Timeline of glaciation

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There have been four major periods of glaciation in the Earth's past. The second, and possibly most severe, is estimated to have occurred from 850 Ma to 635 Ma (million years ago, in the late Proterozoic Age) and it has been suggested that it produced a "Snowball Earth" in which the earth iced over completely. It has been suggested also that the end of this cold period was responsible for the subsequent Cambrian Explosion, a time of rapid diversification of multicelled life during the Cambrian era. However, this theory is still controversial.^{[citation needed]}

A minor series of glaciations occurred from 460 Ma to 430 Ma. There were extensive glaciations from 350 to 250 Ma. The present Pleistocene ice age has seen more or less extensive glaciation on 40,000 and later, 100,000 year cycles. The last glacial period ended about 10,000 years ago.

[edit] Pleistocene glacial cycles

Glacial and interglacial cycles as represented by Atmospheric CO₂, measured from ice core samples going back 650,000 years

Originally, the periods were named after characteristic geological features, and these names vary from region to region. It is now perhaps more common (before the previous interglacial to the current (Holocene) one, the Eemian) to refer to 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. Hence the "names" system is incomplete: the Pastonian glaciation is MIS63, i.e., the 30th interglacial before present.

The last glacial and interglacial phases of the Pleistocene are named, from most recent to most distant, as follows. Dates shown are in thousand years BCE.

Other older periods of the Pleistocene

The Brunhes-Matuyama reversal occurred 780,000 years ago, approximately coincident with MIS19, the "Cromerian Complex" interglacial I, and can be used to date sediment cores.

[edit] Major glacial periods

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

[edit] References

• http://www-qpg.geog.cam.ac.uk/people/gibbard/GTS2004Quat.pdf (fig 22.1)

[edit] See also

• Geologic timescale
• Glacial history of Minnesota
• Ice age
• Varanger glaciation