What is an ice age?
An ice age is an extended period of decrease in the heat of the Earth’s surface and atmosphere, ending in the appearance or extension of continental and glacial ice sheets and alpine glaciers. Earth’s climate fluctuates amid ice ages and greenhouse periods, during which there are no glaciers on the planet. Earth is currently in the Quaternary glaciation, which means, we are in between two ice ages. Single pulses of cold climate within an ice age are termed “glacial periods,” and occasional warm periods within an ice age are called “interglacials” or “interstadials,” with both climatic pulses part of the Quaternary or other periods in Earth’s past.
In simple words, An ice age is when a significant amount of the Earth’s water is bolted up on land in continental glaciers. During the last ice age, which ended about 10,000 years ago, gigantic ice masses covered vast swathes of land now populated by billions of people. Northern US, Canada, Northern Europe, and Northern Asia were all covered in ice.
Canada and the northern USA were covered entirely in ice, as was North Europe and North Asia.
Major ice ages and timeline from Earth’s history
There have been at least five primary ice ages in the Earth’s history (the Huronian, Cryogenian, Andean-Saharan, late Paleozoic, and the latest Quaternary Ice Age). Outside these ages, the Earth appears to have been ice-free even in high latitudes; such periods are identified as greenhouse periods.
Rocks from the oldest well-established ice age, called the Huronian, formed around 2.4 to 2.1 Ga (billion years) ago during the old Proterozoic Eon. Several hundreds of km of the Huronian Supergroup are presented 10–100 km north of the north shore of Lake Huron extending from near Sault Ste. Marie to Sudbury, northeast of Lake Huron, with giant layers of now-lithified till beds, dropstones, varves, outwash, and scoured basement rocks. Correlative Huronian deposits have been found near Marquette, Michigan, and the relationship has been made with Paleoproterozoic glacial sediments from Western Australia. The Huronian ice age was caused by the elimination of atmospheric methane, a greenhouse gas, during the Great Oxygenation Event.
The next well-documented ice age, and probably the most severe of the last billion years, occurred from 720 to 630 million years ago (the Cryogenian period) and may have presented a Snowball Earth in which glacial ice sheets reached the equator, possibly being ended by the accumulation of greenhouse gases such as CO2 created by volcanoes.
The Andean-Saharan occurred from 460 to 420 million years ago, during the Late Ordovician and the Silurian period. Deposit records showing the fluctuating orders of glacials and interglacials during the last several million years.
The evolution of land plants at the onset of the Devonian period caused a long term development in terrestrial oxygen levels and reduced CO2 levels, resulting in the late Paleozoic icehouse. Its former name, the Karoo glaciation, was named after the glacial tills found in the Karoo region of South Africa. There were sizeable polar ice caps at intervals from 360 to 260 million years ago in South Africa during the Carboniferous and early Permian Periods. Correlatives are known from Argentina, also in the center of the old supercontinent Gondwanaland.
What causes an ice age?
Ice ages don’t just come out of nowhere – it takes thousands of years for an ice age to begin.
Several factors are essential: atmospheric composition, such as the concentrations of carbon dioxide and methane; changes in the Earth’s orbit around the Sun known as Milankovitch cycles; the motion of tectonic plates resulting in changes in the appropriate location and amount of continental and marine crust on the Earth’s surface, which affect wind and ocean currents; fluctuations in solar output; the orbital dynamics of the Earth-Moon system; the result of relatively large meteorites and volcanism including bursts of supervolcanoes.
Some of these determinants influence each other. For instance, changes in Earth’s climatic composition may change the climate, while climate change itself can transform the climatic balance.
Source: Primary Education Journal (Texas University), Charles Darwin, Wikipedia, University of Houston-Clear Lake – Disasters Class Notes – Chapter 12: Climate Change.