A new ice age is coming. ice age on earth after ice age

The Ice Age has always been a mystery. We know that he could shrink entire continents to the size of a frozen tundra. We know there have been eleven or so, and they seem to happen on a regular basis. We definitely know that there was a lot of ice. However, there is much more to the ice ages than meets the eye.

Megafauna herbivores are accustomed to foraging in icy environments, adapting to their environment in a variety of ways. For example, Ice Age rhinoceroses may have had a shovel-shaped horn to remove snow. Predators like saber-toothed tigers, short-faced bears, and direwolves (yes, Game of Thrones wolves did once exist) have also adapted to their environment. Although the times were cruel, and the prey could well turn a predator into a prey, there was a lot of meat in it.

ice age people

Since hunting tools at that time were mainly stone knives and arrowheads, complex weapons were rare. To capture and kill huge ice age animals, people used traps. When an animal fell into a trap, people attacked it in a group and beat it to death.

Little Ice Ages

The most recent of these small ice ages began sometime between the 12th and 14th centuries and peaked between 1500 and 1850. For hundreds of years, the weather in the northern hemisphere was damn cold. In Europe, the seas regularly froze over, and mountainous countries (such as Switzerland) could only watch as glaciers moved, destroying villages. There were years without a summer, and nasty weather conditions affected every aspect of life and culture (perhaps this is why the Middle Ages seem gloomy to us).

Science is still trying to figure out what caused this little ice age. Possible causes include a combination of heavy volcanic activity and a temporary decrease in solar energy from the Sun.

warm ice age

Sometimes the events that lead to an ice age are so severe that even if full of greenhouse gases (which trap the sun's heat in the atmosphere, warming the planet), ice still continues to form because, given a thick enough layer of pollution, it will reflect the sun's rays back into space. Experts say this would turn Earth into a giant Baked Alaska dessert - cold on the inside (ice on the surface) and warm on the outside (warm atmosphere).

In addition to many other achievements, it is thanks to Agassiz that we know at least something about the ice ages. Although many have touched on this idea before, in 1837 the scientist became the first person to seriously bring ice ages into science. His theories and publications on the ice fields that covered most of the earth were foolishly dismissed when the author first presented them. Nevertheless, he did not retract his words, and further research eventually led to the recognition of his "crazy theories."

Remarkably, his pioneering work on ice ages and glacial activity was merely a hobby. By occupation, he was an ichthyologist (studying fish).

Man-made pollution prevented the next ice age

Human-caused carbon dioxide emissions are considered an essential part of the global warming problem. However, they have one strange side effect. According to researchers from the University of Cambridge, CO2 emissions may be able to stop the next ice age. How? Although the planetary cycle of the Earth is constantly trying to start an ice age, it will only start if the level of carbon dioxide in the atmosphere is extremely low. By pumping CO2 into the atmosphere, humans may have accidentally made ice ages temporarily unavailable.

And even if the concern about global warming (which is also extremely bad) forces people to reduce their CO2 emissions, there is still time. At present, we have sent so much carbon dioxide into the sky that the ice age will not start for at least another 1000 years.

Plants of the Ice Age

It turns out that everything you wanted. In those days, there were many plants that could have survived the Ice Age. Even in the coldest times, steppe-meadow and tree-shrub areas remained, which allowed mammoths and other herbivores not to die of hunger. These pastures were full of plant species that thrive in cold, dry weather, such as spruces and pines. In warmer areas, birches and willows were abundant. In general, the climate at that time was very similar to Siberian. Although the plants, most likely, were seriously different from their modern counterparts.

All of the above does not mean that the ice ages did not destroy part of the vegetation. If the plant could not adapt to the climate, it could only migrate through the seeds or disappear. Australia once had the longest list of diverse plants until glaciers wiped out a good part of them.

The Himalayas may have caused an ice age

When the landmasses of India and Asia collided 40-50 million years ago, the collision grew massive rock ridges into the Himalaya mountain range. This brought out a huge amount of "fresh" stone. Then the process of chemical erosion began, which removes a significant amount of carbon dioxide from the atmosphere over time. And this, in turn, could affect the climate of the planet. The atmosphere "cooled" and caused an ice age.

snowball earth

What is "Snowball Earth"? The so-called Snowball Earth.

Snowball Earth is the chilling grandfather of the ice ages. This is a complete freezer that literally froze every part of the planet's surface until the Earth froze into a huge snowball flying in space. The few that survived a complete freeze either clung to rare places with relatively little ice, or, in the case of plants, clung to places where there was enough sunlight for photosynthesis.

According to some reports, this event happened at least once, 716 million years ago. But there could be more than one such period.

garden of eden

Just under 200,000 years ago, a particularly hostile ice age was killing species left and right. Fortunately, a small group of early humans were able to survive the terrible cold. They stumbled upon the coast that is now represented by South Africa. Despite the fact that ice was reaping its share all over the world, this area remained ice-free and completely habitable. Her soil was rich in nutrients and provided plenty of food. There were many natural caves that could be used as shelter. For a young species struggling to survive, it was nothing short of heaven.

The human population of the "Garden of Eden" numbered only a few hundred individuals. This theory is supported by many experts, but it still lacks conclusive evidence, including studies that show that humans have much less genetic diversity than most other species.

When you travel through the Swiss Alps or through the Canadian Rockies, you will soon notice a huge amount of scattered rocks. Some are as big as houses and often lie in river valleys, although they are obviously too large to be moved by even the most severe flood. Similar erratic boulders can be found at mid-latitudes around the world, although they may be hidden by vegetation or soil layers.

DISCOVERY OF THE ICE AGE

Itinerant scientists of the 18th century, who laid the foundations of geography and geology, considered the appearance of these boulders mysterious, but the truth about their origin has been preserved in local folklore. Swiss peasants told visitors that long ago they were left behind by huge melting glaciers that were once at the bottom of the valley.

At first, scientists were skeptical about this, but as other evidence of the glacial origin of the fossils came to light, most accepted this explanation of the nature of the boulders in the Swiss Alps. But some have dared to suggest that a once larger glaciation spread from the poles to both hemispheres.

The mineralogist Jene Esmark in 1824 put forward a theory confirming a series of global cold snaps, and the German botanist Karl Friedrich Schimper in 1837 proposed the term "ice age" to describe such phenomena, but this theory was recognized only after a few decades.

ABOUT TERMINOLOGY

Ice ages are hundreds of millions of years of cooling during which extensive continental ice sheets and deposits are formed. Ice ages are divided into ice ages, which last tens of millions of years. Ice ages consist of glacial epochs - glaciations (glacials), alternating with interglacials (interglacials).

Today, the term "ice age" is often erroneously used to refer to the last ice age, which lasted 100,000 years and ended about 12,000 years ago. It is known for large, cold-adapted mammals such as woolly mammoths and rhinos, cave bears and saber-toothed tigers. However, it would be wrong to consider this era as entirely unfavorable. Since the world's main water supply has disappeared under the ice, the planet has experienced colder, but also drier weather at low sea levels. These are ideal conditions for the resettlement of our ancestors from African lands around the world.

CHRONOLOGY

Our current climate is just an interglacial hiatus in an ice age that could resume in about 20,000 years (if no artificial stimulus comes along). Before the discovery of the threat of global warming, many people considered the cold snap to be the greatest danger to civilization.

The most significant, up to the equator, glaciation of the Earth was characterized by the Cryogenian period (850-630 million years ago) of the Late Proterozoic Ice Age. According to the “Snowball Earth” hypothesis, during this era our planet was completely covered with ice. During the Paleozoic Ice Age (460-230 million years ago), glaciations were shorter and less common. The modern Cenozoic Ice Age began relatively recently, 65 million years ago. It is completed by the Quaternary Ice Age (2.6 million years ago - present).

The earth has probably gone through more ice ages, but the geological record of the Precambrian era is almost completely destroyed by slow but irreversible changes in its surface.

CAUSES AND CONSEQUENCES

At first glance, it seems that there is no pattern to the onset of ice ages, so geologists have long argued about their causes. They are probably caused by certain conditions interacting with each other.

One of the most significant factors is continental drift. This is a gradual displacement of lithospheric plates over tens of millions of years.

If the location of the continents blocks warm ocean currents from the equator to the poles, ice sheets begin to form. This usually occurs if a large land mass is above the pole or polar waters surrounded by nearby continents.

In the Quaternary Ice Age, these conditions are met by Antarctica and the land-locked Arctic Ocean. During the major Cryogenian ice age, a large supercontinent was trapped near the Earth's equator, but the effect was the same. Once formed, ice sheets accelerate the process of global cooling by reflecting solar heat and light into space.

Another important factor is the level of greenhouse gases in the atmosphere. One of the ice ages of the Paleozoic Ice Age may have been caused by the presence of large Antarctic land masses and the spread of land plants, which replaced the large amount of carbon dioxide in the Earth's atmosphere with oxygen, offsetting this thermal effect. According to another theory, the main stages of mountain building led to an increase in precipitation and the acceleration of processes such as chemical weathering, which also removed carbon dioxide from the atmosphere.

SENSITIVE EARTH

The described processes occur over millions of years, but there are also short-term phenomena. Today, most geologists recognize the importance of changes in the Earth's orbit around the Sun, known as the Milankovitch cycles. Because other processes have placed the Earth in difficult conditions, it has become extremely sensitive to the level of radiation it receives from the Sun depending on the cycle.

In each ice age, there were probably even shorter-term phenomena that cannot be tracked. Only two of them are known for sure: the medieval climatic optimum in the X-XIII centuries. and the Little Ice Age in the XIV-XIX centuries.

The Little Ice Age is often associated with a decline in solar activity. There is evidence that changes in the amount of solar energy have significantly affected the Earth in the past few hundred million years, but, as with the Milankovitch cycles, it is possible that their short-term impact may be enhanced if the planet's climate has already begun to change.

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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. An interglacial era is usually characterized by conditions similar to what we see today: high sea levels, limited areas of 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 level, warm temperature conditions and, in general, 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 Southeast 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 a long history and survive the Ice Age well, although there are some that evolved 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 of human activity, some 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 lived in the Mediterranean in the past. 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

Under normal conditions, by geological standards, we would soon enough return to 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.

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 a 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. The upright ancestors roamed freely in open areas, and their life no longer depended on the collection of fruits from 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 the rock paintings, which depict 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 human adaptations for everyday survival, were preserved and transmitted from generation to generation. 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.

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. In the 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 flow of heat (sun rays) to the earth's surface and causes global temperature decreases 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, there was an even warm climate throughout the Earth - 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 Bosporus froze, and in 1709 the Adriatic Sea froze along the shores.

In 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)