Ice ages in the history of the Earth
Cooling periods of the climate, accompanied by the formation
Интервалы холодного климата, в течение которых образуются обширные материковые ледниковые покровы и отложения длительностью в сотни миллионов лет, именуются ice ages; in glacial eras stand out ice ages lasting tens of millions of years, which, in turn, consist of ice ages - glaciations (glacials) alternating with interglacials (interglacials).
The following ice ages are known in the history of the Earth:
- Canadian Ice Age - 2.5-2.2 billion years ago, at the beginning of the early, Paleoproterozoic part of the Proterozoic geological era.
- African Ice Age - 900-590 million years ago, in the Late Proterozoic part of the Proterozoic geological era.
- Gondwana Ice Age - 380-240 million years ago, during the Paleozoic geological era.
- Laurasian Ice Age - 20-30 million years ago - present, at the end of the Cenozoic geological era.
Causes of glaciers
In science, there are various theories about the causes of glaciers:
- It is noticed that all the great glaciations coincided withthe largest mountain-building epochs, when the relief of the earth's surface was the most contrasting and the area of the seas decreased. Under these conditions, climate fluctuations have become sharper. However, the average heights of the mountains are now no less, and maybe even more than those that were during the glaciers, nevertheless, now the area of glaciers is relatively small;
- Study of modern and ancient volcanicactivity allowed the volcanologist I. V. Melekestsev to associate glaciation with an increase in the intensity of volcanism. Until now, most researchers have underestimated the role of volcanism in the manifestation of glaciations. However, one should not exaggerate the importance of this factor. It is well known that no significant glaciers existed in the Late Cretaceous and Paleogene, although at that time colossal sheets of volcanic material were formed around the Pacific Ocean;
- Some hypotheses have suggested periodicchanges in the luminosity of the Sun, however, with the development of astrophysics, they had to be abandoned: neither theoretical calculations, nor the results of observations gave grounds for such assumptions. The American physicist Robert Ehrlich created a computer model of the behavior of solar plasma based on the hypothesis of the Hungarian theoretician Attila Grandpierre, who suggested the existence of “resonant diffusion waves” inside the Sun of a peculiar mechanism of self-amplification of fluctuations, leading to noticeable changes in the plasma temperature and, consequently, in the luminosity of the Sun. In Ehrlich's model, it turned out that such fluctuations have a pronounced periodicity, which coincides well with the periodicity of the onset and retreat of glaciers;
- Back in the 19th century, Louis Agassiz, Alphonse Joseph Ademar,James Kroll and others have put forward the idea that a change in the parameters of the Earth's orbit and its axis of rotation can lead to a change in the amount of solar heat that enters the Earth's surface at different latitudes. By the end of the 19th century, the development of celestial mechanics made it possible to calculate changes in the orbital and rotational characteristics of the Earth, and at the beginning of the 20th century, Milutin Milankovich completed the creation of the astronomical theory of ice ages (Milankovitch cycles).
- There is a hypothesis that the offensiveglacier is caused not by a cooling, but by a warming of the global climate. The model, proposed in 1956 by American geophysicists Maurice Ewing and William Donne, provides that the time of glacier growth is the time of maximum heating of the Arctic Ocean. Freeing itself from the ice, it begins to evaporate a huge amount of water, the bulk of which falls in the form of snow on the polar regions of the land. From this snow a glacier is born. But, sucking moisture from the World Ocean, the glacier lowers its level, which ultimately leads to the fact that the Gulf Stream can no longer break through from the Atlantic into the polar seas. As a result, the Arctic Ocean at some point becomes covered with solid, non-melting ice, after which the glacier begins to shrink, since the frozen ocean no longer feeds it with snow. As the glacier melts (more precisely, sublimation, dry evaporation), the level of the World Ocean rises, the Gulf Stream penetrates into the Arctic, polar waters are freed from ice, and the cycle begins anew.
Ice sheet of Antarctica. This is how the surface of the Earth in North America or Northern Europe could have looked during the ice ages of the Ice Age.
The last ice age
Cenozoic Ice Age (30-20 million years ago- present) - the last ice age at the moment. It is assumed that the Cenozoic Ice Age may be a consequence of the cooling caused by the formation of the Drake Passage approximately 37 million years ago.
The present geological period is the Holocene,which began ≈ 12,000 years ago, is characterized as a relatively warm period after the Pleistocene Ice Age, often classified as an interglacial.
During this last ice agealternating episodes of glacier advances and retreats were observed. During the last ice age, the maximum of the last glaciation was about 22,000 years ago.
Towards the end of the event, Homo sapiens migrated toEurasia and Australia. Archaeological and genetic evidence suggests that original human populations of the Paleolithic Age survived the last Ice Age in sparsely forested areas and were dispersed in areas of high primary productivity, while avoiding dense forest cover.
Little Ice Age in Russia
In Russia, the Little Ice Age was marked, in particular, by extremely cold summers in 1601, 1602 and 1603, when frosts hit in July-August, and snow fell in early autumn.
Unusual cold weather resulted in crop failure andfamine, and as a consequence, according to some researchers, became one of the prerequisites for the beginning of the Time of Troubles. The winter of 1656 was so severe that two thousand people and a thousand horses died from frosts in the Polish army that entered the southern regions of the Russian kingdom.
In the Lower Volga region, in the winter of 1778, birds froze in flight and fell dead. During the Russian-Swedish war of 1808-1809. Russian troops over the ice overcame the Baltic Sea.
The Little Ice Age in Siberia was even colder. In 1740-1741. V. Bering's expedition recorded severe frosts in Kamchatka and on the Commander Islands.
How the last ice age affected the Earth
In mid-May, the OceanographicWoods Hole Institute, dedicated to the last ice age on Earth. Scientists have come to the conclusion that the surface of our planet during the last ice age cooled by 6 degrees Celsius.
The analysis of scientists was based on the study of noblegases that are dissolved in groundwater. It turned out that the temperature of the land surface in the middle and low latitudes cooled at that time by almost 6 degrees Celsius.
At the same time, experts emphasized that their datatemperatures are much lower than those previously provided by other experts. The real significance of the work is that previous studies grossly underestimated the cooling during the last ice age, leading to low estimates of the sensitivity of the Earth's climate to greenhouse gases.
The average temperature on Earth during the ice age was about 7.8 degrees Celsius, which is only 6 degrees lower than the average temperature on the planet today.
When is the next ice age?
Researchers at MITInstitute (MIT) discovered that the Earth will enter a global ice age, when the level of solar radiation that the planet receives changes rapidly over a geologically short period of time. The amount of solar radiation should not fall below a certain threshold point.
The research results suggest that,no matter what caused the ice ages on Earth, processes were most likely involved that reduce the amount of solar radiation reaching the planet's surface. For example, volcanic eruptions or biologically induced cloud formation that could significantly block the sun's rays.
Global ice ages on Earth aretemporary due to the planet's carbon cycle. When the planet is not covered in ice, the levels of carbon dioxide in the atmosphere are controlled to some extent by the weathering of rocks and minerals.
When a planet is covered in ice, weathering is greatly reduced, so that carbon dioxide builds up in the atmosphere, creating a greenhouse effect that eventually melts the planet.
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