The Pleistocene Epoch began about 2.6 million years ago and ended 11,700 years ago. At the end of this era passed the last to date ice Age when glaciers covered vast areas of the Earth's continents. There have been at least five documented major ice ages since the Earth began forming 4.6 billion years ago. The Pleistocene is the first epoch in which the Homo sapiens: by the end of the era, people settled almost all over the planet. What was the last ice age?
It was during the Pleistocene period that the continents settled down on Earth in the way we are used to. At some point in the ice age, layers of ice covered all of Antarctica, most of Europe, northern and South America, as well as small areas of Asia. AT North America they extended over Greenland and Canada and parts of the northern United States. Remains of glaciers from this period can still be seen in parts of the world, including Greenland and Antarctica. But the glaciers didn't just "stand still". Scientists note about 20 cycles, when glaciers advanced and retreated, when they melted and grew again.
In general, the climate then was much colder and drier than today. Because most of the water on the Earth's surface was frozen, there was little rainfall—about half what it is today. During peak periods, when most of the water was frozen, global average temperatures were 5 to 10°C below today's temperature norms. However, winter and summer still succeeded each other. True, in those summer money you would not have been able to sunbathe.
While Homo sapiens, in the dire situation of perpetual cold temperatures, began to develop brains to survive, many vertebrates, especially large mammals, also courageously endured severe climatic conditions this period. In addition to the well-known woolly mammoths, during this period, saber-toothed cats, giant ground sloths and mastodons. Although many vertebrates died out during this period, during those years, mammals lived on Earth that can still be found today: including monkeys, cattle, deer, rabbits, kangaroos, bears, and members of the canine and feline families.
Dinosaurs, apart from a few early birds, did not exist during the Ice Age: they became extinct at the end of the Cretaceous period, more than 60 million years before the start of the Pleistocene epoch. But the birds themselves at that time felt good, including relatives of ducks, geese, hawks and eagles. The birds had to compete with mammals and other creatures for limited supplies of food and water, since much of it was frozen. Also during the Pleistocene lived crocodiles, lizards, turtles, pythons and other reptiles.
The vegetation was worse: in many areas it was difficult to find dense forests. More common were individual coniferous trees, such as pines, cypresses and yews, as well as some broad-leaved trees such as beeches and oaks.
Unfortunately, about 13,000 years ago, more than three-quarters of the large animals of the Ice Age, including woolly mammoths, mastodons, saber-toothed tigers and giant bears have become extinct. Scientists have been arguing for many years about the reasons for their disappearance. There are two main hypotheses: human ingenuity and climate change, but neither can explain the extinction on a planetary scale.
Some researchers believe that here, as with dinosaurs, there was some extraterrestrial interference: recent studies show that an extraterrestrial object, possibly a comet about 3-4 kilometers wide, could explode over southern Canada, almost destroying the ancient culture of the Stone Age, and also megafauna like mammoths and mastodons.
Sourced from Livescience.com
The oldest glacial deposits known today are about 2.3 billion years old, which corresponds to the lower Proterozoic of the geochronological scale.
They are represented by petrified basic moraines of the Gouganda Formation in the southeast of the Canadian Shield. The presence in them of typical iron-shaped and tear-shaped boulders with lapping, as well as their occurrence on a bed covered with hatching, testifies to their glacial origin. If the main moraine in the English-language literature is denoted by the term till, then the older glacial deposits that have passed the stage lithification(petrifications), commonly referred to as tillites. The deposits of the Bruce and Ramsey Lake formations, also of Lower Proterozoic age and developed on the Canadian Shield, also have the appearance of tillites. This powerful and complex complex of alternating glacial and interglacial deposits is conditionally assigned to one ice age, called the Huronian.
The deposits of the Bijawar series in India, the Transvaal and Witwatersrand series in South Africa and the Whitewater series in Australia. Consequently, there is reason to speak of the planetary scale of the Lower Proterozoic glaciation.
With the further development of the Earth, it experienced several equally large ice epochs, and the closer to the present they took place, the greater the amount of data on their features we have. After the Huron era, the Gneissic (about 950 million years ago), Sturtian (700, possibly 800 million years ago), Varangian, or, according to other authors, Vendian, Laplandian (680-650 million years ago), then Ordovician (450-430 million years ago) and, finally, the most widely known late Paleozoic Gondwanan (330-250 million years ago) ice ages. Somewhat apart in this list is the Late Cenozoic glacial stage, which began 20-25 million years ago, with the advent of the Antarctic ice sheet and, strictly speaking, continues to this day.
According to the Soviet geologist N. M. Chumakov, traces of the Vendian (Lapland) glaciation have been found in Africa, Kazakhstan, China, and Europe. For example, in the basin of the middle and upper Dnieper, boreholes uncovered layers of tillites several meters thick dating back to this time. According to the direction of ice movement, reconstructed for the Vendian era, it can be assumed that the center of the European ice sheet at that time was somewhere in the area of the Baltic Shield.
The Gondwanan Ice Age has attracted the attention of specialists for almost a century. At the end of the last century, geologists discovered in southern Africa, near the Boer settlement of Neutgedaht, that in the basin of the river. Vaal, well-pronounced glacial pavements with traces of shading on the surface of gently convex “ram foreheads” composed of Precambrian rocks. It was a time of struggle between the theory of drift and the theory of sheet glaciation, and the main attention of researchers was riveted not to age, but to signs of the glacial origin of these formations. The glacial scars of Neutgedacht, "curly rocks" and "ram's foreheads" were so well expressed that A. Wallace, who studied them in 1880, considered them to belong to the last ice age.
Somewhat later, the Late Paleozoic age of glaciation was established. Glacial deposits have been discovered under carbonaceous shales with remains of plants from the Carboniferous and Permian periods. In the geological literature, this sequence is called the Dvaika series. At the beginning of our century, the well-known German specialist in modern and ancient glaciation Alp A. Penk, who personally convinced himself of the amazing similarity of these deposits with young Alpine moraines, was able to convince many of his colleagues of this. By the way, it was Penk who proposed the term "tillite".
Permocarbon glacial deposits have been found on all continents of the Southern Hemisphere. These are Talchir tillites, discovered in India as early as 1859, Itarare in South America, Kuttung and Kamilaron in Australia. Traces of Gondwanan glaciation have also been found on the sixth continent, in the Transantarctic Mountains and the Ellsworth Mountains. Traces of synchronous glaciation of all these territories (with the exception of the then unexplored Antarctica) served as an argument for the outstanding German scientist A. Wegener in putting forward the hypothesis of continental drift (1912-1915). His rather few predecessors pointed to the similarity of the outlines of the western coast of Africa and the eastern coast of South America, which resemble, as it were, parts of a single whole torn in two and separated from each other.
The similarity of the Late Paleozoic flora and fauna of these continents, the commonality of their geological structure, was repeatedly pointed out. But it was precisely the idea of the simultaneous and, probably, a single glaciation of all the continents of the Southern Hemisphere that forced Wegener to put forward the concept of Pangea - the great pro-continent, split into parts, which then began to drift around the globe.
By modern ideas, the southern part of Pangea, called Gondwana, broke up about 150-130 million years ago, in the Jurassic and early Cretaceous. The modern theory of global plate tectonics, which grew out of A. Wegener's conjecture, makes it possible to successfully explain all the facts known to date about the Late Paleozoic glaciation of the Earth. Probably, the South Pole at that time was close to the middle of Gondwana and its significant part was covered with a huge ice shell. A detailed facies and textural study of tillites suggests that its feeding area was in East Antarctica and, possibly, somewhere in the Madagascar region. It has been established, in particular, that when the contours of Africa and South America are combined, the direction of the glacial hatching on both continents coincides. Together with other lithological materials, this indicates the movement of Gondwanan ice from Africa to South America. Some other large glacial flows that existed during this ice age have also been restored.
The glaciation of Gondwana ended in the Permian period, when the parent continent still retained its integrity. Perhaps this was due to the migration of the South Pole in the direction Pacific Ocean. Since then, global temperatures have continued to rise gradually.
The Triassic, Jurassic and Cretaceous periods of the geological history of the Earth were characterized by fairly even and warm climatic conditions over most of the planet. But in the second half of the Cenozoic, about 20-25 million years ago, the ice again began its slow advance at the South Pole. By this time, Antarctica occupied a position close to modern. The movement of fragments of Gondwana led to the fact that there were no significant areas of land near the southern polar continent. As a result, according to the American geologist J. Kennett, a cold circumpolar current arose in the ocean surrounding Antarctica, which further contributed to the isolation of this continent and the deterioration of its climatic conditions. Near the South Pole of the planet began to accumulate ice of the most ancient glaciation of the Earth that has survived to this day.
In the Northern Hemisphere, the first signs of the Late Cenozoic glaciation, according to various experts, are 5 to 3 million years old. There is no need to talk about any noticeable shifts in the position of the continents over such a short period of time by geological standards. Therefore, the cause of the new ice age should be sought in the global restructuring energy balance and climate of the planet.
The Alps are a classic area, on the example of which the history of the ice ages of Europe and the entire Northern Hemisphere has been studied for decades. Proximity to the Atlantic Ocean and mediterranean sea ensured a good supply of moisture to the alpine glaciers, and they sensitively reacted to climate cooling by a sharp increase in their volume. At the beginning of the XX century. A. Penk, having studied the geomorphological structure of the Alpine foothills, came to the conclusion about four major ice ages experienced by the Alps in the recent geological past. These glaciations have received the following names (from the oldest to the youngest): gunz, mindel, riss and wurm. Their absolute age remained unclear for a long time.
Around the same time, information began to come in from various sources that the flat territories of Europe had repeatedly experienced the onset of ice. As the actual material of the position is accumulated polyglacialism(the concept of multiple glaciations) became stronger and stronger. By the 60s. of our century, the scheme of fourfold glaciation of the European plains, close to the Alpine scheme of A. Penk and his co-author E. Brückner, has received wide recognition in our country and abroad.
Naturally, the deposits of the last ice sheet, comparable with the Wurm glaciation of the Alps, turned out to be the most well studied. In the USSR, it was called Valdai, in Central Europe - Vistula, in England - Devensian, in the USA - Wisconsin. The Valdai glaciation was preceded by an interglacial period, which, in terms of its climatic parameters, is close to modern conditions or slightly more favorable. According to the name of the reference size, in which deposits of this interglacial period (the village of Mikulino, Smolensk region) were discovered, in the USSR it was called Mikulinsky. According to the Alpine scheme, this period of time is called the Riess-Würm interglacial.
Before the beginning of the Mikulin interglacial age, the Russian Plain was covered with ice of the Moscow glaciation, which, in turn, was preceded by the Roslavl interglacial. The next step down was the Dnieper glaciation. It is considered to be the largest in size and is traditionally associated with the Ice Age of the Alps. Before the Dnieper Ice Age, warm and humid conditions of the Likhvinian interglacial existed in Europe and America. The deposits of the Likhvinian era are underlain by rather poorly preserved sediments of the Oksky (Mindelian according to the Alpine scheme) glaciation. The Dook warm time is considered by some researchers to be no longer an interglacial, but a preglacial epoch. But in the last 10-15 years there are more and more reports of new, older glacial deposits that have been uncovered at various points in the Northern Hemisphere.
Synchronization and linkage of the stages of development of nature, restored according to various initial data and in different ways geographic location points the globe is a very serious problem.
The fact of the regular alternation of glacial and interglacial epochs in the past, few of the researchers today raises doubts. But the reasons for this alternation have not yet been fully elucidated. The solution of this problem is hampered primarily by the lack of strictly reliable data on the rhythm of natural events: the stratigraphic scale of the Ice Age itself causes a large number of criticisms, and so far there is no reliably verified version of it.
Only the history of the last glacial-interglacial cycle, which began after the degradation of the ice of the Rice glaciation, can be considered relatively reliably established.
The age of the rice ice age is estimated at 250-150 thousand years. The Mikulin (Riess-Würm) interglacial that followed it reached its optimum about 100 thousand years ago. Approximately 80-70 thousand years ago, a sharp deterioration in climatic conditions was recorded throughout the globe, marking the transition to the Wurm glacial cycle. During this period, in Eurasia and North America, broadleaf forests, giving way to the landscape of the cold steppe and forest-steppe, there is a rapid change of faunal complexes: they are dominated by cold-tolerant species - mammoth, hairy rhinoceros, giant deer, arctic fox, lemming. At high latitudes, old ice caps increase in volume and new ones grow. The water necessary for their formation decreases from the ocean. Accordingly, its level begins to decrease, which is recorded along the stairs of sea terraces in the now flooded areas of the shelf and on the islands of the tropical zone. The cooling of ocean waters is reflected in the restructuring of complexes of marine microorganisms - for example, die out foraminifera Globorotalia menardii flexuosa. The question of how far progress was made at this time continental ice while still debatable.
Between 50 and 25 thousand years ago, the natural situation on the planet again improved somewhat - a relatively warm Middle Würmian interval set in. I. I. Krasnov, A. I. Moskvitin, L. R. Serebryanny, A. V. Raukas and some other Soviet researchers, although in the details of their construction they differ quite significantly from each other, they still tend to compare this period of time with an independent interglacial.
However, this approach is contradicted by the data of V.P. Grichuk, L.N. Voznyachuk, N.S. grounds for distinguishing the Middle Würmian interglacial epoch. From their point of view, the early and middle Wurm corresponds to a prolonged period of transition from the Mikulin interglacial to the Valdai (Late Wurm) glaciation.
In all likelihood, this controversial issue will be resolved in the near future due to the increasing use of radiocarbon dating methods.
About 25 thousand years ago (according to some scientists, a little earlier) the last continental glaciation of the Northern Hemisphere began. According to A. A. Velichko, this was the time of the most severe climatic conditions for the entire ice age. An interesting paradox: the coldest climatic cycle, the late Cenozoic thermal minimum, was accompanied by the smallest glaciation in terms of area. Moreover, in terms of duration, this glaciation was very short: having reached the maximum limits of its distribution 20-17 thousand years ago, it disappeared already after 10 thousand years. More precisely, according to the data summarized by the French scientist P. Bellaire, the last fragments of the European ice sheet broke up in Scandinavia between 8 and 9 thousand years ago, and the American ice sheet completely melted only about 6 thousand years ago.
The peculiar nature of the last continental glaciation was determined by nothing more than excessively cold climatic conditions. According to paleofloristic analysis data, summarized by the Dutch researcher Van der Hammen et al., the average July temperatures in Europe (Holland) at that time did not exceed 5°C. Average annual temperatures in temperate latitudes have decreased by about 10°C compared to modern conditions.
Oddly enough, excessive cold prevented the development of glaciation. Firstly, it increased the rigidity of the ice and, therefore, made it difficult for it to spread. Secondly, and most importantly, the cold bound the surface of the oceans, forming an ice cover on them, descending from the pole almost to the subtropics. According to A. A. Velichko, in the Northern Hemisphere its area was more than 2 times larger than the area of modern sea ice. As a result, evaporation from the surface of the World Ocean and, accordingly, the moisture supply of glaciers on land has sharply decreased. At the same time, the reflectivity of the planet as a whole increased, which further contributed to its cooling.
The European ice sheet had a particularly meager diet. The glaciation of America, fed from the unfrozen parts of the Pacific and Atlantic oceans, was in much more favorable conditions. This was due to its significantly large area. In Europe, the glaciers of this era reached 52°N. sh., while on the American continent they descended 12 ° to the south.
An analysis of the history of the Late Cenozoic glaciations in the Northern Hemisphere of the Earth allowed specialists to draw two important conclusions:
1. Glacial epochs have been repeated many times in the recent geological past. Over the past 1.5-2 million years, the Earth has experienced at least 6-8 major glaciations. This indicates the rhythmic nature of climate fluctuations in the past.
2. Along with rhythmic and oscillatory climate changes, there is a clear trend towards directed cooling. In other words, each subsequent interglacial is cooler than the previous one, and the ice ages become more severe.
These conclusions concern only natural patterns and do not take into account the significant technogenic impact on the environment.
Naturally, the question arises as to what prospects this development of events promises for mankind. The mechanical extrapolation of the curve of natural processes into the future leads us to expect the beginning of a new ice age within the next few millennia. It is possible that such a deliberately simplified approach to making a forecast will turn out to be correct. Indeed, the rhythm of climate fluctuations is getting shorter and shorter, and the modern interglacial epoch should soon come to an end. This is also confirmed by the fact that the climatic optimum (the most favorable climatic conditions) of the postglacial period has long since passed. In Europe, the best natural conditions took place 5-6 thousand years ago, in Asia, according to the Soviet paleogeographer N. A. Khotinsky, even earlier. At first glance, there is every reason to believe that the climate curve is descending towards a new glaciation.
However, it is far from being that simple. In order to seriously judge the future state of nature, it is not enough to know the main stages of its development in the past. It is necessary to find out the mechanism that determines the alternation and change of these stages. By itself, the curve of temperature changes cannot serve as an argument in this case. Where is the guarantee that tomorrow the spiral will not begin to unwind in opposite side? And in general, can we be sure that the alternation of glaciations and interglacial periods reflects some kind of uniform pattern in the development of nature? It is possible that each glaciation separately had its own independent cause, and, therefore, there are no grounds for extrapolating the generalizing curve into the future ... This assumption looks unlikely, but it must be kept in mind.
The question of the causes of glaciation arose almost simultaneously with the glacial theory itself. But if the factual and empirical part of this area of science has made tremendous progress over the past 100 years, then the theoretical understanding of the results obtained, unfortunately, went mainly in the direction of a quantitative addition of ideas explaining such a development of nature. Therefore, there is currently no generally accepted scientific theory this process. Accordingly, there is no single point of view on the principles for compiling a long-term geographical forecast. In the scientific literature, one can find several descriptions of hypothetical mechanisms that determine the course of global climate fluctuations. As new material about the Earth's glacial past is accumulated, a significant part of the assumptions about the causes of glaciation is discarded and only the most acceptable options remain. Probably, among them the final solution of the problem should be sought. Paleogeographic and paleoglaciological studies, although they do not give a direct answer to the questions of interest to us, nevertheless serve as practically the only key to understanding natural processes on a global scale. This is their enduring scientific significance.
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Hello readers! I have prepared a new article for you. I would like to talk about the ice age on Earth.Let's figure out how these ice ages come, what are the causes and consequences ...
Imagine for a moment that the cold fettered our planet, and the landscape turned into icy desert(more about deserts), over which ferocious northern winds. Our Earth looked like this during the ice age - from 1.7 million to 10,000 years ago.
About the process of formation of the Earth keeps memories of almost every corner of the globe. Hills running like a wave beyond the horizon, mountains touching the sky, a stone that was taken by man to build cities - each of them has his own story.
These clues, in the course of geological research, can tell us about a climate (about climate change) that was significantly different from today.
Our world was once bound by a thick sheet of ice that carved its way from the frozen poles to the equator.
Earth was a gloomy and gray planet in the grip of cold, carried by snowstorms from the north and south.
From the nature of the glacial deposits (deposited clastic material) and the surfaces worn away by the glacier, geologists concluded that in fact there were several periods.
Even in the Precambrian period, about 2300 million years ago, the first ice age began, and the last, and best studied, took place between 1.7 million years ago and 10,000 years ago in the so-called. Pleistocene epoch. It is simply called the Ice Age.
These ruthless clutches were avoided by some lands, where it was usually also cold, but winter did not reign on the whole Earth.
Vast areas of deserts and tropical forests were located in the region of the equator. For the survival of many species of plants, reptiles and mammals, these warm oases played a significant role.
In general, the climate of the glacier was not always cold. Glaciers, before receding, crawled several times from north to south.
In some parts of the planet, the weather between ice advances was even warmer than today. For example, the climate in southern England was almost tropical.
Paleontologists, thanks to the fossilized remains, claim that elephants and hippos once roamed the banks of the Thames.
Such periods of thaw - also known as interglacial stages - lasted several hundred thousand years until the cold returned.
Ice streams moving south again left behind destruction, thanks to which geologists can accurately determine their path.
On the body of the Earth, the movement of these large masses of ice left "scars" of two types: sedimentation and erosion.
When a moving mass of ice wears away the soil along its path, erosion occurs. Entire valleys in the bedrock were hollowed out by rock fragments brought by the glacier.
Like a gigantic grinding machine that polished the ground beneath it and created large furrows called glacial shading, the movement of crushed stone and ice acted.
The valleys widened and deepened over time, acquiring a distinct U-shape.
When a glacier (about what glaciers are) dumped the rock fragments that it carried, deposits formed. This usually happened when the ice melted, leaving piles of coarse gravel, fine-grained clay and huge boulders scattered over a vast area.
What is called glaciation, scientists still do not know exactly. Some believe that the temperature at the Earth's poles, for the past millions of years, is lower than at any time in the history of the Earth.
Continental drift (more on continental drift) could be the cause. About 300 million million years ago there was only one giant supercontinent - Pangea.
The split of this supercontinent occurred gradually, and as a result, the movement of the continents left the Arctic Ocean almost completely surrounded by land.
Therefore, now, unlike in the past, there is only a slight mixing of the waters of the Arctic Ocean with warm waters to the south.
It comes down to this situation: the ocean never warms up well in summer, and is constantly covered with ice.
Antarctica is located at the South Pole (more about this continent), which is very far from warm currents, which is why the mainland sleeps under the ice.
There are other reasons for global cooling. According to assumptions, one of the reasons is the degree of inclination of the earth's axis, which is constantly changing. Together with the irregular shape of the orbit, this means that the Earth is further from the Sun at some periods than at others.
And if the amount of solar heat changes even by a percentage, this can lead to a difference in temperature on Earth by a whole degree.
The interaction of these factors will be enough to start a new ice age. It is also believed that the ice age may cause the accumulation of dust in the atmosphere as a result of its pollution.
Some scientists believe that when a giant meteor collided with the Earth, the age of dinosaurs ended. This led to the fact that a huge cloud of dust and dirt rose into the air.
Such a catastrophe could block the receipt of the rays of the Sun (more about the Sun) through the atmosphere (more about the atmosphere) of the Earth and cause it to freeze. Similar factors may contribute to the beginning of a new ice age.
In about 5,000 years, some scientists predict a new ice age will begin, while others argue that the ice age never ended.
Considering that the last Pleistocene Ice Age stage ended 10,000 years ago, it is possible that we are now experiencing an interglacial stage, and the ice may return some time later.
On this note, I end this topic. I hope that the story about the ice age on Earth did not “freeze” you 🙂 And finally, I suggest you subscribe to the mailing list of fresh articles so as not to miss their release.
last ice age
During this era, 35% of the land was under the ice cover (compared to 10% at present).
The last ice age was not just a natural disaster. It is impossible to understand the life of planet Earth without considering these periods. In the intervals between them (known as interglacial periods), life flourished, but then in again Ice inexorably approached and brought death, but life did not completely disappear. Every ice age has been marked by a struggle for survival different types, there were global climate changes, and in the last of them a new species appeared, which became (over time) dominant on Earth: it was a man.
ice ages
Ice ages are geological periods characterized by a strong cooling of the Earth, during which vast expanses earth's surface covered with ice, there was a high level of humidity and, of course, exceptional cold, as well as the lowest known modern science sea level. There is no generally accepted theory regarding the causes of the onset of the ice age, however, since the 17th century, various explanations have been proposed. According to current opinion, this phenomenon was not caused by one cause, but was the result of the influence of three factors.
Changes in the composition of the atmosphere - a different ratio of carbon dioxide ( carbon dioxide) and methane - caused a sharp drop in temperature. This is similar to what we now call global warming, but on a much larger scale.
The movements of the continents, caused by cyclical changes in the orbit of the Earth around the Sun, and in addition, a change in the angle of inclination of the planet's axis relative to the Sun, also had an impact.
The earth received less solar heat, it cooled, which led to glaciation.
The earth has experienced several ice ages. The largest glaciation occurred 950-600 million years ago in the Precambrian era. Then in the Miocene epoch - 15 million years ago.
The traces of glaciation that can be observed at the present time represent the legacy of the last two million years and belong to the Quaternary period. This period is best studied by scientists and is divided into four periods: Günz, Mindel (Mindel), Ries (Rise) and Würm. The latter corresponds to the last ice age.
last ice age
The Wurm stage of glaciation began approximately 100,000 years ago, reached its maximum after 18 thousand years, and began to decline after 8 thousand years. During this time, the thickness of the ice reached 350-400 km and covered a third of the land above sea level, in other words, three times more space than now. Based on the amount of ice that currently covers the planet, one can get some idea of the area of glaciation during that period: today glaciers occupy 14.8 million km2, or about 10% of the earth's surface, and during the ice age they covered an area of 44 .4 million km2, which is 30% of the Earth's surface.
Northern Canada was estimated to have covered 13.3 million km2 of ice, while 147.25 km2 is now under ice. The same difference is observed in Scandinavia: 6.7 million km2 in that period compared to 3910 km2 today.
The ice age began simultaneously in both hemispheres, although in the North the ice spread to more extensive areas. In Europe, the glacier captured most of the British Isles, northern Germany and Poland, and in North America, where the Wurm glaciation is called the "Wisconsin glacial stage", a layer of ice that descended from the North Pole covered all of Canada and spread south of the Great Lakes. Like the lakes in Patagonia and the Alps, they were formed on the site of recesses left after the melting of the ice mass.
The sea level dropped by almost 120 m, as a result of which large expanses were exposed that are currently covered sea water. The significance of this fact is enormous, since large-scale human and animal migrations became possible: hominids were able to make the transition from Siberia to Alaska and move from continental Europe to England. It is possible that during the interglacial periods, the two largest ice massifs on Earth - Antarctica and Greenland - have undergone little change over the course of history.
At the peak of the glaciation, indicators medium size temperature drops differed significantly depending on the area: 100 ° C - in Alaska, 60 ° C - in England, 20 ° C - in the tropics and remained practically unchanged at the equator. Conducted studies of the last glaciations in North America and Europe, which occurred during the Pleistocene era, gave the same results in this geological region within the last two (approximately) million years.
The last 100,000 years are of particular importance for understanding the evolution of mankind. Ice ages have become a severe test for the inhabitants of the Earth. After the end of the next glaciation, they again had to adapt, learn to survive. When the climate became warmer, the sea level rose, new forests and plants appeared, the land rose, freed from the pressure of the ice shell.
The hominids turned out to have the most natural data to adapt to the changed conditions. They were able to move to areas with the most food resources, where the slow process of their evolution began.
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1.8 million years ago began the Quaternary (anthropogenic) period of the geological history of the earth, which continues to this day.
River basins expanded. Went fast development fauna of mammals, especially mastodons (which would later become extinct, like many other ancient species of animals), ungulates and higher monkeys. In that geological period man appears in the history of the earth (hence the word anthropogenic in the name of this geological period).
On the Quaternary there is a sharp change in climate throughout the European part of Russia. From a warm and humid Mediterranean, it turned into a temperate cold, and then into a cold Arctic one. This led to glaciation. Ice accumulated on the Scandinavian Peninsula, in Finland, on the Kola Peninsula and spread to the south.
The Oksky glacier, with its southern edge, also covered the territory of the modern Kashirsky region, including our region. The first glaciation was the coldest woody vegetation in the Oka region has disappeared almost completely. The glacier did not last long. The first Quaternary glaciation reached the Oka valley, which is why it received the name “Oksky glaciation”. The glacier left moraine deposits dominated by boulders of local sedimentary rocks.
But such favorable conditions were again replaced by a glacier. The glaciation was on a planetary scale. The grandiose Dnieper glaciation began. The thickness of the Scandinavian ice sheet reached 4 kilometers. The glacier moved across the Baltic Western Europe and European part Russia. The boundaries of the languages of the Dnieper glaciation passed in the area of modern Dnepropetrovsk and almost reached Volgograd.
 mammoth fauna |
The climate warmed up again and became Mediterranean. In place of the glaciers, heat-loving and moisture-loving vegetation spread: oak, beech, hornbeam and yew, as well as linden, alder, birch, spruce and pine, hazel. In the marshes grew ferns, characteristic of modern South America. Perestroika has begun river system and the formation of Quaternary terraces in river valleys. This period was called the interglacial Oxo-Dnieper age.
The Oka served as a kind of barrier to the advancement of ice fields. According to scientists, the right bank of the Oka, i.e. our region has not turned into a continuous icy desert. Here were fields of ice, interspersed with intervals of melted hills, between which rivers flowed from melt water and lakes accumulated.
Ice flows of the Dnieper glaciation brought glacial boulders from Finland and Karelia to our region.
The valleys of the old rivers were filled with mid-moraine and fluvioglacial deposits. It warmed up again, and the glacier began to melt. Streams of melt water rushed south along the channels of new rivers. During this period, the third terraces are formed in the river valleys. Large lakes formed in the depressions. The climate was moderately cold.
In our region, forest-steppe vegetation dominated with a predominance of coniferous and birch forests and large areas of steppes covered with wormwood, quinoa, grasses and herbs.
The interstadial epoch was short. The glacier returned to the Moscow region again, but did not reach the Oka, stopping not far from the southern outskirts of modern Moscow. Therefore, this third glaciation was called Moscow. Some tongues of the glacier reached the Oka valley, but they did not reach the territory of the modern Kashirsky region. The climate was severe, and the landscape of our region becomes close to the steppe tundra. Forests are almost disappearing and their place is taken by steppes.
A new warming has come. The rivers deepened their valleys again. The second terraces of the rivers were formed, the hydrography of the Moscow region changed. It was during that period that the modern valley and basin of the Volga, which flows into the Caspian Sea, was formed. The Oka, and with it our river B. Smedva and its tributaries, entered the Volga river basin.
This interglacial period in terms of climate went through stages from continentally temperate (close to modern) to warm, with a Mediterranean climate. In our region, birch, pine and spruce dominated at first, and then heat-loving oaks, beeches and hornbeams turned green again. In the swamps, the water lily grew, which today you will find only in Laos, Cambodia or Vietnam. At the end of the interglacial period, birch-coniferous forests again dominated.
This idyll was spoiled by the Valdai glaciation. Ice from the Scandinavian Peninsula again rushed to the south. This time the glacier did not reach the Moscow region, but changed our climate to subarctic. For many hundreds of kilometers, including the territory of the present Kashirsky district and the rural settlement of Znamenskoye, the steppe-tundra stretches, with dried grass and rare shrubs, dwarf birches and polar willows. These conditions were ideal for the mammoth fauna and for primitive man, which then already lived on the borders of the glacier.
During the last Valdai glaciation, the first river terraces formed. The hydrography of our region has finally taken shape.
Traces of glacial epochs are often found in the Kashirsky region, but they are difficult to distinguish. Of course, large stone boulders are traces of the glacial activity of the Dnieper glaciation. They were brought by ice from Scandinavia, Finland and from the Kola Peninsula. The most ancient traces of the glacier are moraine or boulder loam, which is a random mixture of clay, sand, brown stones.
The third group of glacial rocks are sands resulting from the destruction of moraine layers by water. These are sands with large pebbles and stones, and the sands are homogeneous. They can be observed on the Oka. These include the Belopesotsky sands. Often found in the valleys of rivers, streams, in ravines, layers of flint and limestone gravel are traces of the bed of ancient rivers and streams.
With new warming, the geological epoch of the Holocene began (it began 11,400 years ago), which continues to this day. The modern river floodplains were finally formed. The mammoth fauna died out, and forests appeared in place of the tundra (at first, spruce, then birch, and later mixed). The flora and fauna of our region has acquired the features of modern - the one that we see today. At the same time, the left and right banks of the Oka are still very different in their forest cover. If mixed forests and many open areas prevail on the right bank, then continuous coniferous forests dominate on the left bank - these are traces of glacial and interglacial climate changes. On our bank of the Oka, the glacier left fewer traces, and our climate was somewhat milder than on the left bank of the Oka.
Geological processes continue today. The earth's crust in the Moscow region over the past 5 thousand years has been rising only slightly, at a rate of 10 cm per century. The modern alluvium of the Oka and other rivers of our region is being formed. Where this will lead after millions of years, we can only guess, because, having briefly met with geological history of our region, we can safely repeat the Russian proverb: "Man proposes, but God disposes." This saying is especially relevant, after we have seen in this chapter that human history is a grain of sand in the history of our planet.
In the distant, distant times, where Leningrad, Moscow, Kyiv are now, everything was different. Dense forests grew along the banks of ancient rivers, and shaggy mammoths with bent tusks, huge furry rhinoceroses, tigers and bears much larger than today roamed there.
Gradually, these places became colder and colder. Far in the north, so much snow fell every year that entire mountains of it accumulated - larger than the present Urals. The snow caked up, turned into ice, then slowly began to spread, spreading in all directions.
Ice mountains have moved over the ancient forests. Cold, evil winds blew from these mountains, trees froze and animals fled from the cold to the south. And the icy mountains crawled further south, twisting the rocks along the way and moving whole hills of earth and stones in front of them. They crawled to the place where Moscow now stands, and crawled even further, into warm southern countries. They reached the hot Volga steppe and stopped.
Here, finally, the sun overpowered them: the glaciers began to melt. Huge rivers flowed from them. And the ice receded, melted, and the masses of stones, sand and clay that the glaciers brought, remained lying in the southern steppes.
More than once, terrible ice mountains approached from the north. Have you seen the cobblestone pavement? Such small stones are brought by the glacier. And there are boulders the size of a house. They still lie in the north.
But the ice can move again. Just not soon. Maybe thousands of years will pass. And not only the sun will then fight the ice. If necessary, people will use NUCLEAR ENERGY and keep the glacier out of our land.
Many of us believe that the Ice Age ended a very long time ago and no traces of it remain. But geologists say we are only approaching the end of the ice age. And the inhabitants of Greenland are still living in the Ice Age.
Approximately 25 thousand years ago, the peoples who inhabited the central part of NORTH AMERICA saw ice and snow all year round. A huge wall of ice stretched from the Pacific to Atlantic Ocean, and to the north - to the very pole. It was during the final stages of the Ice Age, when all of Canada, most of the United States, and northwestern Europe were covered in a layer of ice over one kilometer thick.
But this does not mean that it was always very cold. In the northern part of the United States, the temperature was only 5 degrees below present. Cold summer months caused an ice age. At this time, the heat was not enough to melt the ice and snow. It accumulated and eventually covered the entire northern part of these areas.
The Ice Age consisted of four stages. At the beginning of each of them, ice formed moving south, then melted and retreated to the North POLE. This happened, it is believed, four times. Cold periods are called "glaciation", warm - "interglacial" period.
The first phase in North America is believed to have begun about two million years ago, the second about 1,250,000 years ago, the third about 500,000 years ago, and the last about 100,000 years ago.
The rate of ice melting at the last stage of the ice age in different regions was not the same. For example, in the area of present-day Wisconsin in the United States, ice melt began about 40,000 years ago. The ice that covered the New England area in the US disappeared about 28,000 years ago. And the territory of the modern state of Minnesota was freed by ice only 15,000 years ago!
In Europe, Germany was free of ice 17,000 years ago, while Sweden only 13,000 years ago.
A huge mass of ice, from the formation of which the ice age began in North America, was called the "continental glacier": in the very center its thickness reached 4.5 km. It is possible that this glacier formed and melted four times during the entire ice age.
The glacier that covered other parts of the world has not melted in some places! For example, the huge island of Greenland is still covered by continental ice, except for a narrow coastal strip. In its middle part, the glacier sometimes reaches a thickness of more than three kilometers. Antarctica is also covered by a vast continental glacier up to 4 kilometers thick in some places!
So the reason why there are glaciers in some parts of the world is that they have not melted since the Ice Age. But the bulk of the glaciers that are found now, formed recently. They are mainly located in mountain valleys.
They originate in wide, gently sloping, amphitheater-like valleys. Snow falls here from the slopes as a result of landslides and avalanches. Such snow does not melt in the summer, becoming deeper every year.
Gradually, pressure from above, some thawing, and repeated freezing remove air from the bottom of this snow mass, turning it into solid ice. The impact of the weight of the entire mass of ice and snow compresses the entire mass and causes it to move down the valley. Such a moving tongue of ice is a mountain glacier.
More than 1200 such glaciers are known in Europe in the Alps! They also exist in the Pyrenees, in the Carpathians, in the Caucasus, as well as in the mountains of southern Asia. There are tens of thousands of these glaciers in southern Alaska, some 50 to 100 km long!
Scientists note that the ice age is part of the ice age, when the earth covers ice for long millions of years. But many people call the ice age a segment of the history of the Earth, which ended about twelve thousand years ago.
It is worth noting that ice age history had a huge number of unique features that have not reached our time. For example, unique animals that were able to adapt to existence in this difficult climate are mammoths, rhinos, saber-toothed tigers, cave bears and others. They were covered with thick fur and quite large in size. Herbivores adapted to get food from under the icy surface. Let's take rhinos, they raked ice with their horns and ate plants. Surprisingly, the vegetation was varied. Of course, many plant species disappeared, but herbivores had free access to food.
Despite the fact that the ancient people were not large in size and did not have a cover of wool, they also managed to survive during the Ice Age. Their life was incredibly dangerous and difficult. They built small dwellings for themselves and insulated them with the skins of dead animals, and ate the meat. People came up with various traps to lure large animals there.
Rice. 1 - Ice Age
For the first time, the history of the Ice Age was discussed in the eighteenth century. Then geology began to form as a scientific branch, and scientists began to find out what origin the boulders in Switzerland have. Most researchers agreed in a single point of view that they have a glacial beginning. In the nineteenth century, it was suggested that the planet's climate was subject to severe cooling. A little later, the term itself was announced "ice Age". It was introduced by Louis Agassiz, whose ideas were not at first recognized by the general public, but then it was proved that many of his works really have a basis.
In addition to the fact that geologists were able to establish the fact that the ice age took place, they also tried to find out why it arose on the planet. The most common opinion is that the movement of lithospheric plates can block warm currents in the ocean. This gradually causes the formation of an ice mass. If large-scale ice sheets have already formed on the surface of the Earth, then they will cause a sharp cooling, reflecting sunlight and therefore warm. Another reason for the formation of glaciers could be a change in the level of greenhouse effects. The presence of large arctic massifs and the rapid spread of plants eliminates Greenhouse effect by replacing carbon dioxide with oxygen. Whatever the reason for the formation of glaciers, this is a very long process that can also enhance the influence of solar activity on the Earth. Changes in our planet's orbit around the Sun make it extremely susceptible. The remoteness of the planet from the "main" star also has an influence. Scientists suggest that even during the largest ice ages, the Earth was covered with ice only one third of the entire area. There are suggestions that ice ages also took place, when the entire surface of our planet was covered with ice. But this fact is still controversial in the world of geological research.
To date, the most significant glacial massif is the Antarctic. The thickness of the ice in some places reaches more than four kilometers. Glaciers move at an average speed of five hundred meters per year. Another impressive ice sheet is found in Greenland. Approximately seventy percent of this island is occupied by glaciers, and this is one tenth of the ice of our entire planet. At this point in time, scientists believe that the ice age will not be able to start for at least another thousand years. The thing is that in the modern world there is a colossal release of carbon dioxide into the atmosphere. And as we found out earlier, the formation of glaciers is possible only at a low level of its content. However, this poses another problem for humanity - global warming, which can be no less large-scale than the beginning of the Ice Age.
