Sometimes you can hear the statement that the Ice Age is already behind us and people will not have to deal with this phenomenon in the future. This would be true if we were sure that modern glaciation on the globe is just a remnant of the Great Quaternary glaciation of the Earth and should inevitably soon disappear. In fact, glaciers continue to be one of the leading components of the environment and make an important contribution to the life of our planet.
Formation of mountain glaciers
As you ascend into the mountains, the air becomes colder. At some altitude, winter snow does not have time to melt during the summer; from year to year it accumulates and gives rise to glaciers. A glacier is a mass of multi-year ice of predominantly atmospheric origin, which moves under the influence of gravity and takes the form of a stream, dome or floating slab (in the case of ice sheets and shelves).
In the upper part of the glacier there is an accumulation area where sediment accumulates, which is gradually converted into ice. Constant replenishment of snow reserves, its compaction, and recrystallization lead to the fact that it turns into a coarse-grained mass of ice grains - firn, and then, under the pressure of the overlying layers, into massive glacier ice.
From the accumulation area, ice flows to the lower part - the so-called ablation area, where it is consumed mainly by melting. The upper part of a mountain glacier is usually a firn basin. It occupies a car (or cirque - the extended upper reaches of the valley) and has a concave surface. When leaving the cirque, the glacier often crosses a high mouth step - a crossbar; Here the ice is cut through deep transverse cracks and an icefall occurs. Then the glacier descends in a relatively narrow tongue down the valley. The life of a glacier is largely determined by the balance of its mass. With a positive balance, when the flow of matter on the glacier exceeds its flow, the mass of ice increases, the glacier becomes more active, moves forward, and captures new areas. If negative, it becomes passive, retreats, freeing the valley and slopes from under the ice.
Perpetual motion
Majestic and calm, glaciers are in fact in constant movement. The so-called cirque and valley glaciers flow slowly down the slopes, and ice sheets and domes spread from the center to the periphery. This movement is determined by the force of gravity and becomes possible due to the property of ice to deform under stress. Brittle in individual fragments, in vast massifs the ice acquires plastic properties, like frozen pitch, which cracks if you hit it, but slowly flows along the surface, being “loaded” In one place. There are also frequent cases when ice with almost its entire mass slides along the bed or other layers of ice - this is the so-called block sliding of glaciers. Cracks form in the same places on the glacier, but since new ice masses are involved in this process each time, the old cracks, as the ice moves from the place of their formation, gradually “heal”, that is, they close. Individual cracks stretch across the glacier from several tens to many hundreds of meters, their depth reaches 20-30, and sometimes 50 meters or more.
The movement of thousand-ton ice masses, although very slowly, does a tremendous amount of work - over many thousands of years it transforms the face of the planet beyond recognition. Centimeter by centimeter, ice creeps along solid rocks, leaving grooves and scars on them, breaking them and carrying them with it. From the surface Antarctic continent glaciers annually remove layers of rock with an average thickness of 0.05 mm. This apparent microscopic value already grows to 50 m if we take into account the entire million years of the Quaternary period, when the Antarctic continent was probably covered with ice. Many glaciers in the Alps and Caucasus have an ice movement speed of about 100 m per year. In the larger glaciers of the Tien Shan and Pamir, the ice moves 150-300 m per year, and on some Himalayan glaciers - up to 1 km, that is, 2-3 m per day.
Glaciers have the most different sizes: from 1 km in length - near small cirque glaciers, to tens of kilometers - near large valley glaciers. The largest glacier in Asia, Fedchenko glacier, reaches a length of 77 km. In their movement, glaciers carry over many tens, or even hundreds of kilometers, blocks of rock that have fallen from mountain slopes onto their surface. Such blocks are called erratic, that is, “wandering” boulders, the composition of which differs from the local rocks.
Such boulders are found in thousands on the plains of Europe and North America, in the valleys at their exit from the mountains. The volume of some of them reaches several thousand cubic meters. Known, for example, is the giant Ermolovsky stone in the riverbed of the Terek, at the exit from the Daryal gorge of the Caucasus. The length of the stone exceeds 28 m, and the height is about 17 m. The source of their appearance is the places where the corresponding rocks come to the surface. In America these are the Cordillera and Labrador, in Europe - Scandinavia, Finland, Karelia. And they were brought here from afar, from where huge ice sheets once existed, a reminder of which is the modern ice sheet of Antarctica.
The mystery of their pulsation
In the middle of the 20th century, people were faced with another problem - pulsating glaciers, characterized by sudden advances of their ends, without any apparent connection with climate change. Hundreds of pulsating glaciers are now known in many glacial regions. Most of them are in Alaska, Iceland and Spitsbergen, in the mountains of Central Asia, and in the Pamirs.
The general cause of glacial movements is the accumulation of ice in conditions where its flow is hampered by the narrowness of the valley, moraine cover, mutual damming of the main trunk and side tributaries, etc. Such accumulation creates conditions of instability that cause ice runoff: large chips, heating of the ice with the release of water during internal melting, the appearance of water and water-clay lubricant on the bed and chips. On September 20, 2002, a disaster occurred in the valley of the Genaldon River in North Ossetia. Huge masses of ice, mixed with water and stone material, burst out from the upper reaches of the valley, quickly swept down the valley, destroying everything in its path, and formed a blockage, spreading across the entire Karmadon basin in front of the ridge of the Rocky Range. The culprit of the disaster was the pulsating Kolka glacier, the movements of which occurred several times in the past.
The Kolka glacier, like many other pulsating glaciers, has difficulty draining ice. Over the course of many years, ice accumulates in front of an obstacle, increases its mass to a certain critical volume, and when the braking forces cannot resist the shear forces, a sharp release of tension occurs and the glacier advances. In the past, movements of the Kolka glacier occurred around 1835, in 1902 and 1969. They arose when the glacier accumulated a mass of 1-1.3 million tons. The Genaldon disaster of 1902 guide occurred on July 3, at the height of the hot summer. The air temperature during this period exceeded the norm by 2.7°C, and there were heavy downpours. Having turned into a pulp of ice, water and moraine, the ice ejection turned into a crushing high-speed mudflow that rushed through in a matter of minutes. The 1969 movement developed gradually, reaching its greatest development in winter, when the amount of meltwater in the basin was minimal. This determined the relatively calm course of events. In 2002, a huge amount of water accumulated in the glacier, which became the trigger for movement. Obviously, the water “teared” the glacier from its bed and a powerful water-ice-rock mudflow formed. The fact that the movement was triggered ahead of time and reached a colossal scale was due to the existing complex of factors: the unstable dynamic state of the glacier, which had already accumulated a mass close to critical; powerful accumulation of water in the glacier and under the glacier; landslides of ice and rock that created overload in the rear part of the glacier.
A world without glaciers
The total volume of ice on Earth is almost 26 million km 3, or about 2% of all earth's water. This mass of ice is equal to the flow of all the rivers of the globe over 700 years.
If the existing ice were evenly distributed over the surface of our planet, it would cover it with a layer 53 m thick. And if this ice suddenly melted, the level of the World Ocean would rise by 64 m. At the same time, densely populated fertile coastal plains over an area of about 15 million would be flooded. . km 2 2 . Such a sudden melting cannot occur, but throughout geological epochs, when ice sheets arose and then gradually melted, sea level fluctuations were even greater.
Direct dependency
The influence of glaciers on the Earth's climate is enormous. In winter, extremely little solar radiation reaches the polar regions, since the Sun does not appear above the horizon and the polar night prevails here. And in the summer, due to the long duration of the polar day, the amount of radiant energy coming from the Sun is greater than even in the equator region. However, temperatures remain low, as up to 80% of the incoming energy is reflected back by snow and ice. The picture would have been completely different if there had been no ice cover. In this case, almost all the heat that comes in summer would be absorbed and the temperature in the polar regions would differ from the tropical temperature to a much lesser extent. So, if there had not been the continental ice sheet of Antarctica and the ice sheet of the Arctic Ocean around the earth’s poles, there would not have been the usual division into natural zones on Earth and the entire climate would have been much more uniform. Once the ice masses at the poles melt, the polar regions will become much warmer, and rich vegetation will appear on the shores of the former Arctic Ocean and on the surface of ice-free Antarctica. This is exactly what happened on Earth in the Neogene period - just a few million years ago it had a smooth, mild climate. However, one can imagine another state of the planet, when it is completely covered with a shell of ice. After all, once formed under certain conditions, glaciers are able to grow on their own, since they lower the surrounding temperature and grow in height, thereby spreading into higher and colder layers of the atmosphere. Icebergs breaking off from large ice sheets are carried across the ocean, ending up in tropical waters, where their melting also helps cool the water and air.
If nothing prevents the formation of glaciers, then the thickness of the ice layer could increase to several kilometers due to water from the oceans, the level of which would continuously decrease. In this way, gradually all the continents would be under ice, the temperature on the surface of the Earth would drop to about -90 ° C and organic life on it would cease. Fortunately, this has not happened throughout the entire geological history of the Earth, and there is no reason to think that such glaciation could occur in the future. Currently, the Earth is experiencing a state of partial glaciation, when only a tenth of its surface is covered by glaciers. This state is unstable: glaciers either shrink or increase in size and very rarely remain unchanged.
White cover of the "blue planet"
If you look at our planet from space, you can see that some of its parts look completely white - this is the snow cover that is so familiar to the inhabitants of temperate zones.
Snow has a number of amazing properties that make it an indispensable component in Nature’s “kitchen”. The Earth's snow cover reflects more than half of the radiant energy coming to us from the Sun, the same one that covers the polar glaciers (the cleanest and driest) - in general, up to 90% of the sun's rays! However, snow also has another phenomenal property. It is known that all bodies emit thermal energy, and the darker they are, the greater the heat loss from their surface. But snow, being dazzlingly white, is capable of emitting thermal energy almost like a completely black body. The differences between them do not reach even 1%. So, even the slight heat that the snow cover has is quickly radiated into the atmosphere. As a result, the snow cools even more, and the areas of the globe covered by it become a source of cooling for the entire planet.
Features of the sixth continent
Antarctica is the highest continent on the planet, with an average height of 2,350 m (the average height of Europe is 340 m, Asia is 960 m). This altitude anomaly is explained by the fact that most of the mass of the continent is composed of ice, which is almost three times lighter than rocks. Once it was free of ice and did not differ much in height from other continents, but gradually a powerful ice shell covered the entire continent, and the earth’s crust began to bend under colossal load. Over the past millions of years, this excess load has been “isostatically compensated”, in other words, the earth’s crust has bent, but traces of it are still reflected in the topography of the Earth. Oceanographic studies of coastal Antarctic waters have shown that the continental shelf (shelf), which borders all continents with a shallow strip with depths of no more than 200 m, was 200-300 m deeper off the coast of Antarctica. The reason for this is the lowering of the earth's crust under the weight of ice, which previously covered the continental shelf 600-700 m thick. Relatively recently, the ice retreated from here, but the earth's crust has not yet had time to “unbend” and, in addition, it is held in place by ice lying to the south. The unrestricted expansion of the Antarctic ice sheet has always been hampered by the sea.
Any expansion of glaciers beyond the land is possible only under the condition that the sea near the coast is not deep, otherwise sea currents and waves will sooner or later destroy the ice that has extended far into the sea. Therefore, the boundary of maximum glaciation ran along the outer edge of the continental shelf. Antarctic glaciation in general is greatly influenced by sea level changes. When the level of the World Ocean falls, the ice sheet of the sixth continent begins to advance; when it rises, it retreats. It is known that over the past 100 years, sea level has risen by 18 cm, and continues to rise now. Apparently, the destruction of some Antarctic ice shelves, accompanied by the calving of huge table icebergs up to 150 km long, is associated with this process. At the same time, there is every reason to believe that the mass of Antarctic glaciation is increasing in the modern era, and this may also be associated with ongoing global warming. Indeed, climate warming causes increased atmospheric circulation and increased inter-latitudinal exchange of air masses. Warmer and humid air enters the Antarctic continent. However, an increase in temperature of several degrees does not cause any melting inland, where frosts are now 40-60 ° C, while an increase in the amount of moisture leads to heavier snowfalls. This means that warming causes an increase in nutrition and an increase in glaciation in Antarctica.
Last Maximum Glaciation
The culmination of the last ice age on Earth was 21-17 thousand years ago, when the volume of ice increased to approximately 100 million km 3. In Antarctica, glaciation at this time covered the entire continental shelf. The volume of ice in the ice sheet apparently reached 40 million km 3, that is, it was approximately 40% more than its modern volume. The pack ice boundary shifted northward by approximately 10°. In the Northern Hemisphere, 20 thousand years ago, a gigantic Pan-Arctic 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 km 3, and the level of the World Ocean dropped by no less than 125 m.
The degradation of the Panarctic cover began 17 thousand years ago with the destruction of the ice shelves that were part of it. After this, the “sea” parts of the Eurasian and North American ice sheets, which had lost stability, began to collapse catastrophically. The collapse of glaciation occurred in just a few thousand years. At that time, huge masses of water flowed from the edge of the ice sheets, giant dammed lakes arose, and their breakthroughs were many times larger than today. Natural processes dominated in nature, 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 domination on Earth.
12 thousand years ago, the Holocene began - the modern geological era. Air temperature in temperate latitudes increased by 6° compared to the cold late Pleistocene. Glaciation has taken on modern proportions.
Ancient glaciations...
Ideas about ancient glaciations of mountains were expressed at the end of the 18th century, and about past glaciations of the plains of temperate latitudes - in the first half of the 19th century. The theory of ancient glaciation did not immediately gain recognition among scientists. Also in early XIX centuries, in many places around the globe, streaked boulders of rocks that were clearly not of local origin were found, but scientists did not know what could have brought them. IN
In 1830, the English explorer Charles Lyell came up with his theory, in which he attributed both the spreading of boulders and the shading of rocks to the action of floating sea ice. Lyell's hypothesis met with serious objections. During his famous voyage on the Beagle ship (1831-1835), Charles Darwin lived for some time on Tierra del Fuego, where he saw with his own eyes the glaciers and the icebergs they generate. He subsequently wrote that boulders can be carried across the sea by icebergs, especially during periods of greater glacial development. And after his trip to the Alps in 1857, Lyell himself doubted the correctness of his theory. In 1837, the Swiss explorer L. Agassiz was the first to explain the polishing of rocks, the transport of boulders, and the deposition of moraine by the influence of glaciers. A significant contribution to the development of the glacial theory was made by Russian scientists, and above all P.A. Kropotkin. Traveling through Siberia in 1866, he discovered many boulders, glacial sediments, and smooth polished rocks on the Patom Highlands and connected these finds with the activity of ancient glaciers. In 1871 Russian geographical society sent him to Finland, a country with bright traces of recently retreated glaciers. This trip finally shaped his views. When studying ancient geological deposits, we often find tillites - coarse fossilized moraines and glacial-marine sediments. They were found on all continents in sediments of different ages, and they are used to reconstruct the glacial history of the Earth for 2.5 billion years, during which the planet experienced 4 glacial eras that lasted from many tens to 200 million years. Each such era consisted of ice ages comparable in duration to the Pleistocene, or Quaternary period, and each period consisted of a large number of ice ages.
The duration of glacial eras on Earth is at least a third of the total 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 glaciation eras will take almost as much time as warm, ice-free conditions. The last of the ice ages began almost a million years ago, in Quaternary time, and was marked by the 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 also Siberia were under thick covers of ice. In the Southern Hemisphere, the entire Antarctic continent was under ice, as it is now. During the period of maximum expansion 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. All of northern Europe was under an ice sheet up to 2.5 km thick. Having reached their greatest development 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink. Glaciation was not continuous throughout the Quaternary period. There is geological, paleobotanical and other evidence that during this time glaciers completely disappeared at least three times, giving way to interglacial eras when the climate was warmer than today. However, these warm eras were replaced by cold snaps, and the glaciers spread again. We now live, apparently, at the end of the fourth epoch of the Quaternary glaciation. The Quaternary glaciation of Antarctica developed quite differently than in the Northern Hemisphere. It arose many millions of years before glaciers appeared in North America and Europe. In addition to climatic conditions, this was facilitated by the high continent that had long existed here. Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and then reappeared, the Antarctic ice sheet changed little in its size. The maximum glaciation of Antarctica was only one and a half times greater in volume than the modern one and not much larger in area.
...and their possible causes
The cause of major climate changes and the occurrence of the great glaciations of the Earth still remains a mystery. All hypotheses expressed on this subject can be combined into three groups - the cause of periodic changes in the earth's climate was sought either outside the solar system, or in the activity of the Sun itself, or in processes occurring on Earth.
Galaxy
Cosmic hypotheses include assumptions about the influence on the cooling of the Earth of various parts of the Universe that the Earth passes through, moving in space along with the Galaxy. Some believe that cooling occurs when the Earth passes through areas of global space filled with gas. Others attribute the same effects to the effects of clouds of cosmic dust. According to another hypothesis, the Earth as a whole should experience great changes when, moving along with the Sun, it moves from the star-saturated part of the Galaxy to its outer, rarefied regions. When the globe approaches the apogalactium - the point furthest from the part of our Galaxy where the greatest number stars, it enters the “cosmic winter” zone and the Ice Age begins on it.
Sun
The development of glaciations is also associated with fluctuations in the activity of the Sun itself. Heliophysicists have long figured out the periodicity of the appearance of dark spots, flares, and prominences on it and have learned to predict these phenomena. It turned out that solar activity changes periodically. There are periods of different durations: 2-3, 5-6, 11, 22 and about 100 years. It may happen that the culminations of several periods of different durations coincide and solar activity will be especially high. But it may also be the other way around - several periods of reduced solar activity will coincide, and this will cause the development of glaciation. Such changes in solar activity, of course, are reflected in the fluctuations of glaciers, but are unlikely to cause a great glaciation of the Earth.
CO 2
An increase or decrease in temperature on Earth can also occur if the composition of the atmosphere changes. Thus, carbon dioxide, which freely transmits the sun's rays to the Earth, but absorbs most of its thermal radiation, serves as a colossal screen that prevents the cooling of our planet. Now the content of CO 2 in the atmosphere does not exceed 0.03%. If this figure is halved, then average annual temperatures in temperate zones will decrease by 4-5°, which could lead to the onset of an ice age.
Volcanoes
Volcanic dust emitted during large eruptions up to a height of 40 km can also serve as unique screens. Clouds of volcanic dust, on the one hand, block the sun's rays, and on the other hand, do not allow the earth's radiation to pass through. But the first process is stronger than the second, so periods of increased volcanism should cause the Earth to cool.
Mountains
The idea of a connection between glaciation on our planet and mountain building is also widely known. During the eras of mountain building, the rising large masses of the continents fell into higher layers of the atmosphere, cooled and served as places for the birth of glaciers.
Ocean
According to many researchers, glaciation can also occur as a result of a change in the direction of sea currents. For example, the Gulf Stream was previously diverted by a ridge of land extending from Newfoundland to the Cape Verde Islands, helping to cool the Arctic compared to modern conditions.
Atmosphere
IN Lately Scientists began to associate the development of glaciation with a restructuring of atmospheric circulation - when certain areas of the planet receive significantly more precipitation and, in the presence of sufficiently high mountains, glaciation occurs here.
Antarctica
Perhaps the rise of the Antarctic continent contributed to the emergence of glaciation. As a result of the expansion of the Antarctic ice sheet, the temperature of the entire Earth decreased by several degrees and the level of the World Ocean dropped by several tens of meters, which contributed to the development of glaciation in the north.
"Recent History"
The last retreat of glaciers, which began over 10 thousand years ago, remains in human memory. IN historical era- over about 3 thousand years - the advance of glaciers occurred in centuries with lower air temperatures and increased humidity. 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 Mediterranean and Black Sea countries, on the verge of a new era, the climate was colder and wetter than it is now. In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, blocked mountain passes with ice and destroyed some high-lying villages. This era saw a major advance of the Caucasian glaciers. The climate was completely different at the turn of the 1st and 2nd millennia.
Warmer conditions and the absence of ice in the northern seas allowed northern European sailors to penetrate far to the north. In 870, the colonization of Iceland began, where there were fewer glaciers at that time 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 bushes. They founded the first European colony here, and called this land Greenland.
By the end of the 1st millennium, mountain glaciers in the Alps, the Caucasus, Scandinavia and Iceland had also retreated significantly. The climate began to change seriously again in the 14th century. Glaciers began to advance in Greenland, summer thawing of soil became increasingly 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 usually ended in failure. Since 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 began, called the Little Ice Age. In the south of Europe, severe and long winters often recurred; in 1621 and 1669, the Bosporus Strait froze, and in 1709, the Adriatic Sea froze off the coast. In the second half of the 19th century, the Little Ice Age ended and a relatively warm era began, which continues to this day.
What awaits us?
The warming of the 20th century was especially pronounced in the polar latitudes of the Northern Hemisphere. Fluctuations in glacial systems are characterized by the proportion of advancing, stationary, and retreating glaciers. For example, for the Alps there is data covering the entire past century. If the share of advancing alpine glaciers in the 40-50s was close to zero, then in the mid-60s about 30%, and in the late 70s - 65-70% of the surveyed glaciers, advanced here. Their similar state indicated that the anthropogenic increase in the content of carbon dioxide, 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 century, glaciers throughout the mountains began to retreat, which was a reaction to global warming, the trend of which especially intensified in the 1990s.
It is known that the currently increased amount of aerosol emissions of anthropogenic origin into the atmosphere helps to reduce the influx of solar radiation. In this regard, voices appeared about the beginning of the Ice Age, but they were lost in a powerful wave of fears of impending anthropogenic warming due to the constant increase in CO 2 and other gaseous impurities in the atmosphere.
An increase in CO2 leads to an increase in the amount of retained heat and thereby increases the temperature. The same effect is exerted by some small gas impurities that enter the atmosphere: freons, nitrogen oxides, methane, ammonia, and so on. But nevertheless, not the entire mass of carbon dioxide formed during combustion remains in the atmosphere: 50-60% of industrial CO 2 emissions end up in the ocean or are absorbed by plants. A multiple increase in the concentration of CO 2 in the atmosphere does not lead to the same multiple increase in temperature. Obviously, there is a natural regulation mechanism that sharply slows down the greenhouse effect at CO 2 concentrations exceeding two or three times.
It is difficult to say with certainty what the prospects for an increase in the CO2 content in the atmosphere are in the coming decades and how the temperature will rise as a result of this. Some scientists suggest its increase in the first quarter of the 21st century by 1-1.5°, and even more in the future. However, this position has not been proven; there are many reasons to believe that modern warming is part of a natural cycle of climate fluctuations and will be replaced by cooling in the near future. In any case, the Holocene, which has lasted for more than 11 thousand years, turns out to be the longest interglacial in the last 420 thousand years and will obviously end soon. And while we are concerned about the consequences of the current warming, we must not forget about the possible future cooling on Earth.
Vladimir Kotlyakov, academician, director of the Institute of Geography of the Russian Academy of Sciences
About two million years ago, at the end of the Neogene, continents began to rise again and volcanoes came to life all over the Earth. A huge amount of volcanic ash and soil particles were thrown into the atmosphere and polluted its upper layers to such an extent that the rays of the Sun simply could not penetrate to the surface of the planet. The climate became much colder, huge glaciers formed, which, under the influence of their own gravity, began to move from mountain ranges, plateaus and hills to the plains.
One after another, like waves, periods of glaciation rolled over Europe and North America. But just recently (in a geological sense) the climate of Europe was warm, almost tropical, and its animal population consisted of hippos, crocodiles, cheetahs, antelopes - approximately the same as what we see now in Africa. Four periods of glaciation - Günz, Mindel, Ris and Würm - expelled or destroyed heat-loving animals and plants, and the nature of Europe became basically what we see it now.
Under the pressure of glaciers, forests and meadows perished, rocks collapsed, rivers and lakes disappeared. Furious blizzards howled over the ice fields, and along with the snow, atmospheric dirt fell onto the surface of the glacier and it gradually began to clear.
When the glacier retreated for a short time, tundras with their permafrost remained in place of the forests.
The greatest period of glaciation was the Rissky - it occurred about 250 thousand years ago. The thickness of the glacial shell, which bound half of Europe and two-thirds of North America, reached three kilometers. Altai, Pamir and the Himalayas disappeared under the ice.
South of the glacier boundary now lay cold steppes, covered with sparse grassy vegetation and groves of dwarf birch trees. Even further south, the impenetrable taiga began.
Gradually the glacier melted and retreated to the north. However, off the coast Baltic Sea he stopped. An equilibrium arose - the atmosphere, saturated with moisture, let in just enough sunlight so that the glacier did not grow and did not melt completely.
The great glaciations unrecognizably changed the Earth's topography, its climate, animal and vegetable world. We can still see their consequences - after all, the last, Würm glaciation began only 70 thousand years ago, and the ice mountains disappeared from the northern coast of the Baltic Sea 10-11 thousand years ago.
Heat-loving animals retreated further and further south in search of food, and their place was taken by those that could better withstand the cold.
Glaciers advanced not only from the Arctic regions, but also from the mountain ranges - the Alps, Carpathians, Pyrenees. At times the thickness of the ice reached three kilometers. Like a giant bulldozer, the glacier smoothed out the uneven terrain. After his retreat, a swampy plain remained, covered with sparse vegetation.
This is what the polar regions of our planet presumably looked like in the Neogene and during the Great Glaciation. The area of permanent snow cover increased tenfold, and where the glaciers reached, it was as cold as in Antarctica for ten months of the year.
Climatic changes were most clearly expressed in periodically occurring ice ages, which had a significant impact on the transformation of the land surface located under the body of the glacier, water bodies and biological objects found 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 total 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 eras 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 Quaternary time, and was marked by the 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 also Siberia were under thick covers of ice. In the Southern Hemisphere, the entire Antarctic continent was under ice, as it is now.
The main causes of glaciations are:
space;
astronomical;
geographical.
Space groups of reasons:
change in the amount of heat on 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 reasons:
change in pole position;
the inclination of the earth's axis to the ecliptic plane;
change in the eccentricity of the Earth's orbit.
Geological and geographical groups of reasons:
climate change and the amount of carbon dioxide in the atmosphere (increase in carbon dioxide - warming; decrease - cooling);
changes in the directions of ocean and air currents;
intensive process of mountain building.
The conditions for the manifestation of glaciation on Earth include:
snowfall in the form of precipitation in conditions of low temperatures with its accumulation as material for glacier growth;
negative temperatures in areas where there is no glaciation;
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 a global decrease in temperatures by 1.5-2ºC.
The most ancient 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):
at the Cambrian-Proterozoic boundary (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 expansion 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. All of northern Europe was under an ice sheet up to 2.5 km thick. Having reached their 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 area of the islands of Spitsbergen and Franz Josef Land (according to paleobotanical finds of subtropical plants), there were subtropics at that time.
Reasons for climate change:
the formation of mountain ranges (Cordillera, Andes), which isolated the Arctic region from warm currents and winds (mountain rise by 1 km - cooling by 6ºС);
creation of a cold microclimate in the Arctic region;
cessation of heat flow into the Arctic region from warm equatorial regions.
By the end of the Neogene period, North and South America connected, which created obstacles to 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 the northern waters, created a steam effect;
hair loss has increased sharply large quantity precipitation in the form of rain and snow;
a decrease in temperature by 5-6ºС led to glaciation of vast territories (North America, Europe);
a new period of glaciation began, lasting about 300 thousand years (the periodicity of glaciers-interglacial periods from the end of the Neogene to the Anthropocene (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 glaciers completely disappeared at least three times, giving way to interglacial eras when the climate was warmer than today. However, these warm eras were replaced by cold snaps, and the glaciers spread again. Currently, the Earth is at the end of the fourth epoch of Quaternary glaciation, and, according to geological forecasts, our descendants in a few hundred to thousand years will again find themselves in ice age conditions, not warming.
The Quaternary glaciation of Antarctica developed along a different path. It arose many millions of years before glaciers appeared in North America and Europe. In addition to climatic conditions, this was facilitated by the high continent that had long existed here. Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and then reappeared, the Antarctic ice sheet changed little in its size. The maximum glaciation of Antarctica was only one and a half times greater in volume than the modern one and not much larger 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 km 3. In Antarctica, glaciation at this time covered the entire continental shelf. The volume of ice in the ice sheet apparently reached 40 million km 3, that is, it was approximately 40% more than its modern volume. The pack ice boundary shifted northward by approximately 10°. In the Northern Hemisphere, 20 thousand years ago, a gigantic Pan-Arctic ancient ice sheet 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 km 3, and the level of the World Ocean dropped by no less than 125 m.
The degradation of the Panarctic cover began 17 thousand years ago with the destruction of the ice shelves that were part of it. After this, the “sea” parts of the Eurasian and North American ice sheets, which had lost stability, began to collapse catastrophically. The collapse of glaciation occurred in just a few thousand years (Fig. 25).
At that time, huge masses of water flowed from the edge of the ice sheets, giant dammed lakes arose, and their breakthroughs were many times larger than today. Natural processes dominated in nature, 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 domination on Earth.
The last retreat of glaciers, which began over 14 thousand years ago, remains in human memory. Apparently, it is the process of melting glaciers and rising water levels 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 era. Air temperature in temperate latitudes increased by 6° compared to the cold late Pleistocene. Glaciation has taken on modern proportions.
In the historical era - for about 3 thousand years - the advance of glaciers occurred in separate centuries with lower air temperatures and increased humidity and were called little 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 Mediterranean and Black Sea countries, on the verge of a new era, the climate was colder and wetter than it is now. In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, blocked mountain passes with ice and destroyed some high-lying villages. This era saw a major advance of the Caucasian glaciers.
The climate was completely different at the turn of the 1st and 2nd millennia AD. Warmer conditions and the absence of ice in the northern seas allowed northern European sailors to penetrate far to the north. In 870, the colonization of Iceland began, where there were fewer glaciers at that time 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 bushes, they founded the first European colony here, and this land was called Greenland, or “green land” (which is by no means now talk about the harsh lands of modern Greenland).
By the end of the 1st millennium, mountain glaciers in the Alps, the Caucasus, Scandinavia and Iceland had also retreated significantly.
The climate began to change seriously again in the 14th century. Glaciers began to advance in Greenland, summer thawing of soil became increasingly 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.
Since 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 began, called the Little Ice Age. In the south of Europe, severe and long winters often recurred; in 1621 and 1669, the Bosphorus Strait froze, and in 1709, the Adriatic Sea froze along the shores.
IN 
In 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. Boundaries of the last glaciation
Rice. 25. Scheme of glacier formation and melting (along the profile of the Arctic Ocean - Kola Peninsula - Russian Platform)
State educational institution higher professional education in the Moscow region
International University of Nature, Society and Human "Dubna"
Faculty of Science and Engineering
Department of Ecology and Geosciences
COURSE WORK
By discipline
Geology
Scientific adviser:
Ph.D., Associate Professor Anisimova O.V.
Dubna, 2011
Introduction
1. Ice Age
1.1 Ice ages in the history of the Earth
1.2 Proterozoic Ice Age
1.3 Paleozoic Ice Age
1.4 Cenozoic Ice Age
1.5 Tertiary period
1.6 Quaternary period
2. Last Ice Age
2.2 Flora and fauna
2.3Rivers and lakes
2.4West Siberian Lake
2.5The world's oceans
2.6 Great Glacier
3. Quaternary glaciations in the European part of Russia
4. Causes of Ice Ages
Conclusion
Bibliography
Introduction
Target:
Explore the major glacial epochs in Earth's history and their role in shaping the modern landscape.
Relevance:
The relevance and significance of this topic is determined by the fact that the ice ages are not so well studied to fully confirm their existence on our Earth.
Tasks:
– conduct a literature review;
– establish the main glacial epochs;
– obtaining detailed data on the last Quaternary glaciations;
Establish the main causes of glaciations in the history of the Earth.
At present, little data has been obtained that confirms the distribution of frozen rock layers on our planet in ancient eras. The evidence is mainly the discovery of ancient continental glaciations from their moraine deposits and the establishment of the phenomena of mechanical detachment of glacier bed rocks, the transfer and processing of clastic material and its deposition after the melting of the ice. Compacted and cemented ancient moraines, the density of which is close to rocks such as sandstones, are called tillites. The discovery of such formations of different ages in different regions of the globe clearly indicates the repeated appearance, existence and disappearance of ice sheets, and, consequently, frozen strata. The development of ice sheets and frozen strata can occur asynchronously, i.e. The maximum development of the area of glaciation and the permafrost zone may not coincide in phase. However, in any case, the presence of large ice sheets indicates the existence and development of frozen strata, which should occupy significantly larger areas in area than the ice sheets themselves.
According to N.M. Chumakov, as well as V.B. Harland and M.J. Hambry, the time intervals during which glacial deposits were formed are called glacial eras (lasting the first hundreds of millions of years), ice ages (millions - first tens of millions of years), glacial epochs (first millions of years). In the history of the Earth, the following glacial eras can be distinguished: Early Proterozoic, Late Proterozoic, Paleozoic and Cenozoic.
1. Ice Age
Are there ice ages? Of course yes. The evidence for this is incomplete, but it is quite definite, and some of this evidence extends over large areas. Evidence of the Permian Ice Age is present on several continents, and in addition, traces of glaciers have been found on the continents dating back to other eras of the Paleozoic era up to its beginning, Early Cambrian time. Even in much older rocks, formed before the Phanerozoic, we find traces left by glaciers and glacial deposits. Some of these traces are more than two billion years old, possibly half the age of Earth as a planet.
The ice age of glaciations (glacials) is a period of time in the geological history of the Earth, characterized by a strong cooling of the climate and the development of extensive continental ice not only in the polar, but also in temperate latitudes.
Peculiarities:
·It is characterized by long-term, continuous and severe climate cooling, the growth of ice sheets in polar and temperate latitudes.
· Ice ages are accompanied by a decrease in the level of the World Ocean by 100 m or more, due to the fact that water accumulates in the form of ice sheets on land.
·During ice ages, areas occupied by permafrost expand, and soil and plant zones shift towards the equator.
It has been established that over the past 800 thousand years there have been eight ice ages, each of which lasted from 70 to 90 thousand years.
Fig.1 Ice Age
1.1 Ice ages in the history of the Earth
Periods of climate cooling, accompanied by the formation of continental ice sheets, are recurring events in the history of the Earth. Intervals of cold climate during which extensive continental ice sheets and sediments are formed, lasting hundreds of millions of years, are called glacial eras; In glacial eras, ice ages lasting tens of millions of years are distinguished, which, in turn, consist of ice ages - glaciations (glacials), alternating with interglacials (interglacials).
Geological studies have proven that there was a periodic process of climate change on Earth, spanning the time from the late Proterozoic to the present.
These are relatively long glacial eras that lasted for almost half of the Earth's history. The following glacial eras are distinguished in the history of the Earth:
Early Proterozoic - 2.5-2 billion years ago
Late Proterozoic - 900-630 million years ago
Paleozoic - 460-230 million years ago
Cenozoic - 30 million years ago - present
Let's take a closer look at each of them.
1.2 Proterozoic Ice Age
Proterozoic - from the Greek. the words protheros - primary, zoe - life. The Proterozoic era is a geological period in the history of the Earth, including the history of the formation of rocks of various origins from 2.6 to 1.6 billion years. A period in the history of the Earth that was characterized by the development of the simplest life forms of single-celled living organisms from prokaryotes to eukaryotes, which later, as a result of the so-called Ediacaran “explosion,” evolved into multicellular organisms.
Early Proterozoic glacial era
This is the oldest glaciation recorded in geological history, which appeared at the end of the Proterozoic on the border with the Vendian and, according to the Snowball Earth hypothesis, the glacier covered most of the continents at equatorial latitudes. In fact, it was not one, but a series of glaciations and interglacial periods. Since it is believed that nothing can prevent the spread of glaciation due to an increase in albedo (reflection of solar radiation from the white surface of glaciers), it is believed that the cause of subsequent warming may be, for example, an increase in the amount of greenhouse gases in the atmosphere due to increased volcanic activity , accompanied, as is known, by emissions of huge amounts of gases.
Late Proterozoic glacial era
Identified under the name of the Lapland glaciation at the level of Vendian glacial deposits 670-630 million years ago. These deposits are found in Europe, Asia, West Africa, Greenland and Australia. Paleoclimatic reconstruction of glacial formations from this time suggests that the European and African ice continents of that time were a single ice sheet.
Fig.2 Vend. Ulytau during the Ice Age Snowball
1.3 Paleozoic Ice Age
Paleozoic - from the word paleos - ancient, zoe - life. Palaeozoic. Geological time in the history of the Earth covering 320-325 million years. With an age of glacial deposits of 460 - 230 million years, it includes the Late Ordovician - Early Silurian (460-420 million years), Late Devonian (370-355 million years) and Carboniferous-Permian glacial periods (275 - 230 million years). The interglacial periods of these periods are characterized by a warm climate, which contributed to the rapid development of vegetation. In the places where they spread, large and unique coal basins and horizons of oil and gas fields were later formed.
Late Ordovician - Early Silurian Ice Age.
Glacial deposits of this time, called Saharan (after the name of modern Sahara). Were distributed throughout the area modern Africa, South America, eastern North America and Western Europe. This period is characterized by the formation of an ice sheet over much of northern, northwestern and western Africa, including the Arabian Peninsula. Paleoclimatic reconstructions suggest that the thickness of the Saharan ice sheet reached at least 3 km and was similar in area to the modern glacier of Antarctica.
Late Devonian Ice Age
Glacial deposits from this period were found in the territory of modern Brazil. The glacial area extended from the modern mouth of the river. Amazon to the east coast of Brazil, taking over the Niger region in Africa. In Africa, Northern Niger contains tillites (glacial deposits) that are comparable to those in Brazil. In general, the glacial areas stretched from the border of Peru with Brazil to northern Niger, the diameter of the area was more than 5000 km. The South Pole in the Late Devonian, according to the reconstruction of P. Morel and E. Irving, was located in the center of Gondwana in Central Africa. Glacial basins are located on the oceanic margin of the paleocontinent, mainly in high latitudes (not north of the 65th parallel). Judging by the then high-latitude continental position of Africa, one can assume the possible widespread development of frozen rocks on this continent and, in addition, in the north-west of South America.
Carboniferous-Permian Ice Age
It became widespread in the territory of modern Europe and Asia. During the Carboniferous, there was a gradual cooling of the climate, culminating about 300 million years ago. This was facilitated by the concentration of most of the continents in the southern hemisphere and the formation of the supercontinent Gondwana, the formation of large mountain ranges and changes in ocean currents. During the Carboniferous–Permian, most of Gondwana experienced glacial and periglacial conditions.
The center of the continental ice sheet of Central Africa was located near the Zambezi, from where the ice flowed radially into several African basins and spread to Madagascar, South Africa and parts of South America. With a radius of the ice sheet of approximately 1750 km, according to calculations, the ice thickness could be up to 4 – 4.5 km. In the southern hemisphere, at the end of the Carboniferous–Early Permian, a general uplift of Gondwana occurred and glaciation spread over most of this supercontinent. The Carboniferous-Permian Ice Age lasted at least 100 million years, but there was no single large ice cap. The peak of the Ice Age, when the ice sheets extended far to the north (up to 30° - 35° S), lasted about 40 million years (between 310 - 270 million years ago). According to calculations, the Gondwana glaciation area occupied an area of at least 35 million km 2 (possibly 50 million km 2), which is 2–3 times larger than the area of modern Antarctica. Ice sheets reached 30° – 35°S. The main center of glaciation was the region of the Sea of Okhotsk, which, apparently, was located near the North Pole.
Fig.3 Paleozoic Ice Age
1.4 Cenozoic Ice Age
The Cenozoic Ice Age (30 million years ago - present) is a recently begun glacial era.
The present time - the Holocene, which began ≈ 10,000 years ago, is characterized as a relatively warm interval after the Pleistocene Ice Age, often classified as an interglacial. Ice sheets exist at high latitudes in the northern (Greenland) and southern (Antarctica) hemispheres; Moreover, in the northern hemisphere, the cover glaciation of Greenland extends south to 60° north latitude (i.e., to the latitude of St. Petersburg), fragments of sea ice cover - to 46-43° north latitude (i.e., to the latitude of Crimea) , and permafrost to 52-47° north latitude. In the southern hemisphere, continental Antarctica is covered by an ice sheet 2500-2800 m thick (up to 4800 m in some areas of East Antarctica), with ice shelves accounting for ≈10% of the continent's area above sea level. In the Cenozoic glacial era, the Pleistocene ice age is the strongest: a decrease in temperature led to glaciation of the Arctic Ocean and the northern regions of the Atlantic and Pacific Oceans, while the glaciation boundary ran 1500-1700 km south of the modern one.
Geologists divide the Cenozoic into two periods: Tertiary (65 - 2 million years ago) and Quaternary (2 million years ago - our time), which in turn are divided into epochs. Of these, the first is much longer than the second, but the second - quaternary - has a number of unique features; this is the time of ice ages and the final formation of the modern face of the Earth.
Rice. 4 Cenozoic Ice Age. glacial period. Climate curve for the last 65 million years.
34 million years ago - the birth of the Antarctic ice sheet
25 million years ago - its abbreviation
13 million years ago - its re-growth
About 3 million years ago - the beginning of the Pleistocene Ice Age, repeated appearance and disappearance of ice sheets in the northern regions of the Earth
1.5 Tertiary period
The Tertiary period consists of eras:
·Paleocene
Oligocene
Pliocene
Paleocene era (from 65 to 55 million years ago)
Geography and climate: The Paleocene marked the beginning of the Cenozoic era. At that time, the continents were still in motion as the "great southern continent" Gondwana continued to break apart. South America was now completely cut off from the rest of the world and turned into a kind of floating “ark” with a unique fauna of early mammals. Africa, India and Australia have moved even further away from each other. Throughout the Paleocene, Australia was located near Antarctica. Sea levels have dropped, and new land areas have emerged in many areas of the globe.
Fauna: The age of mammals began on land. Rodents and insectivores appeared. There were also large animals among them, both predators and herbivores. In the seas, marine reptiles were replaced by new species of predatory bony fish and sharks. New varieties of bivalves and foraminifera emerged.
Flora: More and more new species of flowering plants and the insects that pollinate them continued to spread.
Eocene Epoch (from 55 to 38 million years ago)
Geography and climate: During the Eocene, the main land masses began to gradually assume a position close to that which they occupy today. Much of the land was still divided into giant islands of sorts, as the huge continents continued to move away from each other. South America lost contact with Antarctica, and India moved closer to Asia. At the beginning of the Eocene, Antarctica and Australia were still located nearby, but later they began to diverge. North America and Europe also split, and new mountain ranges emerged. The sea flooded part of the land. The climate was warm or temperate everywhere. Much of it was covered with lush tropical vegetation, and large areas were covered with dense swamp forests.
Fauna: Bats, lemurs, and tarsiers appeared on land; ancestors of today's elephants, horses, cows, pigs, tapirs, rhinoceroses and deer; other large herbivores. Other mammals, such as whales and sirenians, have returned to the aquatic environment. The number of freshwater bony fish species has increased. Other groups of animals also evolved, including ants and bees, starlings and penguins, giant flightless birds, moles, camels, rabbits and voles, cats, dogs and bears.
Flora: In many parts of the world, forests grew with lush vegetation, and palm trees grew in temperate latitudes.
Oligocene Epoch (from 38 to 25 million years ago)
Geography and Climate: During the Oligocene era, India crossed the equator and Australia finally separated from Antarctica. The climate on Earth became cooler, and a huge ice sheet formed over the South Pole. To form such a large amount of ice, no less significant volumes were required sea water. This led to lower sea levels across the planet and an expansion of land area. Widespread cooling caused the disappearance of lush Eocene tropical forests in many areas of the globe. Their place was taken by forests that preferred a more temperate (cool) climate, as well as vast steppes spread across all continents.
Fauna: With the spread of the steppes, a rapid flourishing of herbivorous mammals began. Among them, new species of rabbits, hares, giant sloths, rhinoceroses and other ungulates arose. The first ruminants appeared.
Vegetable world: Rainforests decreased in size and began to give way to temperate forests, and vast steppes appeared. New grasses quickly spread, and new types of herbivores developed.
Miocene era (from 25 to 5 million years ago)
Geography and climate: During the Miocene, the continents were still “on the march”, and a number of grandiose cataclysms occurred during their collisions. Africa "crashed" into Europe and Asia, resulting in the appearance of the Alps. When India and Asia collided, the Himalayan mountains rose up. At the same time, the Rocky Mountains and Andes formed as other giant plates continued to shift and slide on top of each other.
However, Austria and South America remained isolated from the rest of the world, and each of these continents continued to develop its own unique fauna and flora. Ice cover in the southern hemisphere has spread throughout Antarctica, causing the climate to cool further.
Fauna: Mammals migrated from continent to continent along newly formed land bridges, which sharply accelerated evolutionary processes. Elephants moved from Africa to Eurasia, and cats, giraffes, pigs and buffaloes moved in the opposite direction. Saber-toothed cats and monkeys, including anthropoids, appeared. Cut off from outside world In Australia, monotremes and marsupials continued to evolve.
Flora: Inland areas became colder and drier, and steppes became more widespread in them.
Pliocene Epoch (from 5 to 2 million years ago)
Geography and climate: A space traveler looking down on the Earth at the beginning of the Pliocene would have found continents in almost the same places as today. A galactic visitor would see the giant ice caps in the northern hemisphere and the huge ice sheet of Antarctica. Because of all this mass of ice, the Earth's climate became even cooler, and the surface of the continents and oceans of our planet became significantly colder. Most of the forests that remained in the Miocene disappeared, giving way to vast steppes that spread throughout the world.
Fauna: Herbivorous ungulate mammals continued to rapidly reproduce and evolve. Towards the end of the period, a land bridge connected South and North America, which led to a huge "exchange" of animals between the two continents. It is believed that increased interspecific competition caused the extinction of many ancient animals. Rats entered Australia, and the first humanoid creatures appeared in Africa.
Flora: As the climate cooled, steppes replaced forests.
Fig.5 Diverse mammals evolved during the Tertiary period
1.6 Quaternary period
Consists of eras:
·Pleistocene
Holocene
Pleistocene era (from 2 to 0.01 million years ago)
Geography and climate: At the beginning of the Pleistocene, most continents occupied the same position as today, and some of them required crossing half the globe to do so. A narrow land bridge connected North and South America. Australia was located on the opposite side of the Earth from Britain. Giant ice sheets were creeping across the northern hemisphere. It was an era of great glaciation with alternating periods of cooling and warming and fluctuations in sea level. This ice age continues to this day.
Fauna: Some animals managed to adapt to the increased cold by acquiring thick fur: for example, woolly mammoths and rhinoceroses. The most common predators are saber-toothed cats and cave lions. This was the age of giant marsupials in Australia and huge flightless birds, such as moas and apiornis, that lived in many areas of the southern hemisphere. The first people appeared, and many large mammals began to disappear from the face of the Earth.
Flora: Ice gradually crawled from the poles, and coniferous forests gave way to the tundra. Further from the edge of the glaciers, deciduous forests were replaced by coniferous ones. In the warmer regions of the globe there are vast steppes.
Holocene era (from 0.01 million years to the present day)
Geography and climate: The Holocene began 10,000 years ago. Throughout the Holocene, the continents occupied almost the same places as they do today; the climate was also similar to the modern one, becoming warmer and colder every few millennia. Today we are experiencing one of the warming periods. As the ice sheets thinned, sea levels slowly rose. The time of the human race began.
Fauna: At the beginning of the period, many animal species became extinct, mainly due to general climate warming, but increased human hunting for them may also have had an impact. Later they could fall victim to competition from new species of animals brought by people from other places. Human civilization has become more developed and spread throughout the world.
Flora: With the advent of agriculture, peasants destroyed more and more wild plants in order to clear areas for crops and pastures. In addition, plants brought by people to new areas sometimes replaced indigenous vegetation.
Rice. 6 Proboscis, the largest land animals of the Quaternary period
glacial era tertiary quaternary
2. Last Ice Age
The last ice age (last glaciation) is the last of the ice ages within the Pleistocene or Quaternary ice age. It began about 110 thousand years ago and ended around 9700-9600 BC. e. For Siberia it is usually called “Zyryanskaya”, in the Alps - “Würmskaya”, in North America - “Wisconsinskaya”. During this era, the expansion and contraction of ice sheets occurred repeatedly. The Last Glacial Maximum, when the total volume of ice in glaciers was greatest, dates back to about 26-20 thousand years ago of individual ice sheets.
At this time, the polar glaciers of the northern hemisphere grew to enormous sizes, uniting into a huge ice sheet. Long tongues of ice extended from it to the south along the beds of large rivers. All the high mountains were also covered in ice. Cooling and the formation of glaciers led to other global changes in nature. Rivers flowing into the northern seas turned out to be dammed by ice walls, they spilled into giant lakes and turned back trying to find a drain in the south. Heat-loving plants moved south, giving way to more cold-tolerant neighbors. At this time, the mammoth faunal complex was finally formed, consisting mainly of large animals well protected from the cold.
2.1 Climate
However, during the last glaciation, the climate on the planet was not constant. Climate warming periodically occurred, the glacier melted along the edge, retreated to the north, the areas of high-mountain ice decreased, and climatic zones shifted south. There have been several such minor changes in climate. Scientists believe that the coldest and most severe period in Eurasia was about 20 thousand years ago.
Rice. 7 Perito Moreno Glacier in Patagonia, Argentina. during the last ice age
Rice. 8 The diagram shows climate changes in Siberia and some other areas of the northern hemisphere over the past 50 thousand years
2.2 Flora and fauna
The cooling of the planet and the formation of giant glacial systems in the north caused global changes in the flora and fauna of the Northern Hemisphere. The boundaries of all natural zones began to shift south. The following were located on the territory of Siberia natural areas.
Along the glaciers, a zone of cold tundras and tundra-steppes stretches tens of kilometers wide. It was located approximately in the areas where there is now forest and taiga.
In the south, the tundra-steppe gradually turned into forest-steppe and forests. Forest areas were very small, and were not everywhere. Most often, forests were located on the southern shores of periglacial lakes and in river valleys and on mountain spurs.
Even further south were dry steppes, in the west of Siberia gradually turning into the Sayan-Altai mountain systems, in the east bordering on the semi-deserts of Mongolia. In some areas, the tundra-steppe and steppe were not separated by a strip of forest, but gradually replaced each other.
Fig.9. Tundra-steppe, the era of the last glaciation
In the new climatic conditions of the Ice Age, the animal world also changed. During the last stages of the Quaternary period, new species of fauna were formed in the Northern Hemisphere. A particularly expressive manifestation of these changes was the appearance of the so-called mammoth faunal complex, which consisted of cold-tolerant animal species.
2.3 Rivers and lakes
Giant ice fields formed a natural dam and blocked the flow of rivers flowing into the Northern Seas. Modern Siberian rivers: the Ob, Irtysh, Yenisei, Lena, Kolyma and many others overflowed along the glaciers, forming giant lakes that were combined into periglacial meltwater drainage systems.
Siberia in the Ice Age. For clarity, modern rivers and cities are indicated. Most of this system was connected by rivers and water flowed out of it to the southwest through the New Euxinian basin system, which was once on the site of the Black Sea. Further, through the Bosphorus and Dardanelles, the water entered the Mediterranean Sea. The total area of this drainage basin was 22 million square meters. km. It served the territory from Mongolia to the Mediterranean.
Fig. 10 Siberia in the Ice Age
In North America, there was also such a system of periglacial lakes. Along the Laurentian ice sheet stretched the now disappeared giant Lake Agassiz, Lake McConnell and Lake Algonque.
2.4 West Siberian Lake
Some scientists believe that one of the largest periglacial lakes in Eurasia was Mansiyskoe, or as it is also called West Siberian Lake. It occupied almost the entire territory of the West Siberian Plain to the foothills of the Kuznetsk Alatau and Altai. The places where the largest cities of Tyumen, Tomsk and Novosibirsk are now located were covered with water during the last ice age. When the glacier began to melt - 16-14 thousand years ago, the waters of Lake Mansi began to gradually flow into the Arctic Ocean, and in its place modern river systems were formed, and in the lowland part of the Taiga Ob region, the largest system of Vasyugan Swamps in Eurasia was formed.
Fig. 11 This is what West Siberian Lake looked like
2.5 Oceans
The planet's ice sheets are formed by the waters of the world's oceans. Accordingly, the larger and higher the glaciers, the less water remains in the ocean. Glaciers absorb water, the ocean level drops, exposing large areas of land. Thus, 50,000 years ago, due to the growth of glaciers, the sea level dropped by 50 m, and 20,000 years ago - by 110-130 m. During this period, many modern islands formed a single whole with the mainland. Thus, the British, Japanese, and New Siberian Islands were inseparable from the mainland. In place of the Bering Strait there was a wide strip of land called Beringia.
Fig. 12 Diagram of sea level changes during the last ice age
2.6 Great Glacier
During the last glaciation, the planet's subpolar part of the Northern Hemisphere was occupied by a huge Arctic ice sheet. It was formed as a result of the merger of the North American and Eurasian ice sheets into a single system.
The Arctic ice sheet consisted of giant ice sheets shaped like flat-convex domes, which formed ice layers 2-3 kilometers high in some places. The total area of ice cover is more than 40 million square meters. km.
The largest elements of the Arctic Ice Sheet:
1. Laurentian shield centered over southwestern Hudson Bay;
2. Kara shield with center above Kara Sea spread to the entire north of the Russian Plain, Western and Central Siberia;
3. Greenland shield;
4. East Siberian shield, covering the Siberian seas, the coast of Eastern Siberia and part of Chukotka;
5. Icelandic shield
Rice. 13 Arctic ice sheet
Even during the harsh Ice Age, the climate was constantly changing. The glaciers gradually advanced south and then retreated again. The ice sheet reached its maximum thickness about 20,000 years ago.
3. Quaternary glaciations in the European part of Russia
Quaternary glaciation - glaciation in the Quaternary period, caused by a decrease in temperature that began at the end of the Neogene period. In the mountains of Europe, Asia, and America, glaciers began to increase, flowing onto the plains; on the Scandinavian Peninsula, a gradually expanding ice cap formed; the advancing ice pushed the animals and plants that lived there to the south.
The thickness of the ice cover reached 2 - 3 kilometers. About 30% of the territory of modern Russia in the north was occupied by sheet glaciation, which either decreased slightly, then moved south again. Interglacial periods with warm, mild climates were followed by cold snaps when the glaciers advanced again.
On the territory of modern Russia there were 4 glaciations - Oka, Dnieper, Moscow and Valdai. The largest of them was the Dnieper, when a giant glacial tongue descended along the Dnieper to the latitude of Dnepropetrovsk, and along the Don to the mouth of the Medveditsa.
Consider the Moscow glaciation
The Moscow glaciation is an ice age dating back to the Anthropogen (Quaternary) period (Middle Pleistocene, about 125-170 thousand years ago), the last of the major glaciations of the Russian (East European) Plain.
It was preceded by the Odintsovo time (170-125 thousand years ago) - a relatively warm period separating the Moscow glaciation from the maximum, Dnieper glaciation (230-100 thousand years ago), also in the Middle Pleistocene.
The Moscow glaciation was identified relatively recently as an independent ice age. Some researchers still interpret the Moscow glaciation as one of the stages of the Dnieper glaciation, or that it was one of the stages of a larger and longer previous glaciation. However, the boundary of the glacier developing during the Muscovite era is drawn with greater validity.
Moscow glaciation only captured the northern part of the Moscow region. The glacier's border ran along the Klyazma River. It was during the melting of the Moscow glacier that the morainic strata of the Dnieper glaciation were almost completely washed away. The watering of the periglacial zone, which directly included the territory of the Shatura region, during the melting of the Moscow glacier was so great that the lowlands were filled with large lakes or turned into powerful valleys of runoff of melted glacial waters. Suspensions settled in them, forming outwash plains with sandy and sandy loam deposits, which are most common within the region at present.
Fig. 14 Position of terminal glacial moraines of different ages within the central part of the Russian Plain. Moraine of the Early Valdai () and Late Valdai () glaciations.
4. Causes of Ice Ages
The causes of the Ice Ages are inextricably linked to the broader issues of global climate change that have occurred throughout Earth's history. From time to time, significant changes in geological and biological conditions occurred. It should be borne in mind that the beginning of all great glaciations is determined by two important factors.
First, over thousands of years, the annual precipitation pattern should be dominated by heavy, long-lasting snowfalls.
Secondly, in areas with such a precipitation regime, temperatures must be so low that summer snowmelt is minimized and firn fields increase year after year until glaciers begin to form. Abundant snow accumulation must dominate the glacier balance throughout the glaciation, since if ablation exceeds accumulation, glaciation will decline. Obviously, for each ice age it is necessary to find out the reasons for its beginning and end.
Hypotheses
1. The pole migration hypothesis. Many scientists believed that the Earth's rotation axis changes its position from time to time, which leads to a corresponding shift in climate zones.
2. Carbon dioxide hypothesis. Carbon dioxide CO2 in the atmosphere acts like a warm blanket to trap the heat emitted by the Earth near its surface, and any significant reduction in CO2 in the air will result in a drop in temperature on Earth. As a result, the temperature of the land will drop, and the Ice Age will begin.
3. Hypothesis of diastrophism (movements of the earth's crust). Significant uplifts of land have repeatedly occurred in the history of the Earth. In general, the air temperature over land decreases by about 1.8. With a rise of every 90 m. In fact, the mountains rose many hundreds of meters, which turned out to be sufficient for the formation of valley glaciers there. In addition, the growth of mountains changes the circulation of moisture-carrying air masses. The uplift of ocean floors can, in turn, change the circulation of ocean waters and also cause climate change. It is not known whether only tectonic movements could have been the cause of glaciation, in any case, they could greatly contribute to its development
4. Volcanic dust hypothesis. Volcanic eruptions are accompanied by the release of huge amounts of dust into the atmosphere. It is obvious that volcanic activity, widespread on Earth for thousands of years, could significantly lower air temperatures and cause the onset of glaciation.
5. Continental drift hypothesis. According to this hypothesis, all modern continents and most large islands were once part of the single continent of Pangea, washed by the World Ocean. The consolidation of continents into such a single landmass could explain the development of the Late Paleozoic glaciation of South America, Africa, India and Australia. The areas covered by this glaciation were probably much further north or south than their present position. The continents began to separate in the Cretaceous, and reached their present position approximately 10 thousand years ago
6. Ewing-Donna conjecture. One of the attempts to explain the reasons for the emergence of the Pleistocene Ice Age belongs to M. Ewing and W. Donne, geophysicists who made a significant contribution to the study of the topography of the ocean floor. They believe that in pre-Pleistocene times the Pacific Ocean occupied the northern polar regions and therefore it was much warmer there than now. The Arctic land areas were then located in the North Pacific Ocean. Then, as a result of continental drift, North America, Siberia and the Arctic Ocean took their modern position. Thanks to the Gulf Stream coming from the Atlantic, the waters of the Arctic Ocean at that time were warm and evaporated intensively, which contributed to heavy snowfalls in North America, Europe and Siberia. Thus, the Pleistocene glaciation began in these areas. It stopped because, as a result of the growth of glaciers, the level of the World Ocean dropped by about 90 m, and the Gulf Stream was eventually unable to overcome the high underwater ridges separating the basins of the Arctic and Atlantic oceans. Deprived of the influx of warm Atlantic waters, the Arctic Ocean froze, and the source of moisture feeding the glaciers dried up.
7. Hypothesis of circulation of ocean waters. There are many currents in the oceans, both warm and cold, which have a significant impact on the climate of the continents. The Gulf Stream is one of the remarkable warm currents that washes the northern coast of South America, passes through the Caribbean Sea and the Gulf of Mexico and crosses the North Atlantic, having a warming effect on Western Europe. Warm currents also exist in the South Pacific and Indian Ocean. The most powerful cold currents are directed from the Arctic Ocean to the Pacific Ocean through the Bering Strait and into Atlantic Ocean- through the straits along the eastern and western coasts of Greenland. One of them, the Labrador Current, cools the New England coast and brings fogs there. Cold waters also enter the southern oceans from Antarctica in the form of particularly powerful currents moving north almost to the equator along the western coasts of Chile and Peru. The strong subsurface Gulf Stream carries its cold waters south into the North Atlantic.
8. Hypothesis of changes in solar radiation. As a result of a long-term study of sunspots, which are strong emissions of plasma in the solar atmosphere, it was discovered that there are very significant annual and longer cycles of changes in solar radiation. Peaks in solar activity occur approximately every 11, 33, and 99 years, when the Sun emits more heat, resulting in a more powerful circulation of the Earth's atmosphere, accompanied by greater cloudiness and heavier precipitation. Due to high clouds blocking the sun's rays, the land surface receives less heat than usual.
Conclusion
During the course work, glacial eras, which include ice ages, were studied. Ice ages have been identified and analyzed with precision. Detailed data on the last ice age has been obtained. The last Quaternary epochs have been identified. The main causes of ice ages have also been studied.
Bibliography
1. Dotsenko S.B. On the glaciation of the Earth at the end of the Paleozoic // Life of the Earth. Geodynamics and mineral resources. M.: Moscow State University Publishing House, 1988.
2. Serebryanny L.R. Ancient glaciation and life / Serebryanny Leonid Ruvimovich; Responsible editor G.A. Avsyuk. - M.: Nauka, 1980. - 128 p.: ill. - (Man and the environment). - Bibliography
3. Secrets of the Ice Ages: Trans. from English/Ed. G.A. Avsyuka; Afterword G.A. Avsyuk and M.G. Grosvalda.-M.: Progress, 1988.-264 p.
4. http://ru.wikipedia.org/wiki/Ice_age (Material from Wikipedia - the free encyclopedia)
5. http://www.ecology.dubna.ru/dubna/pru/geology.html (Article Geological and geomorphological features. N.V. Koronovsky)
6. http://ru.wikipedia.org/wiki/Ice_age (Material from Wikipedia - the free encyclopedia)
7. http://www.fio.vrn.ru/2004/7/kaynozoyskaya.htm (Cenozoic era)
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 repeat on Earth regularly every 180-200 million years. Traces of glaciations are known in sediments that are billions and hundreds of millions of years old - in the Cambrian, Carboniferous, Triassic-Permian. That they could be is “said” by the so-called tillites, breeds very similar to moraine the latter, more precisely last glaciations. These are the remains of ancient glacial deposits, consisting of a clayey mass with inclusions of large and small boulders scratched by movement (hatched).
Separate layers tillites, found even in equatorial Africa, can reach thickness of tens and even hundreds of meters!
Signs of glaciations were found on different continents - in Australia, South America, Africa and India, which is used by scientists for reconstruction of paleocontinents and is often cited as confirmation plate tectonics theories.
Traces of ancient glaciations indicate that glaciations on a continental scale- this is not a random phenomenon at all, it is natural a natural phenomenon, arising under certain conditions.
The last of the ice ages began almost million years ago, in Quaternary time, or the Quaternary period, the Pleistocene and was marked by the extensive spread of glaciers - The Great Glaciation of the Earth.
Under thick, many-kilometer-long covers of ice were the northern part of the North American continent - the North American Ice Sheet, which reached a thickness of up to 3.5 km and extended to approximately 38° north latitude and a significant part of Europe, on which (an ice sheet with a thickness of up to 2.5-3 km) . On the territory of Russia, the glacier descended in two huge tongues along the ancient valleys of the Dnieper and Don.Partial glaciation also covered Siberia - there was mainly the so-called “mountain-valley glaciation”, when glaciers did not cover the entire area with a thick cover, but were only in the mountains and foothill valleys, which is associated with the sharply continental climate and low temperatures in Eastern Siberia . But almost all Western Siberia, due to the fact that the rivers were dammed 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, the entire Antarctic continent was under ice, as it is now.
During the period of maximum expansion of the Quaternary glaciation, glaciers covered over 40 million km 2–about a quarter of the entire surface of the continents.
Having reached their greatest development about 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink as the glaciation period was not continuous throughout the Quaternary period.
There is geological, paleobotanical and other evidence that glaciers disappeared several times, giving way to epochs interglacial when the climate was even warmer than today. However, the warm eras were replaced by cold snaps again, and the glaciers spread again.
We now 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 continent that had long existed here. By the way, now, due to the fact that the thickness of the Antarctic glacier is enormous, 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 then reappeared, the Antarctic ice sheet changed little in its size. The maximum glaciation of Antarctica was only one and a half times larger than the modern one in volume, and not much larger in area.
Now about the hypotheses... There are hundreds, if not thousands, of hypotheses about why glaciations occur, and whether there were any at all!
The following main ones are usually put forward: scientific hypotheses:
- Volcanic eruptions leading to a decrease in the transparency of the atmosphere and cooling throughout the Earth;
- Epochs of orogenesis (mountain building);
- Reducing the amount of carbon dioxide in the atmosphere, which reduces the “greenhouse effect” and leads to cooling;
- Cyclicity of solar activity;
- Changes in the position of the Earth relative to the Sun.
But, nevertheless, the causes of glaciations have not been fully elucidated!
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 amount of solar heat received by our planet decreases, i.e. glaciation occurs when the Earth passes the point of its orbit that is farthest from the Sun.
However, astronomers believe that changes in the amount of solar radiation hitting the Earth alone are not enough to trigger an ice age. Apparently, fluctuations in the activity of the Sun itself also matter, which is a periodic, cyclical process, and changes every 11-12 years, with a cyclicity 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 old.
There is also a hypothesis that the emergence of glaciers is associated with certain areas 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 “cosmic 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 before epochs of cooling there are always epochs of warming, and there is, for example, a hypothesis that the Arctic Ocean, due to warming, at times is completely freed from ice (by the way, this is still happening), and there is increased evaporation from the surface of the ocean , streams of moist 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 during the short and cold summer. This is how ice sheets appear on 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, the warm Atlantic Ocean ceases to communicate with the Arctic Ocean, and it is gradually covered with ice again, evaporation from its surface abruptly stops, less and less snow falls on the continents and less, the “feeding” of the glaciers deteriorates, 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 development cycle 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-mentioned hypotheses.
But it is quite possible that glaciation processes are associated with combined influence of various natural factors, which could act together and replace each other, and the important thing is that, having begun, glaciations, like a “wound clock,” already develop 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 era of the Great Glaciations of the Earth, the ice either retreated 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 ancient glaciation have survived to this day.
Let us 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 of the earth's surface.
How can one determine whether there was glaciation in a given place on Earth or not? This is usually quite easy to determine by the peculiar forms of geographical relief and rocks.
In the fields and forests of Russia there are often large accumulations of huge boulders, pebbles, blocks, sands and clays. They usually lie directly on the surface, but they can also be seen in the cliffs of ravines and on 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 “Research 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-geographical map of European Russia, then we can notice some patterns in the location of hills, hills, basins and valleys of large rivers. So, for example, the Leningrad and Novgorod regions from the south and east are, as it were, limited Valdai Upland shaped like 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 cover glaciers.
Numerous hilly, winding hills are also visible on the West Siberian Plain - "manes" also evidence of the activity of ancient glaciers, or rather glacial waters. Many traces of stopping moving glaciers flowing down the mountain slopes into large basins were discovered in Central and Eastern Siberia.
It is difficult to imagine ice several kilometers thick on the site of 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, moving masses of ice influenced the entire natural environment - topography, landscapes, river flow, soils, vegetation and wildlife.
It should be noted that on the territory of Europe and the European part of Russia, practically no rocks have been preserved from the geological eras preceding the Quaternary period - Paleogene (66-25 million years) and Neogene (25-1.8 million years), they were completely eroded and redeposited during the Quaternary period, 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 - moraine, more precisely moraine loams, sands of various origins (aquaglacial, lake, river), huge boulders, as well as cover loams - all this is evidence of the powerful influence of the glacier.
On the territory of Moscow, traces of three glaciations can be identified (although there are many more of them - different researchers identify from 5 to several dozen periods of ice advances and retreats):
- Oka (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 hydroglacial (fluvio-glacial) deposits - mainly the sands of the Meshchera Lowland.
And the names of the glaciers themselves correspond to the names of those places to which the glaciers reached - the Oka, Dnieper and Don, the Moscow River, Valdai, etc.
Since the thickness of the glaciers reached almost 3 km, one can imagine what colossal work he performed! Some hills and hills on the territory of Moscow and the Moscow region are thick (up to 100 meters!) deposits that were “brought” by the glacier.
The best known are, for example Klinsko-Dmitrovskaya moraine ridge, individual hills on the territory of Moscow ( Vorobyovy Gory and Teplostanskaya Upland). Huge boulders weighing up to several tons (for example, the Maiden Stone in Kolomenskoye) are also the result of the glacier.
Glaciers smoothed out the unevenness of the relief: they destroyed hills and ridges, and with the resulting rock fragments they filled depressions - river valleys and lake basins, transporting huge masses of stone fragments over a distance of more than 2 thousand km.
However, huge masses of ice (given its colossal thickness) put so much pressure on the underlying rocks that even the strongest of them could not stand it and collapsed.
Their fragments were frozen into the body of the moving glacier and, like sandpaper, for tens of thousands of years they scratched rocks composed of granites, gneisses, sandstones and other rocks, creating depressions in them. Numerous glacial grooves, “scars” and glacial polishing on granite rocks, as well as long hollows in the earth’s crust, subsequently occupied by lakes and swamps, are still preserved. An example is the countless depressions of the lakes of Karelia and the Kola Peninsula.
But glaciers did not plow up all the rocks on their way. The destruction was mainly carried out in 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 became 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 thickness. Gradually they merged, forming entire rivers, which over thousands of years formed narrow valleys and washed away a lot of debris.
As already mentioned, the forms of glacial relief are very diverse. For moraine plains Characterized by many ridges and shafts, indicating places where moving ice stops, and the main form of relief among them is shafts of terminal moraines, usually these are low arched ridges composed of sand and clay mixed with boulders and pebbles. The depressions between the ridges are often occupied by lakes. Sometimes among the moraine plains you can see outcasts- blocks hundreds of meters in size and weighing tens of tons, giant pieces of the glacier bed, transported by it over enormous distances.
Glaciers often blocked river flows and near such “dams” huge lakes arose, filling depressions in 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), at their bottom they managed to accumulate lacustrine clays, layered sediments, by counting the layers of which, one can clearly distinguish the periods of winter and summer, as well as how many years these sediments have accumulated.
In the era of the last Valdai glaciation arose Upper Volga periglacial lakes(Mologo-Sheksninskoye, Tverskoye, Verkhne-Molozhskoye, etc.). At first their waters flowed to the southwest, but with the retreat of the glacier they were able to flow to the north. Traces of Lake Mologo-Sheksninsky 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, and the Far East. As a result of ancient glaciation, 135-280 thousand years ago, sharp mountain peaks - “gendarmes” - appeared in Altai, the Sayans, the Baikal region and Transbaikalia, on the Stanovoi Highlands. Here the so-called “ mesh type glaciation", i.e. If you could look from a bird's eye view, you would be able to see how ice-free plateaus and mountain peaks rise against the backdrop of glaciers.
It should be noted that during the ice ages, quite large ice massifs were located on part of the territory of Siberia, for example on archipelago Severnaya Zemlya, 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 Plateau and Chukotka Mountains. These areas are considered centers of glaciations in Siberia.
Traces of these glaciations are numerous bowl-shaped depressions of mountain peaks - circuses or punishments, huge moraine ridges 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 gigantic masses of water through low watersheds rushed with incredible speed into neighboring valleys, crashing into them and forming huge canyons and gorges. For example, in Altai, in the Chuya-Kurai depression, “giant ripples”, “drilling boilers”, gorges and canyons, huge outlier boulders, “dry waterfalls” and other traces of water flows escaping from ancient lakes “only” are still preserved. just” 12-14 thousand years ago.
“Invading” the plains of Northern Eurasia from the north, the ice sheets either penetrated far to the south along relief depressions, or stopped at some obstacles, for example, hills.
It is probably not yet possible to accurately determine which of the glaciations was the “greatest,” however, it is known, for example, that the Valdai glacier was sharply smaller in area than the Dnieper glacier.
The landscapes at the boundaries of the cover glaciers also differed. Thus, during the Oka glaciation era (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.
During the era of the Dnieper glaciation, glaciers were significantly larger. Along the edge of the ice sheet stretched the tundra-steppe (dry tundra) with a very harsh climate. The average annual temperature was approaching 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 there was little snow in winter and there were 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 a harsh climate. Traces of permafrost or cryogenic effects are noticeable in the sands; these are often disturbed, as if “torn” layers, often with high content iron minerals.
Fluvio-glacial deposits with traces of cryogenic impact
The last “Great Glaciation” has been studied for more than 100 years. Many decades of hard work by outstanding researchers went into collecting data on its distribution on the plains and in the mountains, mapping end-moraine complexes and traces of glacial-dammed lakes, glacial scars, drumlins, and areas of “hilly moraine.”
True, there are also researchers who generally deny 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,” nevertheless doubt the correctness of the conclusion about the grandiose scale of glaciations of the past, and they are especially distrustful of the conclusion about ice sheets that overlapped the polar continental shelves; 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 the 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, are “reconstructing” “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 over the entire continent, including its underwater margins, in particular the areas 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 ice area 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 topography of the Chilean coast and the residual ice sheets of the Andes.
"South Alpine complex" of New Zealand– was a smaller copy of Patagonian. It had the same shape and extended onto the shelf in the same way; 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, which arose as a result of the merger North American and Eurasian covers into a single glacial system, Moreover, an important role was played by floating ice shelves, especially the Central Arctic, which covered the entire deep-water part of the Arctic Ocean.
The largest elements of the Arctic ice sheet were the Laurentian Shield of North America and the Kara Shield of Arctic Eurasia, they were shaped like giant flat-convex domes. The center of the first of them was located over the southwestern part of 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.
From other elements of the Arctic cover special attention deserves 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 Tiksi region, are also associated with it grandiose glacial-erosive 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 the ice shelves that united them, floating in the deep ocean.
The periods of time during which glaciers disappeared, or were reduced by 80-90%, are called interglacials. Landscapes freed from ice in a relatively warm climate were transformed: the tundra retreated to the northern coast of Eurasia, and the taiga and deciduous 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 under the ice, peculiar layers of boulder loams and sands were formed, characterized by high density associated with the influence of glacial load - main, or bottom moraine.
Since the size of the glacier is 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 with climate warming, the edges of the glaciers retreat to new, “equilibrium boundaries.” The end parts of the glacial tongues stop moving and gradually melt, and boulders, sand and loam included in the ice are released, forming a shaft that follows the contours of the glacier - terminal moraine; the other part of the clastic material (mainly sand and clay particles) is carried away by meltwater flows and deposited around in the form fluvioglacial sandy plains (Zandrov).
Similar flows also operate deep in 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 piles of hills of various shapes and composition 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) oz and irregular shape kama.
All these forms of glacial landscape are very clearly represented in North America: the boundary of ancient glaciation here is marked by a terminal moraine ridge with heights of up to fifty meters, stretching across the entire continent from its eastern coast to the western. To the north of this “Great Glacial Wall” the glacial deposits are represented mainly by moraine, and to the south of it by a “cloak” of fluvioglacial sands and pebbles.
Just as four glacial epochs have been identified for the territory of the European part of Russia, four glacial epochs have also been identified for Central Europe, named after the corresponding Alpine rivers - Günz, Mindel, Riess and Würm, and in North America - Nebraska, Kansas, Illinois and Wisconsin glaciations.
Climate periglacial The areas (surrounding the glacier) were cold and dry, which is fully confirmed by paleontological data. In these landscapes a very specific fauna appears with a combination cryophilic (cold-loving) and xerophilic (dry-loving) plants – tundra-steppe.
Now similar natural zones, similar to periglacial ones, have been preserved in the form of so-called relict steppes– islands among the taiga and forest-tundra landscapes, for example, the so-called alasy Yakutia, the southern slopes of the mountains of northeastern Siberia and Alaska, as well as the cold, dry highlands of Central Asia.
Tundra-steppe was different in that her the herbaceous layer was formed mainly not by mosses (as in the tundra), but by grasses, and it was here that it took shape cryophilic option herbaceous vegetation with a very high biomass of grazing ungulates and predators – the so-called “mammoth fauna”.
It contained a bizarre mixture of different kinds animals as characteristic of tundra – reindeer, caribou, muskox, lemmings, For steppes - saiga, horse, camel, bison, gophers, and mammoths and woolly rhinoceroses, saber-toothed tiger - Smilodon, and giant hyena.
It should be noted that many climate changes have been repeated, as it were, “in miniature” within 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 sizes exceeded modern ones (snow cover appeared, for example, in the mountains of Ethiopia, where there is none now).
And in the period preceding the Little Ice Age Atlantic optimum(900-1300) glaciers, on the contrary, shrank, and the climate was noticeably milder than the present one. Let us remember that it was during these times 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 in their boats. And the Novgorod Ushkuin merchants traveled along the “Northern Sea Route” to the Gulf of Ob, founding the city of Mangazeya there.
And the last retreat of glaciers, which began over 10 thousand years ago, is well remembered by people, hence the legends about the Great Flood, as a huge amount of meltwater rushed down to the south, rains and floods became frequent.
In the distant past, the growth of glaciers occurred in eras with lower air temperatures 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 Mediterranean and Black Sea countries at the turn of the era the climate was colder and wetter than now.
In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, blocked mountain passes with ice and destroyed some high-lying villages. It was during this era that glaciers in the Caucasus sharply intensified and grew.
But by the end of the 1st millennium, climate warming began again, and mountain glaciers in the Alps, Caucasus, Scandinavia and Iceland retreated.
The climate began to change seriously again only in the 14th century; glaciers began to grow rapidly in Greenland, summer thawing of the soil became increasingly 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, harsh centuries began, which were called the “Little Ice Age”. In the south of Europe, severe and long winters often recurred; in 1621 and 1669, the Bosporus Strait 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 is data covering the entire past century. If the share of advancing alpine glaciers in the 40-50s of the 20th century was close to zero, then in the mid-60s of the 20th century about 30%, and at the end of the 70s of the 20th century, 65-70% of the surveyed glaciers were advancing here.
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 in any way affect the normal course of global atmospheric and glacial processes. However, at the end of the last, twentieth century, glaciers began to retreat 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 currently increased man-made emissions of carbon dioxide, methane, freon and various aerosols into the atmosphere seem to help reduce solar radiation. In this regard, “voices” appeared, first from journalists, then from politicians, and then from scientists about the beginning of a “new ice age.” Environmentalists have “sounded the alarm”, fearing “the coming anthropogenic warming” due to the constant increase in 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 at 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, not all carbon dioxide remains in the atmosphere: 50-60% of industrial CO 2 emissions end up in the ocean, where they are quickly absorbed by animals (corals in the first place), and of course they are also absorbed by plants–Let's 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 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 regulation mechanism that sharply slows down the greenhouse effect at high concentrations of CO 2.
So all the numerous “scientific hypotheses” about the “greenhouse effect”, “rising sea levels”, “changes in the Gulf Stream”, and naturally the “coming Apocalypse” are mostly imposed on us “from above”, by politicians, incompetent scientists, illiterate journalists or simply science scammers. The more you intimidate the population, the easier it is to sell goods and manage...
But in fact, an ordinary natural process is taking place - one stage, one climatic epoch gives way to another, and there is nothing strange about it... But the fact that natural disasters occur, and that there are supposedly more of them - tornadoes, floods, etc. - is 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 floods and tornadoes are possible - along the banks of rivers and oceans, in the deserts of America! Moreover, let us remember that natural disasters have always existed, and even destroyed entire civilizations!
As for the opinions of scientists, which both politicians and journalists love to refer to... Back in 1983, American sociologists Randall Collins and Sal Restivo, in their famous article “Pirates and Politicians in Mathematics,” wrote openly: “...There is no immutable set of norms that guide the behavior of scientists. The only thing that remains constant is the activity of scientists (and other types of intellectuals correlated with them), aimed at acquiring wealth and fame, as well as gaining the opportunity to control the flow of ideas and impose their own. own ideas to others... The ideals of science do not predetermine scientific behavior, but arise from the struggle for individual success in different conditions competitions …".
And a little more about science... Various large companies often provide grants to conduct so-called “ scientific 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” orders, for example, “a certain 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 “well-defined interests,” and it is understandable , that he will most likely “adjust” “his conclusions” to the customer, since the main question is already not a question of scientific research–and what does the customer want to receive, what is the result?. And if the customer's result won't suit, then this scientist won't invite you anymore, and not in any “serious project”, i.e. “monetary”, he will no longer participate, since they will invite another scientist, more “amenable”... Much, of course, depends on his civic position, professionalism, and reputation as a scientist... But let’s not forget how much they “get” in Russia scientists... Yes, in the world, in Europe and 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, etc. o only then can research be worthy of serious attention.
Unless, of course, these “groups”, “institutes” or “laboratories” were funded by the customer of this research or project...
A.A. Kazdym,
Candidate of Geological and Mineralogical Sciences, member of MOIP