Hello readers! I prepared a new article for you. I would like to talk about the glacial period on Earth.Let's be able to understand how these glacial periods occur, what is the cause and effect ...
Ice period on Earth.
Imagine for a moment that coldly fed our planet, and the landscape turned into an ice desert (more about deserts), over which ferocious northern winds are raging. Our land looked so in the glacial period - from 1.7 million to 10,000 years ago.
The process of formation of the Earth stores memories almost any corner of the globe. Running wave for the horizon of the hills, relating to the sky of the mountain, the stone, which was taken by a person to build cities, - each of them has its own story.
These prompts, during geological studies, we can tell us about the climate (about climate change), which was significantly different from today.
Our world was once shoveled by a thick cover of ice, which paved his way from the frozen poles to the Equator.
The land was a gloomy and gray planet in the vice of cold, which carried snow storms from the north and south.
Frozen planet.
According to the nature of the glacial sediments (axial chip material) and the geologists broken, the geologists concluded that there were actually several periods.
Even in the Precambrian period, about 2,300 million years ago, the first ice age began, and the last, and the best studied, took place between 1.7 million years ago and 10,000 years ago in t. N. Pleistocene era. It is his simplisticly called the Ice Age.
Thaw.
These ruthless vice managed to avoid some lands, where it was usually cold, but the winter reigned on the whole earth.
Extensive areas of deserts and rainforests were located in the area of \u200b\u200bthe Equator. To survive a multitude of plant species, reptiles and mammals, precisely these heat oases played a significant role.
In general, the climate of the glacier was not always cold. Glaciers before retreating, crawled several times from the north to south.
In some parts of the planet, the weather in the breaks between the offensive of the ice was even warmer than today. For example, almost tropical was climate in southern England.
Paleontologists, thanks to the petrified remains, argue that in the shores of the Thames once wandered elephants and hippopos.
Such a period of thaws - still known as interglacial stages - lasted several hundred thousand years, until the cold returned.
Newly moving to the south of ice streams, after themselves left 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: deposits and erosion.
When on its way, the moving mass of ice erases the soil, erosion occurs. Whole valleys in the indigenous rock hollow out the fragments of rocks, brought by a glacier.
As a giant grinding machine, which was polished by land and created large grooves, which are called glacial hatching, the movement of crushed stone and ice acted.
The valleys have expanded and deepened over time, acquired a clear U-shaped form.
When the glacier (about what glaciers is,) discharged the fragments of the rocks, which he transferred, formed deposits. Usually these happened when ice was melted, leaving a large gravel, fine-grained clay and huge boulders on the huge territory of piles and huge boulders.
Causes of glaciation.
What is called glaciation, just still do not know scientists. Some believe that the temperature on the earth's poles, the last millions of years, lower than ever in the entire history of the Earth.
The drift of the continents (more about the continent drift) could serve as a reason. About 300 million million years ago, there was only one gigantic supercontinent - Pangeus.
The split of this supercontinent was gradually happening, and as a result, the movement of the mainland left the Northern Arctic Ocean almost completely surrounded by the Earth.
Therefore, now, unlike the past, there is only a minor mixing of the water of the Arctic Ocean with warm waters to the south.
This comes out in which situation: the ocean never warms well in the summer, and is constantly covered with ice.
The South Pole is located Antarctica (more on this mainland), which is very far from warm currents, which is why the mainland sleeps under the ice.
Cold return.
Global cooling has other reasons. According to assumptions, one of the reasons is the degree of inclination of the earth's axis, which is constantly changing. Together with the improper form of the orbit, this means that the land into some periods is further from the Sun than to others.
And if at least the percentage changes the amount of solar heat, it can lead to a difference at the temperature on the ground for a whole degree.
To start a new ice age, there will be quite enough interaction of these factors. It is also believed that the ice age can cause accumulation in the atmosphere of dust as a result of its pollution.
Some scientists believe that when a giant meteor is collided with the land, 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 freezing. The beginning of the new ice age can contribute similar factors.
Approximately 5000 years, some scientists predict the onset of a new ice age, while others argue that the Ice Age never ended.
If we take into account that the stage of the Pleistocene glacier period, which was the last, ended 10,000 years ago, it is possible that now we are experiencing a passage stage, and ice can return after a while.
On such a note, I finish this topic. I hope that the story about the glacial period on Earth, did not "frozen" you 🙂 And finally, I suggest you subscribe to the newsletter of fresh articles by mail so as not to miss their output.
We are in the power of autumn, and is becoming colder. Do we move to the glacial period, is interested in one of the readers.
Funior Danish summer behind. The leaves fall away from the trees, the birds fly south, becomes darker and, of course, colder too.
Our reader Lars Petersen (Lars Petersen) from Copenhagen began to prepare for cold days. And he wants to know how serious he needs to be prepared.
"When does the next Ice Age begins? I learned that the glacial and interdictive periods replace each other regularly. Since we live in the interledstnik, it is logical to assume that the next ice age awaits us ahead, isn't it? " - He writes in a letter to the section "Ask Science" (Spørg Videnskaben).
We will shudder in the editorial when we thought about the cold winter that lies on us at that end of the autumn. We, too, would be happy to recognize if we are not a glacial period.
Until the next glacial period is still far
Therefore, we were addressed to the teacher of the Center for Fundamental Studies of Ice and Climate at Copenhagen Suna Rasmussen University (Sune Olander Rasmussen).
Sune Rasmussen studies cold and receives information about the weather of the past, the storm of Greenland glaciers and icebergs. In addition, he can use his knowledge in order to play the role of a "predictor of the glacial periods".
"In order to come a glacial period, several conditions must coincide. We cannot accurately predict when the glacial period begins, but even if humanity did not affect the climate, our forecast is such that the conditions for it will be shared at best in 40 - 50 thousand years, "Sunmussen reassures us.
Since we still speak with the "Ice Personal Posterness", we can get some more information about which "conditions" are we talking about to understand a little more in the fact that such a glacial period.
That's what a glacial period
Sune Rasmussen says that during the last glacial period, the average temperature on Earth was a few degrees lower than today, and that the climate at higher latitudes was colder.
Most of the northern hemisphere was covered with massive ice cover. For example, Scandinavia, Canada and some other parts of North America were covered with a three-kilometer ice shell.
The huge weight of the ice cover was invented by the globe on a kilometer inside the earth.
Ice periods longer than interledstial
However, 19 thousand years ago began to occur in climate.
This meant that the Earth gradually became warmer, and for the next 7,000 years, he freed himself from the cold grip of the ice age. After that, the interledstial, in which we are now and are located.
Context
New Ice Age? Not soon
THE NEW YORK TIMES 10.06.2004glacial period
Українська True 25.12.2006 In Greenland, the last residues of the shell came up very sharply 11,700 years ago or to be accurate 11 715 years ago. This is evidenced by the study of SUN Rasmussen and his colleagues.It means that since the last glacial period passed 11,715 years, and this is a completely normal length of passionate.
"It's funny that we usually consider the ice age as an" event ", although in fact everything is just the opposite. The middle glacial period lasts 100 thousand years, while the interledstnikier continues from 10 to 30 thousand years. That is, the land is more often in the glacial period than the opposite. "
"A couple of last interleden periods lasted only about 10 thousand years, which explains the widespread, but the erroneous opinion is that our current interledstial period is approaching the end," says Sun Rasmussen.
Three factors affect the ability to start a glacial period
The fact that the earth will plunge into a new ice age after 40-50 thousand years, depends on the fact that the orbits of the Earth's rotation around the Sun have small variations. Variations determine how much sunlight on what latitudes is falling, and thereby affects how warmth or cold there.
This discovery made Serbian Geophysic Milutin Milankovich almost 100 years ago, and therefore it is known as Milankovich's cycles.
Milankovich cycles is:
1. Earth's rotation orbit around the Sun, which varies cyclically about once every 100,000 years. Orbit turns from almost round to more elliptical, and then back. Because of this, the distance to the Sun varies. The further the earth from the Sun, the less solar radiation is obtained by our planet. In addition, when the form of the orbit changes, the length of the age of year is changing.
2. The slope of the earth axis, which fluctuates between 22 and 24.5 degrees relative to the orbit of rotation around the Sun. This cycle covers approximately 41,000 years. 22 or 24.5 degrees - it seems not such a significant difference, but the tilt of the axis is very effectively affected by the severity of different times of the year. The greater the land is inclined, the greater the difference between the winter and summer. At the moment, the slope of the earth's axis is 23.5 and it decreases, which means that the differences between the winter and in the summer will decline in the next thousand years.
3. The direction of the earth's axis relative to the space. The direction changes cyclically with a period of 26 thousand years.
"The combination of these three factors determines whether there are prerequisites for the beginning of the ice age. It is almost impossible to imagine how the interaction of these three factors occurs, but with the help of mathematical models we can calculate how many solar radiation are obtained by certain latitudes at a certain time of the year, and also received in the past and will receive in the future, "says Sun Rasmussen.
Snow in the summer leads to the glacial period
In particular, temperatures are played in this context in this context.
Milankovich realized that the prerequisite for the start of the glacial period, the summer in the northern hemisphere should be cold.
If the snowy winter and most of the northern hemisphere covered with snow, then the temperature and the number of sunny clock are determined in the summer, whether the snow is allowed to stay for all summer.
"If the snow does not melt in the summer, then little sunlight penetrates into the ground. The rest is reflected back into space with a snow-white bedspread. It aggravates the cooling, which began due to changes in the orbit of the Earth's rotation around the Sun, "says Sun Rasmussen.
"Further cooling brings even more snow, which further reduces the amount of absorbed heat, and so on, until the glacial period begins," he continues.
In the same period, the period with hot years leads to the fact that the glacial period ends. Then the hot sun melts the ice enough so that the sunlight can again fall into dark surfaces, like soil or the sea, which absorb it and heat the earth.
People pull the next glacial period
Another factor that matters to the possibility of the beginning of the glacial period is the amount of carbon dioxide in the atmosphere.
Just like snow reflecting the light, enhances the formation of ice or accelerates its melting, increasing the content of carbon dioxide in the atmosphere from 180 ppm to 280 ppm (million dollars) contributed to the removal of the Earth from the last ice age.
However, from the moment the industrialization began, people all the time are engaged in a further increase in carbon dioxide, so now it is almost 400 ppm.
"Nature has taken 7,000 years to increase the share of carbon dioxide to 100 ppm after the end of the glacial period. People managed to do the same in just 150 years. It is of great importance in order whether the Earth will be able to enter the new ice age. This is a very significant impact, which means not only what the ice age cannot begin at the moment, "says Suna Rasmussen.
We thank Lars Petersen for a good question and send in a winter gray T-shirt in Copenhagen. We also thank Sun Rasmussen for a good answer.
And we urge our readers to send more scientific issues on [Email Protected]
Did you know?
Scientists always talk about the glacial period only in the northern hemisphere of the planet. The reason is that there is too little sushi in the southern hemisphere, on which a massive layer of snow and ice can lie.
Over the deduction of Antarctica, the entire southern part of the southern hemisphere is covered with water, which does not provide good conditions for the occurrence of thick ice shell.
Insurance materials contain estimates of exclusively foreign media and do not reflect the position of the EOSMI's editorial office.
Scientists note that the glacial period is part of the ice era, when earth covers hides ice on long millions of years. But many are called the ice age of a segment of the history of the Earth, which ended about twelve thousand years ago.
It is worth noting that history of glacial period There was a huge number of unique features that did not reach our time. For example, unique animals who were able to adapt to existence in this difficult climate - mammoths, rhinos, saber-toothed tigers, cave bears and others. They were covered with thick fur and quite large sizes. Herbivores adapt themselves to extract food from under the searel surface. Take rhinos, they hit the ice horn and fed on plants. As not strange, the vegetation was diverse. Of course, many species of plants disappeared, but herbivores were freely accessible to food.
Despite the fact that the ancient people were small sizes and did not possess the cover of wool, they also were able to survive during the ice age. Their life was incredibly dangerous and difficult. They built small dwellings and insulated their skins of killed animals, and meat used to eat. People came up with various traps to lure large animals there.
Fig. 1 - Ice Age
For the first time about the history of the glacial period, they spoke in the eighteenth century. Then, geology began to be laid as the scientific industry, and scientists began to find out what origin has boulders in Switzerland. Most researchers agreed in a single point of view that they have a glacial beginning. In the nineteenth century, the assumption was put forward that the climate of the planet was susceptible to sharp cooling. And a little later, the term was announced "glacial period". Entered His Louis Agassis, whose ideas were first not recognized as a general public, but then it was proved that many of his works really have grounds.
In addition to the fact that geologists were able to establish the fact that the glacial period had a place to be, they also tried to find out for what reason it arose on the planet. The most common opinion states that the movement of lithospheric plates can block warm flows in the ocean. It gradually causes the formation of an ice array. If large-scale glacial covers have already been formed on the surface of the Earth, they will cause a sharp cooling, reflecting the sunlight, and hence the heat. Another reason for the formation of glaciers could become a change in the level of greenhouse effects. The presence of large arctic arrays and the rapid spread of plants eliminates the greenhouse effect by replacing carbon dioxide for oxygen. No matter what the reason for the formation of glaciers is a very long process that can enhance and the effect of solar activity on the ground. Changes in the orbit of our planet around the sun make it extremely susceptible. The remoteness of the planet from the "main" star also affects the influence. Scientists suggest that even in the times of the largest glacial periods, the earth was covered with ice by only one third of the entire area. There are assumptions that Ice periods had to be also when the whole surface of our planet was covered with ice. But this fact remains controversial in the world of geological research.
To date, the most significant glacial array is Antarctic. Ice power in some places reaches more than four kilometers. Glaciers move on average at a speed of five hundred meters per year. Another impressive icy cover is in Greenland. About seventy percent of this island, glaciers occupy, and this is one tenth ice of our entire planet. At the moment, scientists believe that the Ice Age will not be able to begin at least a thousand years. The thing is that in the modern world there is a colossal emission of carbon dioxide into the atmosphere. And as we found out earlier, the formation of glaciers is possible only with the low level of its content. However, this puts another problem to humanity - global warming, which may be no less large-scale than the beginning of the glacial era.
Climatic changes were most pronounced in periodically advancing glacial periods, which had a significant impact on the conversion of the surface of the sushi under the body of the glacier, water objects and biological objects in the zone of the influence of the glacier.
According to the latest scientific data, the duration of glacial er on Earth is at least a third of all the time of its evolution for the last 2.5 billion years. And if we take into account the long initial phases of the origin of the glaciation and its gradual degradation, then the epochs of the glaces will take almost the same time as warm, rudely, conditions. The last of the glacial periods began almost a million years ago, at a quaternary time, and was marked by the extensive spread of glaciers - the great glaciation of the Earth. Under the powerful cover of ice, the northern part of the North American continent, a significant part of Europe, and possibly Siberia is also also. In the southern hemisphere under the ice, as well as now, there was all Antarctic mainland.
The main causes of glaestations are:
cosmic;
astronomical;
geographical.
Space groups of reasons:
changing the amount of heat on Earth due to the passage of the solar system 1 time / 186 million through the cold zones of the Galaxy;
changes in the amount of heat obtained by the Earth due to the decrease in solar activity.
Astronomical groups of reasons:
changing the position of the poles;
the slope of the earth's axis to the plane of the ecliptic;
change the eccentricity of the Earth orbit.
Geological and geographical groups of reasons:
climate change and the amount of carbon dioxide in the atmosphere (increase in carbon dioxide - warming; reduction - cooling);
changes in the directions of oceanic and air flows;
intensive process of mountain formation.
The conditions of manifestation of glaciation on Earth include:
the fallout of snow in the form of precipitation under conditions of low temperatures with its accumulation as a material for increasing the glacier;
negative temperatures in areas where there are no glaciations;
periods of intense volcanism due to the huge amount of ash ejected by volcanoes, which leads to a sharp decrease in heat intake (sunlight) on the ground surface and causes global temperatures to 1.5-2ºС.
The most ancient glaciation - Proteroza (2300-2000 million years ago) on the territory of South Africa, North America, Western Australia. In Canada, 12 km of sedimentary breeds were postponed, in which three powerful strata of glacial origin are distinguished.
Installed ancient glaciations (Fig. 23):
on the border of Cambrian-Proterozoy (about 600 million years ago);
late Ordovik (about 400 million years ago);
perm and coal periods (about 300 million years ago).
The duration of the glacial periods dozens - hundreds of thousands of years.
Fig. 23. Geochronological scale of geological eras and ancient glaciation
During the maximum spread of quaternary glaciation, the 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 Shield, which thoroughly reaching 3.5 km. Under the glacial cover up to 2.5 km, the entire Northern Europe was. Having achieved the greatest development of 250 thousand years ago, the Quaternary Glaciers of the Northern Hemisphere began to decline gradually.
Before the non -ogenic period throughout the land - a flat warm climate - in the area of \u200b\u200bthe islands of Spitsberena and the Land of Franz Joseph (on the paleobotanic finds of subtropical plants) at that time were subtropics.
Causes of climate cooling:
the formation of mountain ranges (Cordillera, Andes), isolated the area of \u200b\u200bthe Arctic from warm currents and winds (lifting the mountains per 1 km - cooling 6ºС);
creating a cold microclimate in the Arctic area;
termination of heat admission to the Arctic Area from Warm Equatorial Regions.
By the end of the non -ogenic period, North and South America were connected, which created obstacles to the free flow of ocean water, as a result:
equatorial waters turned for north;
warm waters of Golf Stream, sharply cooled in the northern waters, created a steam effect;
the loss of a large amount of precipitation in the form of rain and snow has sharply increased;
the decrease in temperature by 5-6ºС led to the glaciation of huge territories (North America, Europe);
a new period of glaciation began with a duration of about 300 thousand years (the frequency of the ilestone periods from the end of the neogen in anthropogen (4 glaciations) was 100 thousand years old).
The glaciation was not continuous throughout the quaternary period. There are geological, paleobotanic and other evidence that during this time the glaciers have completely disappeared at least three times, replacing the epochs of interdictions when the climate was warmer modern. However, the change of this warm epochs came cooling, and the glaciers applied again. Currently, the Earth is located at the end of the fourth era of quaternary glaciation, and, according to geological forecasts, our descendants in a few hundred thousand years will again be in the conditions of a glacial period, not warming.
On another way, the Quaternary glaciation of Antarctica developed. It arose for many millions of years before the time the glaciers appeared in North America and Europe. In addition to climatic conditions, this contributed to the high mainland existed here. Unlike the ancient glacial coverings of the northern hemisphere, which they disappeared, then again arose, the Antarctic Ice Cover changed little in its sizes. The maximum flying of Antarctica was more modern just a half times in volume and slightly more in the area.
The culmination of the last glacial era on Earth was 21-17 thousand years ago (Fig. 24), when the volume of ice increased approximately 100 million km 3. In Antarctic, the olelion at that time was captured by the entire continental shelf. The volume of ice in glacial cover seems to reach 40 million km 3, that is, it was about 40% more than its modern volume. The border of the packing ice shifted to the north of approximately 10 °. In the northern hemisphere 20 thousand years ago, a giant panarctic pedestrian cover was formed, uniting Eurasian, Greenland, Lavrentinsky and a number of smaller shields, as well as extensive floating shelves. The total shield volume exceeded 50 million km 3, and the level of the world ocean dropped at least 125m.
The degradation of Panarctic Pokrov began 17 thousand years ago from the destruction of the shelf glaciers. After that, the "maritime" parts of the Eurasian and North American Iceprokes, which have lost stability, began to colastically collapse. The collapse of glaciation occurred in just a few thousand years (Fig. 25).
A huge masses of water flowed from the edge of the glacial coverings at that time, gigantic sodium lakes arose, and their breakthroughs were many times more modern. Nature dominated natural processes, immeasurably more active than now. This led to a significant renewal of the natural environment, a partial change of animal and plant world, the beginning of the domination on the Earth of man.
The last recession of glaciers, which began over 14 thousand years ago, remains in memory of people. Apparently, it is the process of melting glaciers and lifting water levels in the ocean with an extensive flooding of the territories described in the Bible as a global flood.
12 thousand years ago, Holocene came - a modern geological era. The air temperature in moderate latitudes increased by 6 ° compared to the cold late Pleistocene. The glaciation took modern sizes.
In the historical era - about 3 thousand years - the advancing of glaciers occurred in separate centuries with a reduced air temperature and increased moisturgencies and got the name of small glacial periods. The same conditions were in the last century past era and in the middle of the past millennium. About 2.5 thousand years ago, a significant cooling climate began. The Arctic Islands were covered with glaciers, in the countries of the Mediterranean and the Black Sea region on the verge of a new era climate was colder and wet than now. In the Alps in the I millennium BC. e. The glaciers have moved to lower levels, closed the mountains of the ice and destroyed some highly located villages. This era accounts for the major advancing of Caucasian glaciers.
The climate at the turn of the I and II Millenniums of the New Era was completely different. Warm conditions and lack of ice in the northern seas allowed northern Europe's navigators to penetrate far from the north. Since 870, Iceland's colonization began, where glaciers at that time were less than now.
In the 10th century, Normans, Lelin-driven by Eyric, found the southern tip of the huge island, whose shores threw a thick grass and a high shrub, they founded here the first European colony, and the land was called Greenland, or the Green Earth (which now in no way You will say about the harsh lands of modern Greenland).
By the end of the first Millennium, the mountain glaciers in the Alps, in the Caucasus, in Scandinavia and Iceland, were strongly retreated.
The climate began to seriously change in the XIV century. Greenland began to advance, the summer thawing of the soils became more and more short-term, and by the end of the century, the eternal permafrost was firmly installed. The Arcticity of the Northern Seas increased, and attempts made in the next century to achieve Greenland in the usual way ended in failure.
Since the end of the 15th century, the advancing of glaciers began in many mountainous countries and polar areas. After a relatively warm XVI century, harsh centuries came, called a small glacial period. In the south of Europe, harsh and long and long winter were often repeated, in 1621 and 1669, the Bosphorus shed, and in 1709 the Adriatic Sea frowned along the shores.
IN 
a small glacial period ended about the second half of the XIX century and a relatively warm era, ongoing and understood, began.
Fig. 24. The boundaries of the last glaciation
Fig. 25. Scheme of the formation and melting of the glacier (according to the Northern Arctic Ocean profile - Kola Peninsula - Russian platform)
The oldest glacial sediments, known today, have age about 2.3 billion, years, which corresponds to the lower proteoda of the geochronological scale.
They are represented by petrified major Moraine Sweets of Gogand in the south-east of the Canadian Shield. The presence of typical values \u200b\u200bof an oral and drowned form in them with sedils, as well as the occurrence on the covered hatch box indicates their glacial origins. If the main mining in the English literature is indicated by the term TILL, then more ancient glacial sediments who have passed the stage leafi (petrification), it is customary to refer tillite. The appearance of Tillitis has and sediments of the Sweet Bruce and Ramsay Lake, also with the Nizhneproterozoic age and developed on the Canadian shield. This powerful and complex complex complex of interpretated glacial and interglacial sediments is conditionally attributed to one glacial era, called Huron.
The deposits of the Bijaar series in India, Transval and Withersradd series in South Africa and Australia series are compared with Guron Tillites. Consequently, there is reason to talk about the planetary scale of the Nizhneproterozoic glaciation.
As the last development of the Earth, she survived several as large glacial eras, and the closer to our time they took place, the more data on their characteristics we have. After the Huronous era, GNE care (about 950 million years ago), Svetskaya (700, possibly 800 million years ago), Varangian, or, on other authors, Venndskaya, Lapland (680-650 million years ago), then Ordovik (450-430 million years ago) and, finally, the most widely well-known Late Paleozoic Gondvskaya (330-250 million years ago) glacier eras. A later mansion on this list is the Late Bindozoic Ice Stage, which began 20-25 million years ago, with the advent of Antarctic Ice Cover and, strictly speaking, continuing to this day.
According to the Soviet geologist N. M. Chumakov, the traces of the Vendian (Lapland) glaciation were found in Africa, Kazakhstan, in China and in Europe. For example, in the middle and upper dnipher pool, drilling fluids are opened by Tillitis, a few meters of power belonging to this time. In the direction of the movement of ice, reconstructed for the Vendian era, it is assumed that the center of European Ice Cover at that time was somewhere in the Baltic Shield District.
The Gondwan Glacier Epoch attracts the attention of specialists throughout the whole century. At the end of the last century, geologists have discovered in southern Africa, near the bucket settlement of Neutghedacht, which in the pool r. Waal, perfectly pronounced glacial bridges with hatching tracks on the surface of hollow-convex "Baranje Lbov", composed of Precambrian rocks. It was the time of the struggle between the theory of drift and the theory of cover glaciation, and the main focus of researchers was riveted not to age, but to the signs of the glacial origin of these formations. Ice scars of the Neutgedacht, "Curchaeous Rocks" and "Barani Liba" were so well expressed that the famous like-minded people who studied them in 1880 A. Wallace considered them belonging to the last glacial era.
Several later, the late-Paleozoic age of glaciation was established. Glacial sediments, occurring under the carbonaceous shale with the remnants of plants of the coal and Perm periods, were discovered. In the geological literature, this thickness received the name of the twine series. At the beginning of our century, a well-known German specialist in modern and ancient glaciation Alps A. Penk, personally convinced of the amazing similarity of these sediments with young Alpine Moraques, managed to convince many of his colleagues. By the way, it was Poinom that the term "Tillit" was proposed.
Permocarbonic glacial sediments were found on all continents of the southern hemisphere. These are Tillitis Talchir, open in India in 1859, Itarara in South America, Kuttung and Camiloron in Australia. Footprints of Gondwan glaciation and the sixth continent, in the transntorctic mountains and the mountains of Elsurta were found. Traces of synchronous glaciation of all these territories (with the exception of the then not yet studied Antarctic) served as an outstanding German scientist A. Vegener with an argument when nominating a hypothesis of continent drift (1912-1915). His rather small predecessors pointed to the similarity of the outlines of the West Bank of Africa and the eastern coast of South America, which resemble as if torn in the same way and removed from each other.
It was repeatedly indicated for the similarity of the Late Palleozoic plant and the animal world of these continents, on the community of their geological structure. But it was exactly the idea of \u200b\u200bsimultaneous and, probably, a single glaciation of all the continents of the southern hemisphere forced Vegeners to put forward the concept of Panghai - the Great Prama Materick, who was glued to the parts, which then began to drift on the globe.
According to modern ideas, the southern part of Panghai, called Gondwana, split about 150-130 million years ago, in the Jurassic and the beginning of the Cretaceous period. The modern theory of global tectonics, the modern theory of global tectonics, which has grown out of guessing, allows you to successfully explain all the facts known to date about the Late Paleozoic War Assignment of the Earth. Probably, the South Pole at that time was close to the middle of the Gondwana and its significant part was covered with a huge ice shell. The detailed facial and textural study of Tillitis suggests that its food area was located in Eastern Antarctica and, possibly, somewhere in the Madagascar area. It was established, in particular, that when combining contours of Africa and South America, the direction of the glacial hatching on both continents coincides. Together with other lithological materials, this testifies to the movement of Gondwan ice from Africa to South America. Some other large glacial flows that existed in this glacial era are restored.
The glaciation of Gondwana ended in the Perm period, when the Pramateric still kept its integrity. Perhaps it was associated with the migration of the southern pole in the direction of the Pacific Ocean. In the future, global temperatures continued to gradually increase.
Triassic, Jurassic and chalk periods of the geological history of the Earth were characterized by rather even and warm climatic conditions on most of the planet. But in the second half of the Cenozoa, about 20-25 million years ago, the ice began their slow offensive on the southern pole. By this time, Antarctica took a position close to modern. The movement of the fragments of Gondwana led to the fact that there were no significant sections of sushi next to the southern polar mainland. As a result, according to the American geologist, J. Kennet, in the ocean surrounding Antarctica, there was a cold circumpolar flow, even more contributing to the isolation of this mainland and the deterioration of its climatic conditions. Near the southern pole of the planet began to accumulate the ice of the most ancient from the latalies of the land.
In the northern hemisphere, the first signs of the Late Bainozoic glaciation, according to the estimates of various specialists, have age from 5 to 3 million years. It is not necessary to talk about any noticeable displacements in the restrain position for such a short period of geological standards. Therefore, the reason for the new Ice Epoch should be sought in the global restructuring of the energy balance and climate of the planet.
A classic area, on the example of which for decades the history of the ice eras of Europe and the entire northern hemisphere was studied, are the Alps. The proximity to the Atlantic Ocean and the Mediterranean Sea provided a good moisture supply of alpine glaciers, and they were sensitive to climate cooling with a sharp increase in their volume. At the beginning of the XX century. A. Penk, examining the geomorphological structure of the Alpine Previation, came to the conclusion of four major glacial epochs, survived by the Alps in a recent geological past. These glaciations received the following names (from the most ancient to the youngest): Gütz, Mindel, Riss and Würm. Their absolute age for a long time remained unclear.
At about the same time, information was made from various sources that the plain territories of Europe have repeatedly experienced the advancing of ice. As the actual material accumulates polyvaniasis (The concept of multiplicity of glaciation) became stronger. By the 60th year. Our century wide recognition in our country and abroad received a diagram of four-time glaciation of European plains, close to the Alpine scheme A. Penka and its co-author E. Trunkner.
Naturally, the most well-studied postponement of the last glacial cover is compared with the Vurm's glaciation of the Alps. In the USSR, he received the name of Valdai, in Central Europe - Vistula, in England - Deministrative, in the USA - Wisconsinsky. The Valdai glaciation was preceded by membrane, in its climatic parameters close to modern conditions or a little more favorable. By the name of the reference size, in which the deposits of this passionland were opened (s. Mikulino Smolensk region) in the USSR, it was called Mikulinsky. On the Alpine Scheme, this period of time is referred to as Riss-Würm's interwork.
Prior to the beginning of the Mikulinsky Inseciend Century, the Russian plain was covered with ice of the Moscow glaciation, which, in turn, was preceded by Roslavl Interlednikia. The next step down the dnipro glaciation was down. It is considered to be maximized according to its size and traditionally is linked to the Alps Glacier Epoch. The Dnieper Ice Age on the territory of Europe and America there were warm and wet conditions of Lichvin Internias. The deposits of the Lichvin era are fed by quite poorly preserved precipitation of the Oksky (Mindelian alpine scheme) of glaciation. DOKOVSKY WARNING TIME Some researchers are already considered no passionate ones, but by the Snadnikovy Epoch. But in the last 10-15 years there are more and more reports about new, more ancient glacier sediments opened at different points of the northern hemisphere.
Synchronization and linkage of the stages of nature development recovered on various source data and in various in their geographical position of the globe points is a very serious problem.
The fact of the natural alternation of glacial and intergaren eras in the past few of the researchers today is in doubt. But the reasons for such alternations are not yet clearly clarified. The solution of this problem is prevented first of all the lack of strictly reliable data on the rhythm of natural events: the alone stratigraphic scale of the glacial period causes a large number of critical comments and does not yet exist for its reliably proven option.
A relatively reliably installed can be considered only the history of the last ice-growing cycle, which began after the degradation of the ice of the rice glaciation.
The age of the rice glacial epoch is estimated at 250-150 thousand years. The Mikulinsky (RISS-Vurm) interlednikia reached its optimum about 100 thousand years ago. Approximately 80-70 thousand years ago, a sharp deterioration in climatic conditions is recorded on the entire globe, marking the transition to the Würm Ice Cycle. During this period, in Eurasia and North America degrade the broadstream forests, replacing the landscape of the cold steppe and forest-steppe, there is a quick change of faunistic complexes: they are in them the leading place is occupied by cold-grade species - mammoth, hairy rhino, giant deer, luming, lemming. In high latitudes are increasing in the volume of old glacial hats and grow new ones. Water necessary for their formation decreases from the ocean. Accordingly, it begins to lower its level, which is recorded on the stairs of the sea terraces at the now flooded sections of the shelf and on the islands of the tropical zone. Cooling ocean waters is reflected in the restructuring of sea microorganisms complexes - for example, die away foraminifera Globorotalia Menardii Flexuosa. The question of how far the mainland ice moved at this time is still discussion.
Between 50 and 25 thousand years ago, the natural situation on the planet was again slightly improved - a relatively warm Middle Merma interval occurred. I. I. Krasnov, A. I. Moskvitin, L. R. Silver, A. V. Raukas and some other Soviet researchers, although in the details of their construction quite significantly differ from each other, yet inclined to compare this period of time with independent Insecrehension.
Such an approach, however, contradict the data of V. P. Grichuk, L. N. Znovychka, N. S. Chebotareva, who, based on the analysis of the history of vegetation development in Europe, deny the existence of a large cover glacier in early Würme and, therefore, do not see The grounds for the allocation of the Middle Affairs of the Epoch. From their point of view, the early and medium Würma corresponds to a stretched period of transition from Mikulinsky Fombing to Valdai (Ladyvyvsky) to Valdai (Ladyvyvsky).
In all likelihood, this controversial issue will be resolved in the near future due to the wider use of radio-carbon dating methods.
About 25 thousand years ago (according to some scientists, a little earlier) the last mainland beaming of the northern hemisphere began. According to A. A. Velichko, it was the time of the most severe climatic conditions for the entire ice age. An interesting paradox: the coldest climatic cycle, the thermal minimum of the late Cenozoic, was accompanied by the most minor in the area of \u200b\u200bglaciation. In addition, in duration, this glaciation was very short: reaching the maximum limits of its spread of 20-17 thousand years ago, it disappeared after 10 thousand years. More precisely, according to the data, a generalized French scientist P. Beller, the last fragments of European glacial cover broke up in Scandinavia between 8 and 9 thousand years ago, and the American glacial shield completely melted only about 6 thousand years ago.
The peculiar nature of the last mainland glaciation was determined by nothing more than the excessively cold climatic conditions. According to paleofloral analysis, a generalized Dutch researcher Van der Hammen with co-authors, the average temperatures of July in Europe (Holland) at that time did not exceed 5 ° C. The average annual temperatures in moderate latitudes decreased by about 10 ° C compared to modern conditions.
Whatever enough, an excessive cold prevented the development of glaciation. First, he increased the stiffness of the ice and, therefore, made it difficult to spread. Secondly, and this is the main thing, the cold sowed the surface of the oceans, forming ice cover on them, descended from the pole to almost subtropics. According to A. A. Velichko, in the northern hemisphere, its area in 2 times exceeded the area of \u200b\u200bmodern sea ice. As a result, evapoability from the surface of the world ocean has sharply decreased and, accordingly, the moisture supply of glaciers on land. At the same time, the reflectivity of the planet as a whole increased, which was even greater degree of cooled.
Especially the meager power supply was at the European Ice Cover. America's glare, receiving nutrition from non-freege parts of the quiet 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 ° C. Sh., While on the American continent, they descended 12 ° south.
An analysis of the history of the Late Bainozoic glaciation of the Northern Hemisphere of the Earth allowed specialists to make two important outputs:
1. Ice eras in a recent geological past repeated repeatedly. Over the past 1.5-2 million years, the Earth survived at least 6-8 large glaciation. This testifies to the rhythmic nature of climate fluctuations in the past.
2. Along with the rhythmic-oscillatory climate change, the trend towards directional cooling is clearly traced. In other words, each subsequent interledstnikov turns out to be cooled by the previous one, and the glacial epochs are becoming more severe.
These findings concern only natural patterns and do not take into account the significant technological impact on the environment.
Naturally, the question arises of which prospects for humanity is such a development of events. Mechanical extrapolation of the curve of natural processes into the future forces us to expect over the next few millennia the beginning of a new glacial era. It is possible that such an intentionally simplified approach to the preparation of the forecast will be correct. In fact, the rhythm of climatic oscillations is becoming in short and the modern interledstial era should come soon. This is also confirmed by the fact that the climatic optimum (the most favorable climatic conditions) post declared has long been passed. In Europe, the optimal natural conditions took place 5-6 thousand years ago, in Asia, according to the Soviet Paleogographer N. A. Khotinsky, even earlier. At first glance, there is every reason to believe that the climatic curve is descended to a new glaciation.
However, this is not so simple. In order to seriously judge the future state of nature, a little know the main stages of its development in the past. It is necessary to find out the mechanism that determines the alternation and shift of these stages. In itself, the curve of temperature changes cannot in this case serve as an argument. Where is the guarantee that from tomorrow the spiral will not start spinning in the opposite direction? And in general, can we be sure that the alternation of glaciation and interdhensive reflects any single pattern of nature development? Perhaps each glaciation separately had its independent cause, and, therefore, for the extrapolation of a generalizing curve to the future there is no reason at all ... This assumption looks unlikely, but it has to keep in mind.
The question of the causes of glaciation arose almost simultaneously with the very glacier theory. But if the factological and empirical part of this direction of science over the past 100 years has achieved great progress, the theoretical understanding of the results obtained, unfortunately, was mainly in the direction of the quantitative addition of ideas explaining such a development of nature. Therefore, there are currently no generally accepted scientific theory of this process. Accordingly, there is no single point of view on the principles of the preparation of a long-term geographic forecast. In scientific literature, you can meet several descriptions of hypothetical mechanisms that determine the course of global climate fluctuations. As the new material accumulates about the land of the land, a significant part of the assumptions about the causes of glaciation is discarded and only the most acceptable options remain. Probably among them and should look for a final solution to the problem. Paleogeographic and paleoglyaciological studies, although they do not give a direct response to the questions you are interested in, nevertheless serve as a practically the only key to the knowledge of the natural processes of a global scale. This is their incredit scientific importance.
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