In the history of the Earth, there have been at least five major periods of consistent glaciation and glacial expansion, known colloquially as 'ice ages'. These ice ages are triggered by a variety of reasons, most commonly due to atmospheric changes which affect how heat is retained on the earths surface. The shared characteristic of these glacial epochs is the presence of ice sheets, which form when low temperatures prevent snow from melting. This snow then compacts and transforms into ice sheets over thousands of years, as new snow accumulates on top and is compressed further. During this process the sea levels also drop considerably, as glaciers move they carve out new terrains, and the rivers that form when they melt cause further changes to the Earth's surface. Looking at the ocean floor today, we can see many areas that were once flourishing eco systems with a diversity of flora and fauna, but have been submerged under water for millennia.
"Old" ice ages
Between 2.4 and 2.1 billion years ago, the Earth underwent its first known ice age, the so-called Huronian Glaciation as it was first discovered near Lake Huron in 1907. This ice age was caused during the Great Oxygenation Event, which eliminated methane in the Earth's atmosphere, and formed water and carbon dioxide (which do not retain heat from the sun as well as methane). This was the oldest and longest lasting ice age, which occurred when only simple, single-celled life existed on Earth (most of which was wiped out by the change in temperature). The second major ice age is still a point of debate for many scientists, although most agree that it was the most severe of the ice ages. Little is known about the Cryogenian Glaciation, with some reports suggesting that it lasted for only 130 million years instead of 215, and it is still not known whether the ice covered the entire planet - 'Snowball Earth' - or if water flowed freely around the equator - 'Slushball Earth'.
"Recent" ice ages
In the past half a billion years, the earth has undergone three major ice ages. The oldest of these, the Andean-Saharan ice age, stretched from the Arabian Peninsula to South America, and was particularly strong in Western Africa and Brazil (although the world's continents were attached during this period, in one supercontinent known as 'Pangea'). 360 million years ago was the Late Paleozoic Icehouse, (formerly known as Karoo ice age) which was caused when the evolution of plant life resulted in a decline in carbon dioxide levels, reducing the temperature of the earth. As oxygen levels rose, this allowed wildfires to spread more and termites to evolve, both of which helped reduce the amount of plant life, and increase carbon dioxide levels again. The most recent ice age has been in effect for the past 2.6 million years, and at its peak (18,000 years ago) the ice sheets were almost 4,000 meters high. However, today only the ice sheets on Greenland and Antarctica remain. Although homo sapiens have been around for hundreds of millennia, the natural development of this ice age has been accelerated in the past 200 years, due to rapid population growth and industrialization across the globe. This man-made climate change is believed to be irreversible by many scientists, and NASA estimate that Greenland's ice sheet may fully melt in the next thousand years. This will result in rising sea levels and an imbalance of fresh and salt water in the oceans, which in turn will increases the surface temperature of the earth, as well as the frequency of natural disasters and food shortages.
Length of each major ice age in the Earth's history
(in millions of years)
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History. (June 7, 2017). Length of each major ice age in the Earth's history (in millions of years) [Graph]. In Statista. Retrieved July 07, 2024, from https://www.statista.com/statistics/1048938/length-all-ice-ages/
History. "Length of each major ice age in the Earth's history (in millions of years)." Chart. June 7, 2017. Statista. Accessed July 07, 2024. https://www.statista.com/statistics/1048938/length-all-ice-ages/
History. (2017). Length of each major ice age in the Earth's history (in millions of years). Statista. Statista Inc.. Accessed: July 07, 2024. https://www.statista.com/statistics/1048938/length-all-ice-ages/
History. "Length of Each Major Ice Age in The Earth's History (in Millions of Years)." Statista, Statista Inc., 7 Jun 2017, https://www.statista.com/statistics/1048938/length-all-ice-ages/
History, Length of each major ice age in the Earth's history (in millions of years) Statista, https://www.statista.com/statistics/1048938/length-all-ice-ages/ (last visited July 07, 2024)
Length of each major ice age in the Earth's history (in millions of years) [Graph], History, June 7, 2017. [Online]. Available: https://www.statista.com/statistics/1048938/length-all-ice-ages/