History of the Ice Age.

The causes of ice ages are cosmic: changes in solar activity, changes in the position of the Earth relative to the Sun. Planetary cycles: 1). 90 - 100 thousand-year cycles of climate change as a result of changes in the eccentricity of the earth's orbit; 2). 40 - 41 thousand-year cycles of change in the tilt of the earth's axis from 21.5 degrees. up to 24.5 degrees; 3). 21 - 22 thousand-year cycles of changes in the orientation of the earth's axis (precession). The results of volcanic activity - the darkening of the earth's atmosphere with dust and ash - have a significant impact.
The oldest glaciation took place 800 - 600 million years ago during the Laurentian period of the Precambrian era.
About 300 million years ago, the Permocarbon glaciation occurred at the end of the Carboniferous - beginning of the Permian period Paleozoic era. At this time, there was only one supercontinent on planet Earth, Pangea. The center of the continent was located near the equator, the edge reached the south pole. Ice ages gave way to warming periods, and then to cold periods again. Such climate changes lasted from 330 to 250 million years ago. During this time, Pangea shifted north. About 200 million years ago, an even, warm climate was established on Earth for a long time.
About 120 - 100 million years ago in Cretaceous period Mesozoic era The continent of Gondwana broke away from the continent of Pangea and remained in the Southern Hemisphere.
At first Cenozoic era, in the early Paleogene during the Paleocene era - ca. 55 million years ago there was a general tectonic rise of the earth's surface by 300 - 800 meters, the split of Pangea and Gondwana into continents and planet-wide cooling began. 49 - 48 million years ago, at the beginning of the Eocene era, a strait formed between Australia and Antarctica. About 40 million years ago, mountain continental glaciers began to form in West Antarctica. Throughout the Paleogene period, the configuration of the oceans changed; the Arctic Ocean, the Northwest Passage, the Labrador and Baffin seas, and the Norwegian-Greenland basin were formed. Along the northern shores of the Atlantic and Pacific Oceans High blocky mountains rose, and the underwater Mid-Atlantic Ridge developed.
At the border of the Eocene and Oligocene - about 36 - 35 million years ago, Antarctica moved to the south pole, separated from South America and was cut off from warm equatorial waters. 28 - 27 million years ago, continuous covers of mountain glaciers formed in Antarctica and then, during the Oligocene and Miocene, the ice sheet gradually filled the entire Antarctica. The continent of Gondwana finally split into continents: Antarctica, Australia, Africa, Madagascar, Hindustan, South America.
15 million years ago, glaciation began in the Arctic Ocean - floating ice, icebergs, and sometimes solid ice fields.
10 million years ago, a glacier in the Southern Hemisphere went beyond Antarctica into the ocean and about 5 million years ago reached its maximum, covering the ocean with an ice sheet to the coasts of South America, Africa, and Australia. Floating ice reached the tropics. At the same time, during the Pliocene era, glaciers began to appear in the mountains of the continents of the Northern Hemisphere (Scandinavian, Ural, Pamir-Himalayan, Cordillera) and 4 million years ago filled the islands of the Canadian Arctic archipelago and Greenland. North America, Iceland, Europe, Northern Asia were covered with ice 3 - 2.5 million years ago. The Late Cenozoic Ice Age reached its maximum in the Pleistocene era, about 700 thousand years ago. This same ice age continues to this day.
So, 2 - 1.7 million years ago the Upper Cenozoic - Quaternary period began. Glaciers in the Northern Hemisphere on land have reached mid-latitudes; in the Southern Hemisphere, continental ice has reached the edge of the shelf, icebergs up to 40-50 degrees. Yu. w. During this period, about 40 stages of glaciation were observed. The most significant were: Pleistocene glaciation I - 930 thousand years ago; Pleistocene glaciation II - 840 thousand years ago; Danube glaciation I - 760 thousand years ago; Danube glaciation II - 720 thousand years ago; Danube glaciation III - 680 thousand years ago.
During the Holocene era, there were four glaciations on Earth, named after valleys
Swiss rivers, where they were first studied. The oldest is the Gyuntz glaciation (in North America - Nebraska) 600 - 530 thousand years ago. Günz I reached its maximum 590 thousand years ago, Günz II peaked 550 thousand years ago. Mindel Glaciation (Kansas) 490 - 410 thousand years ago. Mindel I reached its maximum 480 thousand years ago, Mindel II peaked 430 thousand years ago. Then came the Great Interglacial, which lasted 170 thousand years. During this period, the Mesozoic warm climate seemed to return, and the Ice Age ended forever. But he came back.
The Riss glaciation (Illinois, Zaal, Dnieper) began 240 - 180 thousand years ago, the most powerful of all four. Riess I reached its maximum 230 thousand years ago, Riess II peaked 190 thousand years ago. The thickness of the glacier in Hudson Bay reached 3.5 kilometers, the edge of the glacier in the North Mountains. America reached almost to Mexico, on the plain it filled the basins of the Great Lakes and reached the river. Ohio, went south along the Appalachians and reached the ocean in the southern part of the island. Long Island. In Europe, the glacier filled all of Ireland, Bristol Bay, and the English Channel at 49 degrees. With. sh., North Sea at 52 degrees. With. sh., passed through Holland, southern Germany, occupied all of Poland to the Carpathians, Northern Ukraine, descended in tongues along the Dnieper to the rapids, along the Don, along the Volga to Akhtuba, along the Ural Mountains and then walked through Siberia to Chukotka.
Then came a new interglacial, which lasted more than 60 thousand years. Its maximum occurred 125 thousand years ago. In Central Europe at that time there were subtropics, moist deciduous forests grew. Subsequently, they were replaced by coniferous forests and dry prairies.
115 thousand years ago the last historical glaciation of Wurm (Wisconsin, Moscow) began. It ended about 10 thousand years ago. Early Würm peaked ca. 110 thousand years ago and ended approx. 100 thousand years ago. The largest glaciers covered Greenland, Spitsbergen, and the Canadian Arctic archipelago. 100 - 70 thousand years ago, an interglacial period reigned on Earth. Middle Wurm - approx. 70 - 60 thousand years ago, was much weaker than the Early and even more so the Late. The last ice age - Late Wurm - was 30 - 10 thousand years ago. The maximum of glaciation occurred between 25 and 18 thousand years ago.
The stage of the greatest glaciation in Europe is called Egga I - 21-17 thousand years ago. Due to the accumulation of water in glaciers, the level of the World Ocean dropped by 120 - 100 meters below the present level. 5% of all water on Earth was in glaciers. About 18 thousand years ago, a glacier in the North. America reached 40 degrees. With. w. and Long Island Islands. In Europe, the glacier reached the line: o. Iceland - o. Ireland - Bristol Bay - Norfolk - Schleswig - Pomerania - Northern Belarus - Moscow vicinity - Komi - Middle Urals at 60 degrees. With. w. - Taimyr - Putorana plateau - Chersky ridge - Chukotka. Due to lowering sea levels, land in Asia was located north of the New Siberian Islands and in the northern part of the Bering Sea - “Beringia”. The two Americas were connected by the Isthmus of Panama, which blocked the connection between the Atlantic and Pacific Oceans, resulting in the formation of the powerful Gulf Stream. In the middle part of the Atlantic Ocean from America to Africa there were many islands and the largest among them was the island of Atlantis. The northern tip of this island was at the latitude of Cadiz (37 degrees north latitude). The archipelagos of the Azores, Canaries, Madeira, and Cape Verde are the submerged peaks of the outlying ridges. Ice and polar fronts from the north and south came as close as possible to the equator. The water in the Mediterranean Sea was 4 degrees. With colder modern. The Gulf Stream flowed around Atlantis and ended off the coast of Portugal. The temperature gradient was greater, the winds and currents were stronger. In addition, there were extensive mountain glaciations in the Alps, Tropical Africa, the mountains of Asia, Argentina and Tropical South America, New Guinea, Hawaii, Tasmania, New Zealand and even in the Pyrenees and the mountains of the north-west. Spain. The climate in Europe was polar and temperate, the vegetation was tundra, forest-tundra, cold steppes, taiga.
Stage II of Egg was 16 - 14 thousand years ago. The slow retreat of the glacier began. At the same time, a system of glacier-dammed lakes was formed at its edge. Glaciers up to 2-3 kilometers thick with their mass crushed and sank the continents into magma and thereby raised the ocean floor, forming mid-ocean ridges.
About 15 - 12 thousand years ago, the Atlantean civilization arose on an island heated by the Gulf Stream. The "Atlanteans" created a state, an army, and had possessions in North Africa as far as Egypt.
Early Dryas stage (Luga) 13.3 - 12.4 thousand years ago. The slow retreat of glaciers continued. About 13 thousand years ago, a glacier melted in Ireland.
Tromso-Lyngen stage (Ra; Bölling) 12.3 - 10.2 thousand years ago. About 11 thousand years ago
The glacier melted on the Shetland Islands (the last in the UK), in Nova Scotia and on the island. Newfoundland (Canada). 11 - 9 thousand years ago a sharp rise in the level of the World Ocean began. When the glacier was released from the load, the land began to rise and the bottom of the oceans to fall, tectonic changes in the earth's crust, earthquakes, volcanic eruptions, and floods. Atlantis also perished from these cataclysms around 9570 BC. The main centers of civilization, cities, and the majority of the population perished. The remaining "Atlanteans" partly degraded and went wild, and partly died out. Possible descendants of the “Atlanteans” were the “Guanches” tribe in the Canary Islands. Information about Atlantis was preserved by the Egyptian priests and told about it to the Greek aristocrat and legislator Solon c. 570 BC Solon's narrative was rewritten and brought to posterity by the philosopher Plato c. 350 BC
Preboreal stage 10.1 - 8.5 thousand years ago. Global warming has begun. In the Azov-Black Sea region, sea regression (reduction in area) and water desalination occurred. 9.3 - 8.8 thousand years ago a glacier melted in the White Sea and Karelia. About 9 - 8 thousand years ago the fjords of Baffin Island, Greenland, Norway were freed from ice, and the glacier on the island of Iceland retreated 2 - 7 kilometers from the coast. 8.5 - 7.5 thousand years ago the glacier melted on the Kola and Scandinavian peninsulas. But the warming was uneven; in the Late Holocene there were 5 cold snaps. The first - 10.5 thousand years ago, the second - 8 thousand years ago.
7 - 6 thousand years ago, glaciers in the polar regions and mountains took mainly their modern shape. 7 thousand years ago there was a climatic optimum on Earth (the highest average temperature). The current average global temperature is 2 degrees Celsius lower, and if it drops another 6 degrees Celsius, a new ice age will begin.
About 6.5 thousand years ago, a glacier was localized on the Labrador Peninsula in the Torngat Mountains. About 6 thousand years ago, Beringia finally sank and the land “bridge” between Chukotka and Alaska disappeared. The third cooling in the Holocene occurred 5.3 thousand years ago.
About 5,000 years ago, civilizations formed in the valleys of the Nile, Tigris, Euphrates, and Indus rivers, and the modern historical period on planet Earth began. 4000 - 3500 years ago the level of the World Ocean became equal to the modern level. The fourth cold snap in the Holocene occurred about 2800 years ago. Fifth - the "Little Ice Age" in 1450 - 1850. with a minimum of approx. 1700 The global average temperature was 1 degree C lower than today. There were harsh winters, cold summers in Europe, North. America. The bay in New York was freezing. Mountain glaciers have greatly increased in the Alps, the Caucasus, Alaska, New Zealand, Lapland and even the Ethiopian Highlands.
Currently, the interglacial period continues on Earth, but the planet continues its cosmic path and global changes and climate transformations are inevitable.

During this era, 35% of the land was under ice cover (compared to 10% today).

The last ice age was not just a natural disaster. It is impossible to understand the life of planet Earth without taking these periods into account. In the intervals between them (known as interglacial periods), life flourished, but then once again the ice moved inexorably and brought death, but life did not completely disappear. Every Ice Age was marked by a struggle for survival different types, there were global climate change, and the last one appeared the new kind, who became (over time) dominant on Earth: it was a man.
Ice Ages
Ice ages are geological periods, characterized by strong cooling of the Earth, during which vast areas of the earth's surface were covered with ice, it was observed high level humidity and, naturally, exceptional cold, as well as the lowest known modern science sea ​​level. There is no generally accepted theory regarding the reasons for the onset of the Ice Age, but since the 17th century, a variety of explanations have been proposed. According to the current opinion, this phenomenon was not caused by one reason, but was the result of the influence of three factors.

Changes in the composition of the atmosphere - a different ratio of carbon dioxide ( carbon dioxide) and methane - caused a sharp drop in temperature. It's like the opposite of what we now call global warming, but on a much larger scale.

The movements of the continents, caused by cyclic changes in the orbit of the Earth around the Sun, and in addition the change in the angle of inclination of the planet’s axis relative to the Sun, also had an impact.

The earth received less solar heat, it cooled, which led to glaciation.
The earth has experienced several ice ages. The largest glaciation occurred 950-600 million years ago during the Precambrian era. Then in the Miocene era - 15 million years ago.

Traces of glaciation that can be observed at the present time represent the legacy of the last two million years and belong to the Quaternary period. This period is best studied by scientists and is divided into four periods: Günz, Mindel (Mindel), Ries (Rise) and Würm. The latter corresponds to the last ice age.

Last Ice Age
The Würm stage of glaciation began approximately 100,000 years ago, peaked after 18 thousand years and began to decline after 8 thousand years. During this time, the thickness of the ice reached 350-400 km and covered a third of the land above sea level, in other words, three times the area than now. Based on the amount of ice that currently covers the planet, we can get some idea of ​​the extent of glaciation during that period: today, glaciers occupy 14.8 million km2, or about 10% of the earth's surface, and during the Ice Age they covered an area of ​​44 .4 million km2, which is 30% of the Earth's surface. According to assumptions, in northern Canada, ice covered an area of ​​13.3 million km2, while now there is 147.25 km2 under ice. The same difference is noted in Scandinavia: 6.7 million km2 in that period compared to 3,910 km2 today.

The Ice Age occurred simultaneously in both hemispheres, although in the North the ice spread over larger areas. In Europe, the glacier covered most of the British Isles, northern Germany and Poland, and in North America, where the Würm glaciation is called the “Wisconsin Ice Age,” a layer of ice that descended from the North Pole covered all of Canada and spread south of the Great Lakes. Like the lakes in Patagonia and the Alps, they were formed on the site of depressions left after the melting of the ice mass.

The sea level dropped by almost 120 m, as a result of which large areas were exposed that are currently covered with sea water. The significance of this fact is enormous, since large-scale migrations of humans and animals became possible: hominids were able to make the transition from Siberia to Alaska and move from continental Europe to England. It is quite possible that during interglacial periods, the two largest ice masses on Earth - Antarctica and Greenland - have undergone slight changes throughout history.

At the peak of glaciation, the average temperature drop varied significantly depending on the area: 100 °C in Alaska, 60 °C in England, 20 °C in the tropics and remained virtually unchanged at the equator. Studies of the last glaciations in North America and Europe, which occurred during the Pleistocene era, gave similar results in this geological area within the last two (approximately) million years.

The last 100,000 years are of particular importance to understanding human evolution. Ice ages became a severe test for the inhabitants of the Earth. After the end of the next glaciation, they again had to adapt and learn to survive. When the climate became warmer, sea levels rose, new forests and plants appeared, and the land rose, freed from the pressure of the ice shell.

Hominids had the most natural resources to adapt to changing conditions. They were able to move to areas with the greatest amount of food resources, where the slow process of their evolution began.

Many of us believe that the Ice Age ended a long time ago and no traces of it remain. But geologists say we are only approaching the end of the Ice Age. And the people of Greenland are still living in the Ice Age.

About 25 thousand years ago, the peoples who inhabited the central part of North America saw ice and snow all year round. A huge wall of ice stretched from the Pacific to the Atlantic Ocean, and north to the Pole. This was during the final stage of the Ice Age, when the entire territory of Canada, most of The United States and northwestern Europe were covered with a layer of ice more than one kilometer thick.

But this does not mean that it was always very cold. In the northern part of the United States, temperatures were only 5 degrees lower than today. The cold summer months caused an ice age. At this time, the heat was not enough to melt the ice and snow. It accumulated and eventually covered the entire northern part of these areas.

The Ice Age consisted of four stages. At the beginning of each of them, ice formed moving south, then melted and retreated to the North Pole. This happened, it is believed, four times. Cold periods are called “glaciations”, warm periods are called “interglacial” periods. The first stage in North America is thought to have begun about two million years ago, the second about 1,250,000 years ago, the third about 500,000 years ago, and the last about 100,000 years ago.

Ice melting rate last stage ice age in different areas was different. For example, in the area where the modern state of Wisconsin is located in the USA, the melting of ice began approximately 40,000 years ago. The ice that covered the New England region of the United States disappeared about 28,000 years ago. And the territory of the modern state of Minnesota was freed by ice only 15,000 years ago!

In Europe, Germany became ice-free 17,000 years ago, and Sweden only 13,000 years ago.

Why do glaciers still exist today?

The huge mass of ice that began the Ice Age in North America was called the “continental glacier”: in the very center its thickness reached 4.5 km. This glacier may have formed and melted four times during the entire Ice Age.

The glacier that covered other parts of the world did not melt in some places! For example, the huge island of Greenland is still covered by a continental glacier, except for a narrow coastal strip. In its middle part, the glacier sometimes reaches a thickness of more than three kilometers. Antarctica is also covered by an extensive continental glacier, with ice up to 4 kilometers thick in some places!

Therefore, the reason why there are glaciers in some areas of the globe is because they have not melted since the Ice Age. But the bulk of the glaciers found today were formed recently. They are mainly located in mountain valleys.

They originate in wide, gentle, amphitheatrically shaped valleys. Snow gets here from the slopes as a result of landslides and avalanches. Such snow does not melt in the summer, becoming deeper every year. Gradually, pressure from above, some thawing, and refreezing remove air from the bottom of this snow mass, turning it into solid ice. The impact of the weight of the entire mass of ice and snow compresses the entire mass and causes it to move down the valley. This moving tongue of ice is a mountain glacier.

In Europe, more than 1,200 such glaciers are known in the Alps! They also exist in the Pyrenees, the Carpathians, the Caucasus, and also in the mountains of southern Asia. There are tens of thousands of similar glaciers in southern Alaska, some 50 to 100 km long!

Great Quaternary Glaciation

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

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

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

Having reached their greatest development 250 thousand years ago, Quaternary glaciers began to gradually shrink. The Ice Age was not uniform throughout the Quaternary. Many scientists believe that during this time glaciers 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 again, and the glaciers spread again. We now live, apparently, at the end of the fourth stage of the Quaternary glaciation. After the liberation of Europe and America from under the ice, these continents began to rise - this is how the earth’s crust reacted to the disappearance of the glacial load that had been pressing on it for many thousands of years.

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

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

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

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

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

On the causes of great glaciations

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

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

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

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

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

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

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

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

This hypothesis explains some facts, in particular several advances of glaciers during the Quaternary period, but it also does not answer the main question: what is the cause of the Earth's glaciations.

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

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

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

Development of glaciation in the last millennium

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

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

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

The beginning of the 15th century was approaching. Living conditions became more and more harsh, and our ancestors, who did not understand the reasons for such a cold snap, were very worried about their future. Increasingly, records of cold and difficult years appear in chronicles. In the Tver Chronicle you can read: “In the summer of 6916 (1408) ... then the winter was heavy and cold and snowy, too snowy,” or “In the summer of 6920 (1412) the winter was very snowy, and therefore in the spring there was the water is great and strong.” The Novgorod Chronicle says: “In the summer of 7031 (1523) ... the same spring, on Trinity Day, a great cloud of snow fell, and snow lay on the ground for 4 days, and many bellies, horses and cows froze, and birds died in the forest " In Greenland, due to the onset of cooling by the middle of the 14th century. stopped engaging in cattle breeding and farming; The connection between Scandinavia and Greenland was disrupted due to the abundance of sea ice in the northern seas. In some years, the Baltic and even the Adriatic Sea froze. From the 15th century until the 17th century. mountain glaciers advanced in the Alps and the Caucasus.

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

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

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

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

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

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

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

Scientists note that the ice age is part of the ice era, when the earth's covers are covered with ice for many millions of years. But many people call the Ice Age a period of Earth’s history that ended about twelve thousand years ago.

It is worth noting that ice age history had great amount unique features that have not reached our time. For example, unique animals that were able to adapt to existence in this difficult climate are mammoths, rhinoceroses, saber-toothed tigers, cave bears and others. They were covered with thick fur and quite large in size. Herbivores adapted to get food from under the icy surface. Let's take rhinoceroses, they rake ice with their horns and feed on plants. Oddly enough, the vegetation was varied. Of course, many plant species disappeared, but herbivores had free access to food.

Despite the fact that ancient people were small in size and did not have hair, they too were able to survive during the Ice Age. Their life was incredibly dangerous and difficult. They built themselves small dwellings and insulated them with the skins of killed animals, and ate the meat. People came up with various traps to lure large animals there.

Rice. 1 - Ice Age

The history of the Ice Age was first discussed in the eighteenth century. Then geology began to emerge as a scientific branch, and scientists began to find out the origin of the boulders in Switzerland. Most researchers agreed that they had a glacial origin. In the nineteenth century, it was suggested that the planet's climate was subject to sudden cold snaps. And a little later the term itself was announced "glacial period". It was introduced by Louis Agassiz, whose ideas were not initially recognized by the general public, but then it was proven that many of his works were indeed justified.

In addition to the fact that geologists were able to establish the fact that the Ice Age took place, they also tried to find out why it arose on the planet. The most common belief is that the movement of lithospheric plates can block warm ocean currents. This gradually causes the formation of a mass of ice. If large-scale ice sheets have already formed on the surface of the Earth, then they will cause a sharp cooling, reflecting sunlight, and therefore heat. Another reason for the formation of glaciers could be a change in the level of greenhouse effects. The presence of large arctic areas and the rapid spread of plants eliminates the greenhouse effect by replacing carbon dioxide with oxygen. Whatever the reason for the formation of glaciers, this is a very long process that can also enhance the influence of solar activity on the Earth. Changes in our planet's orbit around the Sun make it extremely susceptible. The distance of the planet from the “main” star also has an influence. Scientists suggest that even during the largest ice ages, the Earth was covered with ice on only one-third of its entire area. There are suggestions that there were ice ages, when the entire surface of our planet was covered with ice. But this fact remains controversial in the world of geological research.

Today, the most significant glacial massif is the Antarctic. The thickness of the ice in some places reaches more than four kilometers. Glaciers move at an average speed of five hundred meters per year. Another impressive ice sheet is found in Greenland. About seventy percent of this island is occupied by glaciers, which is one tenth of the ice on our entire planet. At this point in time, scientists believe that the Ice Age will not begin for at least another thousand years. The whole point is that in modern world There is a colossal emission of carbon dioxide into the atmosphere. And as we found out earlier, the formation of glaciers is possible only at a low level of its content. However, this poses another problem for humanity - global warming, which may be no less large-scale than the beginning of the Ice Age.