Ice ages in the history of the earth. Coursework: Ice ages in the history of the Earth
State educational institution higher professional education of the Moscow region
International University of Nature, Society and Man "Dubna"
Faculty of Natural and Engineering Sciences
Department of Ecology and Earth Sciences
COURSE WORK
By discipline
Geology
Scientific adviser:
Candidate of G.M.S., Associate Professor Anisimova O.V.
Dubna, 2011
Introduction
1. Ice Age
1.1 Ice Ages in Earth's History
1.2 Proterozoic Ice Age
1.3 Paleozoic Ice Age
1.4 Cenozoic Ice Age
1.5 Tertiary period
1.6 Quaternary
2. The Last Ice Age
2.2 Flora and fauna
2.3Rivers and lakes
2.4 West Siberian lake
2.5Oceans
2.6 Great Glacier
3. Quaternary glaciations in the European part of Russia
4. Causes of Ice Ages
Conclusion
Bibliography
Introduction
Target:
To study the main ice ages in the history of the Earth and their role in shaping the modern landscape.
Relevance:
The relevance and significance of this topic is determined by the fact that the glacial epochs are not so well studied to fully confirm the existence on our Earth.
Tasks:
- conduct a literature review;
- establish the main ice ages;
– obtaining detailed data on the last Quaternary glaciations;
Establish the main causes of glaciation in the history of the Earth.
At present, there is still little data that confirms the distribution of frozen rock strata on our planet in ancient epochs. The proof is mainly the discovery of ancient continental glaciations in their moraine deposits and the establishment of the phenomena of mechanical separation of the rocks of the glacier bed, the transfer and processing of detrital material and its deposition after ice melting. Compacted and cemented ancient moraines, the density of which is close to sandstone-type rocks, are called tillites. Detection of such formations different ages in various areas the globe unequivocally indicates the repeated appearance, existence and disappearance of ice sheets, and, consequently, frozen strata. The development of ice sheets and frozen strata can occur asynchronously, i.e. the maximum development over the area of glaciation and cryolithozone may not coincide in phase. However, in any case, the presence of large ice sheets indicates the existence and development of frozen strata, which should occupy much larger areas than the ice sheets themselves.
According to N.M. Chumakov, as well as V.B. Harland and M.J. Hambry, the time intervals during which glacial deposits were formed are called glacial eras (lasting the first hundreds of millions of years), ice ages (millions - the first tens of millions of years), ice ages (the first millions of years). In the history of the Earth, the following glacial eras can be distinguished: Early Proterozoic, Late Proterozoic, Paleozoic and Cenozoic.
1. Ice age
Are there ice ages? Of course yes. The evidence for this is incomplete, but it is well defined, and some of this evidence extends over large areas. Evidence for the existence of the Permian Ice Age is present on several continents, and in addition, traces of glaciers have been found on the continents dating back to other epochs of the Paleozoic era up to its beginning, the Early Cambrian time. Even in much older rocks, pre-Phanerozoic, we find traces left by glaciers and glacial deposits. Some of these footprints are over two billion years old, perhaps half the age of the Earth as a planet.
The glacial epoch of glaciations (glacials) is a period of time in the geological history of the Earth, characterized by a strong cooling of the climate and the development of extensive continental ice not only in the polar, but also in temperate latitudes.
Peculiarities:
It is characterized by a long, continuous and severe cooling of the climate, the growth of ice sheets in the polar and temperate latitudes.
· Glacial epochs are accompanied by a decrease in the level of the World Ocean by 100 m or more, due to the fact that water accumulates in the form of ice sheets on land.
·During glacial epochs, the areas occupied by permafrost are expanding, soil and vegetation zones are shifting towards the equator.
It has been established that over the past 800 thousand years there have been eight glacial epochs, each of which lasted from 70 to 90 thousand years.
Fig.1 Ice Age
1.1 Ice Ages in Earth's History
Periods of climate cooling, accompanied by the formation of continental ice sheets, are recurring events in the history of the Earth. The intervals of cold climate during which extensive continental ice sheets and sediments lasting hundreds of millions of years are formed are called ice ages; in glacial eras, glacial periods lasting tens of millions of years are distinguished, which, in turn, consist of glacial epochs - glaciations (glacials) alternating with interglacials (interglacials).
Geological studies have proved that there was a periodic process of climate change on Earth, covering the time from the late Proterozoic to the present.
These are relatively long ice ages that lasted for almost half of the history of the Earth. The following ice ages are distinguished in the history of the Earth:
Early Proterozoic - 2.5-2 billion years ago
Late Proterozoic - 900-630 million years ago
Paleozoic - 460-230 million years ago
Cenozoic - 30 million years ago - present
Let's consider each of them in more detail.
1.2 Proterozoic Ice Age
Proterozoic - from the Greek. the words proteros - primary, zoe - life. Proterozoic era - a geological period in the history of the Earth, including the history of formation rocks of various origins from 2.6 to 1.6 billion years. A period in the history of the Earth, which was characterized by the development of the simplest forms of life of unicellular living organisms from prokaryotes to eukaryotes, which later evolved into multicellular organisms as a result of the so-called Ediacaran "explosion".
Early Proterozoic Ice Age
This is the oldest glaciation recorded in geological history at the end of the Proterozoic on the border with the Vendian, and according to the Snowball Earth hypothesis, the glacier covered most of the continents at equatorial latitudes. In fact, it was not one, but a series of glaciations and interglacial periods. Since it is believed that nothing can prevent the spread of glaciation due to an increase in albedo (reflection of solar radiation from the white surface of glaciers), it is believed that the subsequent warming can be caused, for example, by an increase in the amount of greenhouse gases in the atmosphere due to an increase in volcanic activity , accompanied, as is well known, by emissions of a huge amount of gases.
Late Proterozoic Ice Age
It was distinguished under the name of the Lapland glaciation at the level of the Vendian glacial deposits 670-630 million years ago. These deposits are found in Europe, Asia, West Africa, Greenland and Australia. The paleoclimatic reconstruction of the glacial formations of this time suggests that the European and African ice continents of that time were a single ice sheet.
Fig.2 Vend. Ulytau during the Ice Age Snowball
1.3 Paleozoic Ice Age
Paleozoic - from the word paleos - ancient, zoe - life. Palaeozoic. Geological time in the history of the Earth covering 320-325 million years. With an age of glacial deposits of 460-230 million years, it includes the Late Ordovician - Early Silurian (460-420 million years), Late Devonian (370-355 million years) and Carboniferous-Permian ice ages (275 - 230 million years). The interglacial period of these periods is characterized by a warm climate, which contributed to the rapid development of vegetation. Large and unique coal basins and horizons of oil and gas fields later formed in the places of their distribution.
Late Ordovician - Early Silurian Ice Age.
Glacial deposits of this time, called the Saharan (after the name of the modern Sahara). They were distributed on the territory of modern Africa, South America, the eastern part North America and Western Europe. This period is characterized by the formation of an ice sheet in most of the northern, northwestern and West Africa including the Arabian Peninsula. Paleoclimatic reconstructions suggest that the thickness of the Saharan ice sheet reached at least 3 km and is similar in area to the modern glacier of Antarctica.
Late Devonian Ice Age
Glacial deposits of this period were found on the territory of modern Brazil. The glacial region extended from the modern mouth of the river. Amazons to the east coast of Brazil, capturing the Niger region in Africa. In Africa, in Northern Niger, tillites (glacial deposits) occur, which are comparable to those in Brazil. In general, glacial regions stretched from the border of Peru with Brazil to northern Niger, the diameter of the region was more than 5000 km. The South Pole in the Late Devonian, according to the reconstruction of P. Morel and E. Irving, was in the center of Gondwana in Central Africa. Glacial basins are located on the oceanic margin of the paleocontinent, mainly at high latitudes (not north of the 65th parallel). Judging by the then high-latitude continental position of Africa, one can assume the possible widespread development of frozen rocks on this continent and, moreover, in the northwest of South America.
The Carboniferous-Permian Ice Age
It has received its distribution in the territory of modern Europe and Asia. During the Carboniferous, there was a gradual cooling of the climate, which culminated about 300 million years ago. This was facilitated by the concentration of most of the continents in the southern hemisphere and the formation of the Gondwana supercontinent, the formation of large mountain ranges and changes in ocean currents. In the Carboniferous - Permian, glacial and periglacial conditions existed in most of Gondwana.
The center of the continental ice sheet of Central Africa was located near the Zambezi, from where the ice flowed radially into several African basins and spread to Madagascar, South Africa and partly to South America. With a radius of the ice sheet of about 1750 km, according to calculations, the thickness of the ice could be up to 4 - 4.5 km. In the southern hemisphere, at the end of the Carboniferous–Early Permian, a general uplift of Gondwana took place, and a sheet glaciation spread over most of this supercontinent. The Stone - Coal-Permian Ice Age lasted at least 100 million years, but there was no single large ice cap. The peak of the ice age, when the ice sheets extended far to the north (up to 30° - 35°S), lasted about 40 million years (between 310 - 270 million years ago). According to calculations, the areas of Gondwana glaciation occupied an area of at least 35 million km 2 (possibly 50 million km 2), which is 2–3 times the area of modern Antarctica. Ice sheets reached 30° - 35°S. The main center of glaciation was the region of the Sea of Okhotsk, which, apparently, was located near the North Pole.
Fig.3 Paleozoic Ice Age
1.4 Cenozoic Ice Age
The Cenozoic Ice Age (30 million years ago - present) is a recently begun ice age.
The present time - the Holocene, which began ≈ 10,000 years ago, is characterized as a relatively warm period after the Pleistocene ice age, often qualified as an interglacial. Ice sheets exist in the high latitudes of the northern (Greenland) and southern (Antarctica) hemispheres; at the same time, in the northern hemisphere, the Greenland glaciation sheet extends south to 60 ° north latitude (i.e., to the latitude of St. Petersburg), fragments of the sea ice cover - up to 46-43 ° north latitude (i.e., to the latitude of Crimea) , and permafrost up to 52-47 ° north latitude. In the southern hemisphere, the continental part of Antarctica is covered by an ice sheet with a thickness of 2500-2800 m (up to 4800 m in some areas of East Antarctica), while ice shelves make up ≈10% of the area of the continent that rises above sea level. In the Cenozoic Ice Age, the Pleistocene Ice Age is the strongest: a decrease in temperature led to glaciation of the Arctic Ocean and the northern regions of the Atlantic and Pacific Ocean, while the glaciation boundary passed 1500-1700 km south of the modern one.
Geologists divide the Cenozoic into two periods: Tertiary (65 - 2 million years ago) and Quaternary (2 million years ago - our time), which in turn are divided into epochs. Of these, the first is much longer than the second, but the second - Quaternary - has a number of unique features; this is the time of the ice ages and the final formation of the modern face of the Earth.
Rice. 4 Cenozoic Ice Age. Ice Age. Climate curve for the last 65 million years.
34 million years ago - the beginning of the Antarctic ice sheet
25 million years ago - its reduction
13 million years ago - its re-growth
About 3 million years ago - the beginning of the Pleistocene ice age, the repeated appearance and disappearance of ice sheets in the northern regions of the Earth
1.5 Tertiary period
The Tertiary period consists of epochs:
·Paleocene
Oligocene
Pliocene
Paleocene epoch (from 65 to 55 million years ago)
Geography and climate: The Paleocene marked the beginning of the Cenozoic era. At that time, the continents were still in motion, as the "great southern continent" Gondwana continued to break apart. South America was now completely cut off from the rest of the world and turned into a kind of floating "ark" with a unique fauna of early mammals. Africa, India and Australia have moved further apart. Throughout the Paleocene, Australia was located near Antarctica. Sea levels have dropped and new landmasses have appeared in many parts of the world.
Fauna: On land, the age of mammals began. Rodents and insectivores appeared. Among them were large animals, both predatory and herbivorous. In the seas, marine reptiles have been replaced by new species of predatory bony fish and sharks. New varieties of bivalves and foraminifera emerged.
Flora: New species of flowering plants and the insects that pollinated them continued to spread.
Eocene epoch (from 55 to 38 million years ago)
Geography and climate: In the Eocene, the main land masses began to gradually assume a position close to that which they occupy today. A large part of the land was still divided into a kind of giant islands, as the huge continents continued to move away from each other. South America has lost contact with Antarctica, and India has moved closer to Asia. At the beginning of the Eocene, Antarctica and Australia were still located nearby, but later they began to diverge. North America and Europe also split apart, creating new mountain ranges. The sea flooded part of the land. The climate was generally warm or temperate. Most of it was covered with lush tropical vegetation, and vast areas were overgrown with dense swampy forests.
Fauna: Bats, lemurs, tarsiers appeared on land; the ancestors of today's elephants, horses, cows, pigs, tapirs, rhinos and deer; other large herbivores. Other mammals, such as whales and sirens, have returned to the aquatic environment. The number of species of freshwater bony fish has increased. Other groups of animals also evolved, including ants and bees, starlings and penguins, giant flightless birds, moles, camels, rabbits and voles, cats, dogs, and bears.
Flora: In many parts of the world, forests with lush vegetation grew, palm trees grew in temperate latitudes.
Oligocene epoch (from 38 to 25 million years ago)
Geography and climate: In the Oligocene era, India crossed the equator, and Australia finally separated from Antarctica. The climate on Earth became cooler, a huge ice sheet formed over the South Pole. For education so a large number ice required no less significant volumes of sea water. This led to a decrease in sea levels throughout the planet and the expansion of the territory occupied by land. The widespread cooling caused the disappearance of violent rainforest Eocene in many parts of the world. Their place was taken by forests, which preferred a more temperate (cool) climate, as well as vast steppes spread over all continents.
Fauna: With the spread of the steppes, the rapid flowering of herbivorous mammals began. Among them, new species of rabbits, hares, giant sloths, rhinos and other ungulates arose. The first ruminants appeared.
Flora: Tropical forests have shrunk and begun to give way to temperate forests, and vast steppes have appeared. New herbs spread rapidly, new types of herbivores developed.
Miocene epoch (from 25 to 5 million years ago)
Geography and climate: During the Miocene, the continents were still "on the march", and during their collisions a number of grandiose cataclysms occurred. Africa "crashed" into Europe and Asia, resulting in the emergence of the Alps. When India and Asia collided, the Himalayan mountains shot up. At the same time, the Rocky Mountains and the Andes formed as other giant plates continued to shift and pile on top of each other.
However, Austria and South America still remained isolated from the rest of the world, and each of these continents continued to develop its own unique fauna and flora. The ice sheet in the southern hemisphere spread to the whole of Antarctica, which led to further cooling of the climate.
Fauna: Mammals migrated from mainland to mainland along the newly formed land bridges, which dramatically accelerated evolutionary processes. Elephants from Africa moved to Eurasia, while cats, giraffes, pigs and buffaloes moved in the opposite direction. Saber-toothed cats and monkeys appeared, including anthropoids. In Australia, cut off from the outside world, monotremes and marsupials continued to develop.
Flora: Inland regions became colder and drier, and steppes spread more and more in them.
Pliocene epoch (from 5 to 2 million years ago)
Geography and Climate: A space traveler looking down on the Earth at the beginning of the Pliocene would find the continents in almost the same places as they are today. The gaze of a galactic visitor would open up giant ice caps in the northern hemisphere and the huge ice sheet of Antarctica. Because of all this mass of ice, the climate of the Earth became even cooler, and it became much colder on the surface of the continents and oceans of our planet. Most of the forests that survived in the Miocene disappeared, giving way to vast steppes that spread all over the world.
Fauna: Herbivorous hoofed mammals continued to multiply and evolve rapidly. Toward the end of the period, a land bridge connected South and North America, which led to a grand "exchange" of animals between the two continents. It is believed that the intensified interspecific competition caused the extinction of many ancient animals. Rats entered Australia, and the first humanoid creatures appeared in Africa.
Flora: As the climate cools, steppes have replaced forests.
Figure 5 Diverse Mammals Evolved During the Tertiary Period
1.6 Quaternary
Consists of epochs:
·Pleistocene
Holocene
Pleistocene epoch (from 2 to 0.01 million years ago)
Geography and climate: At the beginning of the Pleistocene, most of the continents occupied the same position as today, and some of them needed to cross half the globe to do this. A narrow land "bridge" connected North and South America. Australia was located on the opposite side of the Earth from Britain. Giant ice sheets were creeping into the northern hemisphere. It was the era of the great glaciation with alternating periods of cooling and warming and fluctuations in sea level. This ice age continues to this day.
Animals: Some animals have managed to adapt to the increased cold by acquiring thick wool: for example, woolly mammoths and rhinos. Of the predators, saber-toothed cats and cave lions are the most common. This was the age of the giant marsupials in Australia and the huge flightless birds, such as the moa or epiornis, that lived in many parts of the southern hemisphere. The first people appeared, and many large mammals began to disappear from the face of the Earth.
Flora: Ice gradually crept from the poles, and coniferous forests gave way to tundra. Farther from the edge of the glaciers, deciduous forests gave way to coniferous ones. In more warm areas vast steppes spread across the globe.
Holocene epoch (from 0.01 million years to the present day)
Geography and climate: The Holocene began 10,000 years ago. During the entire Holocene, the continents occupied practically the same places as today, the climate was also similar to the modern one, becoming either warmer or colder every few millennia. Today we are experiencing one of the periods of warming. As the ice sheets decreased, the sea level slowly rose. The beginning of the time of the human race.
Fauna: At the beginning of the period, many species of animals became extinct, mainly due to the general warming of the climate, but, perhaps, increased human hunting for them also affected. Later, they may have fallen victim to competition from new animal species introduced by people from other places. Human civilization has become more advanced and spread all over the world.
Flora: With the advent of agriculture, the peasants destroyed more and more wild plants in order to clear areas for crops and pastures. In addition, plants brought by people to areas new to them sometimes crowded out indigenous vegetation.
Rice. 6 Proboscis, the largest land animals of the Quaternary period
Ice Age Tertiary Quaternary
2. The Last Ice Age
The last ice age (last glaciation) is the last of the ice ages within the Pleistocene or Quaternary ice age. It began about 110 thousand years ago and ended around 9700-9600 BC. e. For Siberia, it is customary to call it “Zyryanskaya”, in the Alps - “Würmskaya”, in North America - “Wisconsin”. During this epoch, the growth and reduction of ice sheets repeatedly occurred. The last glacial maximum, when the total volume of ice in the glaciers was the largest, dates back to about 26-20 thousand years ago of individual ice sheets.
At this time, the polar glaciers of the northern hemisphere grew to enormous sizes, uniting into a huge ice sheet. Long tongues of ice moved away from it to the south along the channels of large rivers. All high mountains were also shackled with ice shells. Cooling and the formation of glaciers led to other global changes in nature. The rivers flowing into the northern seas were blocked by ice walls, they overflowed into giant lakes and turned back trying to find a drain in the south. Moved south thermophilic plants, giving way to more cold-hardy neighbors. At this time, the mammoth faunistic complex was finally formed, consisting mainly of large animals well protected from the cold.
2.1 Climate
However, during the last glaciation, the climate on the planet was not constant. Climate warming occurred periodically, the glacier melted along the edge, retreated to the north, the areas of high-altitude ice decreased, and climatic zones shifted to the south. There have been several such minor changes in the climate. Scientists believe that the coldest and most severe period in Eurasia was about 20 thousand years ago.
Rice. 7 Perito Moreno Glacier in Patagonia, Argentina. during the last ice age
Rice. 8 The diagram shows climatic changes in Siberia and in some other regions of the northern hemisphere over the past 50 thousand years
2.2 Flora and fauna
The cooling on the planet and the formation of giant glacial systems in the north caused global changes in the flora and fauna of the Northern Hemisphere. The boundaries of all natural zones began to shift to the south. The following natural zones were located on the territory of Siberia.
Along the glaciers, a zone of cold tundra and tundra steppes stretches for tens of kilometers. It was located approximately in those areas where the forest and taiga are now.
In the south, the tundra-steppe gradually turned into forest-steppes and forests. Forest plots were very small, and were far from everywhere. Most often, forests were located on the southern shores of glacial lakes and in river valleys and on the spurs of mountains.
Even further south were dry steppes, in the west of Siberia gradually turning into the mountain systems of the Sayano-Altai, in the east bordering on the semi-deserts of Mongolia. In some areas, the tundra-steppe and steppe were not separated by a strip of forest, but gradually replaced each other.
Fig.9. Tundrosteppe, the era of the last glaciation
In the new climatic conditions of the glacial period, the animal world also changed. For last stages Quaternary period in the Northern Hemisphere was the formation of new species of fauna. A particularly expressive manifestation of these changes was the appearance of the so-called mammoth faunistic complex, which consisted of cold-tolerant animal species.
2.3 Rivers and lakes
Giant ice fields formed a natural dam and blocked the flow of rivers flowing into northern seas. Modern Siberian rivers: the Ob, Irtysh, Yenisei, Lena, Kolyma and many others overflowed along the glaciers, forming giant lakes, which were combined into periglacial meltwater runoff systems.
Siberia in the Ice Age. Modern rivers and cities are labeled for clarity. Most of this system was connected by rivers and the waters flowed out of it to the southwest through the system of the Novoevksinsky basin, which was once on the site of the Black Sea. Further, through the Bosphorus and the Dardanelles, water entered the Mediterranean Sea. The total area of this drainage basin was 22 million square meters. km. She served the territory from Mongolia to the Mediterranean.
Fig. 10 Siberia in the Ice Age
In North America, such a system of glacial lakes also existed. Along the Laurentian ice sheet stretched the now disappeared giant Lake Agassiz, the McConnell and Algonk lakes.
2.4 West Siberian Lake
Some scientists believe that one of the largest near-glacial lakes in Eurasia was the Mansiysk, or as it is also called the West Siberian Lake. It occupied almost the entire territory of the West Siberian Plain up to the foothills of the Kuznetsk Alatau and Altai. Those places where the largest cities of Tyumen, Tomsk and Novosibirsk are now located were covered with water during the last ice age. When the glacier began to melt - 16-14 thousand years ago, the waters of Lake Mansiysk began to gradually drain into the Arctic Ocean, and modern river systems formed in its place, and in the lowland part of the Taiga Ob region, the largest system in Eurasia, the Vasyugan Swamps, was formed.
Fig. 11 This is how the West Siberian Lake looked like
2.5 Oceans
The ice sheets of the planet are formed by the waters of the oceans. Accordingly, the larger and higher the glaciers, the less water remains in the ocean. Glaciers absorb water, the ocean level drops, exposing large areas of land. So, 50,000 years ago, due to the growth of glaciers, the ocean level dropped by 50 m, and 20,000 years ago - by 110-130 m. During this period, many modern islands formed a single whole with the mainland. Thus, the British, Japanese, New Siberian Islands were inseparable from the mainland. In place of the Bering Strait, there was a wide strip of land called Beringia.
Fig. 12 Diagram of ocean level changes during the last ice age
2.6 Great Glacier
During the last glaciation, a huge Arctic ice sheet occupied the circumpolar part of the Northern Hemisphere of the planet. It was formed as a result of the merger of the North American and Eurasian ice sheets into a single system.
The Arctic ice sheet consisted of giant ice sheets shaped like plano-convex domes, which in some places formed layers of ice 2-3 kilometers high. The total area of the ice cover is more than 40 million square meters. km.
The largest elements of the Arctic Ice Sheet:
1. Laurentian shield centered over the southwestern part of Hudson Bay;
2. Karsk shield centered on by the Kara Sea spread to the entire north of the Russian Plain, Western and Central Siberia;
3. Greenland shield;
4. East Siberian shield covering the Siberian seas, the coast of Eastern Siberia and part of Chukotka;
5. Icelandic shield
Rice. 13 Arctic Ice Sheet
Even during the severe ice age, the climate was constantly changing. Glaciers then gradually advanced to the south, receded again. The ice sheet reached its maximum thickness about 20,000 years ago.
3. Quaternary glaciations in the European part of Russia
Quaternary glaciation - glaciation in the Quaternary period, caused by a decrease in temperature that began at the end of the Neogene period. In the mountains of Europe, Asia, America, glaciers began to increase, flowing onto the plains, a gradually expanding ice cap formed on the Scandinavian Peninsula, advancing ice pushed the animals and plants that lived there to the south.
The thickness of the ice cover reached 2 - 3 kilometers. About 30% of the territory of modern Russia in the north was occupied by a sheet of glaciation, which then somewhat decreased, then again moved south. Interglacial periods with a warm, mild climate gave way to cooling periods when glaciers advanced again.
On the territory of modern Russia there were 4 glaciations - Oka, Dnieper, Moscow and Valdai. The largest of them was the Dnieper, when a giant glacial tongue descended along the Dnieper to the latitude of Dnepropetrovsk, and along the Don to the mouth of the Medveditsa.
Consider the Moscow glaciation
The Moscow glaciation is an ice age belonging to the Anthropogenic (Quaternary) period (Middle Pleistocene, about 125-170 thousand years ago), the last of the major glaciations of the Russian (East European) Plain.
It was preceded by the Odintsovo time (170-125 thousand years ago) - a relatively warm period separating the Moscow glaciation from the maximum, Dnieper glaciation (230-100 thousand years ago), also in the middle Pleistocene.
As an independent ice age, the Moscow glaciation was identified relatively recently. Some researchers still interpret the Moscow glaciation as one of the stages of the Dnieper glaciation, or that it was one of the stages of a larger and longer previous glaciation. However, the boundary of the glacier developing in the Moscow era is drawn with greater validity.
Moscow, glaciation captured only the northern part of the Moscow region. The boundary of the glacier passed along the Klyazma River. It was during the melting of the Moscow Glacier that the moraine strata of the Dnieper glaciation were almost completely eroded. The flooding of the periglacial zone, which directly included the territory of the Shatura region, was so great during the melting of the Moscow glacier that the lowlands were filled with large lakes or turned into powerful valleys for the flow of melted glacial waters. Suspensions settled in them, forming outwash plains with sandy and sandy loam deposits, the most common within the region at present.
Fig.14 The position of the terminal glacial moraines of different ages within the central part of the Russian Plain. Moraine of the early Valdai () and late Valdai () glaciations.
4. Causes of Ice Ages
The causes of ice ages are inextricably linked to the broader problems of global climate change that have taken place throughout the history of the earth. Significant changes in geological and biological settings occurred from time to time. It should be borne in mind that the beginning of all great glaciations is determined by two important factors.
First, for thousands of years, the annual course of precipitation should be dominated by heavy and prolonged snowfalls.
Secondly, in areas with such a precipitation regime, temperatures should be so low that summer snowmelt is minimized, and firn fields increase from year to year until glaciers begin to form. Abundant accumulation of snow should prevail in the balance of glaciers throughout the entire epoch of glaciation, since if ablation exceeds accumulation, glaciation will decline. Obviously, for each ice age it is necessary to find out the reasons for its beginning and end.
Hypotheses
1. Pole migration hypothesis. Many scientists believed that the Earth's axis of rotation changes its position from time to time, which leads to a corresponding shift in climatic zones.
2. Hypothesis of carbon dioxide. Carbon dioxide CO2 in the atmosphere acts like a warm blanket to trap the Earth's radiated heat close to the Earth's surface, and any significant reduction in CO2 in the air will cause the Earth's temperature to drop. As a result, the temperature of the land will drop, and the ice age will begin.
3. Hypothesis of diastrophism (movements of the earth's crust). Significant land uplifts have repeatedly occurred in the history of the Earth. In general, the air temperature over land decreases by about 1.8. With a rise of every 90 m. In reality, the mountains rose many hundreds of meters, which turned out to be sufficient for the formation of valley glaciers there. In addition, the growth of mountains changes the circulation of moisture-bearing air masses. The uplift of ocean floors can, in turn, change the circulation of ocean waters and also cause climate change. Unknown, could only tectonic movements be the cause of glaciation, in any case, they could greatly contribute to its development
4. Hypothesis of volcanic dust. Volcanic eruptions are accompanied by the release of a huge amount of dust into the atmosphere. Obviously, volcanic activity, widespread on Earth for millennia, could significantly lower air temperatures and cause the onset of glaciation.
5. Hypothesis of continental drift. According to this hypothesis, all modern continents and the largest islands were once part of the single mainland Pangea, washed by the oceans. The consolidation of the continents into such a single land mass could explain the development of the Late Paleozoic glaciation of South America, Africa, India and Australia. The territories covered by this glaciation were probably much to the north or south of their present position. The continents began to separate in the Cretaceous, and reached their present position about 10 thousand years ago
6. Hypothesis of Ewing - Donna. One of the attempts to explain the causes of the Pleistocene Ice Age belongs to M. Ewing and W. Donn, geophysicists who made a significant contribution to the study of the topography of the ocean floor. They believe that in pre-Pleistocene times, the Pacific Ocean occupied the northern polar regions and therefore it was much warmer there than it is now. The Arctic land areas were then located in the northern part of the Pacific Ocean. Then, as a result of the drift of the continents, North America, Siberia and the Arctic Ocean took their current position. Thanks to the Gulf Stream, which came from the Atlantic, the waters of the Arctic Ocean at that time were warm and evaporated intensively, which contributed to heavy snowfalls in North America, Europe and Siberia. Thus, the Pleistocene glaciation began in these areas. It stopped due to the fact that as a result of the growth of glaciers, the level of the World Ocean dropped by about 90 m, and the Gulf Stream was eventually unable to overcome the high underwater ridges that separate the basins of the Arctic and Atlantic oceans. Deprived of the influx of warm Atlantic waters, the Arctic Ocean froze, and the source of moisture that feeds the glaciers dried up.
7. Hypothesis of ocean water circulation. There are many currents in the oceans, both warm and cold, which have a significant impact on the climate of the continents. The Gulf Stream is one of the wonderful warm currents that washes the northern coast of South America, passes through the Caribbean Sea and the Gulf of Mexico and crosses the North Atlantic, having a warming effect on Western Europe. There are also warm currents in the South Pacific and the Indian Ocean. The most powerful cold currents are sent from the Arctic Ocean to the Pacific through the Bering Strait and into the Atlantic Ocean - through the straits along the eastern and western coasts of Greenland. One of them - the Labrador Current - cools the coast of New England and brings fog there. Cold water also enters southern oceans from the Antarctic in the form of especially powerful currents moving north almost to the equator along the western coasts of Chile and Peru. The strong subsurface countercurrent of the Gulf Stream carries its cold waters south into the North Atlantic.
8. Hypothesis of change solar radiation. As a result of a long study of sunspots, which are strong plasma ejections in the solar atmosphere, it was found that there are very significant annual and longer cycles of changes in solar radiation. Solar activity peaks approximately every 11, 33, and 99 years, when the Sun radiates more heat, resulting in more powerful circulation of the earth's atmosphere, accompanied by more clouds and more abundant precipitation. Due to high cloud cover blocking Sun rays, the surface of the land receives less heat than usual.
Conclusion
In the course of the course work, ice ages were studied, which include ice ages. The glacial epochs have been established and disassembled with precision. Detailed information about the last ice age has been obtained. The last Quaternary epochs are revealed. And also studied the main causes of ice ages.
Bibliography
1. Dotsenko S.B. On the glaciation of the Earth at the end of the Paleozoic // Life of the Earth. Geodynamics and mineral resources. M.: Publishing House of Moscow State University, 1988.
2. Silver L.R. Ancient glaciation and life / Serebryany Leonid Ruvimovich; Responsible ed. G.A. Avsyuk. - M.: Nauka, 1980. - 128 p.: ill. - (Man and environment). - Bibliography.
3. Secrets of the Ice Ages: Per. from English / Ed. G.A. Avsyuk; Afterword G.A. Avsyuk and M.G. Grosvalda.-M.: Progress, 1988.-264 p.
4. http://ru.wikipedia.org/wiki/Glacial_epoch (Material from Wikipedia - the free encyclopedia)
5. http://www.ecology.dubna.ru/dubna/pru/geology.html (Article Geological and geomorphological features. N.V. Koronovsky)
6. http://ru.wikipedia.org/wiki/Ice_period (Material from Wikipedia - the free encyclopedia)
7. http://www.fio.vrn.ru/2004/7/kaynozoyskaya.htm (Cenozoic era)
The last ice age ended 12,000 years ago. In the most severe period, glaciation threatened man with extinction. However, after the glacier melted, he not only survived, but also created a civilization.
Glaciers in the history of the Earth
The last ice age 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 the interglacial, in one of the warmest periods of the planet's life. Far behind is the most severe ice age - the Late Proterozoic.
Despite global warming, scientists are predicting a new ice age. And if the real one comes only after millennia, then the Little Ice Age, which will reduce annual temperatures by 2-3 degrees, can 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 about 110,000 years ago and ended in the tenth millennium BC. The peak of cold weather fell on the period of 26-20 thousand years ago, the final stage of the Stone Age, when the glacier was the largest.
Little Ice Ages
Even after the glaciers melted, history has known periods of noticeable cooling and warming. Or, in other words, climate pessimism and optima. Pessima are sometimes referred to as Little Ice Ages. In the XIV-XIX centuries, for example, the Little Ice Age began, and the time of the Great Migration of Peoples was the time of the early medieval pessimum.
Hunting and meat food
There is an opinion according to which the human ancestor was rather a scavenger, since he could not spontaneously occupy a higher ecological niche. And all known tools were used to butcher the remains of animals that were taken from predators. However, the question of when and why a person began to hunt is still debatable.
In any case, thanks to hunting and eating meat, the ancient man received a large supply of energy, which allowed him to better endure the cold. The skins of slaughtered animals were used as clothing, shoes and walls of the dwelling, which increased the chances of surviving in a harsh climate.
bipedalism
Bipedalism appeared millions of years ago, and its role was much more important than in the life of modern office worker. Having freed his hands, a person could engage in intensive construction of a dwelling, the production of clothing, the processing of tools, the extraction and preservation of fire. Upright ancestors moved freely in open area, and their life no longer depended on the collection of fruits of tropical trees. Already millions of years ago, they freely moved over long distances and obtained food in river flows.
Walking upright played an insidious role, but it 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
The fire in the life of an ancient person was originally an unpleasant surprise, not a boon. Despite this, the ancestor of man first learned to “extinguish” it, and only later to 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 through the preparation of protein foods, as well as to remain active at night. This further increased the time to create conditions for survival.
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 receded, 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 herbaceous vegetation, a truly “antediluvian” landscape. Wide rivers flowed here, exceeding the size of the Tigris and Euphrates by one and a half times. Sahara in some periods became a wet savanna. The last time this happened was 9,000 years ago. This can be confirmed by cave drawings, which depicts the 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 "collective work" has shown itself more than once in the construction of parking lots and the manufacture of clothing. Deer and wild horses among ancient people enjoyed no less "honor".
Language and communication
Language was, perhaps, the main life hack of an ancient person. It was thanks to speech that important technologies for processing tools, mining and maintaining fire, as well as various fixtures person for daily survival. Perhaps in the Paleolithic language, the details of the hunt for large animals and the direction of migration were discussed.
Allerd warming
Until now, scientists are 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 forage plants. As a result of the extermination of a large number of animal species, a person in harsh conditions was threatened with 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). Nevertheless, warming has become an important factor in the migration of people to regions whose climate has become suitable for the emergence of agriculture.
A detailed study of glacial deposits made it possible to establish the most important property of glaciations - their periodicity. Almost all the continents of our planet at different times, to a large extent, and sometimes entirely, were covered with powerful glaciers.
At present, four major glaciations are distinguished in the history of the Earth: Precambrian; late Ordovician; Permian-Carboniferous; Cenozoic.
The determination of the absolute age of the Proterozoic tillites showed their sharp age difference - from 2 billion to 570 million years, which gave grounds to the English researcher G. Young to speak of at least three independent glaciations.
The first, most ancient Precambrian glaciation - the Lower Proterozoic - occurred about 2.5 billion years ago. Traces of it have been preserved in Canada, South America, South Africa, Karelia, India, Australia in the form of tillites, hatching and polished beds left by moving glaciers.
The second, Upper Proterozoic glaciation (1.5 billion years ago) left traces in equatorial and South Africa and in Australia.
At the end of the Proterozoic, in the Vendian (620-650 million years ago), the third most grandiose Precambrian occurred - the Scandinavian glaciation. Its traces have been found on almost all continents, from Svalbard and Greenland to equatorial Africa and Australia.
There were two glaciations in the Paleozoic. The first glaciation began in the Ordovician period 480 million years ago and continued until the Silurian for 40 million years. Glacial deposits of this age have been found in South America, in Africa - in Morocco, Libya, Spain, France and Scandinavia. According to the results of the reconstruction of the ancient Gondwana continent, the center of glaciation (the South Pole of the Earth at that time) was located near the western coast of central Africa, and the area of glaciation was more than 21 million km2, which is 1.5 times the area of modern Antarctica.
The second glaciation of the Paleozoic, which is sometimes called the great Permian-Carboniferous (or Gondwanan), began in the Carboniferous and continued until the end of the Permian period. According to modern definitions of absolute age, it lasted about 100 million years. It is believed that the center of this glaciation was in South Africa. Its traces in the form of thicknesses of tillites, whose thickness reaches 1000 m, sheep foreheads, hatched rocks are present on the territory of Africa, South America, Australia, India, Antarctica, which were part of the once single continent - Gondwana.
The most studied are the ancient Quaternary glaciations. In the Quaternary (Anthropogenic) period, powerful continental ice covered vast areas in Russia, Western Europe and America. Most researchers recognize the repeated Quaternary glaciations, the total area of which was about 45 million km2 (30% of the entire land), i.e., almost three times the area of modern glaciation. A study of the nature and composition of glacial deposits shows that epochs of glaciation alternated with interglacial periods.
On the territory of Western Europe, glacial deposits are best studied in the Alps. A. Penk and E. Brunner established four glaciations there, and subsequently some clarifications were made by J. Brian. The periodization of glaciations in North America was carried out by F. Flint. Comparison data of glaciations and interglacials are given in Table. 17.1.
For the European part of Russia, the scheme of periodization of glaciations by I.P. Gerasimov and K.K. Markov (see Table 17.1). With some clarifications from other researchers, five continental glaciations are distinguished: Oka (Lower Pleistocene), Dnieper and Moscow (Middle Pleistocene) and Valdai, which are divided into two independent glaciations - Kalinin and Ostashkov (Fig. 17.13). The possibility of identifying even older glaciations than the Oka, in the Lower Pleistocene and Pliocene, is not ruled out. Traces of such a glaciation, called Lithuanian, have been found in the Baltics. All ice ages are separated from each other by interglacials (from bottom to top): Likhvin between the Oka and Dnieper, Odintsovo between the Dnieper and Moscow, Mikulin between Moscow and Kalinin; Mologosheksna between the Kalinin and Ostashkov glaciations.
Ancient Quaternary glaciations covered vast expanses of Russia, Western Europe, North America, Antarctica and other territories. In Europe, the center of glaciation was Scandinavia, where the thickness of the ice sheet reached 2.5-3 km. The maximum distribution area was the Dnieper glaciation, which covered the entire north of Western Europe, and in the territory of the European part of Russia, glaciers descended along the valleys of the Dnieper and Don south of Kyiv, Kharkov, Saratov.
The traces of Pleistocene glaciations in the territory of the Northern Baikal region and the Stanovoi Upland have been studied in detail. Researchers D.-D.B. Bazarov and others provide the following convincing evidence of the multiple Pleistocene glacial epochs: successive nesting of troughs; the number of terminal and lateral moraines (there are at least three of them); them different height and morphological expression; creeping of some moraines on others; tiered arrangement of cars and varying degrees of their preservation; deep erosion separating the traces of one glaciation from another - all this speaks in general of three independent stages glaciations separated by interglacials. The first glaciation was the maximum and belonged to the Middle Pleistocene. It can be compared with the Samarovo glaciation of Western Siberia. Regarding the age of the second, there are different opinions. It is compared with the Taz (late Middle Pleistocene) or Zyryansk (Late Pleistocene) glaciation. The latter most likely occurred in the late Pleistocene and is analogous to the Sartan glaciation.
The facts confirming the glaciation of the Barguzinsky Range are given by V.V. Lamakin, who describes the highly developed moraines of the Baikal coast along the entire coastline. The distribution of the lower moraine shows that the glaciers formed wide piedmont shields on the coast of Baikal, consisting of a whole group of glaciers descending along the neighboring valleys of the Barguzinsky ridge. The thickness of the glaciers in some places reached 500 m. Apparently, small glaciers on the Baikal, Barguzin and Kodar ridges have survived from the last era of the Late Pleistocene glaciation.
In the history of the Earth, there were long periods when the entire planet was warm - from the equator to the poles. But there were also times so cold that glaciations reached those regions that currently belong to the temperate zones. Most likely, the change of these periods was cyclical. During warmer times, there could be relatively little ice, and it was only in the polar regions or on the tops of mountains. An important feature of ice ages is that they change the nature of the earth's surface: each glaciation affects the appearance of the Earth. By themselves, these changes may be small and insignificant, but they are permanent.
History of Ice Ages
We do not know exactly how many ice ages there have been throughout the history of the Earth. We know of at least five, possibly seven, ice ages, starting with the Precambrian, in particular: 700 million years ago, 450 million years ago (Ordovician), 300 million years ago - Permo-Carboniferous glaciation, one of the largest ice ages, affecting the southern continents. The southern continents refer to the so-called Gondwana, an ancient supercontinent that included Antarctica, Australia, South America, India and Africa.
The most recent glaciation refers to the period in which we live. The Quaternary period of the Cenozoic era began about 2.5 million years ago, when the glaciers of the Northern Hemisphere reached the sea. But the first signs of this glaciation date back 50 million years ago in Antarctica.
The structure of each ice age is periodic: there are relatively short warm epochs, and there are longer periods of icing. Naturally, cold periods are not the result of glaciation alone. Glaciation is the most obvious consequence of cold periods. However, there are quite long intervals that are very cold, despite the absence of glaciations. Today, examples of such regions are Alaska or Siberia, where it is very cold in winter, but there is no glaciation, because there is not enough rainfall to provide enough water for the formation of glaciers.
Discovery of ice ages
The fact that there are ice ages on Earth has been known to us since the middle of the 19th century. Among the many names associated with the discovery of this phenomenon, the first is usually the name of Louis Agassiz, a Swiss geologist who lived in the middle of the 19th century. He studied the glaciers of the Alps and realized that they were once much more extensive than they are today. It wasn't just him who noticed. In particular, Jean de Charpentier, another Swiss, also noted this fact.
It is not surprising that these discoveries were made mainly in Switzerland, since there are still glaciers in the Alps, although they are melting quite quickly. It is easy to see that once the glaciers were much larger - just look at the Swiss landscape, the troughs (glacial valleys) and so on. However, it was Agassiz who first put forward this theory in 1840, publishing it in the book "Étude sur les glaciers", and later, in 1844, he developed this idea in the book "Système glaciare". Despite initial skepticism, over time, people began to realize that this was indeed true.
With the advent of geological mapping, especially in Northern Europe, it became clear that earlier glaciers had a huge scale. Then there were extensive discussions about how this information relates to the Flood, because there was a conflict between geological evidence and biblical teachings. Initially, glacial deposits were called deluvial because they were considered evidence of the Flood. Only later it became known that such an explanation is not suitable: these deposits were evidence of a cold climate and extensive glaciation. By the beginning of the 20th century, it became clear that there were many glaciations, and not just one, and from that moment this area of science began to develop.
Ice Age Research
Known geological evidence of ice ages. The main evidence for glaciations comes from the characteristic deposits formed by glaciers. They are preserved in the geological section in the form of thick ordered layers of special deposits (sediments) - diamicton. These are simply glacial accumulations, but they include not only deposits of a glacier, but also deposits of melt water formed by its flows, glacial lakes or glaciers moving into the sea.
There are several forms of glacial lakes. Their main difference is that they are a water body enclosed by ice. For example, if we have a glacier that rises into a river valley, then it blocks the valley like a cork in a bottle. Naturally, when ice blocks a valley, the river will still flow and the water level will rise until it overflows. Thus, a glacial lake is formed through direct contact with ice. There are certain deposits that are contained in such lakes that we can identify.
Due to the way glaciers melt, which depends on seasonal changes in temperature, there is an annual melting of ice. This leads to an annual increase in minor sediments falling from under the ice into the lake. If we then look into the lake, we see stratification (rhythmic layered sediments) there, which is also known by the Swedish name "varves" (varve), which means "annual accumulations". So we can actually see annual layering in glacial lakes. We can even count these varves and find out how long this lake has existed. In general, with the help of this material, we can get a lot of information.
In Antarctica, we can see huge ice shelves that come off the land into the sea. And of course, ice is buoyant, so it floats on water. As it swims, it carries pebbles and minor sediments with it. Due to the thermal action of the water, the ice melts and sheds this material. This leads to the formation of the process of the so-called rafting of rocks that go into the ocean. When we see fossil deposits from this period, we can find out where the glacier was, how far it extended, and so on.
Causes of glaciation
Researchers believe that ice ages occur because the Earth's climate depends on the uneven heating of its surface by the Sun. So, for example, the equatorial regions, where the Sun is almost vertically overhead, are the warmest zones, and the polar regions, where it is at a large angle to the surface, are the coldest. This means that the difference in heating of different parts of the Earth's surface controls the ocean-atmospheric machine, which is constantly trying to transfer heat from the equatorial regions to the poles.
If the Earth were an ordinary sphere, this transfer would be very efficient, and the contrast between the equator and the poles would be very small. So it was in the past. But since there are now continents, they get in the way of this circulation, and the structure of its flows becomes very complex. Simple currents are restrained and altered, in large part by mountains, leading to the circulation patterns we see today that drive the trade winds and ocean currents. For example, one of the theories about why the ice age began 2.5 million years ago links this phenomenon with the emergence of the Himalayan mountains. The Himalayas are still growing very fast and it turns out that the existence of these mountains in a very warm part of the Earth governs things like the monsoon system. The beginning of the Quaternary Ice Age is also associated with the closing of the Isthmus of Panama, which connects the north and south of America, which prevented the transfer of heat from the equatorial Pacific to the Atlantic.
If the position of the continents relative to each other and relative to the equator allowed the circulation to work efficiently, then it would be warm at the poles, and relatively warm conditions would persist throughout the earth's surface. The amount of heat received by the Earth would be constant and vary only slightly. But since our continents create serious barriers to circulation between north and south, we have pronounced climatic zones. This means that the poles are relatively cold while the equatorial regions are warm. When things are happening as they are now, the Earth can change with variations in the amount of solar heat it receives.
These variations are almost completely constant. The reason for this is that over time the earth's axis changes, as does the earth's orbit. Given this complex climatic zoning, orbital change could contribute to long-term changes in climate, resulting in climate wobble. Because of this, we have not continuous icing, but periods of icing, interrupted by warm periods. This happens under the influence of orbital changes. The latest orbital changes are seen as three separate phenomena: one 20,000 years long, the second 40,000 years long, and the third 100,000 years long.
This led to deviations in the pattern of cyclic climate change during the Ice Age. The icing most likely occurred during this cyclic period of 100,000 years. The last interglacial epoch, which was as warm as the current one, lasted about 125,000 years, and then came a long ice epoch, which took about 100,000 years. We are now living in another interglacial era. This period will not last forever, so another ice age awaits us in the future.
Why do ice ages end?
Orbital changes change the climate, and it turns out that ice ages are characterized by alternating cold periods, which can last up to 100,000 years, and warm periods. We call them the glacial (glacial) and interglacial (interglacial) epochs. The interglacial era is usually characterized by roughly the same conditions that we observe today: high sea levels, limited territories icing and so on. Naturally, even now there are glaciations in Antarctica, Greenland and other similar places. But in general, the climatic conditions are relatively warm. This is the essence of interglacial: high sea levels, warm temperature conditions and generally a fairly even climate.
But during the ice age, the average annual temperature changes significantly, the vegetative belts are forced to shift north or south, depending on the hemisphere. Regions like Moscow or Cambridge become uninhabited, at least in winter. Although they may be habitable in summer due to the strong contrast between seasons. But what is actually happening is that the cold zones are expanding substantially, the average annual temperature is dropping, and the overall climate is getting very cold. While the largest glacial events are relatively limited in time (perhaps around 10,000 years), the entire long cold period can last 100,000 years or more. This is what the glacial-interglacial cycle looks like.
Due to the length of each period, it is difficult to say when we will exit the current era. This is due to plate tectonics, the location of the continents on the surface of the Earth. Currently, the North Pole and South Pole are isolated, with Antarctica at the South Pole and the Arctic Ocean to the north. Because of this, there is a problem with heat circulation. As long as the location of the continents does not change, this ice age will continue. In line with long-term tectonic changes, it can be assumed that it will take another 50 million years in the future until significant changes occur that allow the Earth to emerge from the ice age.
Geological implications
This frees up huge sections of the continental shelf that are flooded today. This will mean, for example, that one day it will be possible to walk from Britain to France, from New Guinea to South East Asia. One of the most critical places is the Bering Strait, which links Alaska with Eastern Siberia. It is quite small, about 40 meters, so if the sea level drops to a hundred meters, then this area will become land. This is also important because plants and animals will be able to migrate through these places and get into regions where they cannot go today. Thus, the colonization of North America depends on the so-called Beringia.
Animals and the Ice Age
It is important to remember that we ourselves are the "products" of the ice age: we evolved during it, so we can survive it. However, it is not a matter of individual individuals - it is a matter of the entire population. The problem today is that there are too many of us and our activities have significantly changed the natural conditions. Under natural conditions, many of the animals and plants that we see today have long history and survive the ice age well, although there are those that evolve slightly. They migrate and adapt. There are zones in which animals and plants survived the Ice Age. These so-called refugiums were located further north or south from their present distribution.
But as a result human activity some of the species died or became extinct. This has happened on every continent, with the possible exception of Africa. A huge number of large vertebrates, namely mammals, as well as marsupials in Australia, were exterminated by man. This was caused either directly by our activities, such as hunting, or indirectly by the destruction of their habitat. Animals living in northern latitudes today, in the past lived in the Mediterranean. We have destroyed this region so much that it will most likely be very difficult for these animals and plants to colonize it again.
Consequences of global warming
AT normal conditions by geological standards, we would soon enough be back in the Ice Age. But because of global warming, which is a consequence of human activity, we are postponing it. We will not be able to completely prevent it, since the causes that caused it in the past still exist today. Human activity, an unforeseen element of nature, affects atmospheric warming, which may have already caused a delay in the next glacial.
Today, climate change is a very relevant and exciting issue. If the Greenland Ice Sheet melts, sea levels will rise by six meters. In the past, during the previous interglacial epoch, which was about 125,000 years ago, the Greenland Ice Sheet melted profusely, and sea levels were 4–6 meters higher than today. It's certainly not the end of the world, but it's not time complexity either. After all, the Earth has recovered from catastrophes before, it will be able to survive this one.
The long-term outlook for the planet is not bad, but for humans, that's a different matter. The more research we do, the better we understand how the Earth is changing and where it leads, the better we understand the planet we live on. This is important because people are finally starting to think about changing sea levels, global warming and the impact of all these things on agriculture and the population. Much of this has to do with the study of ice ages. Through these studies, we will learn the mechanisms of glaciation, and we can use this knowledge proactively in an attempt to mitigate some of the changes that we ourselves are causing. This is one of the main results and one of the goals of research on ice ages.
Of course, the main consequence of the Ice Age is huge ice sheets. Where does water come from? Of course, from the oceans. What happens during ice ages? Glaciers form as a result of precipitation on land. Due to the fact that the water does not return to the ocean, the sea level falls. During the most severe glaciations, sea levels can drop by more than a hundred meters.
Climatic changes were most clearly expressed in periodically advancing ice ages, which had a significant impact on the transformation of the land surface under the body of the glacier, water bodies and biological objects that are in the zone of influence of the glacier.
According to the latest scientific data, the duration of glacial eras on Earth is at least a third of the entire time of its evolution over the past 2.5 billion years. And if we take into account the long initial phases of the genesis of glaciation and its gradual degradation, then the epochs of glaciation will take almost as much time as warm, ice-free conditions. The last of the ice ages began almost a million years ago, in the Quaternary, and was marked by an extensive spread of glaciers - the Great Glaciation of the Earth. The northern part of the North American continent, a significant part of Europe, and possibly Siberia as well, were under thick ice sheets. AT southern hemisphere under the ice, as now, was the entire Antarctic continent.
The main causes of glaciation are:
space;
astronomical;
geographical.
Cosmic Cause Groups:
change in the amount of heat on the Earth due to the passage of the solar system 1 time/186 million years through the cold zones of the Galaxy;
change in the amount of heat received by the Earth due to a decrease in solar activity.
Astronomical groups of causes:
change in the position of the poles;
the inclination of the earth's axis to the plane of the ecliptic;
change in the eccentricity of the Earth's orbit.
Geological and geographical groups of causes:
climate change and the amount of carbon dioxide in the atmosphere (increase in carbon dioxide - warming; decrease - cooling);
change in the direction of ocean and air currents;
intensive process of mountain building.
Conditions for the manifestation of glaciation on Earth include:
snowfall in the form of precipitation at low temperatures with its accumulation as a material for building up a glacier;
negative temperatures in areas where there are no glaciations;
periods of intense volcanism due to the huge amount of ash emitted by volcanoes, which leads to a sharp decrease in the supply of heat (sun rays) to earth's surface and causes a global decrease in temperature by 1.5-2ºС.
The oldest glaciation is the Proterozoic (2300-2000 million years ago) in South Africa, North America, and Western Australia. In Canada, 12 km of sedimentary rocks were deposited, in which three thick strata of glacial origin are distinguished.
Established ancient glaciations (Fig. 23):
on the border of the Cambrian-Proterozoic (about 600 million years ago);
late Ordovician (about 400 million years ago);
Permian and Carboniferous periods (about 300 million years ago).
The duration of ice ages is tens to hundreds of thousands of years.
Rice. 23. Geochronological scale of geological epochs and ancient glaciations
During the period of maximum distribution of the Quaternary glaciation, glaciers covered over 40 million km 2 - about a quarter of the entire surface of the continents. The largest in the Northern Hemisphere was the North American Ice Sheet, reaching a thickness of 3.5 km. Under the ice sheet up to 2.5 km thick was the whole of northern Europe. Having reached the greatest development 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink.
Before the Neogene period, the entire Earth had an even warm climate - in the region of the islands of Svalbard and Franz Josef Land (according to paleobotanical finds of subtropical plants) at that time there were subtropics.
Reasons for the cooling of the climate:
the formation of mountain ranges (Cordillera, Andes), which isolated the Arctic region from warm currents and winds (uplift of mountains by 1 km - cooling by 6ºС);
creation of a cold microclimate in the Arctic region;
cessation of heat supply to the Arctic region from warm equatorial regions.
By the end of the Neogene period, North and South America joined, which created obstacles for the free flow of ocean waters, as a result of which:
equatorial waters turned the current to the north;
the warm waters of the Gulf Stream, cooling sharply in northern waters, created a steam effect;
precipitation of a large amount of precipitation in the form of rain and snow has increased sharply;
a decrease in temperature by 5-6ºС led to the glaciation of vast territories (North America, Europe);
a new period of glaciation began, lasting about 300 thousand years (the frequency of glacier-interglacial periods from the end of the Neogene to the Anthropogen (4 glaciations) is 100 thousand years).
Glaciation was not continuous throughout the Quaternary period. There is geological, paleobotanical and other evidence that during this time the glaciers completely disappeared at least three times, giving way to interglacial epochs when the climate was warmer than the present. However, these warm epochs were replaced by cooling periods, and glaciers spread again. At present, the Earth is at the end of the fourth era of the Quaternary glaciation, and, according to geological forecasts, our descendants in a few hundred-thousand years will again find themselves in the conditions of an ice age, and not warming.
The Quaternary glaciation of Antarctica developed along a different path. It arose many millions of years before the time when glaciers appeared in North America and Europe. In addition to climatic conditions, this was facilitated by the high mainland that existed here for a long time. Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and reappeared, the Antarctic ice sheet has changed little in its size. The maximum glaciation of Antarctica was only one and a half times greater than the current one in terms of volume and not much more in area.
The culmination of the last ice age on Earth was 21-17 thousand years ago (Fig. 24), when the volume of ice increased to approximately 100 million km3. In Antarctica, glaciation at that time captured the entire continental shelf. The volume of ice in the ice sheet, apparently, reached 40 million km 3, that is, it was about 40% more than its present volume. The boundary of the pack ice shifted to the north by approximately 10°. In the Northern Hemisphere 20 thousand years ago, a giant Panarctic ancient ice sheet was formed, uniting the Eurasian, Greenland, Laurentian and a number of smaller shields, as well as extensive floating ice shelves. The total volume of the shield exceeded 50 million km3, and the level of the World Ocean dropped by at least 125m.
The degradation of the Panarctic cover began 17 thousand years ago with the destruction of the ice shelves that were part of it. After that, the "marine" parts of the Eurasian and North American ice sheets, which lost their stability, began to disintegrate catastrophically. The disintegration of the glaciation occurred in just a few thousand years (Fig. 25).
Huge masses of water flowed from the edge of the ice sheets at that time, giant dammed lakes arose, and their breakthroughs were many times larger than modern ones. In nature, spontaneous processes dominated, immeasurably more active than now. This led to a significant renewal of the natural environment, a partial change in the animal and plant world, and the beginning of human dominance on Earth.
The last retreat of the glaciers, which began over 14 thousand years ago, remains in the memory of people. Apparently, it is the process of melting glaciers and raising the water level in the ocean with extensive flooding of territories that is described in the Bible as a global flood.
12 thousand years ago the Holocene began - the modern geological epoch. The air temperature in temperate latitudes increased by 6° compared to the cold Late Pleistocene. Glaciation took on modern dimensions.
In the historical epoch - for about 3 thousand years - the advance of glaciers occurred in separate centuries with low air temperature and increased humidity and were called small ice ages. The same conditions developed in the last centuries of the last era and in the middle of the last millennium. About 2.5 thousand years ago, a significant cooling of the climate began. The Arctic islands were covered with glaciers, in the countries of the Mediterranean and the Black Sea on the verge of a new era, the climate was colder and wetter than now. In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, cluttered mountain passes with ice and destroyed some high-lying villages. This epoch is marked by a major advance of the Caucasian glaciers.
The climate at the turn of the 1st and 2nd millennium AD was quite different. Warmer conditions and the lack of ice in the northern seas allowed the navigators of Northern Europe to penetrate far north. From 870, the colonization of Iceland began, where at that time there were fewer glaciers than now.
In the 10th century, the Normans, led by Eirik the Red, discovered the southern tip of a huge island, the shores of which were overgrown with dense grass and tall shrubs, they founded the first European colony here, and this land was called Greenland, or “green land” (which is by no means now say about the harsh lands of modern Greenland).
By the end of the 1st millennium, mountain glaciers in the Alps, the Caucasus, Scandinavia, and Iceland also retreated strongly.
The climate began to seriously change again in the 14th century. Glaciers began to advance in Greenland, the summer thawing of soils became more and more short-lived, and by the end of the century, permafrost was firmly established here. The ice cover of the northern seas increased, and attempts made in subsequent centuries to reach Greenland by the usual route ended in failure.
From the end of the 15th century, the advance of glaciers began in many mountainous countries and polar regions. After the relatively warm 16th century, harsh centuries came, which were called the Little Ice Age. In the south of Europe, severe and long winters often repeated, in 1621 and 1669 the Bosphorus froze, and in 1709 the Adriatic Sea froze along the shores.
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About the second half of the 19th century, the Little Ice Age ended and a relatively warm era began, which continues to this day.
Rice. 24. The boundaries of the last glaciation
Rice. 25. Scheme of the formation and melting of the glacier (along the profile of the Arctic Ocean - Kola Peninsula - Russian Platform)
