of the glacier.
Glaciers smoothed out uneven terrain: they destroyed hills and ridges, and the resulting rock fragments filled depressions - river valleys and lake basins, transferring huge masses of stone fragments over a distance of more than 2 thousand km.
However, huge masses of ice (considering its colossal thickness) pressed so hard on the underlying rocks that even the strongest of them could not stand it and collapsed.
Their fragments were frozen into the body of a moving glacier and, like emery, scratched rocks composed of granites, gneisses, sandstones and other rocks for tens of thousands of years, making depressions in them. Until now, numerous glacial furrows, "scars" and glacial polishing on granite rocks, as well as long hollows in the earth's crust, subsequently occupied by lakes and swamps, have been preserved. An example is the countless depressions of the lakes of Karelia and the Kola Peninsula.
But glaciers did not plow out all the rocks on their way. The destruction was mainly those areas where the ice sheets originated, grew, reached a thickness of more than 3 km and from where they began their movement. The main center of glaciation in Europe was Fennoscandia, which included the Scandinavian mountains, the plateaus of the Kola Peninsula, as well as the plateaus and plains of Finland and Karelia.
Along the way, the ice was saturated with fragments of destroyed rocks, and they gradually accumulated both inside the glacier and under it. When the ice melted, masses of debris, sand and clay remained on the surface. This process was especially active when the movement of the glacier stopped and the melting of its fragments began.
At the edge of glaciers, as a rule, water flows arose, moving along the surface of the ice, in the body of the glacier and under the ice layer. Gradually, they merged, forming whole rivers, which, over thousands of years, formed narrow valleys and washed away a lot of clastic material.
As already mentioned, the forms of glacial relief are very diverse. For moraine plains many ridges and ridges are characteristic, indicating the stops of moving ice and the main form of relief among them are shafts of terminal moraines, usually these are low arched ridges composed of sand and clay with an admixture of boulders and pebbles. The depressions between the ridges are often occupied by lakes. Sometimes among the moraine plains one can see outcasts- blocks hundreds of meters in size and weighing tens of tons, giant pieces of the glacier bed, transferred by it over great distances.
Glaciers often blocked the flow of rivers and near such "dams" huge lakes arose, filling the depressions of river valleys and depressions, which often changed the direction of river flow. And although such lakes existed for a relatively short time (from a thousand to three thousand years), they managed to accumulate on their bottom lake clays, layered precipitation, counting the layers of which, one can clearly distinguish the periods of winter and summer, as well as how many years these precipitations accumulated.
In the era of the last Valdai glaciation arose Upper Volga glacial lakes(Mologo-Sheksninskoe, Tverskoe, Verkhne-Molozhskoe, etc.). At first, their waters had a flow to the southwest, but with the retreat of the glacier, they were able to flow to the north. Traces of the Mologo-Sheksninskoe Lake remained in the form of terraces and coastlines at an altitude of about 100 m.
There are very numerous traces of ancient glaciers in the mountains of Siberia, the Urals, Far East. As a result of ancient glaciation, 135-280 thousand years ago, sharp peaks of mountains appeared - "gendarmes" in Altai, in the Sayans, the Baikal and Transbaikalia, in the Stanovoy Highlands. The so-called "reticulate type of glaciation" prevailed here, i.e. if one could look from a bird's eye view, one could see how ice-free plateaus and mountain peaks rise against the background of glaciers.
It should be noted that during the periods of glacial epochs, rather large ice massifs were located on part of the territory of Siberia, for example, on Severnaya Zemlya archipelago, in the Byrranga mountains (Taimyr Peninsula), as well as on the Putorana Plateau in northern Siberia.
Extensive mountain-valley glaciation was 270-310 thousand years ago Verkhoyansk Range, Okhotsk-Kolyma Highlands and in the mountains of Chukotka. These areas are considered glaciation centers of Siberia.
Traces of these glaciations - numerous bowl-shaped depressions of mountain peaks - circuses or karts, huge moraine shafts and lake plains in place of melted ice.
In the mountains, as well as on the plains, lakes arose near ice dams, periodically the lakes overflowed, and giant masses of water rushed at incredible speed through low watersheds into neighboring valleys, crashing into them and forming huge canyons and gorges. For example, in Altai, in the Chuya-Kurai depression, “giant ripples”, “boilers of drilling”, gorges and canyons, huge outlier blocks, “dry waterfalls” and other traces of water streams escaping from ancient lakes “only - just "12-14 thousand years ago.
"Intruding" from the north on the plains of Northern Eurasia, the ice sheets either penetrated far to the south along the depressions of the relief, or stopped at some obstacles, for example, hills.
Probably, it is not yet possible to determine exactly which of the glaciations was the “greatest”, however, it is known, for example, that the Valdai glacier was sharply inferior in area to the Dnieper glacier.
The landscapes at the borders of the sheet glaciers also differed. So, in the Oka epoch of glaciation (500-400 thousand years ago), to the south of them there was a strip of Arctic deserts about 700 km wide - from the Carpathians in the west to the Verkhoyansk Range in the east. Even further, 400-450 km to the south, stretched cold forest-steppe, where only such unpretentious trees as larches, birches and pines could grow. And only at the latitude of the Northern Black Sea region and Eastern Kazakhstan did comparatively warm steppes and semi-deserts begin.
In the era of the Dnieper glaciation, the glaciers were much larger. Tundra-steppe (dry tundra) with a very harsh climate stretched along the edge of the ice cover. The average annual temperature approached minus 6°C (for comparison: in the Moscow region, the average annual temperature is currently about +2.5°C).
The open space of the tundra, where in winter there was little snow and severe frosts, cracked, forming the so-called "permafrost polygons", which in plan resemble a wedge in shape. They are called "ice wedges", and in Siberia they often reach a height of ten meters! Traces of these "ice wedges" in ancient glacial deposits "speak" of the harsh climate. Traces of permafrost, or cryogenic impact, are also visible in the sands, these are often disturbed, as if “torn” layers, often with a high content of iron minerals.
Water-glacial deposits with traces of cryogenic impact
The last "Great Glaciation" has been studied for over 100 years. Many decades of hard work of outstanding researchers were spent on collecting data on its distribution on the plains and in the mountains, on mapping terminal moraine complexes and traces of glacier-dammed lakes, glacial scars, drumlins, and “hilly moraine” areas.
True, there are researchers who generally deny the ancient glaciations, and consider the glacial theory to be erroneous. In their opinion, there was no glaciation at all, but there was “a cold sea on which icebergs floated”, and all glacial deposits are just bottom sediments of this shallow sea!
Other researchers, "recognizing the general validity of the theory of glaciations", however, doubt the correctness of the conclusion about the grandiose scales of the glaciations of the past, and the conclusion about the ice sheets that leaned on the polar continental shelves is especially strong distrust, they believe that there were "small ice caps of the Arctic archipelagos”, “bare tundra” or “cold seas”, and in North America, where the largest “Laurentian ice sheet” in the Northern Hemisphere has long been restored, there were only “groups of glaciers merged at the bases of domes”.
For Northern Eurasia, these researchers recognize only the Scandinavian ice sheet and isolated "ice caps" of the Polar Urals, Taimyr and the Putorana Plateau, and in the mountains of temperate latitudes and Siberia - only valley glaciers.
And some scientists, on the contrary, “reconstruct” “giant ice sheets” in Siberia, which are not inferior in size and structure to the Antarctic.
As we have already noted, in the Southern Hemisphere, the Antarctic ice sheet extended to the entire continent, including its underwater margins, in particular, the regions of the Ross and Weddell seas.
The maximum height of the Antarctic ice sheet was 4 km, i.e. was close to modern (now about 3.5 km), the area of ice increased to almost 17 million square kilometers, and the total volume of ice reached 35-36 million cubic kilometers.
Two more large ice sheets were in South America and New Zealand.
The Patagonian Ice Sheet was located in the Patagonian Andes, their foothills and on the adjacent continental shelf. Today it is reminded of by the picturesque fjord relief of the Chilean coast and the residual ice sheets of the Andes.
"South Alpine Complex" New Zealand- was a reduced copy of the Patagonian. It had the same shape and also advanced to the shelf, on the coast it developed a system of similar fjords.
In the Northern Hemisphere, during periods of maximum glaciation, we would see huge arctic ice sheet resulting from the union North American and Eurasian covers into a single glacial system, and an important role was played by floating ice shelves, especially the Central Arctic ice shelf, which covered the entire deep-water part of the Arctic Ocean.
The largest elements of the Arctic ice sheet were the Laurentian Shield North America and the Kara Shield of Arctic Eurasia, they had the form of giant plano-convex domes. The center of the first of them was located over the southwestern part of the Hudson Bay, the peak rose to a height of more than 3 km, and its eastern edge extended to the outer edge of the continental shelf.
The Kara ice sheet occupied the entire area of the modern Barents and Kara Seas, its center lay over the Kara Sea, and the southern marginal zone covered the entire north of the Russian Plain, Western and Central Siberia.
Of the other elements of the Arctic cover, the East Siberian Ice Sheet which spread on the shelves of the Laptev, East Siberian and Chukchi seas and was larger than the Greenland ice sheet. He left traces in the form of large glaciodislocations New Siberian Islands and the Tiksi region, are also associated with grandiose glacial-erosion forms of Wrangel Island and the Chukotka Peninsula.
So, the last ice sheet of the Northern Hemisphere consisted of more than a dozen large ice sheets and many smaller ones, as well as of the ice shelves that united them, floating in the deep ocean.
The periods of time in which glaciers disappeared, or were reduced by 80-90%, are called interglacials. The landscapes freed from ice in a relatively warm climate were transformed: the tundra retreated to the northern coast of Eurasia, and the taiga and broad-leaved forests, forest-steppes and steppes occupied a position close to the modern one.
Thus, over the past million years, the nature of Northern Eurasia and North America has repeatedly changed its appearance.
Boulders, crushed stone and sand, frozen into the bottom layers of a moving glacier, acting as a giant "file", smoothed, polished, scratched granites and gneisses, and peculiar strata of boulder loams and sands formed under the ice, differing high density associated with the impact of glacial load - the main, or bottom moraine.
Since the dimensions of the glacier are determined balance between the amount of snow that falls on it annually, which turns into firn, and then into ice, and what does not have time to melt and evaporate during the warm seasons, then as the climate warms, the edges of the glaciers recede to new, “equilibrium boundaries”. The end parts of the glacial tongues stop moving and gradually melt, and the boulders, sand and loam included in the ice are released, forming a shaft that repeats the outlines of the glacier - terminal moraine; the other part of the clastic material (mainly sand and clay particles) is carried out by melt water flows and is deposited around in the form fluvioglacial sand plains (zandrov).
Similar flows also act in the depths of glaciers, filling cracks and intraglacial caverns with fluvioglacial material. After the melting of glacial tongues with such filled voids on the earth's surface, chaotic heaps of hills of various shapes and compositions remain on top of the melted bottom moraine: ovoid (when viewed from above) drumlins, elongated like railway embankments (along the axis of the glacier and perpendicular to the terminal moraines) ozes and irregular shape kamy.
All these forms of the glacial landscape are very clearly represented in North America: the boundary of ancient glaciation is marked here by a terminal moraine ridge with heights of up to fifty meters, stretching across the entire continent from its eastern coast to its western one. To the north of this "Great Ice Wall" glacial deposits are represented mainly by moraine, and to the south of it - by a "cloak" of fluvioglacial sands and pebbles.
As for the territory of the European part of Russia, four epochs of glaciation have been identified, and for Central Europe, four glacial epochs have also been identified, named after the corresponding alpine rivers - gunz, mindel, riss and wurm, and in North America Nebraska, Kansas, Illinois and Wisconsin glaciations.
Climate periglacial(surrounding the glacier) territories was cold and dry, which is fully confirmed by paleontological data. In these landscapes, a very specific fauna appears with a combination of cryophilic (cold-loving) and xerophilic (dry-loving) plants – tundra-steppe.
Now similar natural areas, similar to periglacial ones, have been preserved in the form of so-called relic steppes- islands among the taiga and forest-tundra landscape, for example, the so-called alasy Yakutia, the southern slopes of the mountains of northeastern Siberia and Alaska, as well as the cold, arid highlands of Central Asia.
tundrosteppe differed in that it the herbaceous layer was formed mainly not by mosses (as in the tundra), but by grasses, and it was here that formed cryophilic version herbaceous vegetation with a very high biomass of grazing ungulates and predators - the so-called "mammoth fauna".
In its composition were bizarrely mixed different kinds animals as characteristic tundra – reindeer, caribou, musk ox, lemmings, for steppes - saiga, horse, camel, bison, ground squirrels, as well as mammoths and woolly rhinos, saber-toothed tiger - smilodon, and giant hyena.
It should be noted that many climatic changes were repeated as if "in miniature" in the memory of mankind. These are the so-called "Little Ice Ages" and "Interglacials".
For example, during the so-called "Little Ice Age" from 1450 to 1850, glaciers advanced everywhere, and their size exceeded modern ones (snow cover appeared, for example, in the mountains of Ethiopia, where it is not now).
And in the preceding "Little Ice Age" Atlantic optimum(900-1300) glaciers, on the contrary, decreased, and the climate was noticeably milder than the current one. Recall that it was at that time that the Vikings called Greenland the “Green Land”, and even settled it, and also reached the coast of North America and the island of Newfoundland on their boats. And the Novgorod merchants-Ushkuiniki passed through the "Northern Sea Route" to the Gulf of Ob, founding the city of Mangazeya there.
And the last retreat of the glaciers, which began over 10 thousand years ago, is well remembered by people, hence the legends about the Flood, so a huge amount of melt water rushed down to the south, rains and floods became frequent.
In the distant past, the growth of glaciers occurred in epochs with low air temperature and increased humidity, the same conditions developed in the last centuries of the last era, and in the middle of the last millennium.
And about 2.5 thousand years ago, a significant cooling of the climate began, the Arctic islands were covered with glaciers, in the countries of the Mediterranean and the Black Sea at the turn of the eras, the climate was colder and more humid than now.
In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, cluttered mountain passes with ice and destroyed some high-lying villages. It was during this era that glaciers in the Caucasus became sharply activated and grew.
But by the end of the 1st millennium, climate warming began again, mountain glaciers retreated in the Alps, the Caucasus, Scandinavia and Iceland.
The climate began to seriously change again only in the 14th century, glaciers began to grow rapidly in Greenland, the summer thawing of the soil became more and more short-lived, and by the end of the century permafrost was firmly established here.
From the end of the 15th century, the growth of glaciers began in many mountainous countries and polar regions, and after the relatively warm 16th century, severe centuries came, and were called the Little Ice Age. In the south of Europe, severe and long winters often repeated, in 1621 and 1669 the Bosporus froze, and in 1709 the Adriatic Sea froze off the coast. But the "Little Ice Age" ended in the second half of the 19th century and a relatively warm era began, which continues to this day.
Note that the warming of the 20th century is especially pronounced in the polar latitudes of the Northern Hemisphere, and fluctuations in glacial systems are characterized by the percentage of advancing, stationary and retreating glaciers.
For example, for the Alps there are data covering the entire past century. If the proportion of advancing alpine glaciers in the 40-50s of the XX century was close to zero, then in the mid-60s of the XX century, about 30% of the surveyed glaciers advanced here, and in the late 70s of the XX century - 65-70%.
Their similar state indicates that the anthropogenic (technogenic) increase in the content of carbon dioxide, methane and other gases and aerosols in the atmosphere in the 20th century did not affect the normal course of global atmospheric and glacial processes. However, at the end of the last, twentieth century, glaciers began to recede everywhere in the mountains, and the ice of Greenland began to melt, which is associated with climate warming, and which especially intensified in the 1990s.
It is known that the increased amount of technogenic emissions of carbon dioxide, methane, freon and various aerosols into the atmosphere seems to be helping to reduce solar radiation. In this regard, “voices” appeared, first of journalists, then of politicians, and then of scientists about the beginning of a “new ice age”. Ecologists "sounded the alarm", fearing "the coming anthropogenic warming" due to the constant growth of carbon dioxide and other impurities in the atmosphere.
Yes, it is well known that an increase in CO 2 leads to an increase in the amount of retained heat and thereby increases the air temperature near the Earth's surface, forming the notorious "greenhouse effect".
Some other gases of technogenic origin have the same effect: freons, nitrogen oxides and sulfur oxides, methane, ammonia. But, nevertheless, far from all carbon dioxide remains in the atmosphere: 50-60% of industrial CO 2 emissions end up in the ocean, where they are quickly assimilated by animals (corals in the first place), and of course, assimilated by plants–remember the process of photosynthesis: plants absorb carbon dioxide and release oxygen! Those. the more carbon dioxide - the better, the higher the percentage of oxygen in the atmosphere! By the way, this has already happened in the history of the Earth, in the Carboniferous period ... Therefore, even a multiple increase in the concentration of CO 2 in the atmosphere cannot lead to the same multiple increase in temperature, since there is a certain natural control mechanism that sharply slows down the greenhouse effect at high concentrations of CO 2.
So all the numerous "scientific hypotheses" about " greenhouse effect”, “Rise in the level of the oceans”, “changes in the course of the Gulf Stream”, and naturally “the coming Apocalypse” are mostly imposed on us “from above”, by politicians, incompetent scientists, illiterate journalists, or simply science swindlers. The more you intimidate the population, the easier it is to sell goods and manage ...
But in fact, a normal natural process is taking place - one stage, one climatic epoch is replaced by another, and there is nothing strange in this ... And the fact that natural disasters occur, and that there are supposedly more of them - tornadoes, floods, etc. - so another 100-200 years ago, vast areas of the Earth were simply uninhabited! And now there are more than 7 billion people, and they often live where exactly floods and tornadoes are possible - along the banks of rivers and oceans, in the deserts of America! Moreover, remember that natural disasters have always been, and even ruined entire civilizations!
And as for the opinions of scientists, which both politicians and journalists like to refer to so much ... Back in 1983, American sociologists Randall Collins and Sal Restivo wrote in plain text in their famous article “Pirates and Politicians in Mathematics”: “... There is no fixed set of norms that guide the behavior of scientists. Only the activity of scientists (and other types of intellectuals related to them) is unchanged, aimed at acquiring wealth and fame, as well as gaining the opportunity to control the flow of ideas and impose their own ideas on others ... The ideals of science do not predetermine scientific behavior, but arise from the struggle for individual success in various conditions competition …".
And a little more about science ... Various large companies often provide grants for so-called "research" in certain areas, but the question arises - how competent is the person conducting the research in this area? Why was he chosen out of hundreds of scientists?
And if a certain scientist, a “certain organization”, for example, orders “some research on the safety of nuclear energy”, then it goes without saying that this scientist will be forced to “listen” to the customer, since he has “quite certain interests”, and it is understandable that he, most likely, will “adjust” “his conclusions” for the customer, since the main question is already not a question of scientific research–what does the customer want to get, what result. And if the result of the customer not satisfied, then this scientist will no longer be invited, and not in any "serious project", i.e. "monetary", he will no longer participate, as they will invite another scientist, more "compliant" ... Much, of course, depends on the citizenship, and professionalism, and reputation as a scientist ... But let's not forget how much they "receive" in Russia scientists... Yes, in the world, in Europe and in the USA, a scientist lives mainly on grants... And any scientist also "wants to eat."
In addition, the data and opinions of one scientist, albeit a major specialist in his field, are not a fact! But if the research is confirmed by some scientific groups, institutes, laboratories, t only then can research be worthy of serious attention.
Unless of course these "groups", "institutes" or "laboratories" were not funded by the customer of this study or project ...
A.A. Kazdym,
candidate of geological and mineralogical sciences, member of MOIP
Climatic changes were most clearly expressed in periodically advancing ice ages, which had a significant impact on the transformation of the land surface under the body of the glacier, water bodies and biological objects that are in the zone of influence of the glacier.
According to the latest scientific data, the duration of glacial eras on Earth is at least a third of the entire time of its evolution over the past 2.5 billion years. And if we take into account the long initial phases of the origin of glaciation and its gradual degradation, then the epochs of glaciation will take almost as much time as warm, ice-free conditions. The last of the ice ages began almost a million years ago, in the Quaternary, and was marked by an extensive spread of glaciers - the Great Glaciation of the Earth. The northern part of the North American continent, a significant part of Europe, and possibly Siberia as well, were under thick ice sheets. In the Southern Hemisphere, under the ice, as now, was the entire Antarctic continent.
The main causes of glaciation are:
space;
astronomical;
geographical.
Cosmic Cause Groups:
change in the amount of heat on the Earth due to the passage of the solar system 1 time/186 million years through the cold zones of the Galaxy;
change in the amount of heat received by the Earth due to a decrease in solar activity.
Astronomical groups of causes:
change in the position of the poles;
the inclination of the earth's axis to the plane of the ecliptic;
change in the eccentricity of the Earth's orbit.
Geological and geographical groups of causes:
climate change and the amount of carbon dioxide in the atmosphere (increase in carbon dioxide - warming; decrease - cooling);
change in the direction of ocean and air currents;
intensive process of mountain building.
Conditions for the manifestation of glaciation on Earth include:
snowfall in the form of precipitation at low temperatures with its accumulation as a material for building up a glacier;
negative temperatures in areas where there are no glaciations;
periods of intense volcanism due to the huge amount of ash emitted by volcanoes, which leads to a sharp decrease in the flow of heat (sun rays) to the earth's surface and causes global temperature decreases by 1.5-2ºС.
The oldest glaciation is the Proterozoic (2300-2000 million years ago) in South Africa, North America, and Western Australia. In Canada, 12 km of sedimentary rocks were deposited, in which three thick strata of glacial origin are distinguished.
Established ancient glaciations (Fig. 23):
on the border of the Cambrian-Proterozoic (about 600 million years ago);
late Ordovician (about 400 million years ago);
Permian and Carboniferous periods (about 300 million years ago).
The duration of ice ages is tens to hundreds of thousands of years.
Rice. 23. Geochronological scale of geological epochs and ancient glaciations
During the period of maximum distribution of the Quaternary glaciation, glaciers covered over 40 million km 2 - about a quarter of the entire surface of the continents. The largest in the Northern Hemisphere was the North American Ice Sheet, reaching a thickness of 3.5 km. Under the ice sheet up to 2.5 km thick was the whole of northern Europe. Having reached the greatest development 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink.
Before the Neogene period, the entire Earth had an even warm climate - in the region of the islands of Svalbard and Franz Josef Land (according to paleobotanical finds of subtropical plants) at that time there were subtropics.
Reasons for the cooling of the climate:
the formation of mountain ranges (Cordillera, Andes), which isolated the Arctic region from warm currents and winds (uplift of mountains by 1 km - cooling by 6ºС);
creation of a cold microclimate in the Arctic region;
cessation of heat supply to the Arctic region from warm equatorial regions.
By the end of the Neogene period, North and South America joined, which created obstacles for the free flow of ocean waters, as a result of which:
equatorial waters turned the current to the north;
the warm waters of the Gulf Stream, cooling sharply in northern waters, created a steam effect;
drop has increased dramatically a large number precipitation in the form of rain and snow;
a decrease in temperature by 5-6ºС led to the glaciation of vast territories (North America, Europe);
a new period of glaciation began, lasting about 300 thousand years (the frequency of glacier-interglacial periods from the end of the Neogene to the Anthropogen (4 glaciations) is 100 thousand years).
Glaciation was not continuous throughout the Quaternary period. There is geological, paleobotanical and other evidence that during this time the glaciers completely disappeared at least three times, giving way to interglacial epochs when the climate was warmer than the present. However, these warm epochs were replaced by cooling periods, and glaciers spread again. At present, the Earth is at the end of the fourth era of the Quaternary glaciation, and, according to geological forecasts, our descendants in a few hundred-thousand years will again find themselves in the conditions of an ice age, and not warming.
The Quaternary glaciation of Antarctica developed along a different path. It arose many millions of years before the time when glaciers appeared in North America and Europe. In addition to climatic conditions, this was facilitated by the high mainland that existed here for a long time. Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and reappeared, the Antarctic ice sheet has changed little in its size. The maximum glaciation of Antarctica was only one and a half times greater than the current one in terms of volume and not much more in area.
The culmination of the last ice age on Earth was 21-17 thousand years ago (Fig. 24), when the volume of ice increased to approximately 100 million km3. In Antarctica, glaciation at that time captured the entire continental shelf. The volume of ice in the ice sheet, apparently, reached 40 million km 3, that is, it was about 40% more than its present volume. The boundary of the pack ice shifted to the north by approximately 10°. In the Northern Hemisphere 20 thousand years ago, a giant Panarctic ancient ice sheet was formed, uniting the Eurasian, Greenland, Laurentian and a number of smaller shields, as well as extensive floating ice shelves. The total volume of the shield exceeded 50 million km3, and the level of the World Ocean dropped by at least 125m.
The degradation of the Panarctic cover began 17 thousand years ago with the destruction of the ice shelves that were part of it. After that, the "marine" parts of the Eurasian and North American ice sheets, which lost their stability, began to disintegrate catastrophically. The disintegration of the glaciation occurred in just a few thousand years (Fig. 25).
Huge masses of water flowed from the edge of the ice sheets at that time, giant dammed lakes arose, and their breakthroughs were many times larger than modern ones. In nature, spontaneous processes dominated, immeasurably more active than now. This led to a significant renewal of the natural environment, a partial change in the animal and plant world, and the beginning of human dominance on Earth.
The last retreat of the glaciers, which began over 14 thousand years ago, remains in the memory of people. Apparently, it is the process of melting glaciers and raising the water level in the ocean with extensive flooding of territories that is described in the Bible as a global flood.
12 thousand years ago, the Holocene began - the modern geological epoch. The air temperature in temperate latitudes increased by 6° compared to the cold Late Pleistocene. Glaciation took on modern dimensions.
In the historical epoch - approximately for 3 thousand years - the advance of glaciers occurred in separate centuries with low air temperature and increased humidity and were called small ice ages. The same conditions developed in the last centuries of the last era and in the middle of the last millennium. About 2.5 thousand years ago, a significant cooling of the climate began. The Arctic islands were covered with glaciers, in the countries of the Mediterranean and the Black Sea on the verge of a new era, the climate was colder and wetter than now. In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, cluttered mountain passes with ice and destroyed some high-lying villages. This epoch is marked by a major advance of the Caucasian glaciers.
The climate at the turn of the 1st and 2nd millennium AD was quite different. Warmer conditions and the lack of ice in the northern seas allowed the navigators of Northern Europe to penetrate far north. From 870, the colonization of Iceland began, where at that time there were fewer glaciers than now.
In the 10th century, the Normans, led by Eirik the Red, discovered the southern tip of a huge island, the shores of which were overgrown with thick grass and tall shrubs, they founded the first European colony here, and this land was called Greenland, or “green land” (which is by no means now say about the harsh lands of modern Greenland).
By the end of the 1st millennium, mountain glaciers in the Alps, the Caucasus, Scandinavia, and Iceland also retreated strongly.
The climate began to seriously change again in the 14th century. Glaciers began to advance in Greenland, the summer thawing of soils became more and more short-lived, and by the end of the century, permafrost was firmly established here. The ice cover of the northern seas increased, and attempts made in subsequent centuries to reach Greenland by the usual route ended in failure.
From the end of the 15th century, the advance of glaciers began in many mountainous countries and polar regions. After the relatively warm 16th century, harsh centuries came, which were called the Little Ice Age. In the south of Europe, severe and long winters often repeated, in 1621 and 1669 the Bosphorus froze, and in 1709 the Adriatic Sea froze along the shores.
AT 
About the second half of the 19th century, the Little Ice Age ended and a relatively warm era began, which continues to this day.
Rice. 24. The boundaries of the last glaciation
Rice. 25. Scheme of the formation and melting of the glacier (along the profile of the Arctic Ocean - Kola Peninsula - Russian Platform)
The last ice age ended 12,000 years ago. In the most severe period, glaciation threatened man with extinction. However, after the glacier melted, he not only survived, but also created a civilization.
Glaciers in the history of the Earth
The last ice age in the history of the Earth is the Cenozoic. It began 65 million years ago and continues to this day. Modern man is lucky: he lives in the interglacial, in one of the warmest periods of the planet's life. Far behind is the most severe ice age - the Late Proterozoic.
In spite of global warming scientists are predicting a new ice age. And if the real one comes only after millennia, then the Little Ice Age, which will reduce annual temperatures by 2-3 degrees, can come quite soon.
The glacier became a real test for man, forcing him to invent means for his survival.
last ice age
The Würm or Vistula glaciation began about 110,000 years ago and ended in the tenth millennium BC. The peak of cold weather fell on the period of 26-20 thousand years ago, the final stage of the Stone Age, when the glacier was the largest.
Little Ice Ages
Even after the glaciers melted, history has known periods of noticeable cooling and warming. Or, in other words, climate pessimism and optima. Pessima are sometimes referred to as Little Ice Ages. In the XIV-XIX centuries, for example, the Little Ice Age began, and the time of the Great Migration of Peoples was the time of the early medieval pessimum.
Hunting and meat food
There is an opinion according to which the human ancestor was rather a scavenger, since he could not spontaneously occupy a higher ecological niche. And all known tools were used to butcher the remains of animals that were taken from predators. However, the question of when and why a person began to hunt is still debatable.
In any case, thanks to hunting and eating meat, the ancient man received a large supply of energy, which allowed him to better endure the cold. The skins of slaughtered animals were used as clothing, shoes and walls of the dwelling, which increased the chances of surviving in a harsh climate.
bipedalism
Bipedalism appeared millions of years ago, and its role was much more important than in the life of a modern office worker. Having freed his hands, a person could engage in intensive construction of a dwelling, the production of clothing, the processing of tools, the extraction and preservation of fire. The upright ancestors roamed freely in open areas, and their life no longer depended on the collection of fruits from tropical trees. Already millions of years ago, they freely moved over long distances and obtained food in river flows.
Walking upright played an insidious role, but it became more of an advantage. Yes, man himself came to cold regions and adapted to life in them, but at the same time he could find both artificial and natural shelters from the glacier.
Fire
The fire in the life of an ancient person was originally an unpleasant surprise, not a boon. Despite this, the ancestor of man first learned to “extinguish” it, and only later to use it for his own purposes. Traces of the use of fire are found in sites that are 1.5 million years old. This made it possible to improve nutrition through the preparation of protein foods, as well as to remain active at night. This further increased the time to create conditions for survival.
Climate
The Cenozoic Ice Age was not a continuous glaciation. Every 40 thousand years, the ancestors of people had the right to a “respite” - temporary thaws. At this time, the glacier receded, and the climate became milder. During periods of harsh climate, natural shelters were caves or regions rich in flora and fauna. For example, the south of France and the Iberian Peninsula were home to many early cultures.
The Persian Gulf 20,000 years ago was a river valley rich in forests and herbaceous vegetation, a truly “antediluvian” landscape. Wide rivers flowed here, exceeding the size of the Tigris and Euphrates by one and a half times. Sahara in some periods became a wet savanna. Last time this happened 9000 years ago. This can be confirmed by the rock paintings, which depict the abundance of animals.
Fauna
Huge glacial mammals such as bison, woolly rhinoceros and mammoth became an important and unique source of food for ancient people. Hunting such large animals required a lot of coordination and brought people together noticeably. The effectiveness of "collective work" has shown itself more than once in the construction of parking lots and the manufacture of clothing. Deer and wild horses among ancient people enjoyed no less "honor".
Language and communication
Language was, perhaps, the main life hack of an ancient person. It was thanks to speech that important technologies for processing tools, mining and maintaining fire, as well as various fixtures person for daily survival. Perhaps in the Paleolithic language, the details of the hunt for large animals and the direction of migration were discussed.
Allerd warming
Until now, scientists are arguing whether the extinction of mammoths and other glacial animals was the work of man or caused by natural causes - the Allerd warming and the disappearance of forage plants. As a result of the extermination of a large number of animal species, a person in harsh conditions was threatened with death from lack of food. There are known cases of the death of entire cultures simultaneously with the extinction of mammoths (for example, the Clovis culture in North America). Nevertheless, warming has become an important factor in the migration of people to regions whose climate has become suitable for the emergence of agriculture.
The Paleogene period of the geological history of the Earth, which began 67 million years ago, lasted 41 million years. The next, Neogene, is 25 million years old. The last, the shortest, is about 1 million years old. They call it glacial.
The idea was established that the surface of land and sea, even the bowels of the planet, were influenced by powerful glaciations. Data have been obtained that testify to the gradual cooling of the Earth's climate from the time of the Paleogene (60-65 million years ago) to the present day. The average annual air temperature in temperate latitudes has decreased from 20 ° C characteristic of the tropical zone to 10 ° C. In the current climatic conditions Glaciation processes form and develop over an area of 52 million square kilometers. They cover a tenth of the planet's surface.
Over the past 700 thousand years, scientists believe, in the north of Eurasia and North America there were huge ice sheets in length - much more extensive than modern Greenland and even Antarctic. The dimensions of this paleoglaciation are estimated by a prominent specialist in this field - an American scientist of the Russian Federation. Flint - 45.2 million square kilometers. North America accounted for 18, Greenland - 2, Eurasia - 10 million square kilometers of ice. In other words, the estimated area of glaciation in the Northern Hemisphere was more than twice as large as in today's Antarctica (14 million square kilometers). In the works of glaciologists, ice sheets are reconstructed in Scandinavia, the North Sea, a significant part of England, the plains of Northern Europe, the lowlands and mountainous regions of northern Asia, and almost throughout Canada, Alaska, and the northern United States. The thickness of these shields is determined at 3-4 kilometers. Grandiose (up to global) changes in the natural situation on Earth are associated with them.
Experts paint very impressive pictures of the past. They believe that under the onslaught of ice coming from the North, ancient people and animals left their habitats and sought refuge in the southern regions, where the climate was then much colder than now.
It is believed that the level of the World Ocean at that time dropped by 100-125 meters, since the ice sheets "fettered" a huge amount of its waters. When the glaciers began to melt, the sea flooded the vast low-lying expanses of land. (The legend of the Flood is sometimes associated with the alleged advance of the sea on the continents.)
How true are the ideas that science has about the last ice age? - the question is relevant. Knowledge of the nature, size of ancient glaciers, the scale of their geological activity is necessary to explain many aspects of the development of nature and ancient man. The latter is especially important. We live in the Quaternary period, which is called anthropogenic.
Knowing the past, you can predict the future. Therefore, scientists are thinking about whether a new “great glaciation” threatens humanity in the near or distant future.
So, what can humanity expect if the climate on Earth again becomes much colder than the current one?
WE GET TOGETHER WITH IDEAS AS WITH PEOPLE
The book "Studies on the Ice Age", written by a prisoner of the Peter and Paul Fortress - the famous scientist and revolutionary P.A. Kropotkin, - was published in 1876. His work fully and clearly outlined the ideas about the "great glaciation", which originated in the mountains of Scandinavia, filled the basin of the Baltic Sea and went out to the Russian Plain and the Baltic lowlands. This concept of ancient glaciation has been widely recognized in Russia. One of its main reasons is the fact of the distribution of peculiar deposits on the plains of Northern Europe: unsorted clays and loams containing stone fragments in the form of pebbles and boulders, the dimensions of which reached 3-4 meters in diameter.
Previously, scientists, following the great naturalists of the 19th century C. Lyell and C. Darwin, believed that loams and clays were deposited at the bottom of cold seas - the modern plains of Northern Europe, and boulders were carried by floating ice.
"Drift (from the word "drift") theory", quickly losing supporters, retreated under the onslaught of the ideas of P.A. Kropotkin. They bribed the opportunity to explain many mysterious facts. Where, for example, did deposits containing large boulders come from on the plains of Europe? The glaciers, advancing on a wide front, later melted, and these boulders appeared on the surface of the earth. It sounded quite convincing.
Thirty-three years later, German researchers A. Penk and E. Brückner, who studied the territory of Bavaria and expressed the idea of a fourfold ancient glaciation of the Alps, decided to clearly link each of its stages with the river terraces of the upper Danube basin.
The glaciations have been given names mainly by tributaries of the Danube. The oldest is “gunz”, the younger one is “mindel”, then followed by “riss” and “wurm”. Traces of them subsequently began to be sought and found on the plains of Northern Europe, in Asia, North and South America, and even in New Zealand. Researchers persistently linked the geological history of this or that region with the "reference" Central Europe. No one thought about whether it is legitimate to single out ancient glaciations in North or South America, East Asia, or the islands of the Southern Hemisphere by analogy with the Alps. Soon, glaciations corresponding to the Alpine ones appeared on the paleogeographic maps of North America. They received the names of the states, which, scientists believe, reached by descending to the south. The most ancient - Nebrassian - corresponds to Alpine Gyunts, Kansas - Mindel, Illinois - Rice, Wisconsin - Wurm.
The concept of four ice sheets in the recent geological past was also adopted for the territory of the Russian Plain. They were named (in descending order of age) Oka, Dnieper, Moscow, Valdai and correlated with Mindel, Ris, Wurm. But what about the oldest alpine glaciation - gunz? Sometimes, under different names, a fifth glaciation corresponding to it is distinguished on the Russian Plain.
The attempts made in recent years to “improve” the Alpine model led to the identification of two more pre-Gyuntsev (earliest) “great glaciations” - the Danube and the Biber. And due to the fact that two or three are compared with some of the alleged Alpine glaciations (on the plains of Europe and Asia), their total number in the Quaternary period reaches, according to some scientists, eleven or more.
They get used to ideas, become related, as with people. Parting with them is sometimes very difficult. The problem of the ancient "great glaciations" in this sense is no exception. The data accumulated by scientists on the structure, time of origin and history of the development of the current ice sheets of Antarctica and Greenland, on the regularities of the structure and formation of modern frozen rocks and the phenomena associated with them, cast doubt on many ideas common in science about the nature, extent of manifestation of ancient glaciers and their geological activity. However (traditions are strong, the energy of thinking is great), these data are either not noticed, or they are not given any importance. They are not comprehended in a new way and are not seriously analyzed. Let us consider in their light the problem of ancient ice sheets and try to understand what actually happened to the nature of the Earth in the recent geological past.
FACTS VS THEORIES
A quarter of a century ago, almost all scientists agreed that the modern ice sheets of Antarctica and Greenland developed in sync with the supposed "great glaciers" in Europe, Asia, and North America. The glaciation of the Earth, they believed, began in Antarctica, Greenland, on the Arctic islands, then covered the continents of the Northern Hemisphere. During the interglacial epochs, the Antarctic and Greenland ice melted completely. The level of the World Ocean rose by 60-70 meters above the present. Significant areas of the coastal plains were flooded by the sea. No one doubted that the modern era is an unfinished ice age. Say, the ice sheets simply did not have time to melt. Moreover, during cooling epochs, not only huge glaciers appeared on the continents of the Northern Hemisphere, but the Greenland and Antarctic ice sheets grew significantly ... Years passed, and the results of studies of hard-to-reach polar regions completely refuted these ideas.
It turned out that glaciers in Antarctica appeared long before the "ice age" - 38-40 million years ago, when subtropical forests stretched across the north of Eurasia and North America, and palm trees swayed on the shores of modern Arctic seas. About any glaciation on the continents of the Northern Hemisphere then, of course, there can be no question. The Greenland ice sheet also originated at least 10-11 million years ago. At that time, mixed forests grew on the coasts of the Arctic seas in northern Siberia, Alaska and Canada (among birch, alder, spruce, larch, there were broad-leaved oak, linden, elm), corresponding to a warm, humid climate.
Data on the antiquity of the ice sheets of Antarctica and Greenland sharply raised the question of the causes of the glaciation of the Earth. They are seen in global warmings and coolings of the climate. (Back in 1914, the Yugoslav scientist M.Milankovic drew graphs of fluctuations in the arrival of solar radiation on the earth's surface over the past 600 thousand years, identified with glaciations and interglacial periods.) But we now know that when the climate was warm in the north of Eurasia and North America , Antarctica and Greenland were covered by ice sheets, the size of which later never significantly decreased. This means that it is not a matter of fluctuations in the arrival of solar heat and general cooling and warming of the earth, but in a combination of certain factors leading to glaciation in these specific conditions.
The exceptional stability of the Greenland and Antarctic ice sheets does not support the concept of the repeated development and disappearance of the "great glaciations" on the continents of the Northern Hemisphere. It is not clear why the Greenland ice sheet has continuously existed for more than 10 million years, while next to it in less than 1 million years, due to some completely unclear reasons, the North American one has repeatedly appeared and disappeared.
Put two pieces of ice on the table - one 10 times larger than the other. Which one will melt faster? If the question seems rhetorical, ask yourself: which ice sheet was supposed to disappear first with the general warming of the climate in the Northern Hemisphere - Greenland with an area of \u200b\u200b1.8 million square kilometers or the proposed North American one next to it - 10 times larger? Obviously, the second one was more resistant (in time) to all external changes.
Relying on the now dominant theory, this paradox cannot be explained. According to it, a huge hypothetical North American ice sheet has arisen over the past 500-700 thousand years four or five or more times, that is, approximately every 100-150 thousand years, and the size of the adjacent (incomparably smaller) one has hardly changed. Incredible!
If the stability of the Antarctic ice cover for tens of millions of years (let's assume that the glaciers of the Northern Hemisphere arose and disappeared at that time) can be explained by the proximity of the mainland to the pole, then in relation to Greenland it should be remembered: its southern tip is located near 60 degrees north latitude - on one parallels with Oslo, Helsinki, Leningrad, Magadan. So could the alleged "great glaciations" come and go in the Northern Hemisphere as often as is commonly claimed? Hardly. As for the criteria and methods for establishing their number, they are unreliable. Eloquent proof of this is the discrepancy in estimating the number of glaciations. How many of them were there: 1-4, 2-6, or 7-11? And which of them can be considered the maximum?
The terms "cooling" and "glaciation" are usually used as synonyms. It goes without saying, it seems, of course: the colder the climate of the Earth was, the wider the front that ancient glaciers advanced from the north. They say: "there were so many epochs of cooling", implying that there were the same number of epochs of glaciation. However, the latest research has raised many unexpected questions.
A. Penk and E. Brueckner considered the most ancient or one of the most ancient glaciations of the ice age to be the maximum. They were convinced that the sizes of the subsequent ones were consistently decreasing. In the future, the opinion became stronger and almost completely dominated: the largest was the glaciation that occurred in the middle of the ice age, and the most limited was the last. For the Russian Plain it was an axiom: the most extensive Dnieper glaciation, which had two large "tongues" along the valleys of the Dnieper and Don, descended along them south of the latitude of Kyiv. The borders of the next - Moscow were drawn much to the north (somewhat south of Moscow), even younger - Valdai was drawn north of Moscow (about halfway from it to Leningrad).
The limits of distribution of hypothetical ice covers on the plains are restored in two ways: according to the deposits of ancient glaciers (till - an unsorted mixture of clay, sand, large stone fragments), according to landforms and according to a number of other signs. And here's what is remarkable: within the limits of the distribution of the youngest (from the supposed) glaciation, deposits were found, which were then attributed to all or almost all of the previous ones (two, three, four, etc.). Near the southern borders of the Dnieper glaciation (in the valleys of the Dnieper and Don in their lower reaches), only one layer of till is found, as is the case near the southern limits of the supposedly maximum Illinois (in North America). And here and there to the north, more layers of sediments are established, which, for one reason or another, are classified as glacial.
In the north and especially the northwest, the relief of the Russian Plain has sharp ("fresh") outlines. The general character of the area suggests that until recently there was a glacier, which gave Leningraders and the inhabitants of the Baltic region their favorite places for recreation and tourism - picturesque combinations of ridges, hills and lakes lying in depressions between them. Lakes on the Valdai and Smolensk Uplands are often deep and are characterized by transparency and purity of water. And south of Moscow, the landscape is changing. There are almost no areas of hilly-lake relief. Ridges and gently sloping hills predominate, cut by river valleys, streams and ravines. Therefore, it is believed that the glacial relief that was once here has been reworked and changed almost beyond recognition. Finally, the southern limits of the supposed distribution of glacial covers in Ukraine and along the Don are characterized by dissected spaces cut by rivers, almost devoid of signs of glacial relief (if it was here), which gives, they say, reason to believe that the local glacier is one of the most ancient .. .
All these ideas, which seemed indisputable, in recent times shaken.
PARADOX OF NATURE
The results of studying ice from cores of deep wells in Antarctica, Greenland and bottom sediments of the oceans and seas turned out to be sensational.
From the ratio of heavy to light oxygen isotopes in ice and marine organisms, scientists can now determine the ancient temperatures at which ice accumulated and sediment layers were deposited on the seafloor. It turned out that one of the strongest cold snaps does not occur at the beginning and middle of the "Ice Age", but almost at its very end - at a time interval that is 16-18 thousand years from our days. (It was previously assumed that the largest glaciation was 84-132 thousand years older.) Signs of a very sharp cooling of the climate at the end of the "Ice Age" were also found by other methods in different parts Earth. In particular, along the ice veins in the north of Yakutia. The conclusion that our planet has recently experienced one of the coldest or coldest epochs seems now very reliable.
But how to explain the phenomenal natural paradox, which consists in the fact that the time of a very severe climate corresponds to the minimum of the supposed ground ice sheets? Finding themselves in a "dead end" position, some scientists took the easiest path - they abandoned all previous ideas and suggested that the last glaciation be one of the maximum, since the climate at that time was one of the coldest. Thus, the whole system of geological proofs of the sequence of natural events in the ice age is denied, the whole building of the “classical” glacial concept collapses.
MYTHICAL PROPERTIES OF GLACIERS
Can't figure it out difficult questions the history of the "Ice Age", without having previously studied the problems of the geological activity of ancient glaciers. Their footprints are the only evidence of their spread.
Glaciers are of two main types: large shields or domes, merging into huge sheets, and mountain glaciers (glaciers). The geological role of the former is most fully covered in the works of the American scientist R.F. Flint, who summarized the ideas of many scientists (including Soviet ones), according to which glaciers perform a huge destructive and creative work - they plow out large ruts, depressions and accumulate powerful strata of sediments. It is assumed, for example, that they, like a bulldozer, are capable of scraping out hollows several hundred meters deep, and in some cases (Sogne Fjord in Norway) - up to 1.5-2.5 thousand meters (the depth of this fiord is 1200 m plus the same height slopes). Not bad at all, if we keep in mind that the glacier was supposed to “dig” hard rocks here. True, most often the formation of basins with a depth of "only" 200-300 meters is associated with glacial ploughing. But now it is established with a sufficient degree of accuracy that the ice moves in two ways. Either its blocks slide along the cracks, or the laws of viscoplastic flow operate. Under prolonged and ever-increasing stresses, solid ice becomes plastic and begins to flow, albeit very slowly.
In the central parts of the Antarctic cover, the speed of ice movement is 10-130 meters per year. It slightly increases only in a kind of "ice rivers" flowing in the same icy shores (outflow glaciers). The movement of the bottom part of the glaciers is so slow and smooth that they are physically unable to perform the grandiose work that is attributed to them. And does the glacier touch the surface of its bed everywhere? Snow and ice are good heat insulators (the Eskimos have long built their dwellings from compressed snow and ice), and small amounts of intraterrestrial heat are constantly supplied from the bowels of the earth to its surface. In covers of great thickness, the ice melts from below, rivers and lakes appear under it. In Antarctica, near the Soviet station "Vostok" under the four-kilometer thickness of the glacier, there is a reservoir with an area of 8 thousand square kilometers! This means that the ice not only does not tear off the underlying rocks here, but, as it were, “floats” above them or, if the water layer is small, slides over their wetted surface. Mountain glaciers in the Alps, the Caucasus, Altai and other regions are advancing at an average speed of 100-150 meters per year. Here, too, their bottom layers mainly behave as a viscous-plastic substance and flow in accordance with the law of laminar flow, adapting to the unevenness of the bed. Therefore, they cannot plow the trough-shaped trough-shaped valleys several kilometers wide and 200-2500 meters deep. This is supported by interesting observations.
In the Middle Ages, the area of glaciers in the Alps increased. They moved down the river valleys and buried the buildings of the Roman era under them. And when the Alpine glaciers receded again, from under them appeared the perfectly preserved foundations of buildings destroyed by people and earthquakes, and paved Roman roads with wagon ruts knocked out on them. In the central part of the Alps, near Innsbruck in the valley of the Inn River, under the deposits of a retreating glacier, layered sediments of an ancient lake (with the remains of fish, leaves and tree branches) were found that existed here about 30 thousand years ago. This means that the glacier that has moved onto the lake has practically not damaged the layer of soft sediments - it has not even crushed them.
What is the reason for the large width and trough-shaped shape of the valleys of mountain glaciers? It seems that with the active collapse of the slopes of the valleys as a result of weathering. A huge amount of fragments of stone material turned out to be on the surface of the glaciers. The moving ice, like a conveyor belt, carried them down. The valleys were not cluttered. Their slopes, while remaining steep, quickly receded. They acquired a large width and a transverse profile resembling a trough: a flat bottom and steep sides.
To recognize the ability of glacial flows to mechanically destroy rocks is to attribute mythical properties to them. Due to the fact that glaciers do not plow their bed, in many valleys, now free of ice, ancient river deposits and placers of gold and a number of other valuable minerals associated with them have been preserved. If the glaciers had produced the huge destructive work attributed to them, contrary to facts, logic and physical laws, there would have been no “gold rushes” of Klondike, Alaska in the history of mankind, and Jack London would not have written several wonderful novels and stories.
A variety of creative geological activities are also associated with glaciers. But often this is done without proper justification. In the mountains, indeed, often there are strata, consisting of a chaotic mixture of blocks, rubble and sand, sometimes blocking the valley from one slope to another. They are sometimes composed of sections of valleys that are significant in length. On the plains, deposits of ancient ice sheets usually include unstratified and unsorted clays, loams, sandy loams containing stone inclusions - mainly pebbles and boulders. However, it is known that in cold-water lakes, boulders can be carried by floating ice. They carry them and river ice. Therefore, many varieties of marine and river sediments contain stone inclusions. It is impossible to classify them as glacial deposits on this basis alone. Mudflows play an important role here, most intense in the mountains or foothills and in belts, which are characterized by alternating rainy (wet) and dry periods.
One of the obvious evidence of the glacial origin of such deposits is considered to be "boulder blind areas" - accumulations of boulders, the upper surface of which is allegedly worn away by ice. We just proved that the glacier couldn't do that. Those who have been on the shores of polar rivers and seas know that boulder pavements are a common occurrence here. With sharp movements of ice in the coastal zone, he does an impressive job: as if with a razor, he cuts off the protruding convex edges of boulders, steel pipes and concrete piles. Boulder-bearing deposits of unsorted clays and loams contain remains of shells of marine organisms. Therefore, they accumulated in the sea. Sometimes there are boulders, to the smooth surface of which sea shells are attached. Such finds do not at all testify in favor of the glacial origin of these rounded boulders.
GEOLOGICAL ROLE OF UNDERGROUND GLACIATION
Under the influence of ideas about "great" terrestrial superglaciers, the role of underground glaciation in the history of the Earth was either not noticed, or its nature was interpreted erroneously. This phenomenon was sometimes spoken of as a phenomenon accompanying ancient glaciations.
The distribution zone of frozen rocks on Earth is very large. It occupies about 13 percent of the land area (in the USSR, almost half of the territory), includes vast expanses of the Arctic and Subarctic, and in the eastern regions of the Asian continent it reaches middle latitudes.
Terrestrial and underground glaciation as a whole are characteristic of the cooling regions of the Earth, i.e., regions with negative average annual air temperatures experiencing a heat deficit. Additional condition the formation of terrestrial glaciers - the predominance of solid precipitation (snow) over their consumption, and underground glaciation is confined to areas where there is not enough precipitation. First of all - to the territory of the north of Yakutia, the Magadan region and Alaska. In Yakutia, where very little snow falls, there is a cold pole of the Northern Hemisphere. A record low temperature was recorded here - minus 68°C.
For the zone of distribution of frozen rocks, underground ice is most characteristic. Most often, these are interlayers and veinlets, more or less evenly distributed in the strata of sediments. Intersecting with each other, they often form an ice grid or lattice. There are also deposits of underground ice with a thickness of up to 10-15 meters or more. And its most impressive variety is vertical ice veins 40-50 meters high and over 10 meters wide in the upper (thickest) part.
In accordance with the concept of V.A. Obruchev, large ice veins, lenses and layers of underground ice were quite recently considered buried remains of former ice sheets and substantiated by this the theoretical reconstruction of a huge ice sheet almost throughout Siberia up to the Arctic seas and their islands.
Soviet (mainly) scientists have uncovered the mechanism of formation of ice veins. At low temperatures, the ground, covered with a thin layer of snow, cools intensively, shrinks and breaks into cracks. In winter they get snow, in summer water. It freezes as the lower ends of the cracks penetrate into the sphere of permanently frozen rocks with temperatures below 0°C. The periodic occurrence of new cracks in the old place and their filling with additional portions of snow and water first lead to the formation of wedge-shaped ice veins no more than 12-16 meters high. In the future, they grow in height and width, squeezing out part of the enclosing mineral matter to the earth's surface. The latter is constantly rising due to this - the ice veins, as it were, are "buried" in the ground. With an increase in the depth of occurrence, conditions are created for their further upward growth. It stops when the total ice saturation of the deposits reaches a maximum value of 75-90 percent of the total volume of the entire ice-ground mass. The total increase in the surface can reach 25-30 meters. According to calculations, the formation of ice veins of large vertical extent requires 9-12 thousand years.
When the possibilities for the growth of an ice vein are exhausted, it opens up and begins to thaw. A thermokarst funnel arises, which, in the absence of runoff from it, turns into a lake, which often has a cruciform shape due to the fact that it is located at the mutual intersection of ice veins. There comes a stage of mass thawing of icy rocks.
Ice veins give rise to lakes, and lakes eliminate them, preparing the conditions for the reappearance and development of ice veins.
The question of the connection between the formation of large ice veins and frost cracking of soils and freezing of water in them has been resolved almost unambiguously, only the details of this process and its connection with certain landscapes in continental land conditions are discussed. The problem of the origin of large deposits of underground ice in the form of lenses and layers turned out to be more complex and is still the subject of heated discussion. Some scientists believe that these are the buried remains of ancient glaciers. Others argue that such deposits are formed in the process of soil freezing. Some researchers incorrectly attribute buried lenses and layers of ice that were once carried by the sea to land as glacial.
There are especially many lenses and layers of underground ice in the north of the West Siberian Lowland and the coastal plains of Chukotka. The results of the work of Soviet permafrost scientists there allow us to draw a quite definite conclusion: underground lenses and layers of ice in these areas were formed in the process of freezing of rocks and are a characteristic consequence of it. A number of details of their structure (first of all, the presence of large stone inclusions - pebbles and boulders in underground ice deposits) do not fit into the framework of standard ideas about underground ice formation. It is the boulders that are considered as the main and direct evidence that the ice containing them is the remnants of former ice sheets. However, the hit of boulders in massifs of "pure" underground ice is quite understandable. Rocks are broken by cracks. The water that penetrated into them, freezing, pushed the boulders up, where they were enveloped by “clean” ice.
Another specific feature of underground lenticular ice deposits is their sometimes inherent folding. As they grow towards the surface, the ice veins collapse into dome-shaped folds overlying their deposits. It is assumed that the deformations in the ice reflect the process of the former movement of the glacier, and the crushing of rocks is associated with its dynamic effect on its bed (“glaciodynamic dislocations”). We have already spoken about the unreality of such ideas. Deformed large accumulations of underground ice of a lenticular shape are the intrusions of water and soil in the process of freezing of sediments after their surface was above sea level. The validity of this point of view is unambiguously evidenced by the fact that in a number of cases, accumulations of deformed ice are overlain by marine layered sediments crumpled into gentle folds and containing the remains of marine organisms.
The theory of ancient glaciations is usually used to explain natural phenomena that baffle the researcher, who cannot give a plausible interpretation of the method of their formation. This is exactly the case with the problem of the origin of deposits of underground ice containing boulders. However, the absence of an explanation for a complex natural phenomenon is not evidence that it is necessarily due to the activity of an ancient glacier.
Finally, the study of the area of modern distribution of frozen rocks provides the key to deciphering the origin of the characteristic hilly-depression relief, which is commonly called "typically glacial." The fact is that underground ice in frozen rocks is distributed very unevenly. Its amount is often equivalent to raising the height of the earth's surface by 40-60 meters. Naturally, during the thawing of frozen rocks, depressions of the corresponding depth are formed here. And where the ice content was much less, hills will appear after thawing. The process of local uneven thawing of icy rocks can be observed in the northern areas of permafrost distribution. In this case, a hilly-lake relief arises, completely analogous to that which is taken as "typically glacial" on the plains of Northern Europe. This zone (apart from the above) is characterized by intense peat formation, traces of which have been recorded in the thick chernozems of Europe and Asia.
STUDYING THE PAST, PREDICTING THE FUTURE
So it is clear that the geological role and, consequently, the size and number of ancient terrestrial "great ice sheets" are largely exaggerated. Large climate coolings were indeed characteristic of the last period of the geological history of the Earth, but they apparently led to the development of terrestrial glaciers only in mountainous regions and in the territories adjacent to them, located in a cold but rather humid climate with a high amount of winter precipitation. . The role of underground glaciation in the history of the Earth, on the contrary, is clearly underestimated. It developed most widely in areas with a harsh climate with a certain deficit of solid precipitation.
There is every reason to believe that during the era of cold aridization of the climate (arid climate is dry, characteristic of deserts and semi-deserts; aridization occurs at high or low temperatures air in conditions of low precipitation) the area of underground glaciation in the Northern Hemisphere, as at the present time, far exceeded the scale of terrestrial glaciers. Huge expanses of the seas were also covered with ice.
Whether these epochs for our planet were the result of some astronomical factors or purely terrestrial ones (say, the displacement of the North Pole) - there is no unambiguous answer now. But it can be argued that the last period in the geological history of the Earth is not so much glacial as ice as a whole, because the areas of underground and sea ice exceed (and exceeded) the areas of distribution of land-based glaciers.
By studying the geological past, learning the laws of nature development, scientists are trying to predict its future. What awaits humanity if the Earth's climate again becomes much colder than today? Will glacial supersheets emerge? Will all disappear under them Northern Europe and nearly half of North America? I think we can give a very definite negative answer. Glaciers will appear, apparently, only in Scandinavia and within other mountainous territories, which receive more snow in winter than it is spent in summer, and vast expanses of Eurasia and North America will be the arena for the development of underground glaciation. With a moisture deficit, this will lead to cold aridization of vast regions of the Earth.
Has the climate always been like it is now?
Each of us can say that the climate is not always the same. A number of dry years are replaced by rainy ones; After cold winters come warm ones. But these climate fluctuations are still not so great that they could significantly affect the life of plants or animals within a short period of time. So, for example, the tundra with its polar birches, dwarf willows, mosses and lichens, with the polar animals inhabiting it - arctic foxes, lemmings (pied), reindeer - does not develop in such a short time in those places where cooling occurs. But has it always been like this? Was it always cold in Siberia, and was it as warm in the Caucasus and Crimea as it is now?
It has long been known that the caves in different places, including, for example, in the Crimea and the Caucasus, contain the remains of the culture of an ancient person. Fragments of pottery, stone knives, scrapers and other household items, fragments of animal bones and the remains of long-extinguished fires were found there.
About 25 years ago, archaeologists led by G. A. Bonch-Osmolovsky began excavations of these caves and made remarkable discoveries. In the caves of the Baydarskaya Valley (in the Crimea) and in the vicinity of Simferopol, several cultural layers were found, one above the other. Scientists attribute the middle and lower layers to the ancient stone period of human life, when a person used coarse, unpolished stone tools, the so-called Paleolithic, and the upper layers to the metal period, when a person began to use tools made of metals: copper, bronze and iron. There were no intermediate layers dating back to the new stone period (Neolithic), that is, to the period when man had already learned to grind and drill stones and make pottery.
Among the finds of the ancient stone period, not a single fragment of a clay shard and not a single bone of a domestic animal was found (these finds were found only in upper layers). Paleolithic man did not yet know how to make pottery. All his household items were made of stone and bone. He probably had wooden crafts but they were not preserved. Stone and bone products differed quite a lot. great variety: spearheads and darts (paleolithic people did not know the bow and arrow), scrapers for dressing leather, chisels, thin flint plates - knives, bone needles.
Paleolithic man and domestic animals did not have. In the remains of its fires, many bones of only wild animals were found: mammoth, rhinoceros, giant deer, saigas, cave lion, cave bear, cave hyena, birds, etc. But in other places, at sites of the same time, for example, at the site of Afontova Gora near Krasnoyarsk, in Kostenki near Voronezh, among the animal bones were found the remains of a wolf, which, according to some scientists, belonged to a domesticated wolf, and among the bone crafts on Afontova Gora, some turned out to be very similar to parts of modern reindeer teams. These findings suggest that at the end of the Paleolithic, the first domestic animals probably already appeared in humans. These animals were the dog (the domesticated wolf) and the reindeer.
When they began to carefully study the bones of animals from the Crimean Paleolithic caves, they made another remarkable discovery. In the middle layers, which scientists attribute to the second half of the ancient Stone Age, in other words, to the Upper Paleolithic, numerous bones of polar foxes (Arctic foxes), white hares, reindeer, polar larks, white partridges were found; now they are ordinary inhabitants of the far north - the tundra. But the climate of the Arctic, as you know, is far from being as warm as in the Crimea. Consequently, when polar animals lived in the Crimea, it was colder there than now. The same conclusion was made by scientists after studying the coals from the fires of the Crimean Upper Paleolithic man: it turned out that northern mountain ash, juniper and birch served as firewood for this man. The same thing happened in the sites of the Upper Paleolithic man in the Caucasus, with the only difference that instead of polar animals, representatives of the taiga were found there - elks and representatives of alpine meadows - some sulfur mice (Promethean mice), which now live high in the mountains, and in At that time they lived almost on the very shore of the sea.
Numerous remains of human camps of the Upper Paleolithic period were also discovered in many other places in the Soviet Union: on the Oka, on the Don, on the Dnieper, in the Urals, in Siberia (on the Ob, Yenisei, Lena and Angara); and everywhere in these sites, among the remains of animals, bones of polar animals were found, which now do not live in these places. All this indicates that the climate of the Upper Paleolithic era was more severe than at present.
But if in those distant times it was cold even in the Crimea and the Caucasus, then what was the noise, where Moscow and Leningrad are now? What was at that time in northern and central Siberia, where even now in winter 40 degrees below zero is not uncommon?
Huge territories of Europe and Northern Asia were covered at that time with solid ice, reaching a thickness of two kilometers in places! South of Kyiv, Kharkov and Voronezh, ice descended in two giant tongues along the valleys of the modern rivers of the Dnieper and Don. The Ural and Altai mountains were covered with ice cloaks that descended far into the plains. The same glaciers were in the mountains of the Caucasus, reaching almost to the sea. That is why those animals that now live near the glaciers, high in the mountains, were found in the sites of man of the ancient Stone Age near the sea. Crimea at that time was a refuge for various animals. A huge glacier, which moved into the Russian plain from the north - from Finland and Scandinavia, forced the animals that lived there to retreat to the south. Therefore, in a small area of Crimea, there was such a mixture of steppe and polar animals.
It was the era of the Great Ice Age of the Earth.
What traces did this glacier leave?
The inhabitants of central and northern Russia are well aware of large and small stones - boulders and pebbles, which are found in abundance in plowed fields. Sometimes these stones reach very large sizes (with a house and more). From one such granite boulder, for example, the foundation of the monument to Peter I in Leningrad was made. Some of the boulders are already overgrown with lichens; many of them crumble easily when hit with a hammer. This indicates that they have been lying on the surface for a long time. The boulders are usually round in shape, and if you look closely at them, you can find smooth ground surfaces with grooves and scratches on some of them. Boulders are scattered even on the plains, where there are no mountains. Where did these stones come from?
Sometimes you hear that boulders "grow" from the ground. But this is a profound delusion. One has only to dig with a shovel or carefully look in the ravines, and it will immediately become clear that the boulders are in the ground, in sand or clay. It will wash the earth a little with rain, blow the sand with the wind, and where nothing was visible last year, a boulder will appear on the surface. The next year, the soil will be washed out even more by rain and blown by the wind, and the boulder seems larger. That's what they think he's grown up.
Having studied the composition of boulders, scientists came to the unanimous opinion that many of them are native to Karelia, Sweden, Norway, and Finland. There, rocks of the same composition as boulders form whole rocks, in which gorges and river valleys are cut. The boulders torn off from these rocks represent boulders scattered on the plains of the European part of the USSR, Poland, and Germany.
But how and why did they end up so far from their homeland! Previously, about 75 years ago, they thought that where boulders are now found, there was a sea and they were carried on ice floes, just as now in the polar ocean, floating ice (icebergs), breaking away from the edge of a glacier sinking into the sea, take them with them boulders torn off by a glacier from rocky shores. This assumption has now been abandoned. Now, none of the scientists doubts that the boulders were brought with them by a giant glacier descending from the Scandinavian Peninsula.
Having studied the composition and distribution of glacial boulders in Russia, scientists have established that there were also glaciers in the mountains of Siberia, the polar Urals, Novaya Zemlya, Altai and the Caucasus. Descending from the mountains, they carried boulders with them and left them far on the plains, thus marking the paths and boundaries of their advance. Now boulders, consisting of rocks of the Urals and Novaya Zemlya, are found near Tobolsk, in Western Siberia, at the mouth of the Irtysh, and rocks from the lower reaches of the Yenisei are found in the center of Western Siberia, near the village of Samarovo on the Ob River. Two giant glaciers were moving towards each other at that time. One from the Urals and Novaya Zemlya, the other from the extreme north of Eastern Siberia - from the right bank of the Yenisei or Taimyr. These huge glaciers merged into one continuous ice field that covered the entire north of Western Siberia.
Encountering hard rocks on its way, the glacier polished and smoothed them, and also left deep scars and furrows on them. Such polished and furrowed rocky hills are known as "ram's foreheads". They are especially frequent on the Kola Peninsula, in Karelia.
In addition, the glacier captured huge masses of sand and clay and piled it all up at its edge in the form of ramparts, now overgrown with forest. Such ramparts are very clearly visible, for example, in Valdai (in the Kalinin region). They are called "terminal moraines". From them you can well determine the edge of the former glacier. When the glacier melted, the entire territory once occupied by it turned out to be covered with clay with boulders and pebbles. This clay mantle with boulders, on which modern soil was later formed, is now plowed open.
As we can see, the traces of the former once Great glaciation of the Earth are so clear that no one doubts. We are also convinced of it by the fact that the same traces are left on the earth by modern glaciers that exist in many mountains both in our country and in other countries. Only modern glaciers are much smaller than the one that covered the Earth during the Great Glaciation.
Thus, the remains of animals found in the Crimea during excavations of Upper Paleolithic caves gave a correct indication that there was once a colder climate than now.
But, perhaps, the Crimean sites were earlier or later than the Great glaciation? And we have a very definite answer to this question.
The same sites as in the Crimea were found in many places covered during the Great glaciation solid ice, but these sites have never been found anywhere under the glacial layers. They met either outside the former distribution of the glacier, or (younger ones) within its southern part - in the layers lying above the glacial formations. This convincingly proves that all the studied sites belong to the era of the Great Glaciation (and some of them to the time of the melting of glaciers).
Extremely important discoveries have been made in the last ten years. On the Dnieper and on the Desna River, near Novgorod-Seversky, sites of ancient man and stone tools were found under the glacial layers. The same type of sites were found on the Black Sea coast. This proved that man lived not only during the Great glaciation and after it, but also before this glaciation.
Studying even more ancient layers of the earth, people were also convinced that there was a time when such trees grew in Siberia, which are now found only on the Black Sea coast. Evergreen laurels, magnolias and fig trees once grew on the banks of rivers and lakes, located on the site of the current Baraba steppe (Western Siberia). Monkeys lived in the forests of Ukraine, and ostriches and antelopes lived in the Baikal and Azov steppes, which are now found only in Africa and South America.
