There have been long periods in the history of the Earth when the entire planet was warm - from the equator to the poles. But there were also times so cold that glaciers reached those regions that are currently classified as temperate zones. Most likely, the change of these periods was cyclical. In warm times, there could be relatively little ice, and it was found only in the polar regions or on the mountain tops. 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 can be small and insignificant, but they are permanent.
History of the ice ages
We do not know exactly how many ice ages were during 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 period), 300 million years ago - the Permian-Carboniferous glaciation, one of the largest ice ages. affecting the southern continents. The southern continents refers 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 glaciers in 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 eras, and there are longer periods of icing. Naturally, cold spells are not the result of glaciation alone. Glaciation is the most visible consequence of cold periods. However, there are quite long intervals that are very cold despite the absence of glaciers. Today, examples of such regions are Alaska or Siberia, where it is very cold in winter, but there is no glaciation, since there is not enough rainfall that can provide enough water for glaciers to form.
Discovery of ice ages
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We have known that there are ice ages on Earth since the middle of the 19th century. Among the many names associated with the discovery of this phenomenon, Louis Agassiz, a Swiss geologist who lived in the mid-19th century, is usually named first. He studied the glaciers of the Alps and realized that they were once much more extensive than they are today. Not only he noticed this. In particular, Jean de Charpentier, another Swiss, also noted this fact.
It is not surprising that these discoveries were made mainly in Switzerland, since glaciers still exist in the Alps, although they are melting rather quickly. It is easy to see that once the glaciers were much larger - just look at the Swiss landscape, 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 glaciers used to be huge. At that time, there was extensive discussion about how this information relates to the Flood, because there was a conflict between geological evidence and biblical teachings. Glacial deposits were originally called deluvial because they were considered evidence of the Flood. Only later did it become known that such an explanation did not fit: these deposits were evidence of a cold climate and extensive glaciation. By the beginning of the twentieth century, it became clear that there were many glaciers, and not one, and from that moment this area of science began to develop.
Ice Age Research
Geological evidence of ice ages is known. The main evidence for glaciers comes from 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 drifts of melt water formed by its streams, 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 the valley, the river will still flow and the water level will rise until it overflows the edges. Thus, a glacial lake is formed through direct contact with ice. There are certain sediments that are contained in such lakes that we can identify.
Due to the way glaciers melt, depending on seasonal temperature changes, ice melts every year. 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 layering there (rhythmic layered sediments), which are also known by the Swedish name varve, which means annual accumulation. Thus, we can actually see the annual layering in the glacial lakes. We can even count these barbs 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 descend from land to sea. And naturally, ice is floating, so it stays on the water. As it floats, it carries with it pebbles and minor deposits. Due to the thermal effect of the water, the ice melts and discards 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 stretched, and so on.
Causes of glaciers
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 drives the ocean-atmospheric machine, which is constantly trying to transfer heat from the equatorial regions to the poles.
If the Earth were an ordinary ball, this transfer would be very effective, and the contrast between the equator and the poles is very small. This has been the case 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 being held back and changed - in large part because of the mountains, leading to the circulation patterns we see today that govern 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 to the rise of the Himalayan mountains. The Himalayas are still growing very rapidly, 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 Ice Age 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 Pacific to the Atlantic.
If the location of the continents relative to each other and relative to the equator allowed circulation to work efficiently, then there would be warmth at the poles, and relatively warm conditions would remain 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 obstacles to circulation between north and south, we have pronounced climatic zones. This means that the poles are relatively cold and the equatorial regions are warm. When everything is happening as it is now, the Earth can change due to 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 such complex climatic zoning, orbital changes could contribute to long-term changes in climate, resulting in climate fluctuations. Because of this, we do not have continuous icing, but periods of icing, interrupted by warm periods. This happens under the influence of orbital changes. The latest orbital changes are viewed as three separate events: one 20,000 years long, the second 40,000 years long, and the third 100,000 years old.
This led to deviations in the pattern of cyclical climate changes during the ice age. The icing most likely originated during this cyclical period of 100,000 years. The last interglacial epoch, which was as warm as the current one, lasted about 125 thousand years, and then came the long ice age, which took about 100 thousand years. We are now living in another interglacial era. This period will not last forever, so the next ice age awaits us in the future.
Why are ice ages coming to an end
Orbital changes change the climate, and it turns out that ice ages 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) eras. The interglacial era is usually characterized by approximately the same conditions that we observe today: high sea levels, limited icing areas, and so on. Naturally, and now there are glaciers 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 a generally fairly even climate.
But during the Ice Age, the average annual temperature changes significantly, vegetative zones are forced to move north or south, depending on the hemisphere. Regions like Moscow or Cambridge become uninhabited, at least in winter. Although they can be inhabited in the summer due to the strong contrast between the seasons. But what is actually happening: Cold zones are expanding significantly, the average annual temperature is dropping, and the overall climatic conditions are becoming very cold. While the largest glacial events are relatively limited in time (perhaps around 10,000 years), the entire long cold spell can last 100,000 years or more. This is how glacial-interglacial cyclicity 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 Earth's surface. Currently, the North Pole and South Pole are isolated: Antarctica is at the South Pole and the Arctic Ocean is in the north. Because of this, there is a problem with heat circulation. Until the location of the continents changes, 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 will allow the Earth to exit the ice age.
Geological consequences
This frees up huge areas of the continental shelf that are now flooded. This would 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 shallow, about 40 meters, so if the sea level drops to one 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 to regions where they cannot get 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 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. In natural conditions, many animals and plants that we see today have a long history and survive the ice age perfectly, although there are those that evolve slightly. They migrate, adapt. There are areas in which animals and plants survived the Ice Age. These so-called refugia were located further north or south of their current distribution.
But as a result of human activity, some of the species died or became extinct. This happened on all continents, with the possible exception of Africa. A huge number of large vertebrates, namely mammals, as well as marsupials in Australia, were exterminated by humans. This was caused either directly by our activities, such as hunting, or indirectly - by the destruction of their habitat. The animals that live in northern latitudes today have lived in the Mediterranean in the past. We have destroyed this region so much that it will be very difficult for these animals and plants to re-colonize it.
Consequences of global warming
Under normal geological conditions, we would soon be back in the ice age. But because of global warming, which is a consequence of human activity, we are postponing it. We will not be able to completely prevent it, since the reasons that caused it in the past still exist now. Human activity, an element unforeseen by nature, influences atmospheric warming, which may have already caused a delay in the next glacial.
Today, climate change is a very urgent and exciting issue. If the Greenland ice sheet melts, the sea level will rise by six meters. In the past, during the previous interglacial era, which was about 125 thousand years ago, the Greenland ice sheet melted abundantly, and the sea level became 4-6 meters higher than today. This, of course, is not the end of the world, but it is not a temporary difficulty either. In the end, the Earth has recovered from disasters before, she 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 people. Much of this is related to the study of ice ages. Through this research we are learning the mechanisms of glaciers, and we can use this knowledge proactively to try 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 the huge ice sheets. Where does the water come from? Of course, from the oceans. And 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 drops. During the most severe glaciers, the sea level can drop by more than a hundred meters.