Glaciation

Glaciation

The last Ice Age ended about 13 thousand years ago.

Geography

Keywords

glaciation, ice age, glacial, interglacial, warming, cooling down, climate, ice sheet, glacier, ice, nature, history of the Earth, geography

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Over the history of Earth, Ice Ages brought the greatest climate changes.
An ice age is a period of long-term reduction in the temperature of the Earth´s surface and atmosphere, resulting in the expansion of polar and continental ice sheets, and alpine glaciers.

There is evidence for four major glaciation periods in history:

1. at the Precambrian - Paleozoic boundary (800–600 million years ago)

2. in the Ordovician period of the Paleozoic era (460–430 million years ago)

3. at the Carboniferous - Permian boundary (330–150 million years ago)

4. in the Pleistocene (1.8 million–10 thousand years ago)

Ice ages are characterized by a periodic change of glacial periods (extending ice sheets) and interglacial periods (receding ice sheets). These periods last for about 40–100 thousand years.

Causes of ice ages

1. Decrease of the Sun´s energy output
2. Variations in Earth´s orbit (changes in Earth´s orbital eccentricity and orbital inclination, as well as the swaying motion of the axis of rotation.)
3. Drifting of Earth´s magnetic poles
4. Fluctuations in ocean currents (cooling and warming)
5. Changes in Earth´s atmosphere (greenhouse effect)
6. Changes in the positions of continents

Narration

Glaciation:

The glaciation of the Earth is a process in which the poles are covered with permanent ice sheets. Over the history of the Earth, there have been several major ice ages, which may have lasted for several million years. Within a long-term ice age, minor warmer periods alternate with shorter colder periods at intervals of several thousand years.

From the point of view of the Earth’s history, we are now living during an ice age of the Cenozoic era. Within this, the Earth is currently undergoing an interglacial period, that is a warmer period.

The last glacial period started 110,000 years ago and ended 10,000 years ago. The last ice age played a major role in shaping the current landscape of Europe and America.

Ice eroded the rocks and deposited their sediments; cold winds also eroded the surface, which resulted in the development of sandy surfaces. The average temperature was 5 degrees Celsius (41 degrees Fahrenheit) colder than it is today, the flora and fauna changed, climatic zones were shifted and a number of species became extinct.

The poles witnessed a significant increase in the extent and thickness of ice, and polar glaciers covered a large part of Europe. Extending 2,000 km (1,243 mi) South from Scandinavia, the ice sheet even reached a thickness of 2,000–3,000 m (6,562–9,843 ft) in some parts. Due to the large polar ice mass, sea levels dropped significantly, forming a land bridge, which joined the British Isles to Europe. Much of the isles was covered by glaciers. Alpine glaciers extended as far as Milan, Munich and Geneva, forming moraine ridges.
The drop in the sea level resulted in the karstification of the Northern Adriatic basin. The Mediterranean Sea lost its link to the Atlantic with the closing of the Strait of Gibraltar. Also the Red Sea lost its link to its surrounding ocean, thus turning into an inland sea with no outlet. Much of it therefore dried out.
Himalayan glaciers extended further down, occupying significant territories. As a result of the drop in sea level, dry land connected Japan to Asia, and Indonesia to Asia. Australia was joined to New Guinea and only one strait separated it from Indonesia.
An ice-free land bridge was formed between North America and Asia, which enabled humans and species to migrate to America.
Ice sheets also covered North America extending as far as 40° latitude, with a thickness of 3,000–3,500 m (9,843–11,480 ft) in some areas. Ice extended as far as New York; Long Island was formed by a glacial moraine. Ice extended further down as far as Southern Ohio, which is at the same line of latitude as Sicily.

Warming:

In the history of the Earth, polar ice sheets have not been predominant. These periods were occasionally interrupted by periods of glaciation, or ice ages. An ice age is a period in which the poles are covered in ice sheets. Within an ice age, warmer periods alternate with colder periods. Currently, the Earth is undergoing a warming cycle of the Cenozoic Ice Age.

During the history of the Earth, there have been repeatedly much warmer temperatures than today, as a result of which the polar ice caps disappeared and the average sea level was 100 m (328 ft) higher than it is today. The current warming period has lasted for the past 10,000 years; the rate of warming has speeded up in the last 100 years, probably because of polluting human activities.

The result of the last warming cycle is the current state. Ice sheets disappeared from the Scandinavian territory forming its current face, and the Norwegian fjords were created. The lakes of the Finnish Lakeland were created as a result of the receding polar ice sheet. Several hundred lakes and islands were formed in this way.
With the melting of the polar ice mass the sea level increased; the land bridge connecting the British Isles and the continent ceased to exist. As the Alpine glaciers retreated, they left behind moraine lakes and glacier valleys.
The basin of the Adriatic Sea was again flooded by the sea. The link between the Mediterranean Sea and the Atlantic was re-established; the former land bridge ceased to exist at the Strait of Gibraltar.
The Red Sea was again linked to the Indian Ocean. The Himalayan glaciers receded. The land bridge between Asia and Japan ceased to exist. Indonesia was again an archipelago.
Much of Australia was flooded by the sea; the island of New Guinea was formed. The land bridge connecting America and Asia was covered in water. In America, as glaciers retreated, they formed the Great Lakes. The basins carved by ice were filled with water from the melted ice.

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