Interesting facts about the Ice Age. Ice Age on Earth Why was there an Ice Age?

Consequences of warming

Last glacial period led to the emergence woolly mammoth and a huge increase in the area of ​​glaciers. But it was only one of many that cooled the Earth throughout its 4.5 billion years of history.

So, how often does the planet experience ice ages and when should we expect the next one?

Major periods of glaciation in the history of the planet

The answer to the first question depends on whether you are talking about large glaciations or small ones that occur during these long periods. Throughout history, the Earth has experienced five major periods of glaciation, some of which lasted for hundreds of millions of years. In fact, even now the Earth is experiencing a large period of glaciation, and this explains why it has polar ice caps.

The five main ice ages are the Huronian (2.4-2.1 billion years ago), the Cryogenian glaciation (720-635 million years ago), the Andean-Saharan glaciation (450-420 million years ago), and the Late Paleozoic glaciation (335-260 million years ago). million years ago) and Quaternary (2.7 million years ago to the present).

These major periods of glaciation may alternate between smaller ice ages and warm periods (interglacials). At the beginning of the Quaternary Glaciation (2.7-1 million years ago), these cold ice ages occurred every 41 thousand years. However, in the last 800 thousand years, significant ice ages have occurred less frequently - approximately every 100 thousand years.

How does the 100,000 year cycle work?

The ice sheets grow for about 90 thousand years and then begin to melt during the 10 thousand year warm period. Then the process is repeated.

Given that the last ice age ended about 11,700 years ago, perhaps it's time for another one to begin?

Scientists believe we should be experiencing another ice age right now. However, there are two factors associated with the Earth's orbit that influence the formation of warm and cold periods. Considering also how much carbon dioxide we release into the atmosphere, the next ice age won't start for at least 100,000 years.

What causes an ice age?

The hypothesis put forward by Serbian astronomer Milutin Milanković explains why cycles of glacial and interglacial periods exist on Earth.

As a planet orbits the Sun, the amount of light it receives from it is affected by three factors: its inclination (which ranges from 24.5 to 22.1 degrees on a 41,000-year cycle), its eccentricity (the change in the shape of its orbit around of the Sun, which fluctuates from a near circle to an oval shape) and its wobble (one full wobble occurs every 19-23 thousand years).

In 1976, a landmark paper in the journal Science presented evidence that these three orbital parameters explained the planet's glacial cycles.

Milankovitch's theory is that orbital cycles are predictable and very consistent in the history of the planet. If the Earth is experiencing an ice age, it will be covered with more or less ice, depending on these orbital cycles. But if the Earth is too warm, no change will occur, at least in terms of increasing amounts of ice.

What can affect the warming of the planet?

The first gas that comes to mind is carbon dioxide. Over the past 800 thousand years, carbon dioxide levels have ranged from 170 to 280 parts per million (meaning that out of 1 million air molecules, 280 are carbon dioxide molecules). A seemingly insignificant difference of 100 parts per million results in glacial and interglacial periods. But carbon dioxide levels are significantly higher today than in past periods of fluctuation. In May 2016, carbon dioxide levels over Antarctica reached 400 parts per million.

The Earth has warmed up this much before. For example, during the time of dinosaurs the air temperature was even higher than it is now. But the problem is that in modern world it is growing at a record pace because we have released too much carbon dioxide into the atmosphere in a short time. Moreover, given that the rate of emissions is not currently decreasing, we can conclude that the situation is unlikely to change in the near future.

Consequences of warming

The warming caused by this carbon dioxide will have large consequences because even a small increase average temperature The earth can lead to drastic changes. For example, the Earth was on average only 5 degrees Celsius colder during the last ice age than it is today, but this led to a significant change in regional temperatures, the disappearance of huge parts of flora and fauna, and the emergence of new species.

If global warming causes all the ice sheets of Greenland and Antarctica to melt, sea levels will rise by 60 meters compared to today's levels.

What causes major ice ages?

The factors that caused long periods of glaciation, such as the Quaternary, are not as well understood by scientists. But one idea is that a massive drop in carbon dioxide levels could lead to colder temperatures.

For example, according to the uplift and weathering hypothesis, when plate tectonics causes mountain ranges to grow, new exposed rock appears on the surface. It easily weathers and disintegrates when it ends up in the oceans. Marine organisms use these rocks to create their shells. Over time, stones and shells take carbon dioxide from the atmosphere and its level drops significantly, which leads to a period of glaciation.

Just at the time of the powerful development of all forms of life on our planet, the mysterious ice age begins with its new temperature fluctuations. We have already talked about the reasons for the appearance of this ice age earlier.

Just as the change of seasons led to the selection of more perfect, more adaptable animals and created various breeds of mammals, so now, in this ice age, man stands out from the mammals, in an even more painful struggle with the advancing glaciers than struggle with the changing seasons spanning millennia. Here it was not enough to simply adapt by significantly changing the body. What was needed was a mind that could turn nature itself to its advantage and conquer it.

We have finally reached the highest stage of life development: . He took possession of the Earth, and his mind, developing further and further, learned to embrace the entire universe. With the advent of man, a completely new era of creation truly began. We still stand at one of its lowest levels, we are the simplest among creatures gifted with reason, dominating the forces of nature. The beginning of the path to unknown majestic goals has come!

There have been at least four major ice ages, which in turn break up again into smaller waves of temperature fluctuations. Between the ice ages lay warmer periods; then, thanks to melting glaciers, the damp valleys were covered with lush meadow vegetation. Therefore, it was during these interglacial periods that herbivores could develop especially well.

In the deposits of the Quaternary era, which closes the ice ages, and in the deposits of the Deluvian era, which followed the last general glaciation of the globe, and the direct continuation of which is our time, we come across huge pachyderms, namely the mastodon mammoth, the fossilized remains of which we still have Now we often find it in the tundra of Siberia. Even with this giant, primitive man dared to get involved in a fight, and, in the end, he emerged victorious.

Mastodon (restored) from the Deluvian era.

We involuntarily return our thoughts again to the emergence of the world if we look at the blossoming of the beautiful present from chaotic dark primitive conditions. The fact that in the second half of our research we remained all the time only on our little Earth is explained by the fact that we know all these different stages of development only on it. But, taking into account the uniformity of the matter that forms the world, which we established earlier, and the universality of the forces of nature that govern matter, we will come to complete consistency of all the main features of the formation of the world that we can observe in the sky.

We have no doubt that in the distant universe there must be millions more worlds similar to our Earth, although we do not have any exact information about them. On the contrary, it is among the relatives of the Earth, the other planets of our solar system, which we can better explore due to their greater proximity to us, there are characteristic differences from our Earth, as, for example, sisters of very different ages. Therefore, we should not be surprised if it is on them that we do not encounter traces of life similar to the life of our Earth. Also, Mars with its channels remains a mystery to us.

If we look up at the sky strewn with millions of Suns, then we can be sure that we will meet the gaze of living beings who look at our daylight just as we look at their Sun. Perhaps we are not so far from the time when, having mastered all the forces of nature, man will be able to penetrate into these depths of the universe and send a signal beyond the boundaries of our globe to living beings located on another celestial body - and receive a response from them .

Just as life, at least otherwise we cannot imagine it, came to us from the universe and spread across the Earth, starting with the simplest, so man will eventually expand the narrow horizon that embraces his earthly world, and will communicate with other worlds of the universe, from where these primary elements of life on our planet came. The universe belongs to man, his mind, his knowledge, his power.

But no matter how high our imagination lifts us, we will someday fall down again. The cycle of development of the worlds consists of rise and fall.

Ice Age on Earth

After terrible downpours, like a flood, it became damp and cold. From the high mountains, glaciers slid lower and lower into the valleys, because the Sun could no longer melt the masses of snow continuously falling from above. As a result, those places where earlier during the summer the temperature was still above zero were also covered with ice by for a long time. We are now seeing something similar in the Alps, where individual “tongues” of glaciers descend significantly below the boundary of eternal snow. Eventually, most of the plains at the foot of the mountains were also covered with ever-increasing ice sheets. A general ice age has arrived, traces of which we can indeed observe everywhere on everything. globe.

We must acknowledge the great merit of the world traveler Hans Meyer from Leipzig for the evidence he found that both on Kilimanjaro and on the Cordillera South America, even in tropical areas - everywhere glaciers at that time descended much lower than at present. The connection outlined here between that extraordinary volcanic activity and the onset of the Ice Age was first suggested by the Sarazen brothers in Basel. How did this happen?

After careful research, the following can be answered to this question. The entire chain of the Andes was formed simultaneously during geological periods, which, of course, amount to hundreds of thousands and millions of years, and its volcanoes were the result of this most enormous mountain-building process on Earth. At this time, approximately tropical temperatures prevailed over almost the entire Earth, which, however, very soon after this was to be replaced by a strong general cooling.

Penck found that there were at least four major ice ages, with warmer periods in between. But it seems that these great ice ages are divided into an even greater number of smaller periods of time, in which more insignificant universal events took place. temperature fluctuations. From here you can see what turbulent times the Earth was going through and what constant turmoil the ocean of air was in at that time.

How long this time lasted can only be stated very approximately. It is calculated that the beginning of this ice age can be dated back approximately half a million years ago. Since the last “little glaciation,” only 10 to 20 thousand years have passed, and we are now probably living in only one of those “interglacial periods” that occurred before the last general glaciation.

Through all these ice ages there are traces primitive man, developing from an animal. Tales of the flood, which have come to us from primitive times, may be in connection with the incidents described above. The Persian legend almost certainly points to volcanic phenomena that preceded the onset of the great flood.

This Persian tale describes the great flood as follows: “A great fiery dragon arose from the south. Everything was devastated by him. Day turned into night. The stars have disappeared. The zodiac was covered by a huge tail; only the Sun and Moon could be seen in the sky. Boiling water fell to the Earth and scorched the trees to the very roots. Among the frequent lightning, raindrops the size of a human head fell. Water covered the Earth higher than the height of a man. Finally, after the dragon's struggle lasted 90 days and 90 nights, the enemy of the Earth was destroyed. A terrible storm arose, the water receded, and the dragon sank into the depths of the Earth.”

This dragon, according to the famous Viennese geologist Suess, was nothing more than a powerful volcano, the fiery eruption of which spread across the sky like long tail. All other phenomena described in the legend are fully consistent with the phenomena observed after a strong volcanic eruption.

Thus, on the one hand, we showed that after the splitting and collapse of a huge block the size of a continent, a series of volcanoes should have formed, the eruptions of which were followed by floods and glaciations. On the other hand, we have before our eyes a number of volcanoes in the Andes, located along a huge cliff of the Pacific coast, and we have also proven that soon after the appearance of these volcanoes the Ice Age began. Tales of the flood further complete the picture of this turbulent period in the development of our planet. During the eruption of Krakatoa, we observed on a small scale, but in great detail, the consequences of the volcano's plunge into the depths of the sea.

Taking into account all of the above, we are unlikely to doubt that the relationship between these phenomena was, in fact, such as we assumed. Thus, the entire Pacific Ocean actually arose as a result of the separation and failure of its present bottom, which before that was a huge continent. Was this the “end of the world” as it is usually understood? If the fall happened suddenly, then it was probably the most terrible and most colossal catastrophe that the Earth has ever seen since organic life appeared on it.

This question is now, of course, difficult to answer. But we can still say the following. If there was a collapse on the coast Pacific Ocean was accomplished gradually, then those terrible volcanic eruptions, which at the end of the “Tertiary era” occurred along the entire chain of the Andes and very weak consequences of which are still observed there.

If the coastal region sank there so slowly that it took centuries to detect this subsidence, as we still observe today on some sea coasts, then even then all mass movements in the interior of the Earth would occur very slowly, and would only occur occasionally volcanic eruptions.

In any case, we see that there are counteractions to these forces that produce shifts in the earth's crust, otherwise the sudden shaking of earthquakes could not take place. But we also had to recognize that the stresses resulting from these counteractions cannot become too great, because the earth's crust turns out to be plastic, pliable to large but slowly acting forces. All these considerations lead us to the conclusion, perhaps against our will, that sudden forces must have manifested themselves in these catastrophes.

State educational institution higher vocational education Moscow region

International University of Nature, Society and Human "Dubna"

Faculty of Science and Engineering

Department of Ecology and Geosciences

COURSE WORK

By discipline

Geology

Scientific adviser:

Ph.D., Associate Professor Anisimova O.V.

Dubna, 2011

Introduction

1. Ice Age

1.1 Ice ages in the history of the Earth

1.2 Proterozoic Ice Age

1.3 Paleozoic Ice Age

1.4 Cenozoic Ice Age

1.5 Tertiary period

1.6 Quaternary period

2. Last Ice Age

2.2 Flora and fauna

2.3Rivers and lakes

2.4West Siberian Lake

2.5The world's oceans

2.6 Great Glacier

3. Quaternary glaciations in the European part of Russia

4. Reasons ice ages

Conclusion

Bibliography

Introduction

Target:

Explore the major glacial epochs in Earth's history and their role in shaping the modern landscape.

Relevance:

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

Tasks:

– conduct a literature review;

– establish the main glacial epochs;

– obtaining detailed data on the last Quaternary glaciations;

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

At present, little data has been obtained that confirms the distribution of frozen rock layers on our planet in ancient eras. The evidence is mainly the discovery of ancient continental glaciations from their moraine deposits and the establishment of the phenomena of mechanical detachment of glacier bed rocks, the transfer and processing of clastic material and its deposition after the melting of the ice. Compacted and cemented ancient moraines, the density of which is close to rocks such as sandstones, are called tillites. Detection of such formations of different ages in various regions of the globe clearly indicates the repeated appearance, existence and disappearance of ice sheets, and, consequently, frozen strata. The development of ice sheets and frozen strata can occur asynchronously, i.e. The maximum development of the area of ​​glaciation and the permafrost zone may not coincide in phase. However, in any case, the presence of large ice sheets indicates the existence and development of frozen strata, which should occupy significantly larger areas in area than the ice sheets themselves.

According to N.M. Chumakov, as well as V.B. Harland and M.J. Hambry, the time intervals during which glacial deposits were formed are called glacial eras (lasting the first hundreds of millions of years), ice ages (millions - first tens of millions of years), glacial epochs (first millions of years). In the history of the Earth, the following glacial eras can be distinguished: Early Proterozoic, Late Proterozoic, Paleozoic and Cenozoic.

1. Ice Age

Are there ice ages? Of course yes. The evidence for this is incomplete, but it is quite definite, and some of this evidence extends to large areas. Evidence of the Permian Ice Age is present on several continents, and in addition, traces of glaciers have been found on the continents dating back to other eras of the Paleozoic era up to its beginning, Early Cambrian time. Even in much older rocks, formed before the Phanerozoic, we find traces left by glaciers and glacial deposits. Some of these traces are more than two billion years old, possibly half the age of Earth as a planet.

The Ice Age of glaciations (glacials) is a period of time in the geological history of the Earth, characterized by a strong cooling of the climate and the development of extensive continental ice not only in the polar, but also in temperate latitudes.

Peculiarities:

·It is characterized by long-term, continuous and severe climate cooling, the growth of ice caps in polar and temperate latitudes.

· Ice ages are accompanied by a decrease in the level of the World Ocean by 100 m or more, due to the fact that water accumulates in the form of ice sheets on land.

·During ice ages, areas occupied by permafrost expand, and soil and plant zones shift toward the equator.

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

Fig.1 Ice Age

1.1 Ice ages in the history of the Earth

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

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

These are relatively long glacial eras that lasted for almost half of the Earth's history. The following glacial eras are distinguished in the history of the Earth:

Early Proterozoic - 2.5-2 billion years ago

Late Proterozoic - 900-630 million years ago

Paleozoic - 460-230 million years ago

Cenozoic - 30 million years ago - present

Let's take a closer look at each of them.

1.2 Proterozoic Ice Age

Proterozoic - from the Greek. the words protheros - primary, zoe - life. The Proterozoic era is a geological period in the history of the Earth, including the history of formation rocks of various origins from 2.6 to 1.6 billion years. A period in the history of the Earth that was characterized by the development of the simplest life forms of single-celled living organisms from prokaryotes to eukaryotes, which later, as a result of the so-called Ediacaran “explosion,” evolved into multicellular organisms.

Early Proterozoic glacial era

This is the oldest glaciation recorded in geological history, which appeared at the end of the Proterozoic on the border with the Vendian and, according to the Snowball Earth hypothesis, the glacier covered most of the continents at equatorial latitudes. In fact, it was not one, but a series of glaciations and interglacial periods. Since it is believed that nothing can prevent the spread of glaciation due to the increase in albedo (reflection solar radiation from the white surface of glaciers), it is believed that the cause of subsequent warming may be, for example, an increase in the amount of greenhouse gases due to an increase in volcanic activity, accompanied, as is known, by emissions of huge amounts of gases.

Late Proterozoic glacial era

Identified under the name of the Lapland glaciation at the level of Vendian glacial deposits 670-630 million years ago. These deposits are found in Europe, Asia, West Africa, Greenland and Australia. Paleoclimatic reconstruction of glacial formations from this time suggests that the European and African ice continents of that time were a single ice sheet.

Fig.2 Vend. Ulytau during the Ice Age Snowball

1.3 Paleozoic Ice Age

Paleozoic - from the word paleos - ancient, zoe - life. Palaeozoic. Geological time in the history of the Earth covering 320-325 million years. With an age of glacial deposits of 460 - 230 million years, it includes the Late Ordovician - Early Silurian (460-420 million years), Late Devonian (370-355 million years) and Carboniferous-Permian glacial periods (275 - 230 million years). The interglacial periods of these periods are characterized warm climate, which contributed to the rapid development of vegetation. In the places where they spread, large and unique coal basins and horizons of oil and gas fields were later formed.

Late Ordovician - Early Silurian Ice Age.

Glacial deposits of this time, called Saharan (after the name of modern Sahara). Were distributed throughout the area modern Africa, South America, eastern North America and Western Europe. This period is characterized by the formation of an ice sheet over much of the northern, northwestern and West Africa, including Arabian Peninsula. Paleoclimatic reconstructions suggest that the thickness of the Saharan ice sheet reached at least 3 km and was similar in area to the modern glacier of Antarctica.

Late Devonian Ice Age

Glacial deposits from this period were found in the territory of modern Brazil. The glacial area extended from the modern mouth of the river. Amazon to the east coast of Brazil, taking over the Niger region in Africa. In Africa, Northern Niger contains tillites (glacial deposits) that are comparable to those in Brazil. In general, the glacial areas stretched from the border of Peru with Brazil to northern Niger, the diameter of the area was more than 5000 km. South Pole in the Late Devonian, according to the reconstruction of P. Morel and E. Irving, was located in the center of Gondwana in Central Africa. Glacial basins are located on the oceanic margin of the paleocontinent, mainly in high latitudes (not north of the 65th parallel). Judging by the then high-latitude continental position of Africa, one can assume the possible widespread development of frozen rocks on this continent and, in addition, in the north-west of South America.

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, under the ice, as now, was all Antarctic continent. 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 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 retreated unevenly in different places, humanity settled unevenly.

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

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

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

Almost halfway between Leningrad and Moscow there is a picturesque hilly lake region - the Valdai Upland. Here, among the dense coniferous forests and plowed fields, the waters of many lakes splash: Valdai, Seliger, Uzhino and others. The shores of these lakes are indented, there are many islands on them, densely overgrown with forests. It was here that the border of the last spread of glaciers on the Russian Plain passed. These glaciers left behind strange shapeless hills, the depressions between them were filled with their 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. Found even in Antarctica coal- 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 lay claim to the role scientific theory. Many scientists searched for the cause of the cooling outside the Earth, putting forward astronomical hypotheses. One hypothesis is that glaciation occurred when, due to fluctuations in the distance between the Earth and the Sun, the amount of solar heat received by the Earth changed. This distance depends on the nature of the Earth's motion in its orbit around the Sun. It was assumed that glaciation occurred when winter occurred at aphelion, that is, the point of the orbit furthest from the Sun, at the maximum elongation of the earth's orbit.

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

The development of glaciation is also associated with fluctuations in the activity of the Sun itself. Heliophysicists have long found out that dark spots, flares, prominences appear on the Sun periodically, and we have even learned to predict their occurrence. It turned out that solar activity changes periodically; There are periods of different durations: 2-3, 5-6, 11, 22 and about a hundred years. It may happen that the culminations of several periods of different durations coincide, and solar activity will be especially high. 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 Northern Arctic Ocean, now covered in ice, thawed at times. In this case, increased evaporation occurred from the surface of the Arctic sea, free of ice, and flows humid air headed to the polar regions of America and Eurasia. Here, above the cold surface of the earth, from the wet air masses There was heavy snowfall that 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 there was a strong retreat and mountain glaciers in the Alps, the Caucasus, Scandinavia and Iceland. 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 sunspots and extremely strong outbreaks in the sun. 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 were too few meteorological stations and almost no expeditionary research. But after summing up the results of the International Geophysical Year, it became clear that in Antarctica, as in the Arctic, in the first half of the 20th century. the air temperature rose. There is some interesting evidence for this.

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

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

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