Timeline of glaciation

Showing the major glaciations (Ice Ages) in the context of Earth's entire existence.

There have been five known ice ages in the Earth's history, with the Earth experiencing the Quaternary Ice Age during the present time. Within ice ages, there exist periods of more severe glacial conditions and more temperate referred to as glacial periods and interglacial periods, respectively. The Earth is currently in such an interglacial period of the Quaternary Ice Age, with the last glacial period of the Quaternary having ended approximately 11,700 years ago with the start of the Holocene epoch. Based on climate proxies, paleoclimatologists study the different climate states originating from glaciation.

Known ice ages

500 million year record shows current and previous two major glacial periods

Name	Period (Ma)	Period	Era
Quaternary	2.58 – present	Neogene	Cenozoic
Karoo	360 – 260	Carboniferous and Permian	Paleozoic
Andean-Saharan	450 – 420	Ordovician and Silurian	Paleozoic
Cryogenian (or Sturtian-Varangian)	850 – 635	Cryogenian	Neoproterozoic
Huronian	2400 – 2100	Siderian and Rhyacian	Paleoproterozoic

Descriptions

The second ice age, and possibly most severe, is estimated to have occurred from 850 to 635 Ma (million years) ago, in the Neoproterozoic Era and it has been suggested that it produced a second "Snowball Earth" in which the earth iced over completely. It has been suggested also that the end of this second cold period was responsible for the subsequent Cambrian Explosion, a time of rapid diversification of multicelled life during the Cambrian Period. However, this hypothesis is still controversial, though is growing in popularity among researchers as evidence in its favor has mounted.

A minor series of glaciations occurred from 460 Ma to 430 Ma. There were extensive glaciations from 350 to 250 Ma. The current ice age, called the Quaternary glaciation, has seen more or less extensive glaciation on 40,000 and later, 100,000 year cycles.

Nomenclature of Quaternary glacial cycles

Originally, the glacial and interglacial periods of the Quaternary Ice Age were named after characteristic geological features, and these names varied from region to region. It is now more common for researchers to refer to the periods by their marine isotopic stage number. The marine record preserves all the past glaciations; the land-based evidence is less complete because successive glaciations may wipe out evidence of their predecessors. Ice cores from continental ice accumulations also provide a complete record, but do not go as far back in time as marine data. Pollen data from lakes and bogs as well as loess profiles provided important land-based correlation data. The names system has not been completely filled out since the technical discussion moved to using marine isotopic stage numbers. For example, there are five Pleistocene glacial/interglacial cycles recorded in marine sediments during the last half million years, but only three classic interglacials were originally recognized on land during that period (Mindel, Riss and Würm).

Land-based evidence works acceptably well back as far as MIS 6, but it has been difficult to coordinate stages using just land-based evidence before that. Hence, the "names" system is incomplete and the land-based identifications of ice ages previous to that are somewhat conjectural. Nonetheless, land based data is essentially useful in discussing landforms, and correlating the known marine isotopic stage with them.

The last glacial and interglacial periods of the Quaternary are named, from most recent to most distant, as follows. Dates shown are in thousand years before present.

Land-based chronology of Quaternary glacial cycles

Backwards Glacial Index	Names					Inter/Glacial	Period (ka)	Marine isotope stage (MIS)	Epoch
	Alpine	N. American	N. European	Great Britain	S. American
				Flandrian		interglacial	present – 12	1	Holocene
1st	Würm	Wisconsin	Weichselian	Devensian	Llanquihue or Mérida	glacial period	12 – 71	2-4 & 5a-d	Pleistocene
	Riss-Würm	Sangamonian	Eemian	Ipswichian	Valdivia	interglacial	115 – 130	5e
2nd	Riss	Illinoian	Saalian	Wolstonian or Gipping	Santa María	glacial period	130 – 200	6
	Mindel-Riss	Pre-Illinoian	Holstein	Hoxnian		interglacial(s)	374 – 424	11
3rd – 6th	Mindel	Pre-Illinoian	Elsterian	Anglian	Río Llico	glacial period(s)	424 – 478	12
	Günz-Mindel	Pre-Illinoian		Cromerian*		interglacial(s)	478 – 533 – 563	13-15
7th – 8th	Günz	Pre-Illinoian	Elbe or Menapian	Beestonian	Caracol	glacial period	621 – 676	16

Older periods of the Quaternary

Name	Inter/Glacial	Period (ka)	MIS	Epoch
Pastonian Stage	interglacial	600 – 800
Pre-Pastonian Stage	glacial period	800 – 1300
Bramertonian Stage	interglacial	1300 – 1550

**Table data is based on Gibbard Figure 22.1.

Ice core evidence of recent glaciation

Main article: Ice core

Ice cores are used to obtain a high resolution record of recent glaciation. It confirms the chronology of the marine isotopic stages. Ice core data shows that the last 400,000 years have consisted of short interglacials (10,000 to 30,000 years) about as warm as the present alternated with much longer (70,000 to 90,000 years) glacials substantially colder than present. The new EPICA Antarctic ice core has revealed that between 400,000 and 780,000 years ago, interglacials occupied a considerably larger proportion of each glacial/interglacial cycle, but were not as warm as subsequent interglacials.

See also

• Brunhes–Matuyama reversal (about 780,000 years ago)
• Geologic time scale
• Glacial history of Minnesota
• Glacial period
• Ice age
• Last glacial period
• Varanger glaciation

External links

• 1004 + xv pp. (book downloadable as series of PDF files)
• (Correlation Chart of European Quaternary and cultural stages and fossils)