Jääkaudet

Etelämantereen jäätikköä
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An ice age, or more precisely, a glacial age, is a period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Within a long-term ice age, individual pulses of cold climate are termed "glacial periods" (or alternatively "glacials" or "glaciations" or colloquially as "ice age"), and intermittent warm periods are called "interglacials". Glaciologically, ice age implies the presence of extensive ice sheets in the northern and southern hemispheres. By this definition, we are still in the ice age that began 2.6 million years ago at the start of the Pleistocene epoch, because the Greenland, Arctic, and Antarctic ice sheets still exist.

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There have been at least five major ice ages in the Earth's past

• Huronian 
• Cryogenian 
• Andean-Saharan 
• Karoo Ice Age  
• Pliocene-Quaternary  

Outside these ages, the Earth seems to have been ice-free even in high latitudes

Huronian
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 Paleoproterozic glacial deposits from Western Australia.


Cryogenian (Snowball Earth)

Arrival of Cryogenian
image NASA

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, possibly being ended by the accumulation of greenhouse gases such as CO2 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 CO2 at present." 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.




Andean-Saharan
The Andean-Saharan occurred from 460 to 420 million years ago, during the Late Ordovician and the Silurian period.

Karoo Ice Age
The evolution of land plants at the onset of the Devonian period caused a long term increase in planetary oxygen levels and reduction of CO2 levels, which resulted in the Karoo Ice Age. It is named after the glacial tills found in the Karoo region of South Africa, where evidence for this ice age was first clearly identified. There were extensive 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 ancient supercontinent Gondwanaland.

Pliocene-Quaternary 

Scandinavia under ice
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The current ice age, the Pliocene-Quaternary glaciation, started about 2.58 million years ago during the late Pliocene, when the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods, glacials or glacial advances, and interglacial periods, interglacials or glacial retreats. The earth is currently in an interglacial, and the last glacial period ended about 10,000 years ago. All that remains of the continental ice sheets are the Greenland and Antarctic ice sheets and smaller glaciers such as on Baffin Island.

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Sarja	Vaihe	Alivaihe	Kronozooni	Aika vuotta sitten
Holoseeni			Preboreaali	10 640–11 560
Pleistoseeni	Veiksel-jääkausi	Jääkauden loppuvaihe	Nuorempi Dryas	11 560–12 700
			Allerød	12 700–13 350
			Vanhempi Dryas	13 350–13 480
			Bølling	13 480–13 730
			Vanhin Dryas	13 780–13 860
			Meiendorf	13 860–14 500
		Keski-Veiksel-kausi
			LGM	18 000–28 000
			Denekamp	28 000–32 000
			Hengelo	36 900–38 700
			Moershoofd
			Glinde	48 000–51 000
			Ebersdorf
			Oerel	55 400–57 700
			Schalkholz
		Varhaisjääkausi	Odderade	±74 000
			Rederstall
			Brørup
			Herning	-116 000
	Eem			116 000–128 000
Sinertävä, kylmää, punertava, lämmintä

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