There have been at least five major ice ages in the earth's past (theHuronian, Cryogenian, Andean-Saharan, Karoo Ice Age and theQuaternary glaciation). Outside these ages, the Earth seems to have been ice-free even in high latitudes.[31][32]
Rocks from the earliest well established ice age, called the Huronian, formed around 2.4 to 2.1 Ga (billion years) ago during the early Proterozoic Eon. Several hundreds of km of the Huronian Supergroup are exposed 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 correlation has been made with Paleoproterozoic glacial deposits from Western Australia.
The next well-documented ice age, and probably the most severe of the last billion years, occurred from 850 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which glacial ice sheets reached the equator,[33] possibly being ended by the accumulation of greenhouse gases such as CO
2 produced by volcanoes. "The presence of ice on the continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis, which are the two major sinks for CO
2at present."[34] It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian Explosion, though this model is recent and controversial.
2 produced by volcanoes. "The presence of ice on the continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis, which are the two major sinks for CO
2at present."[34] It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian Explosion, though this model is recent and controversial.
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