Great Quaternary Glaciation

Geologists have divided the entire geological history of the Earth, which has lasted for several billion years, into eras and periods. The last of these, which continues to this day, is the Quaternary period. It began almost a million years ago and was marked by the extensive spread of glaciers across the globe - the Great Glaciation of the Earth.

We found ourselves under powerful ice caps Northern part The North American continent, a significant part of Europe, and possibly also Siberia (Fig. 10). In the southern hemisphere, the entire Antarctic continent was under ice, as now. There was more ice on it - the surface of the ice sheet rose 300 m above its modern level. However, Antarctica was still surrounded on all sides by a deep ocean, and the ice could not move north. The sea prevented the Antarctic giant from growing, and the continental glaciers of the northern hemisphere spread to the south, turning the flourishing spaces into an icy desert.

Man is the same age as the Great Quaternary Glaciation of the Earth. His first ancestors - ape people - appeared at the beginning of the Quaternary period. Therefore, some geologists, in particular the Russian geologist A.P. Pavlov, proposed calling the Quaternary period Anthropocene (in Greek “anthropos” - man). Several hundred thousand years passed before man took on his modern appearance. The advance of glaciers worsened the climate and living conditions of ancient people who had to adapt to the harsh nature around them. People had to lead a sedentary lifestyle, build houses, invent clothing, and use fire.

Having reached their greatest development 250 thousand years ago, Quaternary glaciers began to gradually shrink. The Ice Age was not uniform throughout the Quaternary. Many scientists believe that during this time glaciers at least three times they completely disappeared, giving way to interglacial eras, when the climate was warmer than the modern one. However, these warm eras were replaced by cold snaps again, and the glaciers spread again. We now live, apparently, at the end of the fourth stage of the Quaternary glaciation. After the liberation of Europe and America from under the ice, these continents began to rise - this is how the earth’s crust reacted to the disappearance of the glacial load that had been pressing on it for many thousands of years.

The glaciers “left”, and after them vegetation, animals, and, finally, people settled to the north. Since glaciers retreated unevenly in different places, humanity settled unevenly.

Retreating, the glaciers left behind smoothed rocks - “ram's foreheads” and boulders covered with shading. This shading is formed by the movement of ice along the surface of the rocks. It can be used to determine in which direction the glacier was moving. The classic area for these traits to appear is Finland. The glacier retreated from here quite recently, less than ten thousand years ago. Modern Finland is a land of countless lakes lying in shallow depressions, between which rise low “curly” rocks (Fig. 11). Everything here reminds us of the former greatness of the glaciers, their movement and enormous destructive work. You close your eyes and you immediately imagine how slowly, year after year, century after century, a powerful glacier crawls here, how it plows out its bed, breaks off huge blocks of granite and carries them south, towards the Russian Plain. It is no coincidence that it was while in Finland that P. A. Kropotkin thought about the problems of glaciation, collected many scattered facts and managed to lay the foundations for the theory of the Ice Age on Earth.

There are similar corners at the other “end” of the Earth - in Antarctica; Not far from the village of Mirny, for example, there is the Banger “oasis” - an ice-free land area with an area of ​​600 km2. When you fly over it, small chaotic hills rise under the wing of the plane, and strangely shaped lakes snake between them. Everything is the same as in Finland and... not at all similar, because in Banger’s “oasis” there is no main thing - life. Not a single tree, not a single blade of grass - only lichens on the rocks and algae in the lakes. Probably, all the territories recently freed from under the ice were once the same as this “oasis”. The glacier left the surface of the Banger “oasis” only a few thousand years ago.

The Quaternary glacier also spread to the territory of the Russian Plain. Here the movement of the ice slowed down, it began to melt more and more, and somewhere on the site of the modern Dnieper and Don, powerful streams of meltwater flowed out from under the edge of the glacier. Here was the border of its maximum distribution. Later, on the Russian Plain, many remains of the spread of glaciers were found and, above all, large boulders, like those that were often encountered on the path of Russian epic heroes. The heroes of ancient fairy tales and epics stopped in thought at such a boulder before choosing their long path: to the right, to the left, or to go straight. These boulders have long stirred the imagination of people who could not understand how such colossi ended up on a plain among a dense forest or endless meadows. They came up with various fairy-tale reasons, including the “universal flood”, during which the sea allegedly brought these stone blocks. But everything was explained much more simply - it would have been easy for a huge flow of ice several hundred meters thick to “move” these boulders a thousand kilometers.

Almost halfway between Leningrad and Moscow there is a picturesque hilly lake region - the Valdai Upland. Here, among the dense coniferous forests and plowed fields, the waters of many lakes splash: Valdai, Seliger, Uzhino and others. The shores of these lakes are indented, there are many islands on them, densely overgrown with forests. It was here that the border of the last spread of glaciers on the Russian Plain passed. These glaciers left behind strange shapeless hills, the depressions between them were filled with their meltwater, and subsequently the plants had to work a lot to create good living conditions for themselves.

On the causes of great glaciations

So, glaciers were not always on Earth. Even in Antarctica, coal has been found - a sure sign that there was a warm and humid climate with rich vegetation. At the same time, geological data indicate that the great glaciations were repeated on Earth several times every 180-200 million years. The most characteristic traces of glaciations on Earth are special rocks - tillites, that is, the fossilized remains of ancient glacial moraines, consisting of a clayey mass with the inclusion of large and small hatched boulders. Individual tillite strata can reach tens and even hundreds of meters.

The reasons for such major climate changes and the occurrence of the great glaciations of the Earth still remain a mystery. Many hypotheses have been put forward, but none of them can yet claim to be a scientific theory. Many scientists searched for the cause of the cooling outside the Earth, putting forward astronomical hypotheses. One hypothesis is that glaciation occurred when, due to fluctuations in the distance between the Earth and the Sun, the amount of solar heat received by the Earth changed. This distance depends on the nature of the Earth's motion in its orbit around the Sun. It was assumed that glaciation occurred when winter occurred at aphelion, that is, the point of the orbit furthest from the Sun, at the maximum elongation of the earth's orbit.

However, recent research by astronomers has shown that just changing the amount of solar radiation hitting the Earth is not enough to cause an ice age, although such a change would have its consequences.

The development of glaciation is also associated with fluctuations in the activity of the Sun itself. Heliophysicists have long found out that dark spots, flares, prominences appear on the Sun periodically, and we have even learned to predict their occurrence. It turned out that solar activity changes periodically; There are periods of different durations: 2-3, 5-6, 11, 22 and about a hundred years. It may happen that the culminations of several periods of different durations coincide, and solar activity will be especially high. So, for example, it happened in 1957 - just during the International Geophysical Year. But it may be the other way around - several periods of reduced solar activity will coincide. This may cause the development of glaciation. As we will see later, such changes in solar activity are reflected in the activity of glaciers, but they are unlikely to cause a great glaciation of the Earth.

Another group of astronomical hypotheses can be called cosmic. These are assumptions that the cooling of the Earth is influenced by various parts of the Universe that the Earth passes through, moving through space along with the entire Galaxy. Some believe that cooling occurs when the Earth “floats” through areas of global space filled with gas. Others are when it passes through clouds of cosmic dust. Still others argue that “cosmic winter” on Earth occurs when the globe is in apogalactia - the point furthest from the part of our Galaxy where the most stars are located. At the present stage of scientific development, there is no way to support all these hypotheses with facts.

The most fruitful hypotheses are those in which the cause of climate change is assumed to be on the Earth itself. According to many researchers, cooling, causing glaciation, may occur as a result of changes in the location of land and sea, under the influence of the movement of continents, due to a change in the direction of sea currents (for example, the Gulf Stream was previously diverted by a protrusion of land stretching from Newfoundland to the Green Islands cape). There is a widely known hypothesis according to which, during the eras of mountain building on Earth, the rising large masses of the continents fell into higher layers of the atmosphere, cooled and became places of origin of glaciers. According to this hypothesis, glaciation epochs are associated with mountain building epochs, moreover, they are conditioned by them.

The climate can change significantly as a result of changes in the tilt of the earth's axis and the movement of the poles, as well as due to fluctuations in the composition of the atmosphere: there is more volcanic dust or less carbon dioxide in the atmosphere, and the earth becomes significantly colder. Recently, scientists have begun to link the appearance and development of glaciation on Earth with a restructuring of atmospheric circulation. When, under the same climatic background of the globe, too much precipitation falls into individual mountainous regions, glaciation occurs there.

Several years ago, American geologists Ewing and Donn put forward a new hypothesis. They suggested that the Arctic Ocean, now covered with ice, thawed at times. In this case, increased evaporation occurred from the surface of the ice-free Arctic sea, and flows of moist air were directed to the polar regions of America and Eurasia. Here, above the cold surface of the earth, heavy snow fell from the humid air masses, which did not have time to melt during the summer. This is how ice sheets appeared on the continents. Spreading out, they descended to the north, surrounding the Arctic Sea with an icy ring. As a result of the transformation of part of the moisture into ice, the level of the world's oceans dropped by 90 m, the warm Atlantic Ocean stopped communicating with the Arctic Ocean, and it gradually froze. Evaporation from its surface stopped, snow began to fall on the continents less, and the nutrition of glaciers worsened. Then the ice sheets began to thaw, decrease in size, and the level of the world's oceans rose. Once again, the Arctic Ocean began to communicate with the Atlantic Ocean, its waters warmed, and the ice cover on its surface began to gradually disappear. The cycle of glaciation began all over again.

This hypothesis explains some facts, in particular several glacial advances during the Quaternary period, but main question: what is the reason for the glaciations of the Earth - she also does not answer.

So, we still do not know the causes of the great glaciations of the Earth. With a sufficient degree of certainty we can only speak about the last glaciation. Glaciers usually shrink unevenly. There are times when their retreat is delayed for a long time, and sometimes they quickly advance. It has been noted that such fluctuations in glaciers occur periodically. The longest period of alternating retreats and advances lasts for many centuries.

Some scientists believe that climate changes on Earth, which are associated with the development of glaciers, depend on the relative positions of the Earth, the Sun and the Moon. When these three celestial bodies are in the same plane and on the same straight line, the tides on Earth increase sharply, the circulation of water in the oceans and the movement of air masses in the atmosphere change. Ultimately, the amount of precipitation around the globe increases slightly and the temperature decreases, which leads to the growth of glaciers. This increase in the moisture content of the globe is repeated every 1800-1900 years. The last two such periods occurred in the 4th century. BC e. and the first half of the 15th century. n. e. On the contrary, in the interval between these two maxima, conditions for the development of glaciers should be less favorable.

On the same basis, it can be assumed that in our modern era glaciers should be retreating. Let's see how glaciers actually behaved over the last millennium.

Development of glaciation in the last millennium

In the 10th century Icelanders and Normans, sailing through the northern seas, discovered the southern tip of an immensely large island, the shores of which were overgrown thick grass and tall bushes. This amazed the sailors so much that they named the island Greenland, which means “Green Country”.

Why was the now most glaciated island on the globe so prosperous at that time? Obviously, the peculiarities of the then climate led to the retreat of glaciers and the melting of sea ice in the northern seas. The Normans were able to travel freely on small ships from Europe to Greenland. Villages were founded on the shores of the island, but they did not last long. Glaciers began to advance again, “ice cover” northern seas increased, and attempts in subsequent centuries to reach Greenland usually ended in failure.

By the end of the first millennium AD, mountain glaciers in the Alps, Caucasus, Scandinavia and Iceland had also retreated significantly. Some passes that were previously occupied by glaciers have become passable. The lands freed from glaciers began to be cultivated. Prof. G.K. Tushinsky recently examined the ruins of settlements of Alans (ancestors of the Ossetians) in the Western Caucasus. It turned out that many buildings dating back to the 10th century are located in places that are now completely unsuitable for habitation due to frequent and destructive avalanches. This means that a thousand years ago not only did the glaciers “move” closer to the mountain ridges, but avalanches did not occur here either. However, later winters became increasingly harsh and snowy, and avalanches began to fall closer to residential buildings. The Alans had to build special avalanche dams, their remains can still be seen today. In the end, it turned out to be impossible to live in the previous villages, and the mountaineers had to settle lower in the valleys.

The beginning of the 15th century was approaching. Living conditions became more and more harsh, and our ancestors, who did not understand the reasons for such a cold snap, were very worried about their future. Increasingly, records of cold and difficult years appear in chronicles. In the Tver Chronicle you can read: “In the summer of 6916 (1408) ... then the winter was heavy and cold and snowy, too snowy,” or “In the summer of 6920 (1412) the winter was very snowy, and therefore in the spring there was the water is great and strong.” The Novgorod Chronicle says: “In the summer of 7031 (1523) ... the same spring, on Trinity Day, a great cloud of snow fell, and snow lay on the ground for 4 days, and many bellies, horses and cows froze, and birds died in the forest " In Greenland, due to the onset of cooling by the middle of the 14th century. stopped engaging in cattle breeding and farming; The connection between Scandinavia and Greenland was disrupted due to the abundance of sea ice in the northern seas. In some years, the Baltic and even the Adriatic Sea froze. From the XV to the XVII century. mountain glaciers advanced in the Alps and the Caucasus.

The last major glacial advance dates back to the middle of the last century. In many mountainous countries they have advanced quite far. Traveling through the Caucasus, G. Abikh in 1849 discovered traces of the rapid advance of one of the Elbrus glaciers. This glacier has invaded the pine forest. Many trees were broken and lay on the surface of the ice or protruded through the body of the glacier, and their crowns were completely green. Documents have been preserved that tell about frequent ice avalanches from Kazbek in the second half of the 19th century. Sometimes, due to these landslides, it was impossible to drive along the Georgian Military Road. Traces of rapid advances of glaciers at this time are known in almost all inhabited mountainous countries: in the Alps, in the west North America, in Altai, Central Asia, as well as in the Soviet Arctic and Greenland.

With the advent of the 20th century, climate warming begins almost everywhere on the globe. It is associated with a gradual increase in solar activity. The last maximum of solar activity was in 1957-1958. During these years there was a large number sunspots and extremely strong solar flares. In the middle of our century, the maxima of three cycles of solar activity coincided - eleven-year, secular and super-century. One should not think that increased solar activity leads to increased heat on Earth. No, the so-called solar constant, i.e. a value showing how much heat comes to each area upper limit atmosphere remains unchanged. But the flow of charged particles from the Sun to the Earth and the overall impact of the Sun on our planet are increasing, and the intensity of atmospheric circulation throughout the Earth is increasing. Streams of warm and humid air from tropical latitudes rush to the polar regions. And this leads to quite dramatic warming. In the polar regions it gets warmer sharply, and then it gets warmer all over the Earth.

In the 20-30s of our century, the average annual air temperature in the Arctic increased by 2-4°. The sea ice limit has moved north. The Northern Sea Route has become more passable for sea vessels, and the duration of polar navigation has lengthened. The glaciers of Franz Josef Land, Novaya Zemlya and other Arctic islands have been retreating rapidly over the past 30 years. It was during these years that one of the last Arctic ice shelves, located on Ellesmere Land, collapsed. Nowadays, glaciers are retreating in the vast majority of mountainous countries.

Just a few years ago, almost nothing could be said about the nature of temperature changes in Antarctica: there were too few meteorological stations and almost no expeditionary research. But after summing up the results of the International Geophysical Year, it became clear that in Antarctica, as in the Arctic, in the first half of the 20th century. the air temperature rose. There is some interesting evidence for this.

The oldest Antarctic station is Little America on the Ross Ice Shelf. Here, from 1911 to 1957, the average annual temperature increased by more than 3°. In Queen Mary Land (in the area of ​​modern Soviet research) for the period from 1912 (when the Australian expedition led by D. Mawson conducted research here) to 1959, the average annual temperature increased by 3.6 degrees.

We have already said that at a depth of 15-20 m in the thickness of snow and firn, the temperature should correspond to the average annual one. However, in reality, at some inland stations, the temperature at these depths in the wells turned out to be 1.3-1.8° lower than the average annual temperatures for several years. Interestingly, as we went deeper into these holes, the temperature continued to decrease (down to a depth of 170 m), whereas usually with increasing depth the temperature of the rocks becomes higher. Such an unusual decrease in temperature in the thickness of the ice sheet is a reflection of the colder climate of those years when the snow was deposited, now at a depth of several tens of meters. Finally, it is very significant that the extreme limit of iceberg distribution in the Southern Ocean is now located 10-15° latitude further south compared to 1888-1897.

It would seem that such a significant increase in temperature over several decades should lead to the retreat of Antarctic glaciers. But this is where the “complexities of Antarctica” begin. They are partly due to the fact that we still know too little about it, and partly they are explained by the great originality of the ice colossus, completely different from the mountain and Arctic glaciers familiar to us. Let’s still try to understand what is happening now in Antarctica, and to do this, let’s get to know it better.

The climate in the historical era is discussed in most detail in the monograph by A. S. Monin and Yu. A. Shishkov. Below is a brief description of the climate of the historical era according to these authors.

The end of the first and beginning of the second millennium AD in the history of Europe is known as the Viking Age. At this time, immigrants from Scandinavia - Swedes, Norwegians and Danes - made long trips, discovering and developing new lands. This expansion had political roots, but it was facilitated by the significant warming that ensued.

At this time, the Vikings conquered the Faroe Islands and Iceland, and later Greenland. The Faroe Islands, which means “Sheep” Islands in Norwegian, served as a springboard for the capture of Iceland. After the settlement of Iceland, the discovery and colonization of Greenland (Green Land) occurred.

Icelandic sagas indicate that the Normans repeatedly visited the islands of the Canadian Arctic archipelago. Although until recently their reliability was questioned, nevertheless, relatively recently, the remains of an ancient Norwegian settlement were discovered on the northern tip of Newfoundland. The layout of the house corresponds surprisingly closely to the layout of one of the houses, the ruins of which have been preserved in East Greenland. The widespread expansion of the Vikings into the northern countries was favored by climatic conditions; voyages at that time were not hindered by sea ice, the existence of which is not mentioned in the sagas. For a long time, regular communication was maintained between Greenland and Iceland. The voyage was carried out by the shortest route, along the 65th parallel. However, already in the middle of the 14th century. sea ​​ice began to impede navigation along this route.

The inhabitants of modern Greenland are engaged in catching fish and sea animals, but at that time the villagers were mainly engaged in cattle breeding. This, in turn, indicates not only the absence of ice at that time, but also the wide distribution of meadow vegetation.

During the warming period, they also swam to the northeast. According to some data, it is assumed that they reached the mouth of the river. Ponoy on Kola Peninsula, and according to others - the Northern Dvina. The Normans discovered Spitsbergen, where at that time, as evidenced by spore-pollen analysis of sediments of this age, tundra existed.

According to various estimates, the average annual temperature in South Greenland was 2-4°C higher than at present. The waters of the Atlantic and southern Arctic Ocean were just as warmer. However, the warming of the Viking Age in Europe, due to its short duration, did not lead to large movements of plant zones. In the mountainous regions and Scandinavia, the height of distribution of woody vegetation increased by 100-200 m. At this time, grains were cultivated in Iceland, and the grape growing zone moved 4-5° to the north, and grapes were cultivated in the northern regions of the GDR and the Federal Republic of Germany, in Latvia and Southern England.

In North America, the period of the VIII-XIII centuries. had a favorable climate. Wild grapes, less demanding of heat, common in modern times up to 45° N. sh., at that time it grew at 50° N. w. Settlements were widespread throughout Southern Canada; the main occupation of their inhabitants was agriculture. The Upper Mississippi and Great Lakes regions were significantly warmer than in the modern era. The cooling that began in the 13th-14th centuries led to increased humidity in these areas and to aridity in the southwestern and western United States, which led to sharp decline Agriculture.

Changes in the temperature regime in Greenland, Iceland and England, identified on the basis of variations in the heavy oxygen isotope by W. Dansgaard et al., occurred almost synchronously (6.3).

At the turn of the 1st and 2nd millennia AD, conditions were warmer than at present in Asia and on other continents. In the VII-X centuries. in the river valley On the Yellow River, tangerines and oranges grew and at the same time in China, according to chronicles, there was a minimum number of severe winters. Cold temperatures and heavy snowfalls are observed

in the XII-XIV centuries. During this period, Cambodia, the Mediterranean, Central America and East Africa were wetter.

In the 12th century. cooling began, reaching its maximum at the beginning of the 18th century. It was called the Little Ice Age. We join the opinion of A. S. Monin and Yu. A. Shishkov that this term in use is unauthorized. It reflects the exclusivity of the cooling, and in fact it was only one of several cold snaps that occurred after the climatic optimum, however, due to its proximity to the modern era, this cooling has been well studied on the basis of chronicles and instrumental methods.

The most convincing indicators of changes in climatic conditions in historical times are changes in the position of glaciers and the level of the snow line. Mountain glaciers naturally grow when the amount of solid precipitation increases as a result of lengthening cold seasons or when ablation (melting and evaporation) decreases. Studies of modern glaciers have shown that they do not immediately respond to climate change, but lag for several years and the duration of the lag depends on the size of the glacier, geographical location and topography of the subglacial surface.

After the warm early Middle Ages in the Alps, already in the 13th century. The size of glaciers began to increase. The advance of glaciers is observed not only in the Alps, Scandinavia and Iceland, but also in North America. It especially intensified in the second half of the 16th century. and at the turn of the 16th and 17th centuries. This is evidenced by the remains of moraines and dendrochronological data.

Over the course of several centuries, the glaciers of the Alps changed their area. The maximum advance of alpine glaciers, associated with cooling, occurred at the turn of the 16th and 17th centuries. This is indicated by the remains of buried settlements and mine workings. At the beginning of the 18th century. Glacier growth was observed in Iceland, Norway and Northern Sweden. According to many sources, glacial advances were noted in 1720 (Alps, Scandinavia, USA, Alaska), 1740-1750 (Iceland, Scandinavia, Alaska), 1820 and 1850. (northern Sweden, Iceland). The advance of glaciers in Europe was especially strong in 1750.

V. Brinkmann compiled a generalized graph illustrating the number of maximum glacier advances in the northern hemisphere from 1550 to 1900. Maximum glacier advances occurred in 1610, 1650, 1710, 1750, 1810-1820, 1850, but at the beginning of the 20th century. There is a significant decrease in the area of ​​glaciers.

Climate fluctuations are evidenced not only by pulsating changes in the area of ​​mountain glaciers, but also by the state of the ice situation in the Arctic Ocean, the North and Baltic Seas. There is numerous indirect evidence indicating different temperature conditions and the degree of cooling during the Little Ice Age. For example, in 1300-1350. Icelanders completely abandoned the cultivation of grain crops. There are references in chronicles to harsh winters and cool summers in Rus' in 1454, in the mid-16th and early 17th centuries.

In the XIII-XIV centuries. Weather variability increased and a strong cooling occurred. Many countries experienced harsh winters, heavy snowfalls, as well as severe droughts and catastrophic floods. The ice cover of the polar seas has increased significantly. Greenland and Iceland were covered with ice, and in northern Norway agricultural work completely stopped due to unfavorable climatic conditions.

The next cold wave arrived around the middle of the 16th century. For this time, there are chronicle reports of harsh and long winters in Europe, in particular, the formation of ice cover in the Gulf of Genoa, the freezing of olive trees in France and Italy, and the decline of viticulture in France.

Cooling occurred not only in Europe, but also on other continents. Ancient Chinese chronicles and written documents from other Asian countries indicate cold periods of 1200-1600. According to T. Yamamoto, the advance of glaciers according to radiocarbon dating occurred in 1430 ±80 years, but the maximum cooling occurred in the period 1750-1850. At this time, summer and winter temperatures were 1 - 2 °C lower than in the modern era.

There is no doubt that corresponding changes in temperature and humidity also occurred in tropical latitudes. Indirect evidence of this is the change in river levels during the Little Ice Age.

The Little Ice Age was followed by warming, which began at the end of the 19th century. It manifested itself especially strongly in the 20-30s of the 20th century, when signs of intense warming appeared in the Arctic. According to N.M. Knipovich, the water surface temperature in the Barents Sea in 1919-1928. turned out to be almost 2°C higher than in 1912-1918. According to instrumental observations, in the 1930s the temperature in temperate and high latitudes increased by 5°C compared to the beginning of the century, and in Spitsbergen - even by 8-9°C.

During this period, the retreat of glaciers is observed. In the Alps, glaciers have retreated by 1000-1500 m. Glaciers are retreating in Norway, Sweden, Iceland, Greenland and Spitsbergen. The area of ​​mountain glaciers is decreasing (Caucasus, Pamir, Tien Shan, Altai, Sayan Mountains, Himalayas). The area of ​​glaciers in Africa and the South American Cordillera has greatly decreased. At the same time, many ice islands in the Arctic are disappearing and permafrost and thermokarst phenomena are degrading. Ice conditions in the Arctic improved from 1924 to 1945 and the ice area decreased by approximately 1 million km2.

In the 40s of the XX century. The warming process gave way to cooling, which intensified in the 60s. However, in the mid-60s, average temperatures in the northern hemisphere reached temperatures in the late 10s. During the 1970s, there was a trend towards a significant increase in average annual temperatures. According to M.I. Budyko, in the northern hemisphere, the decrease in temperature ended in the mid-60s and was replaced by an increase in temperature, which accelerated in the early 70s. Research in recent years has shown that for the period 1964-1977. the increase in average annual global temperatures was 0.2-0.3 °C per decade. The greatest increase is typical for high latitudes. According to Budyko, north of 72.5° N. w. rate of temperature rise for 1964-1975. equal to 0.9 °C over 10 years for annual averages and 1.3 °C over 10 years for averages for the cold half-year. Consequently, secular temperature changes were accompanied by strong changes in the mean meridional gradient.

Many authors, including Angell and Korshover, Barnett, Painting, Walsh, based on an analysis of data on air temperature and at various latitudes of the northern hemisphere, unequivocally recognize that the cooling that occurred before the mid-60s was replaced by warming. The development of the 70s warming in the southern hemisphere, and in particular in Antarctica, was noted by Damon and Kuhnen. A. S. Grigorieva and L. A. Strokina analyzed data on temperature fluctuations in the oceanic waters of the northern hemisphere. Changes in water temperature in the Barents Sea and the North Atlantic Ocean are in good agreement with fluctuations in average air temperature, but lag somewhat behind them. This lag can be explained by the high heat capacity of ocean waters.

However, it should be noted that temperature fluctuations in the South Atlantic, North Pacific Ocean and other places do not show a tendency for temperatures to increase in the 70s. This appears to be related to the global system of sea currents.

Observations of the state of the ice situation in the polar regions, at the boundaries of sea ice and mountain glaciers make it possible to draw conclusions not only about the trend of temperature changes, but also about its impact on natural conditions. At the same time, as M.I. Budyko notes, the boundaries of sea ice not only strongly depend on air temperature, but, in turn, they influence the thermal regime of the atmosphere. At high latitudes above the ice-free ocean surface, the air temperature drops only a few degrees below 0°C as the ocean gives off a lot of heat. When the surface of the ocean is covered with ice, the air temperature drops tens of degrees below zero.

According to E. S. Rubinshtein and L. G. Polozova, sea ice cover in the Atlantic sector of the Arctic began to decrease in the 20s of the 20th century. This process in the Barents Sea continued until the mid-50s, after which the ice cover began to increase. The secular variation of ice cover in the Greenland and Barents Seas, calculated by A. S. Grigorieva, shows that the decrease in the area of ​​ice cover occurred after 1920 and reached its maximum value in the mid-50s. In the early 60s, the ice area increased again, but after 1970 it began to decrease significantly. According to R. Sanderson, from 1969 to 1974, ice cover in the Arctic decreased. Similar data are available for the southern hemisphere.

Along with changes in the thermal regime of the atmosphere, the amount of precipitation fluctuates. O.A. Drozdov and A.S. Grigorieva note that during the era of the greatest warming that occurred in the 30s, the number of droughts in zones of insufficient moisture in Eurasia and North America increased significantly. In particular, this is indicated by the drop in the level of the Caspian Sea and the decrease in the full flow of rivers.

Thus, during the 20th century. There were two periods of warming and cooling. The warming that began in late 1969 is currently underway, and temperatures tend to rise further.

For almost 200 years, regular meteorological observations have been carried out in different European countries (in our country they began even earlier - in 1743 in St. Petersburg). And although this period, with historical points of view, scanty, it allows you to catch important patterns in climate change. If during this time the air temperature is averaged over ten-year or even longer periods and, in order to avoid sharp jumps from one period to another, make them sliding, then it will become clear what climate shifts have occurred over the past 100-150 years. Take a closer look at the fig. 11, which shows the course of average January air temperatures in Leningrad from 1805 to 1960, averaged over sliding thirty-five-year periods (the horizontal line marks the average air temperature for all these 155 years), and you will notice that the average January air temperature in Leningrad for over the past century and a half, it has increased by almost 3 degrees. This indicates climate warming. Or, at least, that winters over the past 100 years have become warmer from one decade to the next to another and not only in Leningrad. The exception is, perhaps, the most recent winters, when frosts in many regions of the North and Central Asia became more and more severe. In the winter of 1967/68, the usually ice-free port of Murmansk froze. And meteorologists have not yet noted such a winter as there was in 1968/69 in Central Asia in their observations. But even this still unexplained cooling cannot obscure the picture of the general warming of the climate that occurred over the last century until the sixties.

It must be said, however, that this warming was not the same everywhere. In some places it was more pronounced, in others - weaker, and in some, on the contrary, even cooling was observed. If we take into account not only the climate of the USSR, but also of other countries, then we can cite, for example, the following figures.

On the Greenland coast, winters have warmed by 6 degrees. The climate of Ireland in the first half of this century became the warmest in the previous 750 years. But in Australia, according to observations in Adelaide, winters, on the contrary, have become colder by 2 degrees.

Climate warming was evidenced not only by meteorological observation data, but also by a decrease in ice cover in the northern seas, the appearance of heat-loving fish in the Arctic, a reduction in the period of ice off the coast of Iceland, the migration of many species of birds far to the north, and a number of other facts.

But perhaps the most accurate indicator of climate warming on Earth can be considered the almost universal retreat of glaciers. Observing the level of the world's oceans, scientists noticed that in the last century it has risen, according to some data, by 10, and according to others, even by 50-60 cm. Such a rise in level could only be caused by increased melting of glaciers, since precipitation falling above the surface ocean, are balanced by evaporation. Taking the area of ​​the world's oceans to be 360 ​​million square meters. km, and the ice density is 0.8, you can count how much

ice would have to melt every year to cause sea levels to rise by 10 cm per century. It will be about 45 thousand cubic meters. km. What is the actual loss of ice on the globe has not yet been precisely determined. But no one doubts that glaciers are retreating, and in many places around the world have even disappeared completely in recent years. This retreat is taking place very unevenly and not everywhere equally. Periods of rapid retreat are followed by periods of peace or even a new offensive. In nature there is, as it were, a great battle between ice and the sun. There is a lot of documentary data about this fight, collected over the past 500 years. Particularly strong evidence has been obtained for the Alpine zone, the most studied mountain region in the world. The first observations of glaciers here date back to the end XVI century, when the widespread advance of glaciers was noted, driving the Alpine mountaineers from their homes. Until this time, for apparently several centuries, the Alpine glaciers were in a stationary or little-moving state, since several generations of local residents were able to take deep roots here.

At the end XVI and the beginning XVII centuries, the climate in Europe became noticeably colder. The glaciers came to life and began to quickly conquer new territories, sweeping away farms and villages along the way. This offensive lasted 25-30 years. Then there was a period of calm and even a slight retreat of the ice. The last advances of Alpine glaciers were observed between 1814 and 1820, and also between 1850 and 1855. During these years, the ice again reached the boundaries they had conquered at the end XVI centuries. The records of Scandinavia and Iceland also contain much evidence of the advance and retreat of glaciers over the past few centuries. Comparing all this data, scientists found that the main periods of glacial advance and retreat in Europe largely coincide. The history of the settlement of Iceland by the Scandinavians confirms that since IX By XIV century the climate on the island was mild. At the end XIII century, cooling and the onset of glaciers began, and by the end XVIIcentury, the climate changed so much that the Settlements that had existed here for several centuries were buried under a layer of ice and were freed from it only very recently.

The ice conquered not only the land, but also the sea. Before XIII centuries, the Scandinavians freely sailed directly to Greenland.

Later, their path began to lie much further south, and at the beginning XV century, Europe's connection with Greenland was completely terminated. When in XVI century, Europeans “discovered” it again, they did not even find traces of ancient settlements there. Everything turned out to be covered with ice.

The history of the duel between ice and sun was recorded not only by people, but also by nature itself. The chronicles written by her go back thousands of years. Nature has well preserved in its memory the last 10-12 thousand years of Earth's history. She captured them in terminal moraines and ribbon clays deposited at the bottom of glacial lakes and swamps, in plant remains, in peat deposits, and on coastal rocks. But perhaps most interesting information, which nature has preserved almost unchanged in its depths, is pollen and spores of plants that lived many tens and even hundreds of thousands of years ago.

Everyone knows the amazing ability of plants to produce spores and pollen in huge quantities. It is enough, for example, to point out that only one oak inflorescence generates 500 thousand dust particles during the summer, a sorrel inflorescence produces up to 4 million, and a pine inflorescence produces up to 6 million dust particles per flowering. When trees bloom, sometimes so much pollen rises into the air that it even takes on a unique color. When pollen settles on the ground, it covers not only the soil, but also the surfaces of water bodies. Then it settles to their bottom and, buried in layers of peat and lake silt, remains there, not rotting, not being destroyed over time, sometimes for millions of years. (By the way, the shells of spores and pollen can withstand heating up to temperatures of 300 degrees and cannot be treated with alkalis and acids.)

Under a microscope, such shells or, as they are called, pollen grains resemble in their shape small shells, sometimes with very original and beautiful patterns. Each plant has its own pattern. The task of paleobotanists is to determine which plant species or pollen pattern belongs to which plant. And I must say, botanists have mastered this art to perfection. Now there are no more “white spots” in pollen analysis. The types of spores and pollen of all the most common plants from the most ancient geological eras to the present day have been identified and classified. It is easy to understand that by detecting one or another type of pollen when taking samples, scientists can determine what plants lived in a particular era and what the climate was like then.

Using the pollen method, scientists seem to read the chronicle of nature in reverse order. But the analysis of pollen and spores by itself cannot yet establish the absolute age of the layer of soil or peat in which it is found, so its use must be combined with the main methods of determining the age of the Earth.

Considering, for example, a multi-meter layer of peat in some ancient swamp, scientists know in advance that its growth averaged 0.5-1 mm per year or 100 cm per century. Therefore, when they take a sample, for example, from a depth of two meters, they already know that the plant pollen preserved there was buried 2-4 thousand years ago. Sometimes unexpected “milestones” also contribute to such an analysis. In Germany, near Hamburg, for example, in one of the peat bogs at a depth of 1 to 1.8 m, scientists discovered an ancient road in the form of a deck made of logs. Coins minted during the Roman Empire, about 2 thousand years ago, were found on this road. This unique benchmark made it possible to more accurately determine both the age of the peat bog and the rate of its growth, which turned out to be equal to 0.5-1 mm per year.

Scientists often come to the aid of data from dendrochronology (the science of determining the age of trees), which allows one to read what happened in nature from the rings of centuries-old trees growing in unfavorable conditions and very sensitive to lack of heat and moisture. As you know, trees form one ring every year. In wet years these rings are wider, in dry years they are narrow. An unsightly-looking bristlecone pine grows on the rocks of the White Mountains in California. From year to year she fights for her harsh existence, but lives for several thousand years. If you cut down such a pine tree and polish its cut, then with the help of a magnifying glass you can clearly see each ring and determine by year how the climate there has changed over the past 2-4 thousand years. American scientist Edmund Shulman in 1957 discovered bristlecone pine, which he counted 4,600 annual rings. This pine tree, which settled high in the mountains, survived the glaciers moving through the neighboring valleys and could serve as a witness to their “battles.”

As it advanced, the glacier dragged down tree trunks, stones, layers of soil, and even animal carcasses. And when he retreated, all this remained in the place where the ice had reached, forming the so-called terminal moraine. Scientists have found ways to determine the age of moraines and, from them, the time of glacier retreat. One of these methods is radioactive, developed by physical chemists in 1947. Among the mixture of gases that make up air, there is a very small proportion of radioactive carbon, the atomic weight of which is 14 1 (C 14). Like any radioactive element, C 14 gradually decays, then turning into nitrogen, from which it is formed under the influence of neutrons flying from space. The half-life of radioactive carbon is about 5,600 years, with three-quarters of the decay occurring in 11,400 years and complete decay in 70,000 years.

Any living creature that lived in one era or another absorbs C 14 in the process of breathing or through food. The absorbed radiocarbon goes into the structure of its tissues, and in animals, into the creation of the bone skeleton. With the death of an animal or plant, the intake of radiocarbon into the body stops, and the previously absorbed carbon begins to decay. By measuring the intensity of its decay using special device, a researcher can determine the time of death of an animal or plant with a small error. Thus, the use of this method allows us to look into the history of the Earth 70 thousand years ago.

By comparing the data obtained from the study of terminal glacial moraines with the results obtained using other methods (for example, dendrochronology), it is possible to quite accurately determine the time of glacier retreat.

There are also more ways, which are often used by scientists to determine the period of ice retreat. In addition to the terminal moraines, the glacier leaves behind lakes into which water flows during the melting of the ice. If you take a soil sample from the bottom of these lakes, you can see that it consists of separate horizontal pairs of layers or ribbons - one thick, the other thin. Each pair, like an annual ring on a tree, forms at the bottom of a glacial lake within one year. In the spring, when the ice melts and muddy water flows into the lake, only the most large particles. In winter, when the melting stops and the water in the lake becomes calm, small suspended particles settle to the bottom. They form a second silt layer, covering the summer sandy and looser layer. By drilling down to the lowest layer and counting the total number of layers, you can determine the year when the glacier began to retreat. This is how, for example, glacial lakes in Scandinavia were studied. Swedish geologist De Geer found that the end of glaciation in Sweden occurred about 12 thousand years ago. A study of remnants of terminal moraines and marshy lakes in the United States found that glaciers there retreated almost 11,400 years ago. Thus, it can be considered proven that the largest of the last glaciations, which covered most of Europe and North America, called by scientists the Great Glaciation, ceased to exist about 11-12 thousand years ago. And the study of pollen deposited in the depths of swamps, at the bottom of lakes or in deeper layers of soil over the past 11-12 thousand years, along with other direct and indirect methods of studying the biography of our planet, made it possible to establish that during this period, sometimes called During the Holocene, the climate in the northern hemisphere changed at least three times.

Immediately after the retreat of the glaciers, despite the warming, the climate was still cool and very humid. At the end of this period, the remaining glaciers attempted a new offensive and reached their maximum size somewhere around 8.5-9.0 thousand years ago. During these years, the disappeared ice again covered the Arctic islands (Spitsbergen, Franz Josef Land, etc.), descended to the foothills of the mountains of Scandinavia and occupied many previously free valleys in the mountains of North America and Europe. Since after the retreat of glaciers, cold-loving tundra vegetation first settles in their place, which is then replaced by more heat-loving coniferous forests, spruce pollen predominates at this time in all glacial deposits of Northern Europe and North America.

Following this comparatively cold and wet period, a second warm period began, from the end of which only some three thousand years separate us.

There is a lot of "witness testimony" from nature about the presence of this period. And one of them is traces of the former coastline, which at that time was 1.5-1.8 m higher than the current level of the world ocean. The sea then flooded much larger areas of land than it does now. On coastal sea shallows in tropical latitudes, heat-loving coral reefs have even managed to grow. At the same time, on the continents of the northern hemisphere, spruce and fir gave way first to pine, and then to oak and other heat-loving deciduous trees. An analysis of pollen taken, for example, from the excavation site of an ancient human site in Veretye ​​(this site was located near the mouth of the Kineshma River and dates back to the beginning of the second century BC), showed that in those days pine, spruce, birch with a large admixture of oak and elm. If we consider that oak does not grow there now, we can say that the climate here at that time was much warmer.

We have already said that the analysis of pollen taken from peat bogs near Hamburg, the age of which dates back to the time of the Roman Empire, that is, about 2 millennia, indicates that a warm and relatively dry climate also prevailed in western Europe at that time , much warmer and drier than at present. In the northern hemisphere, there is much evidence of the end of a period of warm and relatively dry climate, or the so-called subboreal phase. After all, the last 2.5-3 millennia is a period of human history already well known to us. The third and last climate change after the Great Glaciation, which scientists called the Subatlantic phase, began 2.5 millennia ago, continues to this day. It is characterized by wetter and cooler conditions, with frequent harsh winters, which caused freezing not only of the river. Danube, but also the appearance of ice off the coast of the Aegean Sea. It is quite clear that climatic conditions during this phase also did not remain constant. Harsh and snowy winters were followed by long dry periods. At the beginning of our era, for example, the climate in Europe was much warmer than it is now.

IN VII century, Alpine passes, which are still blocked by ice and snow and accessible only to skiers or climbers, were opened. Trade routes from Rome to Central Europe passed along them. Thus, everything confirms that the climate after the Great Glaciation was very heterogeneous. The glaciers that survived in some places either came to life or froze again, but their activity was local in nature and limited to mountainous areas. They no longer crawled onto the plain. Glaciation in the northern hemisphere could only be found in Greenland.

Well, what do scientists say about the Great Glaciation itself?

Radioactive carbon preserved in the fossilized remains of animals and plants allows us to partially answer this question and clarify the area occupied by the glacier. On March twenty-fifth, 1967, Greece reported that on the island of Chios, which is located in the Aegean Sea, paleontologists discovered the skeleton of a prehistoric a mammoth, whose age they determined to be 20 million years. How this mammoth got to the small island remains a mystery. Apparently, the island in those days was connected to land, and the modern Mediterranean Sea had different outlines, mammoths were heat-loving animals and the fact that they were found in the area Mediterranean Sea, is not of much interest to climate scientists. But the fact that mammoths were discovered in northern Siberia, Yakutia and northern America, and there are already about 40 such finds from 1692 to the present, is extremely significant.

Studies of the age of the world-famous Berezovsky mammoth, discovered by an Evenk hunter in 1900, showed that it lived in these places about 30 thousand years ago. The age of the young mammoth found in the North. America, estimated to be 21,300 years old. There were other mammoths whose death occurred about 11-12 thousand years ago. The conclusion suggests itself. Heat-loving animals could live in the Arctic and Subarctic only if there was a sufficiently warm climate here. Apparently, in the period from 12-15 to 30 thousand years ago, the climate of the Far North and northeast of Siberia and northern America was quite warm, and if there were glaciers, they were only high in the mountains. A different picture was then observed over Europe and the northern part Western Siberia.

The famous Soviet glaciologist V. M. Kotlyakov in his book “We Live in the Ice Age” indicates that the area of ​​glaciers at that time reached 40 million square meters. km, and the average thickness of the ice cover is 2.5 km. The ice boundary in the south extended to 50° north latitude, that is, to the southern regions of the Voronezh and Belgorod regions. The Volga region and Zhiguli were covered with ice. How long the period of the last glaciation lasted, perhaps no one can say for sure. According to the American scientist D. Wirthman (1964), the development of major glaciation (from the steady advance of glaciers to the maximum development of the ice sheet) requires 15-30 thousand years. But for the destruction of the glacier, in his opinion, it takes only about 2-4 millennia. And if this is so, then, knowing that the European continent was freed from ice cover about 10 - 12 thousand years ago and adding another 4 thousand years for the period of its melting, we can say that the destruction of the last glaciation in the northern hemisphere began only about 20 thousand years ago. However, many scientists believe that it began much earlier. They estimate the entire period of glaciation at 40-50, and some even at 70 thousand years. This glaciation, called the Würm glaciation in Europe and the Wiskon glaciation in America, was, of course, not the only one. It was preceded by even earlier glaciations, each of which scientists usually call by the name of the place where their traces were found. On the Russian Plain, early glaciations, for example, by S.V. Kolesnik are called Yaroslavl, Likhvonsky and Dnieper, and the latest - New Quaternary glaciation is divided into Moscow, Kalinin and Valdai. Thus, almost the entire last period of the geological history of our planet is characterized by long glaciations, followed by shorter interglacial ones. It is not for nothing that this entire period, which according to some sources lasted from 1 to 2 million, and according to others a little more than 500 thousand years, was called by scientists the Pleistocene, or Ice Age.

Nature has preserved the remains of this era in the form of a reserve to the present day: in the northern hemisphere it is the Greenland Glacier, and in the southern hemisphere it is Antarctica.

Based on observational data in Antarctica and Greenland, we can judge with sufficient accuracy the main features of the climate that dominated the vast territory of the Soviet Union occupied by a glacier just some 15-20 thousand years ago.

Summer temperatures on the snow surface in the center of Greenland usually do not rise above -5, -10 degrees, and the average monthly temperature air is 12-13 degrees below zero. Such a low temperature is, of course, also facilitated by the high altitude of the glacial surface, which is about 2500 m, and in some places reaches 3200 m above sea level. The air temperature above glaciers at such an altitude, even in moderate latitudes, in summer cannot rise above 8-10 degrees below zero. This is how it was, apparently, during the Ice Age over the ice-covered European territory of our country. Precipitation at that time was no more than 200-250 mm per year, that is, 3-4 times less than now. And they only fell out in solid form. Most of the time the weather was clear over the glacier. The dazzling snow sparkled under the rays of the sun. The air was as transparent as it is now only on cold winter evenings, when the dawn seems golden-green. The days were calm or with light winds blowing up the barely visible glacial slope. But as soon as the sun dropped to the horizon, the wind abruptly changed its direction to the opposite and fell down the same slope with rapid force, continuously increasing its speed as it approached its foot. Where the glacial slope was steeper, storm and hurricane winds raged even in summer around the clock, raising clouds of snow dust as sharp as sandpaper into the air. The blue sky shone through it, and the sun seemed surrounded by fantastic rainbow halos with a whole system of multi-colored pillars and false suns.

During periods when there were short calms, the wind suddenly weakened, and the blowing snow was replaced by a weak drifting snow. Her tongues slowly curled between the tall sastrugi, polishing them to a shine. If the drifting snow was strong enough, then jets of snow, bumping into the sastrugi, flew up in fountains. In the evenings, when the rays of the low sun were refracted in the snow crystals of the blizzard and decomposed into the constituent colors of the rainbow, the entire surface of the glacier was covered, as it were, with a light colored blanket, decorated with many multi-colored fountains. On some particularly “hot” summer days, when the temperature at the snow surface at noon rose to minus 4-5 degrees, small wings of cumulus clouds formed above the glacier at an altitude of only 100-200 meters from the snow surface. Sometimes such clouds appeared at the very surface. They merged with each other, forming a layer of swirling snow fog. From the outside, such a layer looked like a huge fire. In cloudy weather, when the sky was covered with a low veil of gray and monotonous stratus clouds, through which the sun's rays could not penetrate, “white darkness” dominated the surface of the glaciers. On such days, despite the greater transparency of the air, the horizon was not visible at all. All the sastrugi and snowdrifts merged with the background of the sky, the contrasts disappeared, the surface of the glacier seemed to turn into a plain. But dark objects accidentally brought onto it were visible incredibly far away. It seemed that they had increased in volume and rose somewhat above the surface. Any living creature that found itself on a glacier in such weather ceased to see what was happening before its eyes and could not take a single step without tripping. Everyone became blind in this completely transparent air.

Summer over the glacier lasted no more than three to four months. In September, the temperature immediately dropped by 10-15 degrees. The katabatic winds intensified and blew continuously around the clock, although their speed weakened somewhat during the day. All the summer phenomena just described disappeared, only the colored snowstorm still covered the icy surface with a rainbow veil, and fantastic winter rainbows, circles, crowns and colorful pillars near the sun hung in the sky throughout the day. From October to April, winter prevailed with severe frosts, fierce winds and snowstorms. Frosts in any of these months could reach 40, and in the north 50 and even 60 degrees. Where the icy surface had even the slightest slope, the cold air rolled down it, accelerating like a skier. On steep slopes, its speed near the foot reached the force of a storm or even a hurricane. Strong snowstorms in some places tore off and in others deposited countless snowdrifts - sastrugi, continuously changing the face of the glacial surface. Despite the abundance of ice and snow, the air above the glacier was almost as dry as in the desert. Precipitation fell only when cyclones arrived from the then-unfrozen Arctic Ocean or from the Atlantic.

March and April, although they were winter months, were distinguished by an abundance of sunlight and some warming of the air during the daytime hours. But May was a real spring month. In terms of weather and temperature conditions, it was similar to March somewhere in northern Europe. During May, average air temperatures everywhere rose by 10-15° and reached only 15-20° below zero in most parts of the territory. The winds died down. The snowstorms were weakening. The sun was very hot at midday. Spring lasted 1.5 months and was replaced by a kind of “summer”, which has already been discussed (it can still be observed over the glacial expanses of Antarctica and Greenland). After the strong melting of glaciers began and no winter precipitation could compensate for the loss of water that flowed into rivers and seas, ice and snow began to be freed - not only the territory of the earth near the edge of the glacier, but also the most elevated areas of land where the ice sheet was the least powerful. Original oases appeared among this icy desert, such as currently exist in Antarctica. These oases already had their own local climate. The surface temperature here in summer could rise tens of degrees above zero. The air was also drier and warmer than above the glacier. Over the oases, their own air circulation arose, local winds blew, which changed direction during the day, following the course of the sun. Such oases, being a kind of thermal centers among the surrounding icy desert, contributed to the destruction of glaciers from the rear, greatly accelerating the process of their melting and retreat. One can only guess what happened on our land after huge masses of ice began to melt so quickly. How much water was formed then during the warm period of the year, how great and terrifying the global floods were at that time, and how high the level of the world's oceans rose in 4-5 thousand years. If we consider the volume of melted ice to be approximately 100 million cubic meters. km, and the ocean area is close to the modern one (360 million sq. km), then the annual rise in its level will be about 4-5 cm, and the total rise over 4 thousand years is more than 200 meters. It is not known exactly what this rise in level actually was. D. L. Dyson in his book “In a World of Ice” (1963) indicates that during the Würm glaciation the sea level was 76 meters lower than now. If this figure is correct, then we can assume that the period of melting of the glacier lasted not 4 thousand years, but twice as long. Be that as it may, in both cases the annual rise in sea level was catastrophic, sea ​​waters Huge coastal areas were flooded, and the flooding caused by flood waters is even difficult to imagine. The annual melting of ice required for such a rise in sea level should be approximately 0.6-1 meter. Let us imagine for a moment that in one winter 2.5 meters of snow fell somewhere in the center of Russia (the amount of water in 1 meter of ice is approximately equivalent to the amount of water obtained from 2.5 meters of snow), and all this snow melted with the onset of spring .

Residents of Novgorod remember the recent spring of 1965, when in the Leningrad, Pskov and Novgorod regions the snow height at the beginning of spring reached 60-80 cm. That year, snow melting caused the water in the rivers to rise by 6-8 meters or more. A significant part of Novgorod remained covered with water until June. Against the background of all that has been said, the biblical legend of the global flood does not seem so implausible. Let us remember that this legend was born in the homeland of the Sumerians in Mesopotamia. If we look at the map, we will see that the Mesopotamian lowland is cut from north to south by two huge rivers - the Tigris (1950 km) and the Euphrates (2760 km). For people moving at a speed of 5-10 km per hour, this lowland seemed like Peace. There is no doubt that during the Great Glaciation, the mountains of Asia Minor - the Taurus, from which the Tigris and Euphrates originate, as well as the Caucasus mountains, were covered with a thick layer of ice. During the period of climate warming in the northern hemisphere, when glaciers began to rapidly melt, masses of water poured through these rivers into the Persian Gulf, flooding the Mesopotamian lowland. Such a flood, of course, led to the death of almost the entire population living in this territory, and for those who escaped, the flood could truly seem worldwide. Scientists from different countries have long had no big doubts about this, but expressing their assumptions without any material evidence meant going against the powerful foundations of religion. But in the 70s of the last century, an employee of the British Museum in London, D. Smith, deciphering tablets with ancient cuneiform writing that he received from Nineveh, discovered that they contained an ancient poem about the exploits of the Sumerian hero named Gilgamesh. It also spoke of a global flood, the description of which very closely coincided with a similar biblical legend. This was already material evidence with which it was possible to oppose the church version of the Flood. Legends are often poeticized history. You just need to decipher them. Therefore, the translation of the legend published by Smith not only met a furious storm of protest from the “pious” ignoramuses and clergy of Victorian England, who saw in it an undermining of the Holy Bible, but also aroused great interest among scientists from various branches of science. One of these enthusiastic scientists was the famous English archaeologist Leonard Woolley. Having gone to the region of the former Sumerian kingdom and having found its ancient capital, he began his excavations there. Breaking through the so-called cultural layer of soil, formed as a result of the life activity of subsequent generations of people, to a depth of 14 meters, he discovered on the outskirts of the ancient city the tombs of Sumerian kings buried at the beginning of the 3rd millennium BC. e. They contained great values, but they were not what interested the scientist. He was attracted to the more ancient period of human history. Therefore, excavations were continued. Imagine the scientist’s surprise when he discovered that the deeper layers of the soil consisted of sedimentary rocks. It was river silt, which could only form at the bottom of a river about 8-10 meters deep. After carrying out topographic calculations, Woolley came to the conclusion that such a river could flow here only temporarily, since the soil lay too high here. Having excavated this layer, the thickness of which turned out to be three meters, the scientist discovered underneath it an older cultural layer, in which he found bricks, ashes and fragments of ceramics. The shape and ornament of the ceramics spoke of some completely unknown culture. The conclusion suggested itself. Once upon a time there was a very ancient human settlement here, which, apparently, was flooded during a catastrophe and buried at the bottom of the resulting river or lake. The presence of a layer of silt and sand above it indicated that the flood was enormous. In order for 3 meters of silt to be deposited, water had to stand here for at least several thousand years. Perhaps these millennia separate the “antediluvian” civilization from the most ancient civilization known to us - the Sumerians, who settled the gradually dried-up Mesopotamian lowland, believing that no one had ever lived here before them. Let's hope that scientists, having modern methods for determining the absolute age of ancient burials, in the near future will be able to establish both the absolute age of silt deposits and the mystery of the people flooded by the “universal” flood, who, apparently, lived here just during the Great Glaciation.

Well, what was the post-glacial period like on our Russian Plain? If this period could be filmed at a speed of 25 or 50 years per minute, then in the first frames we would still see how the glacier is retreating. From under it flow rapid streams of melt water, which then merge into huge rivers: the Volga, Dnieper, Don, Western Dvina, etc., several times wider than modern ones. The area where the glacier was just located is a treeless tundra covered with boulders and cluttered with stone shafts of terminal moraines. All the depressions, as far as one can see, are filled with countless lakes with clear blue water and clearly defined rocky shores.

To the southeast of the seemingly lifeless tundra, reminiscent of modern Antarctic oases, stretches a wide dark green zone of coniferous forests. Its southern border goes far beyond Moscow, and on the Volga it almost reaches Kuibyshev. To the south there is a light green strip of deciduous forests with a predominance of oak, beech, maple and birch. It occupies almost the entire Ukraine and, gradually narrowing to the east, merges with the deciduous forests of the Southern Urals and Northern Kazakhstan. And only in the southeastern regions of the European territory of our country does it turn into steppes. But only a minute or two passes, and we see on the screen how the former rocky tundra is first covered with typical tundra vegetation with low-growing single specimens of conifers, then the woody vegetation becomes denser and denser until it completely covers this recently treeless region. The tundra has now moved far to the north and northwest, following the glacier, which has retreated into the mountains of Scandinavia and no longer represents a single whole. It took only a few centuries after the glaciation for the landscape of the northern part of the Russian Plain to completely change its appearance. The rapid melting of huge masses of ice, which caused the retreat of powerful glaciers, contributed to the formation of more than one “global” flood in different regions of the northern hemisphere. Water flooded all low-lying places, forming huge lakes and rivers of unprecedented size. Their size can now be judged only by the huge valleys, ledges descending to the bottom of the floodplain, in which modern streams and rivers flow along a very narrow channel.

Imagine a snowdrift that melts in the spring. With the onset of warmer weather, the snow settles, and the boundaries of the snow melt less and retreat from the “winter” ones, streams flow from under the snowdrift... And on the earth’s surface everything accumulated by the snowdrift during wintering is spread out: garbage, leaves, fallen branches, etc. all kinds of dirt. Now try to imagine the same snowdrift, but larger in size, about a million times, which means that the pile of “garbage” left behind after the melting of the glacier will be mountain-like in size! The melting of a large glacier is called retreat, and this retreat leaves even more "debris" behind. Everything that a glacier left behind on the earth’s surface is usually called glacial deposits or moraine.

Along the way, glaciers destroy valleys and wear and scratch rock ledges. In addition, the glacier can also transport all this garbage over enormous distances, from the places where it received it. Glacial deposits are distinguished from where the debris is located and how it was transported by the glacier.

On the surface of a glacier, surficial deposits form - all the materials that fall onto the glacier. Most of debris accumulates on adjacent slopes. Here ridges of lateral moraines are created, and if the glacier has more than one tongue, then when they merge into one common tongue, the lateral moraines will become median. After the glacier melts, the moraines become like elongated mounds that stretch down the valley along the slopes.

The glacier is constantly moving. Since a glacier is a viscoplastic body, it is characterized by the property of flowing. Consequently, even a fragment that fell from a cliff, not a glacier, after a while can move far from the place of fall. Debris accumulates (collects) most often at the edges of the glacier, in the place where glacier melt dominates ice accumulation. The accumulated debris follows the contours of the glacial tongue and forms the shape of a curved embankment that partially blocks the valley. During the retreat of the glacier, the terminal moraine melts into its original place and is eventually eroded by warm currents. When the glacier melts, it is possible to accumulate many ridges of terminal glacial deposits, which will “speak” about the intermediate stages of the tongue.

The glacier has thawed. A ridge of glacial deposits remained in front of him. But the retreat continues. And behind the final glacial deposits, glacial waters accumulate. A glacial lake is formed and a natural dam is held back. When a lake of this type breaks out, a mudflow is often created - a destructive flow of stones and mud.

As the glacier moves into the lower parts of the valley, it destroys its main part. Often this process, which, by the way, is called “exaration,” is performed unevenly. And at this time, crossbars are created - steps in the glacial bed.

Sheet glaciers have significantly larger and more varied glacial deposits, but their topography is less well preserved. After all, they are often more ancient. And the location on the plain is much worse traced than, for example, in a mountain glacial valley.

In the last ice age, a huge glacier advanced from the Baltic crystalline shield, from the Kola and Scandinavian peninsulas. In places where the crystalline bed was plowed out by the glacier, selgi - long ridges - and elongated lakes were formed. There are many such lakes and selgas in Finland and Karelia.

It was from those places that the glacier brought piles of crystalline rocks such as granite. Given the long transportation, the ice wore away the irregularities in the debris, which turned into boulders. Granite boulders are still found in the Moscow region to this day. These fragments, brought from afar, are called erratic. From the stage of the last maximum glaciation - the Dnieper, when the end of the glacier began to reach the valleys of the modern part of the Don and Dnieper, only glacial deposits and boulders remained.

The cover glacier, after its complete thawing, left only a moraine plain - a hilly space. Also, many streams of glacial waters burst out from under the edges of the glacier. These flows eroded the bottom and terminal moraine, carried away fine clay particles and left outwash - sandy fields in front of the edge of the glacier. Melt water often created tunnels under the glacier, which could no longer move. Such tunnels contained large quantities of washed-out glacial sediments such as boulders, pebbles and sand. Clusters of moraines that remain in the form of long, sinuous ridges are called eskers.

Indo-Europeans of Eurasia and the Slavs Gudz-Markov Alexey Viktorovich

Chapter 1. Glacier retreat to the north. Revitalizing life in Eurasia

The retreat of the fourth and last Würm glaciation in the history of the Earth began in the 18th millennium BC. e. However, Northern Europe remained shackled by an ice shell, the thickness of which reached two kilometers, for another ten millennia. A frozen sea of ​​blue ice rested on the northern spurs of the Alps and Carpathians.

On the slopes of the Ural ridge, a powerful ice tongue reached the heart of the Eurasian plain. The mountain peaks of the Pyrenees, Apennines, Balkans, Caucasus, and Central Asia were covered with huge ice caps, sending cold-freezing streams of ice and snow into the deep valleys surrounding them. From Middle England to the Middle Dnieper and further to the Pacific Ocean, the Eurasian continent was surrounded by a wide belt of tundra. The Arctic cold scorched the waters and shores of the Mediterranean, Black and Caspian Seas with piercing cold. And in Southern Europe, in Asia Minor, across the vast expanses of Central Asia and Siberia, the ocean of taiga stretches like evergreen pine needles.

By the 14th millennium BC. e. The lands of modern Denmark, Germany, Poland, Southern Lithuania, parts of Northern Russia and Siberia were freed from under the ice cover. The glacier retreating into the Arctic left huge lakes everywhere and piles of huge boulders scattered everywhere. The contours of the northern seas emerged from under the ice. Following the retreating glacier, mammoths, woolly rhinoceroses, and reindeer moved north. To the south of them, on the vast Eurasian expanses, herds of wild horses, bulls, deer, and bison grazed. They were constantly hunted by hyenas, bears, and cave lions. The mammoths and woolly rhinoceroses that reached the north of the continent soon died and now remind of themselves only through fossilized frozen remains preserved by permafrost.

In the XIV–XI millennium BC. e. The final, Gothic, phase of the last (Würm) glaciation of the Earth has passed. From century to century, the rocks of Northern Britain and Scandinavia, polished by ice and cold, became more and more clearly visible. The sun rescued them from icy captivity, which lasted almost a hundred thousand years. Following the retreating glacier, the tundra, scorched by the arctic cold, was lined with a boundless green carpet. And after it, the taiga crossed the Carpathian and Alpine barriers. Year after year, she moved further north, towards the steaming cold of the Arctic, dwarf birch trees torn by the prickly winds and shapeless, spreading pines, clinging to the death to the thawing earth with light yellow crooked trunks. Following the persistent green dwarfs, the seas of coniferous forests advanced in living waves to the north.

For ten thousand years, a gigantic ice sheet slid meter by meter from Europe.

The planet was thawing, the climate was softening. The continent was covered with mixed forest. Its fragrant, delicate green canopy hid the earth from the piercingly cold air currents from the north. Glacial lakes were filled with life, their marshy shores were overgrown with lush grasses. Silent unwitting wanderers, eternal companions of the glacier - boulders, fragments of distant northern rocks, gloomy uninvited guests in Europe - were dressed in moss and grew into the turf. In northern Eurasia, warmed by the sun, oak groves, spreading lindens, and elms were added from century to century.

But in the 9th millennium BC. e. Europe still fully felt the cold of the receding Arctic ice. The steep cliffs of Britain and Scandinavia, polished almost to a mirror shine by the salty waves of the Atlantic, blue ice floes and cruel winds, said goodbye for an endlessly long time to the vast sparkling ice field creeping to the north.

During the 9th–6th millennium BC. e. The forest-tundra of Northern Europe is overgrown with mixed forest. The canopy of the forests was filled with many red deer, boars, fur-bearing animals, and a rich feathered world. Europe was turning into a hunting paradise. The climate became milder from century to century.

Freed from ice captivity, the Baltic took on its modern shape. The waters of Lake Ladoga made their way to the Gulf of Finland and formed a new river - the Neva. The land that existed between Britain and the continent gradually sank more and more into the depths of the sea. The resulting English Channel separated the islands of the British archipelago from Europe. The Black Sea for a long time remained a lake connected to the Caspian Sea, but its breakthrough by the waters of the Bosphorus Isthmus was approaching, and around the 5th millennium BC. e. this event happened. Europe was taking on its modern shape.

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