Geologists define an ice age as a period when sheets of ice cover the large portion of the continents. In other words, we can say that when cool temperatures remain for an extended period of time, the polar ice advances into lower latitudes, and eventually covers most of the northern hemisphere by sheets of ice.
The last ice ages occurred during Pleistocene Epoch, which began approximately 2 million years ago and lasted until 11,000 years ago.
This last ice age is referred to as the “Great Ice Age” or “Ice Age”. Geologists believe that during the last ice age, 26 percent of the land was covered in ice.
In North America, the ice covered Canada and moved southwards. In Europe, ice moved down from Scandinavia into Germany and Poland, the British Isles and the Alps also had ice caps. In Asia, the Russia, plateaus of Central Asia, Siberia, and the Kamchatka Peninsula were covered by glaciers.
We can still see the effect of the last ice age, the greenland is still covered in ice.
Geologists believe that apart from the last ice age, there have been four major ice ages over a geological time.
- 1.7 to 2.3 billion years ago (Huronian Era, Precambrian)
- 670 million years ago (Proterozoic Era, Precambrian)
- 420 million years ago (Paleozoic Era, between the Ordovician and Silurian Periods)
- 290 million years ago (Paleozoic Era, between late Carboniferous and early Permian Periods)
There is no exact reason why ice ages occur, but several theories are there. some geologists think they are caused by changes in the Earth’s orbit around the sun. Another theory is that debris or an increase in dust would reflect more of the sun’s light into space (albedo). This results in cooling down of the atmosphere and eventually causing more ice to form. However this theory can’t explain what causes the ice sheets to retreat.
Currently earth is nearing the end of warmer (interglacial) period. Many geologists believe that the ice age is not over yet, another ice age might occur after a thousand years.