Paleogene period geological history Earth, which began 67 million years ago, lasted 41 million years. The next one, Neogene, is 25 million years old. The last one, the shortest, is about 1 million years. This is what they call glacial.
There is an established idea that the surface of land and sea, even the interior of the planet, were influenced by powerful glaciations. Data have been obtained indicating a consistent cooling of the Earth's climate since the Paleogene (60-65 million years ago) to the present day. The average annual air temperature in temperate latitudes has decreased from 20° C, typical for the tropical zone, to 10. Under current climatic conditions, glaciation processes form and develop over an area of 52 million square kilometers. A tenth of the planet's surface is exposed to them.
Over the past 700 thousand years, scientists believe, in the north of Eurasia and North America there were huge ice sheets - much more extensive than the modern Greenland and even Antarctic. The extent of this paleoglaciation is estimated by a major specialist in this field - an American scientist of the Russian Federation. Flint is 45.2 million square kilometers. North America accounted for 18, Greenland - 2, Eurasia - 10 million square kilometers of ice. In other words, the estimated area of glaciation in the Northern Hemisphere was more than twice as extensive as that in today's Antarctica (14 million square kilometers). The works of glaciologists reconstruct ice sheets in Scandinavia, the North Sea, large parts of England, the plains of Northern Europe, the lowlands and mountains of northern Asia and almost all of Canada, Alaska and the northern United States. The thickness of these shields is determined to be 3-4 kilometers. They are associated with grandiose (even global) changes in the natural situation on Earth.
Experts paint very impressive pictures of the past. They believe that under the pressure of ice advancing from the North, ancient people and animals left their habitats and sought refuge in the southern regions, where the climate was then much colder than it is now.
It is believed that the level of the World Ocean at that time dropped by 100-125 meters, since the ice sheets “fettered” a huge amount of its waters. As the glaciers began to melt, the sea flooded vast low-lying areas of land. (The legend of the Great Flood is sometimes associated with the supposed advance of the sea onto the continents.)
How accurate are the scientific ideas about the last ice age? - the question is relevant. Knowledge of the nature and size of ancient glaciers, the scale of their geological activity is necessary to explain many aspects of the development of nature and ancient man. The latter is especially important. We live in the Quaternary period, which is called anthropogenic.
By knowing the past, you can predict the future. Therefore, scientists are thinking about whether a new “great glaciation” threatens humanity in the near or distant future.
So, what can humanity expect if the climate on Earth again becomes much colder than it is now?
IDEAS ARE GET TOGETHER LIKE PEOPLE
The book “Research on the Ice Age”, written by a prisoner of the Peter and Paul Fortress - the famous scientist and revolutionary P.A. Kropotkin, was published in 1876. His work fully and clearly presented ideas about the “great glaciation” that originated in the mountains of Scandinavia and filled the basin Baltic Sea and reached the Russian Plain and the Baltic lowlands. This concept of ancient glaciation was widely accepted in Russia. One of its main reasons is the fact of the distribution of peculiar deposits on the plains of Northern Europe: unsorted clays and loams containing stone fragments in the form of pebbles and boulders, the size of which reached 3-4 meters in diameter.
Previously, scientists, following the great naturalists of the 19th century, Charles Lyell and Charles Darwin, believed that loams and clays were deposited at the bottom of cold seas - the modern plains of Northern Europe, and boulders were carried by floating ice.
“Drift (from the word “drift”) theory,” quickly losing supporters, retreated under the onslaught of the ideas of P.A. Kropotkin. They were captivating with the opportunity to explain many mysterious facts. Where, for example, did sediments containing large boulders come from on the plains of Europe? The glaciers, advancing in a wide front, later melted, and these boulders ended up on the surface of the earth. It sounded quite convincing.
Thirty-three years later, German researchers A. Penck and E. Brückner, who studied the territory of Bavaria and expressed the idea of a fourfold ancient glaciation of the Alps, decided to clearly link each of its stages with the river terraces of the upper Danube basin.
Glaciations received names mainly from tributaries of the Danube. The oldest is “Günz”, the youngest is “Mindel”, followed by “Riess” and “Würm”. Traces of them subsequently began to be sought and found on the plains of Northern Europe, Asia, North and South America, and even in New Zealand. Researchers persistently linked the geological history of a particular region with the “standard” Central Europe. No one thought about whether it is legitimate to distinguish ancient glaciations in North or South America, East Asia or the islands of the Southern Hemisphere by analogy with the Alps. Soon, glaciations corresponding to the Alpine ones appeared on paleogeographic maps of North America. They received the names of the states that scientists believe they reached while descending to the south. The most ancient - Nebraskan - corresponds to the Alpine Günz, Kansas - Mindel, Illinois - Rissa, Wisconsin - Würm.
The concept of four glaciations in the recent geological past was also accepted for the territory of the Russian Plain. They were named (in descending order of age) Oka, Dnieper, Moscow, Valdai and correlated with Mindel, Ris, and Wurm. But what about the most ancient Alpine glaciation - the Günz? Sometimes, under different names, a fifth glaciation corresponding to it is identified on the Russian Plain.
Attempts made in recent years to “improve” the Alpine model led to the identification of two more pre-Gyuntsev (earliest) “great glaciations” - the Danube and Biber. And due to the fact that two or three are compared with some of the supposed Alpine glaciations (on the plains of Europe and Asia), their total number in the Quaternary period reaches, according to some scientists, eleven or more.
They get used to ideas, become close to them, like people. It is sometimes very difficult to part with them. The problem of the ancient “great glaciations” in this sense is no exception. The data accumulated by scientists on the structure, time of origin and history of development of the current ice sheets of Antarctica and Greenland, on the patterns of structure and formation of modern frozen rocks and the phenomena associated with them, cast doubt on many existing ideas in science about the nature, scale of manifestation of ancient glaciers and their geological activity. However (traditions are strong, the energy of thinking is great) these data are either not noticed or are not given importance. They are not rethought or seriously analyzed. Let us consider in their light the problem of ancient ice sheets and try to understand what actually happened to the nature of the Earth in the recent geological past.
FACTS VERSUS THEORY
A quarter of a century ago, almost all scientists agreed that the modern ice sheets of Antarctica and Greenland developed in sync with the supposed "great glaciers" in Europe, Asia and North America. The glaciation of the Earth, they believed, began in Antarctica, Greenland, and the Arctic islands, then covered the continents of the Northern Hemisphere. During interglacial periods, the Antarctic and Greenland ice melted completely. The level of the World Ocean rose 60-70 meters above the present level. Significant areas of the coastal plains were flooded by the sea. No one doubted that modern era- still unfinished glacial. They say that the ice sheets simply did not have time to melt. Moreover: during periods of cooling, not only did huge glaciers appear on the continents of the Northern Hemisphere, but the Greenland and Antarctic ice sheets grew significantly... Years passed, and the results of studies of inaccessible polar regions completely refuted these ideas.
It turned out that glaciers in Antarctica appeared long before the “ice age” - 38-40 million years ago, when subtropical forests stretched across the north of Eurasia and North America, and palm trees swayed on the shores of modern Arctic seas. Then, of course, there can be no talk of any glaciation on the continents of the Northern Hemisphere. The Greenland ice sheet also appeared at least 10-11 million years ago. At that time, on the coasts of the Arctic seas in the north of Siberia, Alaska and Canada, they grew mixed forests(among the birches, alders, spruces, and larches there were broad-leaved oaks, lindens, and elms), corresponding to the warm, humid climate.
Data on the antiquity of the ice sheets of Antarctica and Greenland sharply raised the question of the causes of glaciation of the Earth. They are seen in planetary warming and cooling of the climate. (Back in 1914, the Yugoslav scientist M. Milankovic drew graphs of fluctuations in the arrival of solar radiation on earth's surface over the past 600 thousand years, identified with glaciations and interglacial periods.) But we now know that when the climate was warm in the north of Eurasia and North America, Antarctica and Greenland were covered with ice sheets, the size of which never significantly decreased later. This means that the point is not in fluctuations in the arrival of solar heat and global cooling and warming, but in a combination of certain factors leading to glaciation in these specific conditions.
The exceptional stability of the Greenland and Antarctic ice sheets does not support the idea of the repeated development and disappearance of “great glaciations” on the continents of the Northern Hemisphere. It is not clear why the Greenland ice sheet has continuously existed for more than 10 million years, while next to it in less than 1 million years, for some completely unclear reasons, the North American ice sheet has repeatedly appeared and disappeared.
Place two pieces of ice on the table - one 10 times larger than the other. Which one will melt faster? If the question seems rhetorical, ask yourself: which ice sheet should have disappeared first with the general warming of the climate in the Northern Hemisphere - the Greenland ice sheet with an area of 1.8 million square kilometers or the supposed North American ice sheet next to it - 10 times larger? Obviously, the second one had greater resistance (over time) to all external changes.
Based on the currently dominant theory, this paradox cannot be explained. According to it, the huge hypothetical North American ice sheet has arisen over the past 500-700 thousand years four or five or more times, i.e. approximately every 100-150 thousand years, and the size of the one located next door (incomparably smaller) has hardly changed. Incredible!
If the stability of the Antarctic ice cover for tens of millions of years (let us assume that the glaciers of the Northern Hemisphere appeared and disappeared during this time) can be explained by the proximity of the continent to the pole, then in relation to Greenland it should be remembered: its southern tip is located near 60 degrees north latitude - at one parallels with Oslo, Helsinki, Leningrad, Magadan. So could the supposed “great glaciations” come and go in the Northern Hemisphere as often as is commonly claimed? Hardly. As for the criteria and methods for establishing their quantity, they are unreliable. Eloquent proof of this is the discrepancy in estimates of the number of glaciations. How many of them were there: 1-4, 2-6, or 7-11? And which of them can be considered maximum?
The terms “cooling” and “glaciation” are usually used as synonyms. It goes without saying, it seems, of course: the colder the Earth’s climate was, the wider the front the ancient glaciers advanced from the north. They say: “there were so many eras of cooling,” implying that there were the same number of eras of glaciation. However, here too, the latest research has raised many unexpected questions.
A. Penk and E. Brückner considered the most ancient or one of the most ancient glaciations of the Ice Age to be maximum. They were convinced that the sizes of subsequent ones were consistently decreasing. Subsequently, the opinion became stronger and almost undividedly dominated: the largest glaciation was that occurring in the middle of the ice age, and the most limited was the last one. For the Russian Plain it was an axiom: the most extensive Dnieper glaciation, which had two large “tongues” along the valleys of the Dnieper and Don, descended along them south of the latitude of Kyiv. The borders of the next one, the Moscow one, were drawn much further north (somewhat south of Moscow), and the even younger one, the Valdai one, was drawn north of Moscow (about halfway from it to Leningrad).
The limits of distribution of hypothetical ice covers on the plains are reconstructed in two ways: by the deposits of ancient glaciers (till - an unsorted mixture of clay, sand, large stone fragments), by landforms and by a number of other features. And here’s what’s remarkable: within the distribution of the youngest (of the supposed) glaciations, deposits were found that were then attributed to all or almost all previous ones (two, three, four, etc.). Near the southern boundaries of the Dnieper glaciation (in the valleys of the Dnieper and Don in their lower reaches) only one layer of till is found, as well as at the southern limits of the presumably maximum Illinois (in North America). And here and there, to the north, more layers of sediments are established, which, for one reason or another, are classified as glacial.
In the north and especially the northwest, the relief of the Russian Plain has sharp (“fresh”) outlines. General character The area allows us to believe that until recently there was a glacier here, which gave Leningraders and residents of the Baltic states their favorite places for recreation and tourism - picturesque combinations of ridges, hills and lakes lying in the depressions between them. Lakes on the Valdai and Smolensk Uplands are often deep and distinguished by the transparency and purity of their water. But south of Moscow the landscape is changing. There are almost no areas of hilly-lake terrain here. The area is dominated by ridges and gentle hills, cut by river valleys, streams and ravines. Therefore, it is believed that the glacial relief that was once here has been reworked and changed almost beyond recognition. Finally, the southern limits of the supposed distribution of ice sheets in Ukraine and along the Don are characterized by dissected spaces, cut by rivers, almost devoid of signs of glacial relief (if there was one), which, they say, gives reason to believe that the local glacier is one of the most ancient.. .
All these ideas, which seemed indisputable, Lately shaken.
PARADOX OF NATURE
The results of studying ice from cores of deep wells in Antarctica, Greenland and bottom sediments of oceans and seas turned out to be sensational.
By looking at the ratio of heavy and light oxygen isotopes in ice and marine organisms, scientists can now determine the ancient temperatures at which ice accumulated and layers of sediment were deposited on the seafloor. It turned out that one of the strongest cold snaps occurred not at the beginning and middle of the “ice age”, but almost at its very end - during a time interval 16-18 thousand years distant from our days. (Previously, it was assumed that the largest glaciation was 84-132 thousand years older.) Signs of a very sharp climate cooling at the end of the “ice age” were also discovered by other methods in different parts of the Earth. In particular, along ice veins in the north of Yakutia. The conclusion that our planet has recently experienced one of its coldest or coldest eras now seems very credible.
But how can we explain the phenomenal natural paradox that the minimum of the supposed land-based glaciations corresponds to a very harsh climate? Finding themselves in a “dead end” situation, some scientists took the easiest path - they abandoned all previous ideas and proposed that the last glaciation be considered one of the maximum, since the climate at that time was one of the coldest. Thus, the entire system of geological evidence of the sequence of natural events during the Ice Age is denied, and the entire edifice of the “classical” glacial concept collapses.
MYTHICAL PROPERTIES OF GLACIERS
Can't figure it out complex issues history of the “Ice Age” without first studying the problems of geological activity of ancient glaciers. The traces they leave are the only evidence of their spread.
Glaciers come in two main types: large sheets or domes that merge into huge sheets, and mountain glaciers (glaciers). The geological role of the former is most fully illuminated in the works of the American scientist R. F. Flint, who summarized the ideas of many scientists (including Soviet ones), according to which glaciers perform enormous destructive and creative work - they plow out large potholes, basins and accumulate powerful layers of sediment. It is assumed, for example, that they, like a bulldozer, are capable of scraping out basins several hundred meters deep, and in some cases (Sognefjord in Norway) - up to 1.5-2.5 thousand meters (the depth of this fjord is 1200 m plus the same height slopes). Not bad at all, if you keep in mind that the glacier had to “dig” hard rock here. True, most often the formation of basins with a depth of “only” 200-300 meters is associated with glacial gouging. But it has now been established with a fair degree of accuracy that ice moves in two ways. Either its blocks slide along chips and cracks, or the laws of viscoplastic flow apply. Under prolonged and ever-increasing stresses, solid ice becomes plastic and begins to flow, albeit very slowly.
In the central parts of the Antarctic cover, the speed of ice movement is 10-130 meters per year. It increases somewhat only in peculiar “ice rivers” flowing in icy banks (outlet glaciers). The movement of the bottom part of the glaciers is so slow and smooth that they are physically unable to perform the tremendous work that is attributed to them. And does the glacier touch the surface of its bed everywhere? Snow and ice are good heat insulators (Eskimos have long built houses from compressed snow and ice), and intraterrestrial heat is constantly supplied in small quantities from the bowels of the earth to its surface. In sheets of great thickness, the ice from below melts, and rivers and lakes appear beneath it. In Antarctica, near the Soviet Vostok station, under a four-kilometer thick glacier, there is a reservoir with an area of 8 thousand square kilometers! This means that the ice not only does not tear off the underlying rocks here, but, as it were, “floats” above them or, if the layer of water is small, slides along their wetted surface. Mountain glaciers in the Alps, Caucasus, Altai and other areas are advancing with average speed 100-150 meters per year. Their bottom layers here also generally behave as a viscous-plastic substance and flow in accordance with the law of laminar flow, adapting to the unevenness of the bed. Consequently, they cannot plow out trough-shaped valleys-troughs several kilometers wide and 200-2500 meters deep. This is confirmed by interesting observations.
During the Middle Ages, the area of glaciers in the Alps increased. They moved down river valleys and buried Roman-era buildings beneath them. And when the Alpine glaciers retreated again, from under them appeared the perfectly preserved foundations of buildings destroyed by people and earthquakes, and paved Roman roads with cart ruts carved into them. In the central part of the Alps, near Innsbruck in the valley of the Inn River, under the sediments of a retreating glacier, layered sediments of an ancient lake (with remains of fish, leaves and tree branches) that existed here about 30 thousand years ago were discovered. This means that the glacier that moved onto the lake practically did not damage the layer of soft sediments - it did not even crush them.
What is the reason for the large width and trough-shaped shape of the valleys of mountain glaciers? It seems that with the active collapse of the valley slopes as a result of weathering. A huge amount of fragments of stone material appeared on the surface of the glaciers. The moving ice, like a conveyor belt, carried them down. The valleys were not cluttered. Their slopes, while remaining steep, quickly retreated. They acquired greater width and a transverse profile reminiscent of a trough: a flat bottom and steep sides.
To recognize the ability of glacial flows to mechanically destroy rocks means to attribute mythical properties to them. Due to the fact that glaciers do not plow up their beds, ancient river deposits and associated placers of gold and a number of other valuable minerals have been preserved in many valleys, now free of ice. If glaciers had carried out the enormous destructive work attributed to them, contrary to facts, logic and physical laws, there would have been no “gold rushes” of the Klondike and Alaska in the history of mankind, and Jack London would not have written several wonderful novels and short stories.
A variety of creative geological activities are also associated with glaciers. But often this is done without proper justification. In the mountains, indeed, there are often strata consisting of a chaotic mixture of blocks, rubble and sand, sometimes blocking the valleys from one slope to the other. They sometimes form large sections of valleys. On the plains, deposits of ancient ice sheets usually include unlayered and unsorted clays, loams, sandy loams containing stone inclusions - mainly pebbles and boulders. However, it is known that in cold-water lakes boulders can be carried away by floating ice. They carry them and river ice. Therefore, many varieties of marine and river sediments contain rock inclusions. It is impossible to classify them as glacial deposits on this basis alone. A major role here belongs to mudflows, which are most intense in the mountains or foothills and in belts, which are characterized by alternating rainy (wet) and dry periods.
One of the obvious evidence of the glacial origin of such deposits is considered to be “boulder blinds” - accumulations of boulders, the upper surface of which is supposedly worn away by ice. We just proved that the glacier couldn't do it. Those who have been on the banks of circumpolar rivers and seas know: boulder blinds are a common phenomenon here. During sudden ice movements in the coastal zone, it does an impressive job: it cuts off the protruding convex edges of boulders, steel pipes and concrete piles like a razor. Boulder-containing deposits of unsorted clays and loams contain remains of shells of marine organisms. Therefore, they accumulated in the sea. Sometimes there are boulders with sea shells attached to their smooth surface. Such finds do not at all testify to the glacial origin of these rounded stone blocks.
GEOLOGICAL ROLE OF UNDERGROUND glaciation
Under the influence of ideas about “great” terrestrial superglaciers, the role of underground glaciation in the history of the Earth was either not noticed, or its nature was interpreted erroneously. This phenomenon was sometimes spoken of as a phenomenon accompanying ancient glaciations.
The distribution zone of frozen rocks on Earth is very large. It occupies about 13 percent of the land area (almost half the territory in the USSR), includes vast expanses of the Arctic and Subarctic, and in the eastern regions of the Asian continent reaches mid-latitudes.
Ground and underground glaciations are generally characteristic of cooling areas of the Earth, that is, regions with negative average annual air temperatures experiencing heat deficiency. An additional condition for the formation of land glaciers is the predominance of solid precipitation (snow) over its discharge, and underground glaciation is confined to areas where there is not enough precipitation. First of all - to the territory of the north of Yakutia, the Magadan region and Alaska. Yakutia, where very little snow falls, is the cold pole of the Northern Hemisphere. A record low temperature was recorded here - minus 68°C.
For the zone of frozen rocks, underground ice is most typical. Most often, these are small-sized layers and veins more or less evenly distributed throughout the sediment strata. Intersecting each other, they often form an ice network or lattice. There are also deposits of underground ice up to 10-15 meters thick or more. And its most impressive variety is vertical ice veins 40-50 meters high and over 10 meters wide in the upper (thickest) part.
In accordance with the concept of V.A. Obruchev, large ice veins, lenses and layers of underground ice were until recently considered buried remnants of former ice sheets and this served as the basis for the theoretical reconstruction of a huge ice sheet over almost the entire territory of Siberia, right up to the Arctic seas and their islands.
Soviet (mainly) scientists discovered the mechanism of ice vein formation. At low temperatures, the soil, covered with a thin layer of snow, intensively cools, contracts and breaks into cracks. In winter they get snow, in summer they get water. It freezes because the lower ends of the cracks penetrate into the sphere of permanently frozen rocks having a temperature below 0°C. The periodic appearance of new cracks in the old place and their filling with additional portions of snow and water first lead to the formation of wedge-shaped ice veins no more than 12-16 meters high. Subsequently, they grow in height and width, squeezing part of the mineral substance containing them to the earth's surface. Due to this, the latter constantly increases - the ice veins seem to be “buried” in the ground. With increasing depth, conditions are created for their further upward growth. It stops when the total ice saturation of sediments reaches a maximum value of 75-90 percent of the total volume of the entire ice-soil mass. The overall increase in the surface can reach 25-30 meters. According to calculations, the formation of ice veins of large vertical extent requires 9-12 thousand years.
When the growth potential of an ice vein is exhausted, it opens up and begins to thaw. A thermokarst funnel appears, which, in the absence of drainage from it, turns into a lake, which often has a cross-shaped shape due to the fact that it is located at the mutual intersection of ice veins. The stage of mass thawing of icy rocks begins.
Ice wedges give rise to lakes, and lakes eliminate them, preparing the conditions for the reappearance and development of ice wedges.
The question of the connection between the formation of large ice veins and frost cracking of soils and the freezing of water in them has been resolved almost unambiguously; only the details of this process and its connection with certain landscapes in continental land conditions are discussed. The problem of the origin of large deposits of underground ice, in the form of lenses and interlayers, turned out to be more complex and is still the subject of heated debate. Some scientists believe that these are the buried remains of ancient glaciers. Others argue: such deposits are formed during the process of soil freezing. Some researchers incorrectly classify buried lenses and layers of ice that were once brought to land by the sea as glacial.
There are especially many lenses and layers of underground ice in the north of the West Siberian Lowland and the coastal plains of Chukotka. The results of the work of Soviet permafrost scientists there allow us to draw a very definite conclusion: underground lenses and layers of ice in these areas were formed during the process of freezing of rocks and are a characteristic consequence of it. A number of details of their structure (primarily the presence of large stone inclusions in underground ice deposits - pebbles and boulders) do not fit into the framework of standard ideas about underground ice formation. It is the boulders that are considered as the main and direct evidence that the ice containing them is the remnants of former ice sheets. However, the entry of boulders into masses of “pure” underground ice is quite understandable. Rocks are broken by cracks. The water that penetrated into them, freezing, pushed the boulders up, where they were enveloped by “pure” ice.
Another specific feature of underground lens-shaped ice deposits is their sometimes inherent folding. As ice veins grow toward the surface, they crush the overlying sediments into dome-shaped folds. It is assumed that deformations in the ice reflect the process of the former movement of the glacier, and the collapse of rocks is associated with its dynamic effect on its bed (“glaciodynamic dislocations”). It has already been said above that such ideas are unrealistic. Deformed large accumulations of lens-shaped underground ice represent intrusions of water and soil during the freezing process of sediments after their surface is above sea level. The validity of this point of view is clearly evidenced by the fact that in a number of cases, accumulations of deformed ice are covered by marine layered sediments, crushed into gentle folds, containing the remains of marine organisms.
The theory of ancient glaciations is usually used to explain natural phenomena that perplex the researcher, who cannot give a plausible interpretation of the method of their formation. This is exactly the case with the problem of the origin of deposits of underground ice containing boulders. However, the lack of an explanation for a complex natural phenomenon is not proof that it is necessarily caused by the activity of an ancient glacier.
Finally, studying the area of modern distribution of frozen rocks provides the key to deciphering the origin of the characteristic hilly-depression relief, which is usually called “typically glacial.” The fact is that underground ice in frozen rocks is distributed very unevenly. Its amount is often equivalent to raising the height of the earth's surface by 40-60 meters. Naturally, when frozen rocks thaw, depressions of corresponding depth are formed here. And where the ice content was much less, hills will appear after thawing. The process of local uneven thawing of icy rocks can be observed in the northern regions of permafrost. In this case, a hilly-lacustrine relief arises, completely similar to that which is considered “typically glacial” on the plains of Northern Europe. This zone (in addition to what was said above) is characterized by intensive peat formation, traces of which are recorded in thick chernozems of Europe and Asia.
STUDYING THE PAST TO PREDICT THE FUTURE
So it is clear that the geological role and, consequently, the size and number of ancient land-based “great ice sheets” are largely exaggerated. Large climate coolings were indeed characteristic of the last period of the geological history of the Earth, but they apparently led to the development of land glaciers only in mountainous regions and in adjacent territories located in a cold but fairly humid climate with a high amount of winter precipitation . The role of underground glaciation in the history of the Earth, on the contrary, is clearly underestimated. It developed most widely in areas with a harsh climate with some shortage of solid precipitation.
There is every reason to believe that in eras of cold climate aridization (arid climate is dry, characteristic of deserts and semi-deserts; aridization occurs at high or low air temperatures in conditions of low precipitation), the area of underground glaciation in the Northern Hemisphere, as at present, far exceeded the scale of land glaciers. Vast areas of the seas were also covered with ice.
Whether these epochs for our planet were the result of some astronomical factors or purely terrestrial ones (say, the displacement of the North Pole) - there is no clear answer now. But we can say: last period in the geological history of the Earth, it is not so much glacial as glacial in general, because the areas of underground and sea ice exceed (and have exceeded) the areas of distribution of land glaciers.
By studying the geological past, understanding the patterns of development of nature, scientists are trying to predict its future. What awaits humanity if the Earth's climate again becomes much colder than today? Will glacial super-covers emerge? Will all of Northern Europe and almost half of North America disappear under them? I think we can give a very definite negative answer. Glaciers will appear, apparently, only in Scandinavia and within other mountainous territories that receive more snow in winter than is consumed in summer, and vast areas of Eurasia and North America will be the arena for the development of underground glaciation. With a lack of moisture, this will lead to cold aridization of vast regions of the Earth.
State educational institution higher professional education in the Moscow region
International University of Nature, Society and Human "Dubna"
Faculty of Science and Engineering
Department of Ecology and Geosciences
COURSE WORK
By discipline
Geology
Scientific adviser:
Ph.D., Associate Professor Anisimova O.V.
Dubna, 2011
Introduction
1. Ice Age
1.1 Ice ages in the history of the Earth
1.2 Proterozoic Ice Age
1.3 Paleozoic Ice Age
1.4 Cenozoic Ice Age
1.5 Tertiary period
1.6 Quaternary period
2. Last Ice Age
2.2 Flora and fauna
2.3Rivers and lakes
2.4West Siberian Lake
2.5The world's oceans
2.6 Great Glacier
3. Quaternary glaciations in the European part of Russia
4. Causes of Ice Ages
Conclusion
Bibliography
Introduction
Target:
Explore the major glacial epochs in Earth's history and their role in shaping the modern landscape.
Relevance:
The relevance and significance of this topic is determined by the fact that the ice ages are not so well studied to fully confirm their existence on our Earth.
Tasks:
– conduct a literature review;
– establish the main glacial epochs;
– obtaining detailed data on the last Quaternary glaciations;
Establish the main causes of glaciations in the history of the Earth.
At present, little data has been obtained that confirms the distribution of frozen rock layers on our planet in ancient eras. The evidence is mainly the discovery of ancient continental glaciations from their moraine deposits and the establishment of the phenomena of mechanical detachment of glacier bed rocks, the transfer and processing of clastic material and its deposition after the melting of the ice. Compacted and cemented ancient moraines, the density of which is close to rocks such as sandstones, are called tillites. The discovery of such formations of different ages in different regions of the globe clearly indicates the repeated appearance, existence and disappearance of ice sheets, and, consequently, frozen strata. The development of ice sheets and frozen strata can occur asynchronously, i.e. The maximum development of the area of glaciation and the permafrost zone may not coincide in phase. However, in any case, the presence of large ice sheets indicates the existence and development of frozen strata, which should occupy much larger areas in area than the ice sheets themselves.
According to N.M. Chumakov, as well as V.B. Harland and M.J. Hambry, the time intervals during which glacial deposits were formed are called glacial eras (lasting the first hundreds of millions of years), ice ages (millions - first tens of millions of years), glacial epochs (first millions of years). In the history of the Earth, the following glacial eras can be distinguished: Early Proterozoic, Late Proterozoic, Paleozoic and Cenozoic.
1. Ice Age
Are there ice ages? Of course yes. The evidence for this is incomplete, but it is quite definite, and some of this evidence extends over large areas. Evidence of the Permian Ice Age is present on several continents, and in addition, traces of glaciers have been found on the continents dating back to other eras of the Paleozoic era up to its beginning, Early Cambrian time. Even in much older rocks, formed before the Phanerozoic, we find traces left by glaciers and glacial deposits. Some of these traces are more than two billion years old, possibly half the age of Earth as a planet.
The Ice Age of glaciations (glacials) is a period of time in the geological history of the Earth, characterized by a strong cooling of the climate and the development of extensive continental ice not only in the polar, but also in temperate latitudes.
Peculiarities:
·It is characterized by long-term, continuous and severe climate cooling, the growth of ice sheets in polar and temperate latitudes.
· Ice ages are accompanied by a decrease in the level of the World Ocean by 100 m or more, due to the fact that water accumulates in the form of ice sheets on land.
·During ice ages, areas occupied by permafrost expand, and soil and plant zones shift towards the equator.
It has been established that over the past 800 thousand years there have been eight ice ages, each of which lasted from 70 to 90 thousand years.
Fig.1 Ice Age
1.1 Ice ages in the history of the Earth
Periods of climate cooling, accompanied by the formation of continental ice sheets, are recurring events in the history of the Earth. Intervals of cold climate during which extensive continental ice sheets and sediments are formed, lasting hundreds of millions of years, are called glacial eras; In glacial eras, ice ages lasting tens of millions of years are distinguished, which, in turn, consist of ice ages - glaciations (glacials), alternating with interglacials (interglacials).
Geological studies have proven that there was a periodic process of climate change on Earth, spanning the time from the late Proterozoic to the present.
These are relatively long glacial eras that lasted for almost half of the Earth's history. The following glacial eras are distinguished in the history of the Earth:
Early Proterozoic - 2.5-2 billion years ago
Late Proterozoic - 900-630 million years ago
Paleozoic - 460-230 million years ago
Cenozoic - 30 million years ago - present
Let's take a closer look at each of them.
1.2 Proterozoic Ice Age
Proterozoic - from the Greek. the words protheros - primary, zoe - life. The Proterozoic era is a geological period in the history of the Earth, including the history of the formation of rocks of various origins from 2.6 to 1.6 billion years. A period in the history of the Earth that was characterized by the development of the simplest life forms of single-celled living organisms from prokaryotes to eukaryotes, which later, as a result of the so-called Ediacaran “explosion,” evolved into multicellular organisms.
Early Proterozoic glacial era
This is the oldest glaciation recorded in geological history, which appeared at the end of the Proterozoic on the border with the Vendian and, according to the Snowball Earth hypothesis, the glacier covered most of the continents at equatorial latitudes. In fact, it was not one, but a series of glaciations and interglacial periods. Since it is believed that nothing can prevent the spread of glaciation due to an increase in albedo (reflection of solar radiation from the white surface of glaciers), it is believed that the cause of subsequent warming may be, for example, an increase in the amount of greenhouse gases in the atmosphere due to increased volcanic activity , accompanied, as is known, by emissions of huge amounts of gases.
Late Proterozoic glacial era
Identified under the name of the Lapland glaciation at the level of Vendian glacial deposits 670-630 million years ago. These deposits are found in Europe, Asia, West Africa, Greenland and Australia. Paleoclimatic reconstruction of glacial formations from this time suggests that the European and African ice continents of that time were a single ice sheet.
Fig.2 Vend. Ulytau during the Ice Age Snowball
1.3 Paleozoic Ice Age
Paleozoic - from the word paleos - ancient, zoe - life. Palaeozoic. Geological time in the history of the Earth covering 320-325 million years. With an age of glacial deposits of 460 - 230 million years, it includes the Late Ordovician - Early Silurian (460-420 million years), Late Devonian (370-355 million years) and Carboniferous-Permian glacial periods (275 - 230 million years). The interglacial periods of these periods are characterized by a warm climate, which contributed to the rapid development of vegetation. In the places where they spread, large and unique coal basins and horizons of oil and gas fields were later formed.
Late Ordovician - Early Silurian Ice Age.
Glacial deposits of this time, called Saharan (after the name of modern Sahara). Were distributed throughout the area modern Africa, South America, eastern North America and Western Europe. This period is characterized by the formation of an ice sheet over much of northern, northwestern and western Africa, including the Arabian Peninsula. Paleoclimatic reconstructions suggest that the thickness of the Saharan ice sheet reached at least 3 km and was similar in area to the modern glacier of Antarctica.
Late Devonian Ice Age
Glacial deposits from this period were found in the territory of modern Brazil. The glacial area extended from the modern mouth of the river. Amazon to the east coast of Brazil, taking over the Niger region in Africa. In Africa, Northern Niger contains tillites (glacial deposits) that are comparable to those in Brazil. In general, the glacial areas stretched from the border of Peru with Brazil to northern Niger, the diameter of the area was more than 5000 km. The South Pole in the Late Devonian, according to the reconstruction of P. Morel and E. Irving, was located in the center of Gondwana in Central Africa. Glacial basins are located on the oceanic margin of the paleocontinent, mainly in high latitudes (not north of the 65th parallel). Judging by the then high-latitude continental position of Africa, one can assume the possible widespread development of frozen rocks on this continent and, in addition, in the north-west of South America.
Carboniferous-Permian Ice Age
It became widespread in the territory of modern Europe and Asia. During the Carboniferous, there was a gradual cooling of the climate, culminating about 300 million years ago. This was facilitated by the concentration of most of the continents in the southern hemisphere and the formation of the supercontinent Gondwana, the formation of large mountain ranges and changes in ocean currents. During the Carboniferous–Permian, most of Gondwana experienced glacial and periglacial conditions.
Center of the continental ice sheet 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 approximately 1750 km, according to calculations, the ice thickness could be up to 4 – 4.5 km. In the southern hemisphere, at the end of the Carboniferous–Early Permian, a general uplift of Gondwana occurred and glaciation spread over most of this supercontinent. The Carboniferous-Permian Ice Age lasted at least 100 million years, but there was no single large ice cap. The peak of the Ice Age, when the ice sheets extended far to the north (up to 30° - 35° S), lasted about 40 million years (between 310 - 270 million years ago). According to calculations, the Gondwana glaciation area occupied an area of at least 35 million km 2 (possibly 50 million km 2), which is 2–3 times larger than the area of modern Antarctica. Ice sheets reached 30° – 35°S. The main center of glaciation was the region Sea of Okhotsk, which apparently was located near the North Pole.
Fig.3 Paleozoic Ice Age
1.4 Cenozoic Ice Age
The Cenozoic Ice Age (30 million years ago - present) is a recently begun glacial era.
The present time - the Holocene, which began ≈ 10,000 years ago, is characterized as a relatively warm interval after the Pleistocene Ice Age, often classified as an interglacial. Ice sheets exist at high latitudes in the northern (Greenland) and southern (Antarctica) hemispheres; Moreover, in the northern hemisphere, the cover glaciation of Greenland extends south to 60° north latitude (i.e., to the latitude of St. Petersburg), fragments of sea ice cover - to 46-43° north latitude (i.e., to the latitude of Crimea) , and permafrost to 52-47° north latitude. In the southern hemisphere, continental Antarctica is covered by an ice sheet 2500-2800 m thick (up to 4800 m in some areas of East Antarctica), with ice shelves accounting for ≈10% of the continent's area above sea level. In the Cenozoic glacial era, the Pleistocene ice age is the strongest: a decrease in temperature led to glaciation of the Arctic Ocean and the northern regions of the Atlantic and Pacific Oceans, while the glaciation boundary ran 1500-1700 km south of the modern one.
Geologists divide the Cenozoic into two periods: Tertiary (65 - 2 million years ago) and Quaternary (2 million years ago - our time), which in turn are divided into epochs. Of these, the first is much longer than the second, but the second - quaternary - has a number of unique features; this is the time of ice ages and the final formation of the modern face of the Earth.
Rice. 4 Cenozoic Ice Age. Glacial period. Climate curve for the last 65 million years.
34 million years ago - the birth of the Antarctic ice sheet
25 million years ago - its abbreviation
13 million years ago - its re-growth
About 3 million years ago - the beginning of the Pleistocene Ice Age, repeated appearance and disappearance of ice sheets in the northern regions of the Earth
1.5 Tertiary period
The Tertiary period consists of eras:
·Paleocene
Oligocene
Pliocene
Paleocene era (from 65 to 55 million years ago)
Geography and climate: The Paleocene marked the beginning of the Cenozoic era. At that time, the continents were still in motion as the "great southern continent" Gondwana continued to break apart. South America was now completely cut off from the rest of the world and turned into a kind of floating “ark” with a unique fauna of early mammals. Africa, India and Australia have moved even further away from each other. Throughout the Paleocene, Australia was located near Antarctica. Sea levels have dropped, and new land areas have emerged in many areas of the globe.
Fauna: The age of mammals began on land. Rodents and insectivores appeared. There were also large animals among them, both predators and herbivores. In the seas, marine reptiles were replaced by new species of predatory bony fish and sharks. New varieties of bivalves and foraminifera emerged.
Flora: More and more new species of flowering plants and the insects that pollinate them continued to spread.
Eocene Epoch (from 55 to 38 million years ago)
Geography and climate: During the Eocene, the main land masses began to gradually assume a position similar to that which they occupy today. Much of the land was still divided into giant islands of sorts, as the huge continents continued to move away from each other. South America lost contact with Antarctica, and India moved closer to Asia. At the beginning of the Eocene, Antarctica and Australia were still located nearby, but later they began to diverge. North America and Europe also split, and new mountain ranges emerged. The sea flooded part of the land. The climate was warm or temperate everywhere. Much of it was covered with lush tropical vegetation, and large areas were covered with dense swamp forests.
Fauna: Bats, lemurs, and tarsiers appeared on land; ancestors of today's elephants, horses, cows, pigs, tapirs, rhinoceroses and deer; other large herbivores. Other mammals, such as whales and sirenians, have returned to the aquatic environment. The number of freshwater bony fish species has increased. Other groups of animals also evolved, including ants and bees, starlings and penguins, giant flightless birds, moles, camels, rabbits and voles, cats, dogs and bears.
Flora: Lush forests grew in many parts of the world, and palm trees grew in temperate latitudes.
Oligocene Epoch (from 38 to 25 million years ago)
Geography and Climate: During the Oligocene era, India crossed the equator and Australia finally separated from Antarctica. The climate on Earth became cooler, and a huge ice sheet formed over the South Pole. To form such a large amount of ice required equally significant volumes of sea water. This led to lower sea levels across the planet and an expansion of land area. Widespread cooling caused the disappearance of lush Eocene tropical forests in many areas of the globe. Their place was taken by forests that preferred a more temperate (cool) climate, as well as vast steppes spread across all continents.
Fauna: With the spread of the steppes, a rapid flourishing of herbivorous mammals began. Among them, new species of rabbits, hares, giant sloths, rhinoceroses and other ungulates arose. The first ruminants appeared.
Flora: Tropical forests decreased in size and began to give way to temperate forests, and vast steppes appeared. New grasses quickly spread, and new types of herbivores developed.
Miocene era (from 25 to 5 million years ago)
Geography and climate: During the Miocene, the continents were still “on the march”, and a number of grandiose cataclysms occurred during their collisions. Africa "crashed" into Europe and Asia, resulting in the appearance of the Alps. When India and Asia collided, the Himalayan mountains rose up. At the same time, the Rocky Mountains and Andes formed as other giant plates continued to shift and slide on top of each other.
However, Austria and South America remained isolated from the rest of the world, and each of these continents continued to develop its own unique fauna and flora. Ice cover in the southern hemisphere has spread throughout Antarctica, causing the climate to cool further.
Fauna: Mammals migrated from continent to continent along newly formed land bridges, which sharply accelerated evolutionary processes. Elephants moved from Africa to Eurasia, and cats, giraffes, pigs and buffaloes moved in the opposite direction. Saber-toothed cats and monkeys, including anthropoids, appeared. In Australia, cut off from the outside world, monotremes and marsupials continued to develop.
Flora: Inland areas became colder and drier, and steppes became more widespread in them.
Pliocene Epoch (from 5 to 2 million years ago)
Geography and climate: A space traveler looking down on the Earth at the beginning of the Pliocene would have found continents in almost the same places as today. A galactic visitor would see the giant ice caps in the northern hemisphere and the huge ice sheet of Antarctica. Because of all this mass of ice, the Earth's climate became even cooler, and the surface of the continents and oceans of our planet became significantly colder. Most of the forests that remained in the Miocene disappeared, giving way to vast steppes that spread throughout the world.
Fauna: Herbivorous ungulate mammals continued to rapidly reproduce and evolve. Towards the end of the period, a land bridge connected South and North America, which led to a huge "exchange" of animals between the two continents. It is believed that increased interspecific competition caused the extinction of many ancient animals. Rats entered Australia, and the first humanoid creatures appeared in Africa.
Flora: As the climate cooled, steppes replaced forests.
Fig.5 Diverse mammals evolved during the Tertiary period
1.6 Quaternary period
Consists of eras:
·Pleistocene
Holocene
Pleistocene era (from 2 to 0.01 million years ago)
Geography and climate: At the beginning of the Pleistocene, most continents occupied the same position as today, and some of them required crossing half the globe to do so. A narrow land bridge connected North and South America. Australia was located on the opposite side of the Earth from Britain. Giant ice sheets were creeping across the northern hemisphere. It was an era of great glaciation with alternating periods of cooling and warming and fluctuations in sea level. This ice age continues to this day.
Fauna: Some animals managed to adapt to the increased cold by acquiring thick fur: for example, woolly mammoths and rhinoceroses. The most common predators are saber-toothed cats and cave lions. This was the age of giant marsupials in Australia and huge flightless birds, such as moas and apiornis, that lived in many areas of the southern hemisphere. The first people appeared, and many large mammals began to disappear from the face of the Earth.
Flora: Ice gradually crawled from the poles, and coniferous forests gave way to the tundra. Further from the edge of the glaciers, deciduous forests were replaced by coniferous ones. In the warmer regions of the globe there are vast steppes.
Holocene era (from 0.01 million years to the present day)
Geography and climate: The Holocene began 10,000 years ago. Throughout the Holocene, the continents occupied almost the same places as they do today; the climate was also similar to the modern one, becoming warmer and colder every few millennia. Today we are experiencing one of the warming periods. As the ice sheets thinned, sea levels slowly rose. The time of the human race began.
Fauna: At the beginning of the period, many animal species became extinct, mainly due to general climate warming, but increased human hunting for them may also have had an impact. Later they could fall victim to competition from new species of animals brought by people from other places. Human civilization has become more developed and spread throughout the world.
Flora: With the advent of agriculture, peasants destroyed more and more wild plants in order to clear areas for crops and pastures. In addition, plants brought by people to new areas sometimes replaced indigenous vegetation.
Rice. 6 Proboscis, the largest land animals of the Quaternary period
glacial era tertiary quaternary
2. Last Ice Age
The last ice age (last glaciation) is the last of the ice ages within the Pleistocene or Quaternary ice age. It began about 110 thousand years ago and ended around 9700-9600 BC. e. For Siberia it is usually called “Zyryanskaya”, in the Alps - “Würmskaya”, in North America - “Wisconsinskaya”. During this era, the expansion and contraction of ice sheets occurred repeatedly. The Last Glacial Maximum, when the total volume of ice in glaciers was greatest, dates back to about 26-20 thousand years ago of individual ice sheets.
At this time, the polar glaciers of the northern hemisphere grew to enormous sizes, uniting into a huge ice sheet. Long tongues of ice extended from it to the south along the beds of large rivers. All high mountains were also bound by ice shells. Cooling and the formation of glaciers led to other global changes in nature. Rivers flowing into the northern seas turned out to be dammed by ice walls, they spilled into giant lakes and turned back trying to find a drain in the south. Heat-loving plants moved south, giving way to more cold-tolerant neighbors. At this time, the mammoth faunal complex was finally formed, consisting mainly of large animals well protected from the cold.
2.1 Climate
However, during the last glaciation, the climate on the planet was not constant. Climate warming periodically occurred, the glacier melted along the edge, retreated to the north, the areas of high-mountain ice decreased, and climatic zones shifted south. There have been several such minor changes in climate. Scientists believe that the coldest and most severe period in Eurasia was about 20 thousand years ago.
Rice. 7 Perito Moreno Glacier in Patagonia, Argentina. during the last ice age
Rice. 8 The diagram shows climate changes in Siberia and some other areas of the northern hemisphere over the past 50 thousand years
2.2 Flora and fauna
The cooling of the planet and the formation of giant glacial systems in the north caused global changes in the flora and fauna of the Northern Hemisphere. The boundaries of everyone natural areas began to move south. The following natural zones were located on the territory of Siberia.
Along the glaciers, a zone of cold tundras and tundra-steppes stretches tens of kilometers wide. It was located approximately in the areas where there is now forest and taiga.
In the south, the tundra-steppe gradually turned into forest-steppe and forests. Forest areas were very small, and were not everywhere. Most often, forests were located on the southern shores of periglacial lakes and in river valleys and on mountain spurs.
Even further south were dry steppes, in the west of Siberia gradually turning into the Sayan-Altai mountain systems, in the east bordering on the semi-deserts of Mongolia. In some areas, the tundra-steppe and steppe were not separated by a strip of forest, but gradually replaced each other.
Fig.9. Tundra-steppe, the era of the last glaciation
In the new climatic conditions of the Ice Age, the animal world also changed. During the last stages of the Quaternary period, new species of fauna were formed in the Northern Hemisphere. A particularly expressive manifestation of these changes was the appearance of the so-called mammoth faunal complex, which consisted of cold-tolerant animal species.
2.3 Rivers and lakes
Giant ice fields formed a natural dam and blocked the flow of rivers flowing into the Northern Seas. Modern Siberian rivers: the Ob, Irtysh, Yenisei, Lena, Kolyma and many others overflowed along the glaciers, forming giant lakes that were combined into periglacial meltwater drainage systems.
Siberia in the Ice Age. For clarity, modern rivers and cities are indicated. Most of this system was connected by rivers and water flowed out of it to the southwest through the system of the New Euxine basin, which was once on the site of the Black Sea. Further, through the Bosphorus and Dardanelles, the water entered the Mediterranean Sea. The total area of this drainage basin was 22 million square meters. km. It served the territory from Mongolia to the Mediterranean.
Fig. 10 Siberia during the Ice Age
In North America, there was also such a system of periglacial lakes. Along the Laurentian ice sheet stretched the now disappeared giant Lake Agassiz, Lake McConnell and Lake Algonque.
2.4 West Siberian Lake
Some scientists believe that one of the largest periglacial lakes in Eurasia was Mansiyskoe, or as it is also called West Siberian Lake. It occupied almost the entire territory of the West Siberian Plain to the foothills of the Kuznetsk Alatau and Altai. The places where they are now located Largest cities Tyumen, Tomsk and Novosibirsk were covered with water during the last ice age. When the glacier began to melt - 16-14 thousand years ago, the waters of Lake Mansi began to gradually flow into the Arctic Ocean, and in its place modern river systems were formed, and in the lowland part of the Taiga Ob region, the largest system of Vasyugan Swamps in Eurasia was formed.
Fig. 11 This is what West Siberian Lake looked like
2.5 Oceans
The planet's ice sheets are formed by the waters of the world's oceans. Accordingly, the larger and higher the glaciers, the less water remains in the ocean. Glaciers absorb water, the ocean level drops, exposing large areas of land. Thus, 50,000 years ago, due to the growth of glaciers, the sea level dropped by 50 m, and 20,000 years ago - by 110-130 m. During this period, many modern islands formed a single whole with the mainland. Thus, the British, Japanese, and New Siberian Islands were inseparable from the mainland. In place of the Bering Strait there was a wide strip of land called Beringia.
Fig. 12 Diagram of sea level changes during the last ice age
2.6 Great Glacier
During the last glaciation, the planet's subpolar part of the Northern Hemisphere was occupied by a huge Arctic ice sheet. It was formed as a result of the merger of the North American and Eurasian ice sheets into a single system.
The Arctic ice sheet consisted of giant ice sheets shaped like flat-convex domes, which formed ice layers 2-3 kilometers high in some places. The total area of ice cover is more than 40 million square meters. km.
The largest elements of the Arctic Ice Sheet:
1. Laurentian shield centered over southwestern Hudson Bay;
2. 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 harsh Ice Age, the climate was constantly changing. The glaciers gradually advanced south and retreated again. The ice sheet reached its maximum thickness about 20,000 years ago.
3. Quaternary glaciations in the European part of Russia
Quaternary glaciation - glaciation in the Quaternary period, caused by a decrease in temperature that began at the end of the Neogene period. In the mountains of Europe, Asia, and America, glaciers began to increase, flowing onto the plains; on the Scandinavian Peninsula, a gradually expanding ice cap formed; the advancing ice pushed the animals and plants that lived there to the south.
The thickness of the ice cover reached 2 - 3 kilometers. About 30% of the territory modern Russia in the north it was occupied by cover glaciation, which either decreased somewhat, then moved south again. Interglacial periods with warm, mild climates were followed by cold snaps when the glaciers advanced again.
On the territory of modern Russia there were 4 glaciations - Oka, Dnieper, Moscow and Valdai. The largest of them was the Dnieper, when a giant glacial tongue descended along the Dnieper to the latitude of Dnepropetrovsk, and along the Don to the mouth of the Medveditsa.
Consider the Moscow glaciation
The Moscow glaciation is an ice age dating back to the Anthropocene (Quaternary) period (Middle Pleistocene, about 125-170 thousand years ago), the last of the major glaciations of the Russian (East European) Plain.
It was preceded by the Odintsovo time (170-125 thousand years ago) - a relatively warm period separating the Moscow glaciation from the maximum, Dnieper glaciation (230-100 thousand years ago), also in the Middle Pleistocene.
The Moscow glaciation was identified relatively recently as an independent ice age. Some researchers still interpret the Moscow glaciation as one of the stages of the Dnieper glaciation, or that it was one of the stages of a larger and longer previous glaciation. However, the boundary of the glacier developing during the Muscovite era is drawn with greater validity.
Moscow glaciation only captured the northern part of the Moscow region. The glacier's border ran along the Klyazma River. It was during the melting of the Moscow glacier that the morainic strata of the Dnieper glaciation were almost completely washed away. The flooding of the periglacial zone, which directly included the territory of the Shatura region, during the melting of the Moscow glacier was so great that the lowlands were filled with large lakes or turned into powerful valleys for the runoff of melted glacial waters. Suspensions settled in them, forming outwash plains with sandy and sandy loam deposits, which are most common within the region at present.
Fig. 14 Position of terminal glacial moraines of different ages within the central part of the Russian Plain. Moraine of the Early Valdai () and Late Valdai () glaciations.
4. Causes of Ice Ages
The causes of the Ice Ages are inextricably linked to the broader issues of global climate change that have occurred throughout Earth's history. From time to time, significant changes in geological and biological conditions occurred. It should be borne in mind that the beginning of all great glaciations is determined by two important factors.
First, over thousands of years, the annual precipitation pattern should be dominated by heavy, long-lasting snowfalls.
Secondly, in areas with such a precipitation regime, temperatures must be so low that summer snowmelt is minimized and firn fields increase year after year until glaciers begin to form. Abundant snow accumulation must dominate the glacier balance throughout the glaciation, since if ablation exceeds accumulation, glaciation will decline. Obviously, for each ice age it is necessary to find out the reasons for its beginning and end.
Hypotheses
1. The pole migration hypothesis. Many scientists believed that the Earth's rotation axis changes its position from time to time, which leads to a corresponding shift in climate zones.
2. Carbon dioxide hypothesis. Carbon dioxide CO2 in the atmosphere acts like a warm blanket to trap the heat emitted by the Earth near its surface, and any significant reduction in CO2 in the air will result in a drop in temperature on Earth. As a result, the temperature of the land will drop, and the Ice Age will begin.
3. Hypothesis of diastrophism (movements earth's crust). Significant uplifts of land have repeatedly occurred in the history of the Earth. In general, the air temperature over land decreases by about 1.8. With a rise of every 90 m. In fact, the mountains rose many hundreds of meters, which turned out to be sufficient for the formation of valley glaciers there. In addition, the growth of mountains changes the circulation of moisture-carrying air masses. The uplift of ocean floors can, in turn, change the circulation of ocean waters and also cause climate change. It is not known whether only tectonic movements could have been the cause of glaciation, in any case, they could greatly contribute to its development
4. Volcanic dust hypothesis. Volcanic eruptions are accompanied by the release of huge amounts of dust into the atmosphere. It is obvious that volcanic activity, widespread on Earth for thousands of years, could significantly lower air temperatures and cause the onset of glaciation.
5. Continental drift hypothesis. According to this hypothesis, all modern continents and the largest islands were once part of the single continent of Pangea, washed by the World Ocean. The consolidation of continents into such a single landmass could explain the development of the Late Paleozoic glaciation of South America, Africa, India and Australia. The areas covered by this glaciation were probably much further north or south than their present position. The continents began to separate in the Cretaceous, and reached their present position approximately 10 thousand years ago
6. Ewing-Donna conjecture. One of the attempts to explain the reasons for the emergence of the Pleistocene Ice Age belongs to M. Ewing and W. Donne, geophysicists who made a significant contribution to the study of the topography of the ocean floor. They believe that in pre-Pleistocene times the Pacific Ocean occupied the northern polar regions and therefore it was much warmer there than now. The Arctic land areas were then located in the North Pacific Ocean. Then, as a result of continental drift, North America, Siberia and the Arctic Ocean took their modern position. Thanks to the Gulf Stream coming from the Atlantic, the waters of the Arctic Ocean at that time were warm and evaporated intensively, which contributed to heavy snowfalls in North America, Europe and Siberia. Thus, the Pleistocene glaciation began in these areas. It stopped because, as a result of the growth of glaciers, the level of the World Ocean dropped by about 90 m, and the Gulf Stream was eventually unable to overcome the high underwater ridges separating the basins of the Arctic and Atlantic oceans. Deprived of the influx of warm Atlantic waters, the Arctic Ocean froze, and the source of moisture feeding the glaciers dried up.
7. Hypothesis of circulation of ocean waters. There are many currents in the oceans, both warm and cold, which have a significant impact on the climate of the continents. The Gulf Stream is one of the remarkable warm currents that washes the northern coast of South America, passes through the Caribbean Sea and the Gulf of Mexico and crosses the North Atlantic, having a warming effect on Western Europe. Warm currents also exist in the South Pacific and Indian Ocean. The most powerful cold currents are directed from the Arctic Ocean to the Pacific Ocean through the Bering Strait and to the Atlantic Ocean through the straits along the eastern and western coasts of Greenland. One of them, the Labrador Current, cools the New England coast and brings fogs there. Cold waters also enter southern oceans from Antarctica in the form of particularly powerful currents moving north almost to the equator along the western coasts of Chile and Peru. The strong subsurface Gulf Stream carries its cold waters south into the North Atlantic.
8. Hypothesis of changes in solar radiation. As a result of a long-term study of sunspots, which are strong plasma emissions in the solar atmosphere, it was discovered that there are very significant annual and longer cycles of changes in solar radiation. Peaks in solar activity occur approximately every 11, 33, and 99 years, when the Sun emits more heat, resulting in a more powerful circulation of the Earth's atmosphere, accompanied by greater cloudiness and heavier precipitation. Due to high clouds blocking the sun's rays, the land surface receives less heat than usual.
Conclusion
During the course work, glacial eras, which include ice ages, were studied. Ice ages have been identified and analyzed with precision. Detailed data on the last ice age has been obtained. The last Quaternary epochs have been identified. The main causes of ice ages have also been studied.
Bibliography
1. Dotsenko S.B. On the glaciation of the Earth at the end of the Paleozoic // Life of the Earth. Geodynamics and mineral resources. M.: Moscow State University Publishing House, 1988.
2. Serebryanny L.R. Ancient glaciation and life / Serebryanny Leonid Ruvimovich; Responsible editor G.A. Avsyuk. - M.: Nauka, 1980. - 128 p.: ill. - (Man and environment). - Bibliography
3. Secrets of the Ice Ages: Trans. from English/Ed. G.A. Avsyuka; Afterword G.A. Avsyuk and M.G. Grosvalda.-M.: Progress, 1988.-264 p.
4. http://ru.wikipedia.org/wiki/Ice Age (Material from Wikipedia - the free encyclopedia)
5. http://www.ecology.dubna.ru/dubna/pru/geology.html (Article Geological and geomorphological features. N.V. Koronovsky)
6. http://ru.wikipedia.org/wiki/Ice_age (Material from Wikipedia - the free encyclopedia)
7. http://www.fio.vrn.ru/2004/7/kaynozoyskaya.htm (Cenozoic era)
The last ice age ended 12,000 years ago. During the most severe period, glaciation threatened man with extinction. However, after the glacier disappeared, he not only survived, but also created a civilization.
Glaciers in the history of the Earth
The last glacial era in the history of the Earth is the Cenozoic. It began 65 million years ago and continues to this day. Modern man is lucky: he lives in an interglacial period, one of the warmest periods of the planet’s life. The most severe glacial era - the Late Proterozoic - is far behind.
Despite global warming, scientists predict the onset of a new ice age. And if the real one will come only after millennia, then the little ice age, which will reduce annual temperatures by 2-3 degrees, may come quite soon.
The glacier became a real test for man, forcing him to invent means for his survival.
Last Ice Age
The Würm or Vistula glaciation began approximately 110,000 years ago and ended in the tenth millennium BC. The peak of cold weather occurred 26-20 thousand years ago, the final stage of the Stone Age, when the glacier was at its largest.
Little Ice Ages
Even after the glaciers melted, history has known periods of noticeable cooling and warming. Or, in another way - climate pessimums And optimums. Pessimums are sometimes called Little Ice Ages. In the XIV-XIX centuries, for example, the Little Ice Age began, and during the Great Migration of Nations there was an early medieval pessimum.
Hunting and meat food
There is an opinion according to which the human ancestor was more of a scavenger, since he could not spontaneously occupy a higher ecological niche. And all known tools were used to cut up the remains of animals that were taken from predators. However, the question of when and why people began to hunt is still a matter of debate.
In any case, thanks to hunting and meat food, ancient man received a large supply of energy, which allowed him to better endure the cold. The skins of killed animals were used as clothing, shoes and walls of the home, which increased the chances of survival in the harsh climate.
Upright walking
Upright walking appeared millions of years ago, and its role was much more important than in the life of a modern office worker. Having freed his hands, a person could engage in intensive housing construction, clothing production, processing of tools, production and preservation of fire. The upright ancestors moved freely in open areas, and their life no longer depended on collecting the fruits of tropical trees. Already millions of years ago, they moved freely over long distances and obtained food in river drains.
Upright walking played an insidious role, but it still became more of an advantage. Yes, man himself came to cold regions and adapted to life in them, but at the same time he could find both artificial and natural shelters from the glacier.
Fire
Fire in the life of ancient man was initially an unpleasant surprise, not a blessing. Despite this, the human ancestor first learned to “extinguish” it, and only later use it for his own purposes. Traces of the use of fire are found in sites that are 1.5 million years old. This made it possible to improve nutrition by preparing protein foods, as well as to remain active at night. This further increased the time to create survival conditions.
Climate
The Cenozoic Ice Age was not a continuous glaciation. Every 40 thousand years, the ancestors of people had the right to a “respite” - temporary thaws. At this time, the glacier was retreating and the climate became milder. During periods of harsh climate, natural shelters were caves or regions rich in flora and fauna. For example, the south of France and the Iberian Peninsula were home to many early cultures.
The Persian Gulf 20,000 years ago was a river valley rich in forests and grassy vegetation, a truly “antediluvian” landscape. Wide rivers flowed here, one and a half times larger in size than the Tigris and Euphrates. The Sahara in certain periods became a wet savannah. The last time this happened was 9,000 years ago. This can be confirmed by cave drawings, which depict an abundance of animals.
Fauna
Huge glacial mammals, such as bison, woolly rhinoceros and mammoth, became an important and unique source of food for ancient people. Hunting such large animals required a lot of coordination and brought people together noticeably. The effectiveness of “teamwork” has proven itself more than once in the construction of parking lots and the manufacture of clothing. Deer and wild horses enjoyed no less “honor” among ancient people.
Language and communication
Language was perhaps the main life hack of ancient man. It was thanks to speech that they were preserved and passed on from generation to generation. important technologies processing tools, making and maintaining fire, as well as various human adaptations for everyday survival. Perhaps the details of hunting large animals and migration directions were discussed in Paleolithic language.
Allörd warming
Scientists are still arguing whether the extinction of mammoths and other glacial animals was the work of man or caused by natural causes - the Allerd warming and the disappearance of food plants. As a result of the extermination of a large number of animal species, people in harsh conditions faced death from lack of food. There are known cases of the death of entire cultures simultaneously with the extinction of mammoths (for example, the Clovis culture in North America). However, warming became an important factor in the migration of people to regions whose climate became suitable for the emergence of agriculture.
There are several hypotheses about the causes of glaciations. The factors underlying these hypotheses can be divided into astronomical and geological. Astronomical factors causing cooling on earth include:
1.
Changing the tilt of the earth's axis
2.
Deviation of the Earth from its orbit away from the Sun
3.
Uneven thermal radiation from the Sun.
Geological factors include mountain-forming processes, volcanic activity, and continental movement.
Each of the hypotheses has its drawbacks. Thus, the hypothesis connecting glaciation with the eras of mountain building does not explain the absence of glaciation in the Mesozoic, although mountain-building processes were quite active during this era.
The intensification of volcanic activity, according to some scientists, leads to warming of the earth's climate, while others believe it leads to cooling. According to the hypothesis of continental movement, huge areas of land throughout the history of the development of the earth's crust periodically moved from a warm climate to a cold climate, and vice versa.
Over the course of the planet's geological history of more than 4 billion years, the Earth has experienced several periods of glaciation. The oldest Huronian glaciation is 4.1 - 2.5 billion years old, the Gneissian glaciation is 900 - 950 million years old. Further ice ages were repeated quite regularly: Sturt - 810 - 710, Varangian - 680 - 570, Ordovician - 410 - 450 million years ago. The penultimate ice age on Earth was 340 - 240 million years ago and was called Gondwana. Now there is another ice age on Earth, 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 large areas in Europe, North America and partly in Asia are occupied by cover glaciers, or 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 the period of another interglacial, which is called the Holocene.
The central problem of cryology of the Earth is the identification and study of the general patterns of glaciation of our planet. The Earth's cryosphere experiences both continuous seasonal and periodic fluctuations and centuries-long changes.
Currently, the Earth has passed the Ice Age and is in an interglacial period. But what happens next? What is the forecast for the process of glaciation of the Earth? Could a new glacial advance begin soon?
The answers to these questions concern not only scientists. Glaciation of the Earth is a gigantic planetary process that is of concern to all of humanity. To find the answer to these questions, you need to penetrate the mysteries of glaciation, reveal the patterns of development of ice ages, and establish the main reasons for their occurrence.
The works of many outstanding scientists were devoted to solving 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 the theories and hypotheses, we can combine them into three main groups.
Planetary - where the main reason for the onset of ice ages is considered to be significant changes occurring on the planet: shifting poles, movement of continents, mountain building processes, which are accompanied by changes in the circulation of air and ocean currents and the appearance of glaciers, atmospheric pollution by products of volcanic activity, changes in the concentration of carbon dioxide and ozone in the atmosphere .
Planetary hypotheses also include astronomical hypotheses that explain the glaciation of the planet by changes in the Earth’s orbit, changes in the angle of inclination of its axis of rotation, distance from the Sun, etc.
Solar - hypotheses and theories that explain the emergence of glaciation periods by the rhythmicity of energy processes occurring in the depths of the Sun. As a result of these processes, periodic changes occur in the amount of solar energy reaching the Earth. The duration of these periods is several hundred million years, which is consistent with the periodicity of the Ice Ages.
As a first approximation, the rhythmicity 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 help explain the cyclical nature of climate change and the onset of ice ages on Earth. Such reasons may include flows of radiant energy or flows of particles that cause changes in energy processes both inside the Sun and inside the Earth, clouds of cosmic dust that partially absorb the energy of the Sun, as well as factors still unknown to us. For example, the hypothesis about the possibility of interaction of a neutrino flux with the matter of the earth's interior is of great interest. The coincidence of the period of alternation of ice ages (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 (given 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 gigantic masses of matter rotating at enormous speed from the center of the Galaxy. By the way, the last wave of this shock disturbance, which occurred 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 occurrence 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 more precisely, about the probabilistic course of thermal processes on astrophysical time scales.
Closely related to the problem of predicting the natural course of glaciation on our planet is the problem of artificially changing 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, beyond which changes in the physical-geographical shell that are very undesirable for humanity may occur (flooding of land during the melting of Antarctic and other glaciers, excessive increase in air temperature and thawing of the frozen strata of the Earth) .
What determines the decrease in the average temperature of the Earth?
It has been suggested that the cause is a change in the amount of heat received from the Sun. Above we talked about the 11-year periodicity of solar radiation. There may be longer periods. In this case, cold snaps may be associated with minimum 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 first emphasized the enormous role of carbon dioxide as a temperature regulator of surface layers of air. Carbon dioxide freely transmits the sun's rays to the earth's surface, but absorbs most of the earth's thermal radiation. It is a colossal screen that prevents the cooling of our planet. Currently, the carbon dioxide content in the atmosphere does not exceed 0.03%. If this figure is halved, then average annual temperatures in temperate zones will decrease by 4-5 ° C, which could lead to the onset of an ice age.
The study of modern and ancient volcanic activity allowed volcanologist I.V. Melekestsev associated the cooling and the glaciation that caused 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 volcanic ash material. Huge masses of ash, measured in billions of tons, are ejected by volcanoes into the upper atmosphere and then carried by jet streams throughout the globe. A few days after the Bezymyanny volcano erupted in 1956, its ashes were discovered in the upper troposphere over London. Ash material released 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 by 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 large cloud developments. Increasing cloudiness, in turn, significantly reduces the amount of solar radiation. According to Brooks' calculations, an increase in cloudiness from 50 (typical for the present) to 60% would lead to a decrease in the average annual temperature on the globe by 2 ° C.
In the Cenozoic era, mammals began to be exposed to a special factor that, as far as we know, did not exist in the Cretaceous. This factor is climate cooling. Therefore, to the noted changes that the continents underwent during the Cenozoic era, we must add one more thing - a change in the prevailing climate. The land masses have become colder. The cooling was strongest in the polar regions, the weakest in the equatorial regions, but one way or another it manifested itself everywhere. The influence of this cooling was widespread and affected not only mammals, but also other organisms. Let's start with a review of the data on which we base our conclusion about the temperature changes that have occurred since the beginning of the Cenozoic.
Evidence of climate change. First of all, three groups of facts should be noted.
1. When drilling in the deep-sea regions of the ocean, fossil shells of microscopic invertebrates were found in layers of fine-clastic Cenozoic sediments. In some layers, shells of animals living in cold water; above and below lie layers containing shells of animals characteristic of warmer water.
2. In some layers of fine-clastic sediments that make up the bottom in the deep-sea regions of the ocean around Antarctica, grains of quartz sand are found that bear traces of glacial processing on the surface. These grains were probably carried into the sea with icebergs, from which, as they melted, the sandy material sank to the bottom of the sea. Sand grains of this type have been found in bottom sediments since the Eocene, which indicates the existence of glaciers in Antarctica already at that time. These grains of sand are found in the same layers that contain fossil shells of cold-water invertebrates.
3. Fossil leaves of plants that grew in cold climates were found in some layers of Cenozoic sediments on the continents. Fossil plants characteristic of warmer climates are found in layers both above and below.
Thus, there are three types of data, different, but indicating the same thing: a decrease in temperatures in the Cenozoic, most pronounced in the high latitudes of the southern hemisphere. Based on these and some other data, a curve was constructed (Fig. 62), which shows increases and decreases in temperature during the Cenozoic era. With the exception of the far right portion, the curve is constructed solely based on the information listed above. The curve also shows that the temperature changes were slow and gradual, but by no means constant.
Rice. 62. Estimated pattern of temperature fluctuations on the earth’s surface throughout the Cenozoic to the present day. The curve is inaccurate, as it is given in a generalized form for the entire Earth. It shows the main epochs of rising and falling temperatures. More complete information might have made it possible to highlight the many small fluctuations superimposed on the large ones shown on the curve
Climate fluctuations: ice ages. Climate change has not been permanent. Temperatures fluctuated again and again, from warmer to colder and back to warmer. Cooling appeared first in Antarctica, then in Alaska and other areas of the Far North. But cooling hit the mid-latitudes only about two million years ago, and when it did, the cooling effect was very strong and obvious. At these latitudes, snow accumulated and huge, powerful glaciers formed, covering most of North America and the northern part of Europe. Relatively recent epochs, when huge sheets of ice advanced over areas of mid-latitudes, represent what we are accustomed to calling glacial epochs; that is what they are called in Figure 62. Yet, strictly speaking, in areas such as Antarctica and Alaska, similar ice ages occurred many millions of years earlier than shown in the figure. These ancient ice ages are much less known; they were established only in the 60s of our century, and it is not yet clear how to change the definition of the term "Ice Age" so that it includes these ancient events. However, what is much more important is that within the Quaternary period alone there were several ice ages, perhaps even more than are schematically shown by the winding curve in our diagram.
Last Ice Age. The last ice age was relatively recent. It reached its highest point only 20,000 years ago, when a powerful ice sheet, a huge glacier, occupied almost all of Canada and much of the United States; its edge extended far to the south from the areas of the present cities of New York, Chicago, and Seattle. Another glacier covered the territory of Europe, spreading south to the places where the cities of Copenhagen, Berlin and Leningrad are now located. The total area of glaciers covering North America and Europe exceeded 23 million km 2, and the thickness of the ice was more than one and a half kilometers, so that the ice completely hid almost all the mountains located in the territory occupied by ice. Thus, the volume of glaciers could probably reach 37 million km 3 of ice. Now the total volume of glaciers in the United States (excluding Alaska) is less than 83 km 3. Currently, ice exists in the form of thousands of small mountain glaciers, mostly located in the states of Washington and Oregon. In Canada, the volume of ice is now much larger, supposedly about 41,000 km 3, because Canada is partly in the cold Arctic regions and the ice there takes longer to melt. But even 41,000 km 3 is only a tiny fraction of the volume of ice cover that existed in Canada 20,000 years ago.
When we think about the astonishing amount of ice that so recently covered the earth's surface, two main questions arise. First, was the Ice Age an exceptional phenomenon unique to the Cenozoic era? And secondly, what are the reasons for the occurrence of ice ages? Let's try to answer these questions.
Ancient Ice Ages. So, first, did glaciations occur in earlier geological periods, long before the start of the Cenozoic era? Of course yes. The evidence for this is incomplete, but it is quite definite, and some of this evidence extends over large areas. Evidence of the Permian Ice Age is present on several continents (it is possible that these continents were part of the same land mass at that time), 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, the Early Cambrian time. Even in much older rocks, formed before the Phanerozoic, we find traces left by glaciers and glacial deposits. Some of these footprints are more than two billion years old, perhaps half the age of Earth as a planet. Is it possible to say that there were no even more ancient, still undiscovered ice ages?
In any case, even considering only the glaciations known to us, which occurred over more than two billion years, we must admit that they do not contradict the principle of actualism, according to which - as applied to geological processes - there is nothing new under the Sun. Therefore, the glacial events that occurred 20,000 years ago - or the modern glaciation of Antarctica - are simply a repetition of the same events that have repeated themselves in one form or another for as long as the Earth has existed.
This is the answer to the first of two questions. Glaciation is no more unusual an event than the emergence of a huge mountain range - both are repeated whenever the appropriate conditions are created. This answer makes it easier to understand the second question - why do glaciations occur? All we have to do is identify the “relevant conditions” and then understand what happens when those conditions arise.
Why do glaciations happen?
Basic conditions. The answer to this question can only be given in the light of some general information about glaciers. In many mid-latitude regions, such as the United States and Europe, some of the precipitation falls as snow. Even in the high mountains, snowfall occurs mainly in winter. If winter temperatures are low enough, snow remains on the ground, but as spring and summer arrive, it melts. However, in very high mountains, such as the northern Rocky Mountains, temperatures are so low even in summer that patches of snow cover persist throughout the summer and are covered with freshly fallen snow the following winter. Accumulating in this way year after year, the snow on the mountain slope becomes compacted and is exposed to downward gravity. This impact causes him to slide down the slope. During this sliding process, the compressed snow becomes a glacier. If the snowfall is heavy enough and the temperature is low enough that the snow does not melt, the glacier can take on a tongue-like shape and continue to increase in length, moving down the mountain valley, like a stream of water, but of course much more slowly.
Hundreds of large, blade-shaped ice tongues located next to each other can be seen in mountains such as the Alps. Glaciers in adjacent valleys merge as one valley flows into another. At the base of the mountains, all the ice that slowly moves down the valleys merges, spreading into one continuous sheet of ice. What can stop ice from spreading indefinitely? There is only one, but very significant circumstance - melting. As you descend from the mountains or move to lower latitudes, the temperature rises. And sooner or later, the temperature at the outer edge of the moving glacier rises so much - just so much - that all the ice that is brought there in the form of a slow-moving ice stream melts. From this point on, the edge of the glacier cannot advance any further. True, the ice continues to move, but all incoming ice melts as it arrives and turns into meltwater streams.
These are the conditions for the existence of tongue-shaped glaciers, which tourists usually see in the Alps, Canadian Rockies and other mountainous regions. Such glaciers occupy mountain valleys, and the position of their lower ends is determined by the ratio of the speed of ice flow and the rate of melting. Under current climates, glaciers cannot change significantly. But as soon as the temperature on the Earth’s surface drops even a little, they will all begin to increase in length. If temperatures drop sufficiently, a repeat of the Ice Age will occur, when half of North America was uninhabitable for humans and most animals.
The meaning of what has been said is that the Ice Age is a natural result of a decrease in temperature ( The immediate cause of glaciation is much more complex - it lies in an increase in the amount of solid sediment accumulated on land, which in turn can depend on two different reasons: a decrease in temperature, which reduces melting, and an increase in temperature (the air becomes wetter, precipitation increases). - Approx. edit) on Earth by only a few degrees. The mystery of glaciations is not where the snow and ice come from, but the reason for the decrease in temperature. As long as the principle of actualism remains unshakable and as long as the water cycle continues in nature, snow and ice will always exist in the coldest places on the planet. The Ice Age begins only when temperatures drop so much that precipitation falls as snow over large areas, summers become cool, and ice melt decreases.
This balance is very unstable. And now we are not as far from glaciation as many people think. Calculation data based on long-term weather observations in the mountains of southern Norway, in the ski resort area between Oslo and Bergen, show that a decrease in average annual temperature of just 3°C over a long period would be enough to cause changes in glaciers such that As a result, a new glaciation of Europe will begin. Indeed, much of the ice that spread to its maximum extent in northwestern Europe about 20,000 years ago had its source in snowfall in these mountains of southern Norway. Of course, to this was added the snow that fell over a much larger area of the glacier itself, and, once begun, the glaciation grew like a snowball rolling down the slope.
It is absolutely clear that the condition of the glacier depends mainly on climate. Where temperatures are high enough, there are no glaciers. Where temperatures are low, glaciers form, but the limit of their distribution is the line where the influx of ice is balanced by melting. It follows that the Ice Age, when glaciers are large and numerous, is an era of low temperatures and therefore a time when precipitation occurs in the form of snow. The natural result of this is that the equilibrium line of ice influx and melting shifts to lower latitudes, so that ice covers large areas. After the "peak" of glaciation is reached, as temperatures rise, the critical line shifts back to high latitudes, glaciers shrink and the Ice Age comes to an end.
By now, the peak of the last ice age is far behind us - 20,000 years ago. Most of the ice, which reached a volume of more than 23 million km 3 20,000 years ago, melted and the meltwater flowed into the sea. But even today, 20,000 years after the coldest point, ice persists where high altitudes or cold climates prevent it from melting. Even now, there are still over a thousand glaciers in the United States (not including Alaska) and over 1,200 in the Alps. There is still one large glacier [ice sheet] in Greenland. - Ed.], covering most of the island and having 2,400 kilometers in length and 800 kilometers in width. The volume of the Greenland glacier, which represents the largest ice mass in the northern hemisphere, reaches 3.3 million km 3. All this ice was formed as a result of the fact that snow fell here sometime in the past and has not yet melted.
Turning to the southern hemisphere, we see in the very center of it, just around the South Pole, the continent of Antarctica. Compared to the size of the ice sheet of this continent, the huge block of the Greenland glacier seems insignificant. Its volume is more than 20 million km 3 ( The ice volume of Antarctica is 24 million km3, Greenland - 1 million km3. - Approx. edit), representing more than 90% of all ice on Earth and more than 75% of total fresh water in both liquid and solid form. The Antarctic ice sheet covers almost the entire continent, and its area is almost 1/3 larger than the entire area of the United States, including Alaska. Therefore, it would be fair to assume that in Antarctica, unlike North America, the Ice Age did not end. Ice still almost completely covers this continent, although it is possible that its area was even greater 20,000 years ago. There have been several glaciations in North America, with glaciers coming and going, but as far as we can tell, Antarctica has been continuously covered in ice for at least the last 10 million years. The ice sheet increased or decreased in volume with climate fluctuations, but probably did not disappear completely, unlike the ice sheets of North America and Europe. The reason for this difference is obvious, since Antarctica is the highest continent and has the highest average surface elevations. An even more important circumstance is that it is located at the South Pole, where temperatures are constantly very low. All precipitation falls here in the form of snow and does not melt. Therefore, once formed, ice persists not only throughout the year, but also for millions of years. It slides down towards the outer edge of the continent it covers, like a huge mass of dough in a frying pan. When the ice reached the shore and descended into the ocean, blocks broke off to form large, flat-topped icebergs. Several icebergs measured turned out to be huge. One iceberg was twice the size of the state of Connecticut. Having turned into an iceberg floating in the sea, the ice gradually melts, but the movement of ice along the surface of the continent towards the sea occurs continuously.
Ripple. To summarize the basic conditions necessary for the formation of glaciers, we note that this requires only that the land be located at sufficient altitudes or at sufficiently high latitudes to ensure such low temperatures that the snow there does not melt throughout the year. As we have seen, hills are formed by the movement of crustal plates and the collision of continents. From time to time, high mountains are formed, but such movements occur very slowly. The measured speed of movement of the crustal plates is on the order of several centimeters per year. If plate movements and the formation of new mountains were the only causes of glaciations, then the glaciation could not (as it actually did) end in just 20,000 years or less. If everything were explained by the movements of the crustal plates, then nothing would prevent a glacier, once formed and spread over most of the continent, from persisting for millions of years until the mountains were gradually lowered by erosion or until the continent, floating along with the crustal plate, slowly transported to warmer latitudes where the ice cover could melt.
Glaciations, at least those that occurred in the middle latitudes, began and ended much more quickly than would have been the case if they had been caused by the slow and inflexible process of continental movement. The changes took place not over millions, but over thousands of years. Thanks to numerous radiocarbon dates, it has become possible to construct an approximate, but fairly reliable chronological scale, reproducing the melting process of the huge mass of ice that occupied most of North America only 20,000 years ago. The process of glacier destruction began approximately 15,000 years ago and ended approximately 6,000 years ago. In other words, the melting of this entire huge ice sheet took only about 9,000 years (Fig. 63). At the same time, about 37 million km 3 of ice was turned into water, which flowed into the nearest rivers and through them into the ocean.
Not only did this process last only 9,000 years, but in the initial stages its progress was interrupted several times by periods when the thickness of the ice increased and it advanced again, and then its contraction began again. Such periods occurred in Europe, North America and New Zealand at approximately the same time. Hence the obvious conclusion is that there is another cause of climate change, which acts quickly and manifests itself simultaneously throughout the world and does not depend on mountain building and the movement of the Earth’s crustal plates.
Rice. 63. Pattern of melting of North American glaciers at the end of the last ice age (mainly based on data from the Geological Survey of Canada). A. North America 20,000-15,000 years ago
Rice. 63. Pattern of melting of North American glaciers at the end of the last ice age (mainly based on data from the Geological Survey of Canada). B. About 12,000-10,000 years ago
Rice. 63. Pattern of melting of North American glaciers at the end of the last ice age (mainly based on data from the Geological Survey of Canada). B. About 9000 years ago
Rice. 63. Pattern of melting of North American glaciers at the end of the last ice age (mainly based on data from the Geological Survey of Canada). D. About 7000 years ago
Many attempts have been made to establish this cause and several hypotheses have been proposed, but none of them is generally accepted among scientists studying this problem. We will have to be content with one hypothesis that explains the facts, although it has not yet been proven. This theory suggests that the amount of thermal energy the Earth receives from the Sun varies by slowly pulsing, causing temperatures to constantly fluctuate within small ranges. The idea is simple enough, but we don't yet have the means to prove it right or wrong. Accepting this hypothesis for lack of a better one, we can argue that during the predominance of lowlands and vast seas (say, in the Cretaceous period) there could have been very few glaciers on Earth (or none at all), and, therefore, the supposed slow pulsations of thermal energy arriving at the Earth's surface could have only a weak effect on the climate. But at that time (let’s say, in the Cenozoic), when there were highlands and numerous mountainous regions, and a significant part of the continents’ area was located at fairly high latitudes, many glaciers could exist on the highlands. In this case, a pulsation that lowered the temperature even slightly could lead to a catastrophic increase in the area of glaciers. Conversely, a small increase in temperature could have the opposite, but equally catastrophic, result. We can't say more for now.
Impact of glaciers on the Earth's surface
Glacial erosion. Mapping ancient glaciers is possible mainly because moving ice leaves visible traces on the surface over which it moves. Ice scrapes, polishes, and in various other ways erodes the surface, and then it deposits the products of rock destruction. As a result, one can often see how loose glacial deposits lie on the glacier-eroded surface, separated from it by a sharp boundary. Both the rock surface and the sediments lying on it bear distinct, in most cases easily recognizable, traces of the former presence of the glacier.
Rock fragments of various sizes, picked up by moving ice, freeze into the lower surface of the ice and, like sand particles on sandpaper, scrape and scratch the rocky surface, leaving on the glacier bed many intermittent grooves and scratches (photo 51), which do not at all look like tracks, left by water streams. In some places, entire blocks of rock are separated along cracks from the bedrock and carried away by the glacier, increasing the amount of debris frozen into the base of the glacier.
Photo 51. Glacial streaks and scratches on the surface of sandstones. The debris was left by a glacier that moved in the direction away from the camera.
Glacial accumulation. Rock fragments included in the ice are carried by it and deposited along the path of the glacier, forming a layer of sediments, which in places, closer to the edge of the glacier, can reach significant thickness. Since ice is a solid body, the deposition of debris by ice occurs very differently than by a river. In a river, particles are deposited according to their size. The deposition of clastic material at the base of the glacier occurs in the same order as during transport, that is, without any sorting, coarse particles mixed with fine ones, boulders next to silt particles (photo 52). The resulting sediment often looks like a pile of soil that has been shoveled by a bulldozer. In addition, unlike rounded river pebbles, which are turned over and rolled around by the flow, rock fragments in glacial deposits retain an irregular shape and have flat edges formed by friction against the rocky surface of a fragment frozen into the base of the glacier (photo 53).
Photo 52. Clastic deposits of the last glaciation, consisting of unrounded rock fragments of various sizes, unsorted and unlayered. These features distinguish them from aquatic sediments. The ice ax handle is 45 cm long. North slope of Mount Rainier, Washington State
In some places along and near the outer edge of the glacier, deposited debris is moved by water as the glacier melts. In such places, this material loses its typical glacial character and acquires sorting and layering as a result of processing by flowing waters. In this case, a series of layered deposits randomly alternate with layers of non-layered material.
Photo 53. Six pebbles randomly selected from glacial deposits in New York State. Each pebble has one or more flat edges smoothed by a glacier
But whether they contain layered material or not, in general glacial deposits tend to form large or small ridges along the edge of the glacier. Such a ridge represents a terminal moraine, a characteristic shape created by glaciation. In some areas there are several moraines located one after the other, each of which records the position of the edge of the glacier at the time of its deposition.
Streams of meltwater flowing from the edge of the glacier, marked by a terminal moraine, deposited pebbles and sand in their valleys, sorted and layered like real river deposits. Some of these deposits are 30 meters thick or more, and extend across the entire width of the valley. Many sand-pebble deposits along the Ohio or Mississippi River valleys, which can be traced along the Mississippi Valley to the delta, are of glacial origin. And yet, despite the large volume of these deposits, even if we add to them the glacial deposits common within the glacial boundaries further north, the total thickness of the layer of weathering products and bedrock removed by the huge ice sheets that once covered North America and Europe turns out to be surprisingly small. We don’t know exactly, but we can assume that on average the thickness of this layer is probably no more than 7.5 meters.
Lake depressions. A more obvious result of the influence of the glacier, and in particular the great ice sheets, on the relief was the formation of large and small depressions, many of which filled with water and became lakes. Any good large-scale map of Canada, the United States or Northern Europe will show that most lakes are concentrated in areas of ancient glaciation. In North America alone, the number of lakes is in the hundreds of thousands.
Depressions are created by a glacier in several ways. Some are formed as a result of partial removal of fractured bedrock by moving ice. Others are depressions in the uneven surface of glacial deposits. Still others are river valleys dammed by glacial deposits. (The Great Lakes of America have this origin, at least in part.) Many small depressions were formed by the melting of blocks of ice ranging in size from several meters to tens of kilometers in diameter, which were buried under glacial sediments. When such a block melts, a depression is formed into which the sediments previously lying on the ice sink. Among the many thousands of lakes in Minnesota, many are of this origin.
Weaker climate fluctuations
Climate after 1800 Temperature measurements taken by government agencies in most countries show changes in temperatures since the early 19th century. In the very general view these changes are shown in the curve of Figure 64. It indicates that over the past hundred years, average annual temperatures have increased by more than half a degree Celsius, and this increase has been uneven. It affected most of the planet, both tropical and high latitudes, both the northern and southern hemispheres. Then, after 1940, a period of cooling began. Temperatures dropped, and by 1970 they had reached the level observed around 1920. Thus, the fact is established that the Earth's climates are not something constant and unchanging, but are subject to significant changes. The warm winters and hot summers experienced in the western United States during the 1930s appear to be part of a general warming of the climate that was occurring on a large scale.
It is not surprising that the record of fluctuations in the size of small glaciers in the mountains of North America and the Alps shows similarities with the temperature curve (Fig. 64). Measurements taken on the same glaciers over a number of years show that between late XIX V. and the middle of the 20th century. many glaciers have shrunk overall. But starting around 1950, some glaciers began to grow again. Their regime reflects a change in trend, which is established by the temperature curve, but too little time has passed to judge whether the direction of development of glaciers has changed.
Rice. 64. Temperature fluctuation curve (average for periods of five years)
Climate over the last 1000 years. Temperature measurements with a thermometer began only shortly before the beginning of the 18th century, but a general idea of temperature variations on a large scale in Europe, as well as in Japan, over the last thousand years can be obtained using various indirect methods. Various data show that from approximately the 11th to the 13th centuries. the climate was warmer than at any time since then. This was the "Viking period" - a time when summers were so warm and dry and when the northern seas were so free from floating ice that the Norwegians could sail everywhere in small boats. They even founded colonies in southern Greenland with a population of 3,000 people or more, trading agricultural products with Europe. However, after approximately 1500, trade ceased and communication with Europe was almost interrupted. The colonies found themselves isolated, and in the 18th century. the ship that arrived there did not find the descendants of the settlers of this once prosperous colony.
Conducted in the 20th century. Archaeological studies of one hundred burials in a cemetery in one of the colonies have helped to reconstruct part of the later history of the colony. The ground at the burial site was frozen, as is now the case in most Arctic regions, although it is obvious that it was not frozen at the time the burial took place. The remains belonged to young people, indicating a short life expectancy, short stature, which, combined with skeletal deformation and unusually severely decayed teeth, suggests poor nutrition. It is likely that these people died from disease, hunger and other causes that were the result of a long, gradual deterioration of the climate.
After the "Viking period" and until the 17th century. A general decrease in temperature was felt throughout Europe. In Norway and the Alps, residents of mountain villages were forced to retreat in the face of advancing glaciers. The lower limit of tree vegetation in the Alps gradually decreased, crops stopped producing and vineyards in the mountains of Germany were abandoned. Winters have become longer and colder. Anyone who has looked closely at 17th-century Dutch landscapes will remember that many of them depict winter scenes of people skating on frozen canals. You don't see this often these days.
To summarize, the record of climate change over the past thousand years includes both an early “Viking period” that was warmer than today, and a later cold period that was colder than today. Warming at the beginning of this century marked the end of this very cold period. In general, the data presented confirm climate variability.
Last 10,000 years. In Sweden, Finland and other northern countries, vegetation is distributed in clearly defined zones, which are mainly determined by temperature (remember Fig. 35). The territory of these countries is dotted with lake depressions created by the great glaciers of the past, as described above. Almost all of the depressions are younger than 15,000 years old, and many are younger than 10,000 years old (Fig. 63). Some lakes were completely filled with sediment, mainly plant remains in the form of peat, and turned into swamps. Others, although still lakes, are gradually filling with peat. The sediments include not only plant stems and leaves, but also large amounts of pollen from plants growing around the lake.
Scientists assumed that by drilling into the peat deposits that filled a swamp or lake and identifying the plants found in each layer, they would be able to reconstruct in detail the succession of vegetation that surrounded the lake (Fig. 65). The change in vegetation composition from one layer to another would reflect climate change that began with the melting of the glacier. They expected that the vegetation would vary from tundra in the lower horizons (represented by arctic grasses and shrubs that grew near the glacier) to modern woody vegetation in the upper part of the section.
Rice. 65. A swamp occupying a depression in glacial deposits, in which pollen from plants growing in the surrounding area is deposited annually. Gradually, layers of fallen leaves, stems and other plant debris accumulate in it, forming peat
After doing this experiment, scientists discovered and identified fossil plants (mainly by pollen), but were surprised by the change in vegetation from bottom to top. The vegetation changed from tundra to spruce and fir forests, then to birch and pine forests and then to oak, beech, alder and hazel, thus showing a gradual warming. But higher up, in the upper layers, these plants were again replaced by birch and pine, which mainly grow here at the present time. Oak, beech and hazel now grow much further south. However, radiocarbon dating of a layer containing oak, beech and hazel shows that this layer was formed about 5,000 years ago.
In this case, it is obvious that the warmest climate was about 5000 years ago (3000 BC). At this time, average temperatures were higher than modern ones (at the same points) by approximately 1 ° C. Then the trend of climate change changed to the opposite, the climate became wetter and the sky was cold, the oak trees surrounding the swamp died and were replaced by birch and pine. Thus we have another reliable evidence of climate fluctuations; Instead of becoming gradually warmer since the glaciers began to melt during the Great Ice Age, the climate 5,000 years ago became drier and warmer than it is today. At that time, glaciers in the Alps and Rocky Mountains were less numerous and smaller. Many of the modern glaciers began to form less than 5,000 years ago and thus represent "modern" glaciers rather than remnants of glaciers from the last ice age ( Changes in climate and the size of glaciers occur continuously. Cooling and increase in glaciers occurred in the 18th - early XIX centuries (“Little Ice Age”), in the 40-60s of the 19th century. (minor), warming in the 1920s-1940s, in the 1970s (minor). - Approx. edit).
Future
Scientists who study the history of climate are often asked two questions. The first of them: “Will there be a new glaciation?”, and the second: “If there is, then when?” The easiest way to answer the first question. Most scientists agree to say, "Yes, probably," because several glaciations have already occurred in the last two million years, and the main conditions necessary for glaciation to occur are rising land mass, numerous mountains, and the presence of a vast ice sheet at the South Pole - still exist.
The answer to the second question will be much less clear. The information we have about climates is still not accurate enough to judge whether there is a clear pattern in the frequency of glaciations. If we knew that such a pattern existed, and could measure the intervals between glaciations of the past, then we could predict what the climate of the future holds for us. Perhaps such a prediction will become possible in the future, but at present it is impossible.
Literature
Flint R. F. 1971, Glacial and Quaternary geology: John Wiley & Sons, New York. There is a Russian translation: Flint RF., Glaciers and paleogeography of the Pleistocene, M., IL, 1963.
Hovgaard William, 1925, The Norsemen in Greenland: "Georg. Rev.", v. 15, p. 605-616.
Lamb H. H., 1965, The early medieval warm epoch and its sequel: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 1, p. 13-37.
Pjst Austin, LaChapelle E. R., 1971, Glacier ice: The Mountaineers: University of Washington Press, Seattle.
Schwarzbach Martin, 1963, Climates of the past: D. Van Nostrand Company, Princeton, N.J. There is a Russian translation: Schwarzbach M., Climates of the past, M., IL, 1955.