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 so cold times that glaciations reached those regions that currently belong to temperate zones. Most likely, the change of these periods was cyclical. In warm times, ice could be relatively small, and it was located only in the polar regions or on the mountain peaks. An important feature of the glacial periods is that they change the nature of the earth’s surface: every glaciation affects the appearance of the Earth. By themselves, these changes can be small and minor, but they are permanent.
History of the Ice Age
We do not know exactly how many ice ages were during the history of the Earth. We know of at least five, perhaps seven, glacial periods, beginning with the Precambrian, in particular: 700 million years ago, 450 million years ago (Ordovician period), 300 million years ago – Permo-Carboniferous glaciation, one of the largest ice ages, affecting the southern continents. Under the southern continents is meant the so-called Gondwana – the ancient supercontinent, which 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 from 50 million years ago in the Antarctic.
The structure of each glacial period is periodic: there are relatively short warm epochs, and there are longer periods of icing. Naturally, the cold periods are not a consequence of glaciation alone. Glaciation is the most obvious consequence of cold periods. However, there are sufficiently long intervals, which 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 are no glaciations, as there are not enough precipitation capable of providing sufficient water for the formation of glaciers.
The discovery of glacial periods
We know about the fact that there are glacial periods on Earth since the middle of the XIX century. Among the many names associated with the discovery of this phenomenon, the first usually called the name of Louis Agassiz, a Swiss geologist who lived in the middle of the XIX century. He studied the glaciers of the Alps and realized that at one time they were much more extensive than today. This was noticed not only by him. In particular, Jean de Charpentier, another Swiss, also noted this fact.
It is not surprising that these discoveries were made mainly in Switzerland, since the Alps still have glaciers, although they quickly disappear. It’s easy to see that once 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, published 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 is really 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 on 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 a proof of the World Flood. Only then it became known that such an explanation does not work: these deposits were evidence of a cold climate and extensive glaciations. By the beginning of the twentieth century it became clear that there were many glaciations, and not one, and from that moment this area of science began to develop.
Studies of glacial periods
Geological confirmations of glacial periods are known. The main evidence of 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 glacier deposits, but also meltwater deposits formed by its streams, glacial lakes or glaciers moving into the sea.
There are several forms of glacial lakes. Their main difference lies in the fact that they are a water body, fenced with ice. For example, if we have a glacier that rises to the river valley, it blocks the valley like a cork in a bottle. Naturally, when the ice blocks the valley, the river will still flow, and the water level will rise until it overflows. Thus, the glacial lake is formed through direct contact with the ice. There are certain deposits that are contained in such lakes and which we can identify.
Because of the melting of glaciers, which depends on the seasonal temperature changes, there is an annual ice breakdown. This leads to an annual increase in the small deposits deposited from under the ice in the lake. If we then look at the lake, we will see there layering (rhythmic layered sediments), which are also known under the Swedish name “barbarians” (varve), which means “annual accumulation”. Thus, we can really see the annual stratification in glacial lakes. We can even count these barbarians and find out how long this lake existed. In general, with the help of this material, we can get a lot of information.
In the Antarctic, we can see the huge size of the ice shelves that descend from the earth into the sea. And of course, the ice is floating, so it keeps on the water. As he swims, he carries pebbles and insignificant deposits. Due to the thermal effects of water, ice melts and sheds this material. This leads to the formation of a process of so-called rafting of rocks that go into the ocean. When we see the fossil deposits of this period, we can find out where the glacier was, how far it stretched, and so on.
Causes of glaciations
Researchers believe that glacial periods occur because the Earth’s climate depends on the uneven heating of its surface by the Sun. For example, the equatorial regions where the Sun is almost vertically above the head 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 the heating of different parts of the Earth’s surface is controlled by the ocean-atmospheric machine, which constantly tries to transfer heat from the equatorial regions to the poles.
If the Earth was a regular sphere, this transfer would be very effective, and the contrast between the equator and the poles is very small. So it was in the past. But since there are continents now, they become in the way of this circulation, and the structure of its flows becomes very complex. Simple streams are restrained and changed – largely because of the mountains, which leads to those circulation patterns that we see today and which control the trade winds and ocean currents. For example, one of the theories about why the ice age began 2.5 million years ago relates this phenomenon to 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 controls things like the monsoon system. The beginning of the Quaternary glacial period is also associated with the closure of the Isthmus of Panama, which connects the north and south of America, which prevented the transfer of heat from the equatorial zone of the Pacific Ocean to the Atlantic.
If the location of the continents relative to each other and relative to the equator allowed circulation to work efficiently, it would be warm at the poles, and relatively warm conditions would be maintained throughout the earth’s surface. The amount of heat received by the Earth would be constant and only slightly varied. But since our continents create serious barriers to circulation between the north and south, we have pronounced climatic zones. This means that the poles are relatively cold, and the equatorial regions are warm. When everything happens as it is now, the Earth can change under the influence of 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 climate zoning, a change in orbit can contribute to long-term climate change, leading to climate variability. Because of this, we have not a continuous icing, but periods of icing, interrupted by warm periods. This happens under the influence of orbital changes. The last orbital changes are considered as three separate phenomena: one is 20 thousand years old, the second – 40 thousand years, and the third – 100 thousand years.
This led to deviations in the scheme of cyclical climate changes during the Ice Age. The icing, most likely, arose during this cyclic period of 100 thousand years. The last interglacial epoch, which was as warm as the current one, lasted about 125 thousand years, and then a long glacial epoch took place, which took about 100 thousand years. Now we live in the next interglacial era. This period will not last forever, so in the future we are waiting for another glacial epoch.
Why ice ages are coming to an end
Orbital changes change the climate, and it turns out that glacial periods are characterized by alternations of cold periods, which can last up to 100 thousand years, and warm periods. We call them glacial (glacial) and interglacial (interglacial) epochs. The interglacial epoch is usually characterized by approximately the same conditions that we observe today: high sea level, limited icing areas 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 the interglacial: high sea level, warm temperature conditions and generally fairly even climate.
But during the glacial epoch, the average annual temperature varies considerably, the vegetative belts are forced to shift north or south depending on the hemisphere. Regions like Moscow or Cambridge are becoming uninhabited, at least in winter. Although they can be inhabited in the summer because of the pronounced contrast between the seasons. But what actually happens: the cold zones expand substantially, the average annual temperature decreases, and the general climatic conditions become very cold. While the largest glacial events are relatively time-limited (perhaps around 10,000 years), the entire long cold period can last 100,000 years or more. This is how the glacial-interglacial cycle looks.
Because of the duration of each period, it is difficult to say when we will emerge from the current era. This is due to plate tectonics, the location of continents on the surface of the Earth. At present, the North Pole and the South Pole are isolated: the Antarctic is at the South Pole, and the Arctic Ocean in the north. Because of this, there is a problem with the circulation of heat. Until the location of the continents changes, this ice age will continue. In accordance with long-term tectonic changes, it can be assumed that it will take another 50 million years in the future, until significant changes take place that will allow the Earth to emerge from the ice age.
Of course, the main consequence of the glacial period is the huge glacial shields. Where does the water come from? Of course, from the oceans. And what happens during the glacial periods? Glaciers are formed as a consequence of precipitation on land. Because the water does not return to the ocean, the sea level drops. In times of the most severe glaciation, sea level may fall by more than a hundred meters.
This frees up huge sections of the continental shelf that are now flooded. 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 that connects Alaska with Eastern Siberia. It is rather shallow, about 40 meters, so if the sea level drops to one hundred meters, then this section will become a land. This is also important because plants and animals can migrate through these places and get to regions where they can not get to 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 glacial period: we have evolved over it, so we can survive it. However, it’s not a matter of individuals, it’s a matter of the whole population. The problem today is that there are too many of us and our activities have significantly changed the natural conditions. In natural conditions, many animals and plants that we see today have a long history and perfectly survive the glacial period, although there are also those that evolve insignificantly. They migrate, adapt. There are zones in which animals and plants survived the ice age. These so-called refugiums were located farther north or south of their current location of distribution.
But as a result of human activity, some species died or died out. It happened on all continents, perhaps, with the 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, for example by hunting, or indirectly by the destruction of their habitat. Animals living in the northern latitudes today, in the past lived in the Mediterranean. We have destroyed this region so much that it will most likely be very difficult for these animals and plants to colonize it again.
Consequences of global warming
Under normal conditions, by geological measures, we would rather soon return to the ice age. But because of global warming, which is a consequence of human activity, we delay it. We can not completely prevent it, because the reasons that caused it in the past exist even now. Human activity, an element not considered by nature, affects atmospheric warming, which may already have caused a delay in the next glacial.
Today, climate change is a very urgent and exciting issue. If the Greenland ice sheet melts, then the sea level will rise by six meters. In the past, during the previous interglacial era, which was approximately 125,000 years ago, the Greenland ice sheet was melting, and the sea level was 4-6 meters higher than today’s. This, of course, is not the end of the world, but also not a temporary difficulty. In the end, the Earth recovered from catastrophes before, it can survive this one.
The long-term forecast for the planet is not bad, but for people this is another matter. The more we conduct research, the more we understand how the Earth changes and what it leads to, the better we understand the planet on which we live. This is important because people have finally begun to think about changing sea level, global warming and the impact of all these things on agriculture and the population. Much of this is associated with the study of glacial periods. With the help of these studies, we learn the mechanisms of glaciation, and we can use this knowledge with anticipation, trying to mitigate some of these changes, which we ourselves call. This is one of the main results and one of the goals of the research of the glacial periods.