Ice ages in the history of the earth are the causes of glaciations. Why do glaciations occur

Traces of ancient cooling, left by widespread ice sheets, are found on all modern continents, on the bottom of the oceans, in deposits of different geological epochs.

The Proterozoic era began with the accumulation of the first, oldest of the glacial deposits found so far. In the period from 2.5 to 1.95 billion years BC, the Huron epoch of glaciation was marked. Approximately a billion years later, a new, Gneissian, epoch of glaciation began (950-900 million years ago), and after another 100-150 thousand years, the Sterskaya glacial epoch. The Precambrian ends with the Varangian epoch of glaciation (680-570 million years BC).

Phanerozoic begins with a warm Cambrian period, but after 110 million years from its beginning, the Ordovician glaciation (460-410 million years BC) was noted, and about 280 million years ago the Gondwana glaciation (340-240 million years BC) culminated. ). The new warm epoch continued until about the middle of the Cenozoic era, when the contemporary Cenozoic epoch of glaciation began.

Taking into account the phases of development and completion, glacial epochs have occupied about half of the time of the Earth's evolution over the past 2.5 billion years. Climatic conditions during the epochs of glaciations were more variable than during the warm "ice-free" epochs. Glaciers retreated and advanced, but invariably remained at the poles of the planet. During the epochs of glaciations, the average temperature of the Earth was 7-10 °C lower than during warm epochs. When the glaciers grew, the difference increased to 15-20 °C. For example, in the closest warm period to us, the average temperature on Earth was about 22 ° C, and now - in the Cenozoic Ice Age - only 15 ° C.

The Cenozoic era is the era of a gradual and consistent decrease in the average temperature on the Earth's surface, the era of transition from the warm era to the glaciation era, which began about 30 million years ago. The climatic system in the Cenozoic changed in such a way that about 3 million years ago the general drop in temperature was replaced by its almost periodic fluctuations, which is associated with the periodic growth of ice sheets.

In high latitudes, the cooling was the strongest - several tens of degrees - while in the equatorial zone it was several degrees. Climatic zoning, close to modern, was established about 2.5 million years ago, although the areas of severe Arctic and Antarctic climate in that era were smaller, and the boundaries of the temperate, subtropical and tropical climate were at higher latitudes. Fluctuations in climate and glaciation of the Earth consisted in the alternation of "warm" interglacial and "cold" glacial epochs.

In the "warm" epochs, the Greenland and Antarctic ice sheets had dimensions close to modern - 1.7 and 13 million square meters. km, respectively. In cold epochs, glaciers, of course, increased, but the main increment of glaciation occurred due to the emergence of large ice sheets in North America and Eurasia. The area of glaciers reached approximately 30 million km³ in the Northern Hemisphere and 15 million km³ in the southern. The climatic conditions of the interglacials were similar to modern ones and even warmer.

About 5.5 thousand years ago, the "climatic optimum" was replaced by the so-called "Iron Age cooling", which culminated about 4 thousand years ago. Following this cooling, a new warming began, which continued into the first millennium of our era. This warming is known as the "Little Climatic Optimum" or the "Forgotten Geographical Discoveries" period.

The first explorers of new lands were Irish monks, who, thanks to the improved navigation conditions in the North Atlantic due to warming, discovered the Faroe Islands, Iceland and, as modern scientists suggest, America in the middle of the first millennium. Following them, this discovery was repeated by the Vikings of Normandy, who at the beginning of this millennium settled the Faroe Islands, Iceland and Greenland, and subsequently reached America. The Vikings swam approximately to the latitude of the 80th parallel, and the ice as an obstacle to navigation is practically not mentioned in the ancient sagas. In addition, if in modern Greenland the inhabitants are mainly engaged in the extraction of fish and sea animals, then cattle breeding was developed in the Norman settlements - excavations showed that cows, sheep and goats were bred here. Cereals were cultivated in Iceland, and the grape growing area overlooked the Baltic Sea, i.e. was 4-5 geographical degrees north of the modern one.

In the first quarter of our millennium, a new cooling began, which continued until the middle of the 19th century. Already in the XVI century. sea ice cut off Greenland from Iceland and led to the death of settlements founded by the Vikings. The latest information about Norman settlers in Greenland dates back to 1500. Natural conditions in Iceland in the 16th-17th centuries became unusually harsh; suffice it to say about this that from the beginning of the cold snap until 1800, the population of the country was halved due to famine. On the plains of Europe, in Scandinavia, severe winters became frequent, previously non-freezing water bodies were covered with ice, crop failures and livestock falling became more frequent. The coasts of France were reached by individual icebergs.

The warming that followed the "Little Ice Age" began already at the end of the 19th century, but as a large-scale phenomenon it attracted the attention of climatologists only in the 1930s. XX century, when a significant increase in water temperature in the Barents Sea was discovered.

In the 30s. the air temperature in temperate and especially in high northern latitudes was much higher than at the end of the 19th century. Thus, winter temperatures in western Greenland increased by 5 °C, and in Spitsbergen - even by 8-9 °C. The largest global increase in average temperature near the Earth's surface during the climax of warming was only 0.6 °C, but even with such a small change - several times less than during the Little Ice Age - a noticeable change in the climate system was associated.

Mountain glaciers reacted violently to warming, retreating everywhere, and the magnitude of this retreat was hundreds of meters long. The ice islands that existed in the Arctic disappeared; only in the Soviet sector of the Arctic from 1924 to 1945. the area of ice during the navigation period at that time decreased by almost 1 million km², i.e. half. This allowed even ordinary ships to sail to high latitudes and make through voyages along the Northern Sea Route during one navigation. The amount of ice in the Greenland Sea also decreased, despite the fact that the removal of ice from the Arctic Basin increased. The duration of the ice blockade of the coast of Iceland was reduced from 20 weeks at the end of the 19th century. up to two weeks in 1920-1939. Everywhere there was a retreat to the north of the boundaries of permafrost - up to hundreds of kilometers, the depth of thawing of frozen soils increased, and the temperature of the frozen strata increased by 1.5-2 ° C.

The warming was so intense and prolonged that it led to a change in the boundaries of ecological areas. The gray-headed thrush began to nest in Greenland, and swallows and starlings appeared in Iceland. The warming of oceanic waters, especially noticeable in the north, led to a change in the places of spawning and fattening of commercial fish: for example, cod and herring appeared in commercial quantities off the coast of Greenland, and Pacific sardine in Peter the Great Bay. Around 1930, mackerel appeared in the waters of Okhotsk mine, and in the 1920s. - saury. The statement of the Russian zoologist, academician N.M. Knipovich: "In some fifteen years and even a shorter period of time, there was such a change in the distribution of representatives of the marine fauna, which is usually associated with the idea of long geological intervals." Warming also affected the Southern Hemisphere, but to a much lesser extent, and it manifested itself most clearly in winter at high latitudes of the Northern Hemisphere.

In the late 1940s cold weather has reappeared. After some time, the reaction of glaciers became noticeable, which in many parts of the Earth went on the offensive or slowed down the retreat. After 1945, there was a noticeable increase in the area of distribution of Arctic ice, which began to appear more often off the coast of Iceland, as well as between Norway and Iceland. From the beginning of the 40s to the end of the 60s. 20th century the area of ice in the Arctic basin has increased by 10%.

Dnieper glaciation
was maximum in the middle Pleistocene (250-170 or 110 thousand years ago). It consisted of two or three stages.

Sometimes the last stage of the Dnieper glaciation is distinguished into an independent Moscow glaciation (170-125 or 110 thousand years ago), and the period of relatively warm time separating them is considered as the Odintsovo interglacial.

At the maximum stage of this glaciation, a significant part of the Russian Plain was occupied by an ice sheet, which, in a narrow tongue along the Dnieper valley, penetrated south to the mouth of the river. Aurélie. Permafrost existed in most of this territory, and the average annual air temperature was then no higher than -5-6°C.
In the southeast of the Russian Plain, in the middle Pleistocene, the so-called "early Khazar" rise in the level of the Caspian Sea by 40-50 m occurred, which consisted of several phases. Their exact dating is unknown.

Mikulin interglacial
Following the Dnieper glaciation followed (125 or 110-70 thousand years ago). At that time, in the central regions of the Russian Plain, winter was much milder than now. If at present the average January temperatures are close to -10°С, then during the Mikulin interglacial they did not fall below -3°С.
Mikulin time corresponded to the so-called "Late Khazar" rise in the level of the Caspian Sea. In the north of the Russian Plain, a synchronous rise in the level of the Baltic Sea was noted, which then connected with the Ladoga and Onega lakes and, possibly, the White Sea, as well as the Arctic Ocean. The general fluctuation of the level of the world ocean between the epochs of glaciation and melting of ice was 130-150 m.

Valdai glaciation
After the Mikulin interglacial, consisting of the Early Valdai or Tver (70-55 thousand years ago) and Late Valdai or Ostashkov (24-12:-10 thousand years ago) glaciations, separated by the Middle Valdai period of repeated (up to 5) temperature fluctuations, during which the climate was much colder modern (55-24 thousand years ago).
In the south of the Russian platform, the early Valdai corresponds to a significant "Attelian" lowering - by 100-120 meters - of the level of the Caspian Sea. It was followed by the "early Khvalynian" rise in sea level by about 200 m (80 m above the initial mark). According to A.P. Chepalyga (Chepalyga, t1984), the influx of moisture into the Caspian basin of the Upper Khvalynian time exceeded its losses by approximately 12 cubic meters. km per year.
After the "Early Khvalynian" rise in sea level, the "Enotaevsk" lowering of the sea level followed, and then again the "Late Khvalynian" rise in sea level by about 30 m relative to its initial position. According to G.I. Rychagov, at the end of the Late Pleistocene (16 thousand years ago). The late Khvalynian basin was characterized by water column temperatures somewhat lower than modern ones.
The new lowering of the sea level occurred rather quickly. It reached its maximum (50 m) at the very beginning of the Holocene (0.01-0 million years ago), about 10 thousand years ago, and was replaced by the last - the “Novo-Caspian” sea level rise by about 70 m about 8 thousand years ago.
Approximately the same fluctuations in the water surface occurred in the Baltic Sea and the Arctic Ocean. The general fluctuation of the level of the world ocean between the epochs of glaciation and melting of ice was then 80-100 m.

According to radioisotope analyzes of more than 500 different geological and biological samples taken in southern Chile, the mid-latitudes in the western Southern Hemisphere experienced warming and cooling events at the same time as the mid-latitudes in the western Northern Hemisphere.

Chapter " The world in the Pleistocene. Great glaciations and exodus from Hyperborea" / Eleven glaciations of the Quaternaryperiod and nuclear wars

© A.V. Koltypin, 2010

State Educational Institution of Higher Professional Education of the Moscow Region

International University of Nature, Society and Man "Dubna"

Faculty of Natural and Engineering Sciences

Department of Ecology and Earth Sciences

COURSE WORK

By discipline

Geology

Scientific adviser:

Candidate of G.M.S., Associate Professor Anisimova O.V.

Dubna, 2011

Introduction

1. Ice Age

1.1 Ice Ages in Earth's History

1.2 Proterozoic Ice Age

1.3 Paleozoic Ice Age

1.4 Cenozoic Ice Age

1.5 Tertiary period

1.6 Quaternary

2. The Last Ice Age

2.2 Flora and fauna

2.3Rivers and lakes

2.4 West Siberian lake

2.5Oceans

2.6 Great Glacier

3. Quaternary glaciations in the European part of Russia

4. Causes of Ice Ages

Conclusion

Bibliography

Introduction

Target:

To study the main ice ages in the history of the Earth and their role in shaping the modern landscape.

Relevance:

The relevance and significance of this topic is determined by the fact that the glacial epochs are not so well studied to fully confirm the existence on our Earth.

Tasks:

- conduct a literature review;

- establish the main ice ages;

– obtaining detailed data on the last Quaternary glaciations;

Establish the main causes of glaciation in the history of the Earth.

At present, there is still little data that confirms the distribution of frozen rock strata on our planet in ancient epochs. The proof is mainly the discovery of ancient continental glaciations in their moraine deposits and the establishment of the phenomena of mechanical separation of the rocks of the glacier bed, the transfer and processing of detrital material and its deposition after ice melting. Compacted and cemented ancient moraines, the density of which is close to sandstone-type rocks, 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 over the area of glaciation and cryolithozone 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 much larger areas 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 - the first tens of millions of years), ice ages (the 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 well defined, and some of this evidence extends over large areas. Evidence for the existence 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 epochs of the Paleozoic era up to its beginning, the Early Cambrian time. Even in much older rocks, pre-Phanerozoic, we find traces left by glaciers and glacial deposits. Some of these footprints are over two billion years old, perhaps half the age of the Earth as a planet.

The glacial epoch 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 a long, continuous and severe cooling of the climate, the growth of ice sheets in the polar and temperate latitudes.

· Glacial epochs 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 glacial epochs, the areas occupied by permafrost are expanding, soil and vegetation zones are shifting towards the equator.

It has been established that over the past 800 thousand years there have been eight glacial epochs, each of which lasted from 70 to 90 thousand years.

Fig.1 Ice Age

1.1 Ice Ages in Earth's History

Periods of climate cooling, accompanied by the formation of continental ice sheets, are recurring events in the history of the Earth. The intervals of cold climate during which extensive continental ice sheets and sediments lasting hundreds of millions of years are formed are called ice ages; in glacial eras, glacial periods lasting tens of millions of years are distinguished, which, in turn, consist of glacial epochs - glaciations (glacials) alternating with interglacials (interglacials).

Geological studies have proved that there was a periodic process of climate change on Earth, covering the time from the late Proterozoic to the present.

These are relatively long ice ages that lasted for almost half of the history of the Earth. The following ice ages 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 consider each of them in more detail.

1.2 Proterozoic Ice Age

Proterozoic - from the Greek. the words proteros - 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, which was characterized by the development of the simplest forms of life of unicellular living organisms from prokaryotes to eukaryotes, which later evolved into multicellular organisms as a result of the so-called Ediacaran "explosion".

Early Proterozoic Ice Age

This is the oldest glaciation recorded in geological history 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 subsequent warming can be caused, for example, by an increase in the amount of greenhouse gases in the atmosphere due to an increase in volcanic activity , accompanied, as is well known, by emissions of a huge amount of gases.

Late Proterozoic Ice Age

It was distinguished under the name of the Lapland glaciation at the level of the Vendian glacial deposits 670-630 million years ago. These deposits are found in Europe, Asia, West Africa, Greenland and Australia. The paleoclimatic reconstruction of the glacial formations of 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 ice ages (275 - 230 million years). The interglacial period of these periods is characterized by a warm climate, which contributed to the rapid development of vegetation. Large and unique coal basins and horizons of oil and gas fields later formed in the places of their distribution.

Late Ordovician - Early Silurian Ice Age.

Glacial deposits of this time, called the Saharan (after the name of the modern Sahara). They were distributed on the territory of 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 is similar in area to the modern glacier of Antarctica.

Late Devonian Ice Age

Glacial deposits of this period were found on the territory of modern Brazil. The glacial region extended from the modern mouth of the river. Amazons to the east coast of Brazil, capturing the Niger region in Africa. In Africa, in Northern Niger, tillites (glacial deposits) occur, which are comparable to those in Brazil. In general, glacial regions stretched from the border of Peru with Brazil to northern Niger, the diameter of the region was more than 5000 km. The South Pole in the Late Devonian, according to the reconstruction of P. Morel and E. Irving, was in the center of Gondwana in Central Africa. Glacial basins are located on the oceanic margin of the paleocontinent, mainly at 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, moreover, in the northwest of South America.

The Carboniferous-Permian Ice Age

It has received its distribution in the territory of modern Europe and Asia. During the Carboniferous, there was a gradual cooling of the climate, which culminated 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 Gondwana supercontinent, the formation of large mountain ranges and changes in ocean currents. In the Carboniferous - Permian, glacial and periglacial conditions existed in most of Gondwana.

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 partly to South America. With a radius of the ice sheet of about 1750 km, according to calculations, the thickness of the ice 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 took place, and a sheet glaciation spread over most of this supercontinent. The Stone - Coal-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 areas of Gondwana glaciation occupied an area of at least 35 million km 2 (possibly 50 million km 2), which is 2–3 times 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 ice age.

The present time - the Holocene, which began ≈ 10,000 years ago, is characterized as a relatively warm period after the Pleistocene ice age, often qualified as an interglacial. Ice sheets exist in the high latitudes of the northern (Greenland) and southern (Antarctica) hemispheres; at the same time, in the northern hemisphere, the Greenland glaciation sheet extends south to 60 ° north latitude (i.e., to the latitude of St. Petersburg), fragments of the sea ice cover - up to 46-43 ° north latitude (i.e., to the latitude of Crimea) , and permafrost up to 52-47 ° north latitude. In the southern hemisphere, the continental part of Antarctica is covered by an ice sheet with a thickness of 2500-2800 m (up to 4800 m in some areas of East Antarctica), while ice shelves make up ≈10% of the area of the continent that rises above sea level. In the Cenozoic Ice Age, 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 Ocean, while the glaciation boundary passed 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 the ice ages and the final formation of the modern face of the Earth.

Rice. 4 Cenozoic Ice Age. Ice Age. Climate curve for the last 65 million years.

34 million years ago - the beginning of the Antarctic ice sheet

25 million years ago - its reduction

13 million years ago - its re-growth

About 3 million years ago - the beginning of the Pleistocene ice age, the repeated appearance and disappearance of ice sheets in the northern regions of the Earth

1.5 Tertiary period

The Tertiary period consists of epochs:

·Paleocene

Oligocene

Pliocene

Paleocene epoch (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 further apart. Throughout the Paleocene, Australia was located near Antarctica. Sea levels have dropped and new landmasses have appeared in many parts of the world.

Fauna: On land, the age of mammals began. Rodents and insectivores appeared. Among them were large animals, both predatory and herbivorous. In the seas, marine reptiles have been replaced by new species of predatory bony fish and sharks. New varieties of bivalves and foraminifera emerged.

Flora: New species of flowering plants and the insects that pollinated them continued to spread.

Eocene epoch (from 55 to 38 million years ago)

Geography and climate: In the Eocene, the main land masses began to gradually assume a position close to that which they occupy today. A large part of the land was still divided into a kind of giant islands, as the huge continents continued to move away from each other. South America has lost contact with Antarctica, and India has 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 apart, creating new mountain ranges. The sea flooded part of the land. The climate was generally warm or temperate. Most of it was covered with lush tropical vegetation, and vast areas were overgrown with dense swampy forests.

Fauna: Bats, lemurs, tarsiers appeared on land; the ancestors of today's elephants, horses, cows, pigs, tapirs, rhinos and deer; other large herbivores. Other mammals, such as whales and sirens, have returned to the aquatic environment. The number of species of freshwater bony fish 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 with lush vegetation grew, palm trees grew in temperate latitudes.

Oligocene epoch (from 38 to 25 million years ago)

Geography and climate: In the Oligocene era, India crossed the equator, and Australia finally separated from Antarctica. The climate on Earth became cooler, a huge ice sheet formed over the South Pole. For the formation of such a large amount of ice, no less significant volumes of sea water were required. This led to a decrease in sea levels throughout the planet and the expansion of the territory occupied by land. Widespread cooling caused the disappearance of the lush rainforests of the Eocene in many parts of the globe. Their place was taken by forests, which preferred a more temperate (cool) climate, as well as vast steppes spread over all continents.

Fauna: With the spread of the steppes, the rapid flowering of herbivorous mammals began. Among them, new species of rabbits, hares, giant sloths, rhinos and other ungulates arose. The first ruminants appeared.

Flora: Tropical forests have shrunk and begun to give way to temperate forests, and vast steppes have appeared. New herbs spread rapidly, new types of herbivores developed.

Miocene epoch (from 25 to 5 million years ago)

Geography and climate: During the Miocene, the continents were still "on the march", and during their collisions a number of grandiose cataclysms occurred. Africa "crashed" into Europe and Asia, resulting in the emergence of the Alps. When India and Asia collided, the Himalayan mountains shot up. At the same time, the Rocky Mountains and the Andes formed as other giant plates continued to shift and pile on top of each other.

However, Austria and South America still remained isolated from the rest of the world, and each of these continents continued to develop its own unique fauna and flora. The ice sheet in the southern hemisphere spread to the whole of Antarctica, which led to further cooling of the climate.

Fauna: Mammals migrated from mainland to mainland along the newly formed land bridges, which dramatically accelerated evolutionary processes. Elephants from Africa moved to Eurasia, while cats, giraffes, pigs and buffaloes moved in the opposite direction. Saber-toothed cats and monkeys appeared, including anthropoids. In Australia, cut off from the outside world, monotremes and marsupials continued to develop.

Flora: Inland regions became colder and drier, and steppes spread more and more 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 find the continents in almost the same places as they are today. The gaze of a galactic visitor would open up giant ice caps in the northern hemisphere and the huge ice sheet of Antarctica. Because of all this mass of ice, the climate of the Earth became even cooler, and it became much colder on the surface of the continents and oceans of our planet. Most of the forests that survived in the Miocene disappeared, giving way to vast steppes that spread all over the world.

Fauna: Herbivorous hoofed mammals continued to multiply and evolve rapidly. Toward the end of the period, a land bridge connected South and North America, which led to a grand "exchange" of animals between the two continents. It is believed that the intensified interspecific competition caused the extinction of many ancient animals. Rats entered Australia, and the first humanoid creatures appeared in Africa.

Flora: As the climate cools, steppes have replaced forests.

Figure 5 Diverse Mammals Evolved During the Tertiary Period

1.6 Quaternary

Consists of epochs:

·Pleistocene

Holocene

Pleistocene epoch (from 2 to 0.01 million years ago)

Geography and climate: At the beginning of the Pleistocene, most of the continents occupied the same position as today, and some of them needed to cross half the globe to do this. 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 into the northern hemisphere. It was the era of the great glaciation with alternating periods of cooling and warming and fluctuations in sea level. This ice age continues to this day.

Animals: Some animals have managed to adapt to the increased cold by acquiring thick wool: for example, woolly mammoths and rhinos. Of the predators, saber-toothed cats and cave lions are the most common. This was the age of the giant marsupials in Australia and the huge flightless birds, such as the moa or epiornis, that lived in many parts of the southern hemisphere. The first people appeared, and many large mammals began to disappear from the face of the Earth.

Flora: Ice gradually crept from the poles, and coniferous forests gave way to tundra. Farther from the edge of the glaciers, deciduous forests gave way to coniferous ones. In the warmer regions of the globe, there are vast steppes.

Holocene epoch (from 0.01 million years to the present day)

Geography and climate: The Holocene began 10,000 years ago. During the entire Holocene, the continents occupied practically the same places as today, the climate was also similar to the modern one, becoming either warmer or colder every few millennia. Today we are experiencing one of the periods of warming. As the ice sheets decreased, the sea level slowly rose. The beginning of the time of the human race.

Fauna: At the beginning of the period, many species of animals became extinct, mainly due to the general warming of the climate, but, perhaps, increased human hunting for them also affected. Later, they may have fallen victim to competition from new animal species introduced by people from other places. Human civilization has become more advanced and spread all over the world.

Flora: With the advent of agriculture, the peasants destroyed more and more wild plants in order to clear areas for crops and pastures. In addition, plants brought by people to areas new to them sometimes crowded out indigenous vegetation.

Rice. 6 Proboscis, the largest land animals of the Quaternary period

Ice Age Tertiary Quaternary

2. The 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 customary to call it “Zyryanskaya”, in the Alps - “Würmskaya”, in North America - “Wisconsin”. During this epoch, the growth and reduction of ice sheets repeatedly occurred. The last glacial maximum, when the total volume of ice in the glaciers was the largest, 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 moved away from it to the south along the channels of large rivers. All high mountains were also shackled with ice shells. Cooling and the formation of glaciers led to other global changes in nature. The rivers flowing into the northern seas were blocked by ice walls, they overflowed 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 faunistic 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 occurred periodically, the glacier melted along the edge, retreated to the north, the areas of high-altitude ice decreased, and climatic zones shifted to the south. There have been several such minor changes in the 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 climatic changes in Siberia and in some other regions of the northern hemisphere over the past 50 thousand years

2.2 Flora and fauna

The cooling on 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 to the south. The following natural zones were located on the territory of Siberia.

Along the glaciers, a zone of cold tundra and tundra steppes stretches for tens of kilometers. It was located approximately in those areas where the forest and taiga are now.

In the south, the tundra-steppe gradually turned into forest-steppes and forests. Forest plots were very small, and were far from everywhere. Most often, forests were located on the southern shores of glacial lakes and in river valleys and on the spurs of mountains.

Even further south were dry steppes, in the west of Siberia gradually turning into the mountain systems of the Sayano-Altai, 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. Tundrosteppe, the era of the last glaciation

In the new climatic conditions of the glacial period, the animal world also changed. During the last stages of the Quaternary period, the formation of new species of fauna took place in the Northern Hemisphere. A particularly expressive manifestation of these changes was the appearance of the so-called mammoth faunistic 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 North Seas. Modern Siberian rivers: the Ob, Irtysh, Yenisei, Lena, Kolyma and many others overflowed along the glaciers, forming giant lakes, which were combined into periglacial meltwater runoff systems.

Siberia in the Ice Age. Modern rivers and cities are labeled for clarity. Most of this system was connected by rivers and the waters flowed out of it to the southwest through the system of the Novoevksinsky basin, which was once on the site of the Black Sea. Further, through the Bosphorus and the Dardanelles, water entered the Mediterranean Sea. The total area of this drainage basin was 22 million square meters. km. She served the territory from Mongolia to the Mediterranean.

Fig. 10 Siberia in the Ice Age

In North America, such a system of glacial lakes also existed. Along the Laurentian ice sheet stretched the now disappeared giant Lake Agassiz, the McConnell and Algonk lakes.

2.4 West Siberian Lake

Some scientists believe that one of the largest near-glacial lakes in Eurasia was the Mansiysk, or as it is also called the West Siberian Lake. It occupied almost the entire territory of the West Siberian Plain up to the foothills of the Kuznetsk Alatau and Altai. Those 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 Mansiysk began to gradually drain into the Arctic Ocean, and modern river systems formed in its place, and in the lowland part of the Taiga Ob region, the largest system in Eurasia, the Vasyugan Swamps, was formed.

Fig. 11 This is how the West Siberian Lake looked like

2.5 Oceans

The ice sheets of the planet are formed by the waters of the 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. So, 50,000 years ago, due to the growth of glaciers, the ocean 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, 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 ocean level changes during the last ice age

2.6 Great Glacier

During the last glaciation, a huge Arctic ice sheet occupied the circumpolar part of the Northern Hemisphere of the planet. 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 plano-convex domes, which in some places formed layers of ice 2-3 kilometers high. The total area of the ice cover is more than 40 million square meters. km.

The largest elements of the Arctic Ice Sheet:

1. Laurentian shield centered over the southwestern part of Hudson Bay;

2. The Kara shield centered over the Kara Sea extended 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 severe ice age, the climate was constantly changing. Glaciers then gradually advanced to the south, receded 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, America, glaciers began to increase, flowing onto the plains, a gradually expanding ice cap formed on the Scandinavian Peninsula, 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 a sheet of glaciation, which then somewhat decreased, then again moved south. Interglacial periods with a warm, mild climate gave way to cooling periods when 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 belonging to the Anthropogenic (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.

As an independent ice age, the Moscow glaciation was identified relatively recently. 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 in the Moscow era is drawn with greater validity.

Moscow, glaciation captured only the northern part of the Moscow region. The boundary of the glacier passed along the Klyazma River. It was during the melting of the Moscow Glacier that the moraine strata of the Dnieper glaciation were almost completely eroded. The flooding of the periglacial zone, which directly included the territory of the Shatura region, was so great during the melting of the Moscow glacier that the lowlands were filled with large lakes or turned into powerful valleys for the flow of melted glacial waters. Suspensions settled in them, forming outwash plains with sandy and sandy loam deposits, the most common within the region at present.

Fig.14 The position of the 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 ice ages are inextricably linked to the broader problems of global climate change that have taken place throughout the history of the earth. Significant changes in geological and biological settings occurred from time to time. It should be borne in mind that the beginning of all great glaciations is determined by two important factors.

First, for thousands of years, the annual course of precipitation should be dominated by heavy and prolonged snowfalls.

Secondly, in areas with such a precipitation regime, temperatures should be so low that summer snowmelt is minimized, and firn fields increase from year to year until glaciers begin to form. Abundant accumulation of snow should prevail in the balance of glaciers throughout the entire epoch of 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. Pole migration hypothesis. Many scientists believed that the Earth's axis of rotation changes its position from time to time, which leads to a corresponding shift in climatic zones.

2. Hypothesis of carbon dioxide. Carbon dioxide CO2 in the atmosphere acts like a warm blanket to trap the Earth's radiated heat close to the Earth's surface, and any significant reduction in CO2 in the air will cause the Earth's temperature to drop. 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 land uplifts 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 reality, 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-bearing 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 be the cause of glaciation, in any case, they could greatly contribute to its development.

4. Hypothesis of volcanic dust. Volcanic eruptions are accompanied by the release of a huge amount of dust into the atmosphere. Obviously, volcanic activity, widespread on Earth for millennia, could significantly lower air temperatures and cause the onset of glaciation.

5. Hypothesis of continental drift. According to this hypothesis, all modern continents and the largest islands were once part of the single mainland Pangea, washed by the oceans. The consolidation of the continents into such a single land mass could explain the development of the Late Paleozoic glaciation of South America, Africa, India and Australia. The territories covered by this glaciation were probably much to the north or south of their present position. The continents began to separate in the Cretaceous, and reached their present position about 10 thousand years ago

6. Hypothesis of Ewing - Donna. One of the attempts to explain the causes of the Pleistocene Ice Age belongs to M. Ewing and W. Donn, 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 it is now. The Arctic land areas were then located in the northern part of the Pacific Ocean. Then, as a result of the drift of the continents, North America, Siberia and the Arctic Ocean took their current position. Thanks to the Gulf Stream, which came 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 due to the fact that 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 that separate 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 that feeds the glaciers dried up.

7. Hypothesis of ocean water circulation. 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 wonderful 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. There are also warm currents in the South Pacific and the Indian Ocean. The most powerful cold currents are sent from the Arctic Ocean to the Pacific through the Bering Strait and into the Atlantic Ocean - through the straits along the eastern and western coasts of Greenland. One of them - the Labrador Current - cools the coast of New England and brings fog there. Cold waters also enter the southern oceans from the Antarctic in the form of particularly powerful currents moving north almost to the equator along the western coasts of Chile and Peru. The strong subsurface countercurrent of the Gulf Stream carries its cold waters south into the North Atlantic.

8. Hypothesis of changes in solar radiation. As a result of a long study of sunspots, which are strong plasma ejections in the solar atmosphere, it was found that there are very significant annual and longer cycles of changes in solar radiation. Solar activity peaks approximately every 11, 33, and 99 years, when the Sun radiates more heat, resulting in more powerful circulation of the earth's atmosphere, accompanied by more clouds and more abundant precipitation. Due to the high cloud cover that blocks the sun's rays, the land surface receives less heat than usual.

Conclusion

In the course of the course work, ice ages were studied, which include ice ages. The glacial epochs have been established and disassembled with precision. Detailed information about the last ice age has been obtained. The last Quaternary epochs are revealed. And also studied the main causes of ice ages.

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.: Publishing House of Moscow State University, 1988.

2. Silver L.R. Ancient glaciation and life / Serebryany Leonid Ruvimovich; Responsible ed. G.A. Avsyuk. - M.: Nauka, 1980. - 128 p.: ill. - (Man and environment). - Bibliography.

3. Secrets of the Ice Ages: Per. from English / Ed. G.A. Avsyuk; Afterword G.A. Avsyuk and M.G. Grosvalda.-M.: Progress, 1988.-264 p.

4. http://ru.wikipedia.org/wiki/Glacial_epoch (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_period (Material from Wikipedia - the free encyclopedia)

7. http://www.fio.vrn.ru/2004/7/kaynozoyskaya.htm (Cenozoic era)

There are several hypotheses about the causes of glaciation. The factors underlying these hypotheses can be divided into astronomical and geological. Astronomical factors that cause cooling on the earth include:

1. Change in the tilt of the earth's axis
2. Deviation of the Earth from its orbit towards the distance from the Sun
3. Uneven thermal radiation of the Sun.

Geological factors include the processes of mountainous, volcanic activity, and the movement of continents.
Each of the hypotheses has its drawbacks. Thus, the hypothesis linking glaciation with mountain building epochs does not explain the absence of glaciation in the Mesozoic, although mountain building processes were quite active in this era.
The intensification of volcanic activity, according to some scientists, leads to a warming of the climate on earth, according to others to a cooling. According to the hypothesis of the movement of continents, huge areas of land during the history of the development of the earth's crust periodically moved from a warm climate to a cold climate, and vice versa.

During the geological history of the planet, numbering more than 4 billion years, the Earth has experienced several periods of glaciation. The oldest Huron glaciation has an age of 4.1 - 2.5 billion years, Gneiss - 900 - 950 million years. Further, the ice ages were repeated quite regularly: Sturt - 810 - 710, Varang - 680 - 570, Ordovician - 410 - 450 million years ago. The penultimate ice age on Earth was 340 - 240 million years ago and was called the Gondwana. Now on the Earth is another ice age, called the Cenozoic, which began 30 - 40 million years ago with the appearance of the Antarctic ice sheet. Man appeared and lives in the Ice Age. In the last few million years, the glaciation of the Earth either grows, and then significant areas in Europe, North America and partly in Asia are occupied by ice sheets, or it shrinks to the size that exists today. For the last million years, 9 such cycles have been identified. Typically, the period of growth and existence of ice sheets in the Northern Hemisphere is about 10 times longer than the period of destruction and retreat. Periods of glacier retreat are called interglacials. We are now living in another interglacial period called the Holocene.

The central problem of Earth cryology is the identification and study of the general patterns of glaciation of our planet. The Earth's cryosphere experiences both continuous seasonal-periodic fluctuations and centuries-old changes.

At present, the Earth has passed the ice age and is in the interglacial period. But what will happen next? What is the forecast of the process of glaciation of the Earth? Could a new advance of glaciers begin in the near future?

Answers to these questions concern not only scientists. The glaciation of the Earth is a gigantic planetary process that is not indifferent to all mankind. To find the answer to these questions, you need to penetrate the secrets of glaciation, reveal the patterns of development of ice ages, and establish the main causes of their occurrence.
The works of many eminent scientists were devoted to the solution of these problems. But the complexity of the issues is so great that, according to the famous climatologist M. Schwarzbach, it is almost impossible to penetrate the mystery of glaciation.

There are many theories and hypotheses that try to solve this mystery. Without going into details of all theories and hypotheses, we can combine them into three main groups.
Planetary - where the main cause of the onset of ice ages are considered to be significant changes occurring on the planet: the displacement of the poles, the movement of continents, mountain building processes, which are accompanied by a change in the circulation of air and ocean currents and the emergence of glaciers, atmospheric pollution by volcanic activity products, changes in the concentration of carbon dioxide and ozone in the atmosphere .

Astronomical hypotheses also adjoin planetary hypotheses, explaining the glaciation of the planet by a change in the Earth's orbit, a change in the angle of inclination of the axis of its rotation, distance from the Sun, etc.

Solar - hypotheses and theories that explain the emergence of epochs of glaciation by the rhythm of energy processes occurring in the bowels of the Sun. As a result of these processes, there are periodic changes in the amount of solar energy entering the Earth. The duration of these periods is several hundred million years, which is consistent with the periodicity of ice ages.

In the first approximation, the rhythm of the processes of advance and retreat of glaciers within each ice age is also explained.

Space hypotheses and theories. According to them, there are cosmic factors that can explain the cyclical nature of climate change and the onset of ice ages on Earth. Radiant energy flows or particle flows that cause changes in energy processes both inside the Sun and inside the Earth, cosmic dust clouds that partially absorb the Sun's energy, as well as still unknown factors can be attributed to such reasons. For example, the hypothesis of the possibility of interaction between the neutrino flux and the substance of the earth's interior is of great interest. The coincidence of the period of alternation of glacial epochs (about 250 million years) with the period of revolution of the solar system around the center of the Galaxy (220-230 million years) deserves close attention. Even more striking is the closeness (considering the low accuracy of determining such quantities) of this period with a periodicity (about 300 million years) of waves of matter condensation in the arms of our Galaxy, which arise as a result of the ejection of giant masses of matter rotating at a tremendous speed from the center of the Galaxy. By the way, the last wave of this shock disturbance, which passed 60 million years ago, surprisingly coincides with the geological time of the disappearance of giant reptiles at the end of the Cretaceous period of the Mesozoic era.

It seems that it is possible to understand and study the dynamics of climate and the emergence of ice ages only on the basis of a synthesis of cosmic, solar and planetary factors.
A few words about the forecast of the thermal fate of the Earth, or rather, about the probabilistic course of thermal processes on astrophysical time scales.
The problem of predicting the natural course of glaciation of our planet is closely related to the problem of artificial change in the planet's climate. Scientists involved in cryology are faced with the task of establishing a threshold for the growth of energy production on Earth, after which changes in the physical and geographical envelope that are very undesirable for mankind can occur (flooding of land during the melting of Antarctic and other glaciers, an excessive increase in air temperature and thawing of the frozen layers of the Earth) .

What determines the decrease in the average temperature of the Earth?

It has been suggested that the reason lies in the change in the amount of heat received from the Sun. Above, we spoke about the 11-year periodicity of solar radiation. Perhaps there are longer periods. In this case, cooling may be associated with minima of solar radiation. An increase or decrease in temperature on Earth occurs even with a constant amount of energy coming from the Sun, and is also determined by the composition of the atmosphere.
In 1909, S. Arrhenius was the first to emphasize the enormous role of carbon dioxide as a regulator of the temperature of near-surface air layers. Carbon dioxide freely transmits the sun's rays to the earth's surface, but absorbs most of the thermal radiation of the earth. It is a colossal screen that prevents the cooling of our planet. Now the content of carbon dioxide in the atmosphere does not exceed 0.03%. If this figure is halved, then the average annual temperatures in the temperate zones will drop by 4-5 ° C, which may lead to the onset of an ice age.

The study of modern and ancient volcanic activity allowed the volcanologist I.V. Melekestsev to associate the cooling and the glaciation that causes it with an increase in the intensity of volcanism. It is well known that volcanism significantly affects the earth's atmosphere, changing its gas composition, temperature, and also polluting it with finely divided material of volcanic ash. Huge masses of ash, measured in billions of tons, are ejected by volcanoes into the upper atmosphere, and then carried by jet streams around the globe. A few days after the 1956 eruption of the Bezymyanny volcano, its ash was found in the upper troposphere above London. Ash material ejected during the 1963 eruption of Mount Agung on the island of Bali (Indonesia) was found at an altitude of about 20 km above North America and Australia. Pollution of the atmosphere with volcanic ash causes a significant decrease in its transparency and, consequently, a weakening of solar radiation by 10-20% against the norm. In addition, ash particles serve as condensation nuclei, contributing to the large development of cloudiness. An increase in cloudiness, in turn, significantly reduces the amount of solar radiation. According to Brooks' calculations, an increase in cloudiness from 50 (typical for the present time) to 60% would lead to a decrease in the average annual temperature on the globe by 2 ° C.

About two million years ago, at the end of the Neogene, the 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 break through 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 uplands to the plains.

One after another, like waves, periods of glaciation rolled over Europe and North America. But quite recently (in the geological sense) the climate of Europe was warm, almost tropical, and its animal population consisted of hippos, crocodiles, cheetahs, antelopes - about the same as we see now in Africa. Four periods of glaciation - Gunz, Mindel, Ris and Würm - expelled or destroyed heat-loving animals and plants, and the nature of Europe became basically the same as we see it now.

Under the onslaught 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 on the surface of the glacier and it gradually began to clear.

When the glacier receded for a short time, the tundra with its permafrost remained in place of the forests.

The greatest period of glaciation was the Rissian - it happened about 250 thousand years ago. The thickness of the ice shell, which bound half of Europe and two-thirds of North America, reached three kilometers. The Altai, the Pamirs and the Himalayas hid under the ice.

South of the glacier line now lay cold steppes covered with sparse herbaceous vegetation and groves of dwarf birches. Further south, the impenetrable taiga began.

Gradually the glacier melted and retreated to the north. However, he stopped off the coast of the Baltic Sea. Equilibrium arose - the atmosphere, saturated with moisture, let in just enough sunlight to prevent the glacier from growing and completely melting.

The great glaciations unrecognizably changed the relief of the Earth, its climate, flora and fauna. We can still see their consequences - after all, the last Wurm 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 in search of food retreated south and south, and their place was occupied by those that endured the cold better.

Glaciers advanced not only from the Arctic regions, but also from mountain ranges - the Alps, the Carpathians, the Pyrenees. At times, the thickness of the ice reached three kilometers. Like a giant bulldozer, the glacier smoothed out uneven terrain. After his retreat, there remained a swampy plain covered with sparse vegetation.

So, presumably, the polar regions of our planet looked like in the Neogene and in the era of the Great Glaciation. The area of permanent snow cover increased dozens of times, and where the tongues of glaciers reached, it was cold for ten months a year, like in Antarctica.