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.[1][2]

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. We are currently in an interglacial period, as the last glacial period ended about 10,000 years ago.

Contents

[edit] Major glacial periods in earth's history

500 million year record shows current and previous two major glacial periods
500 million year record shows current and previous two major glacial periods
Name Period (Ma) Period Era
  30 - present Neogene Cenozoic
Karoo 360 - 260 Carboniferous and Permian Paleozoic
Andean-Saharan 450 - 420 Ordovician and Silurian Paleozoic
Cryogenian
(or Sturtian-Varangian)		 800 - 635 Cryogenian Neoproterozoic
Huronian glaciation 2100 - 2400 Siderian and Rhyacian Paleoproterozoic

Image:GlaciationsinEarthExistancelicenced.jpg

[edit] Pleistocene glacial cycles

Glacial and interglacial cycles as represented by atmospheric CO2, measured from ice core samples going back 650,000 years
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 varied from region to region. It is now more common to refer to periods by their marine isotopic stage number.[3] 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.[4] 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).[5]

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.[4]

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 before present.

[edit] Land-based chronology of Pleistocene glacial cycles

Backwards
Glacial
Index		 Names Inter/Glacial Period (ka) MIS Epoch
Alpine N. American N. European Great Britain
Flandrian interglacial present – 12 1 Holocene
1st Würm Wisconsin Weichsel
or Vistula		 Devensian glacial period 12 – 110 2-4
& 5a-d		 Pleistocene
Riss-Würm Sangamon Eemian Ipswichian interglacial 110 – 130 5e
2nd Riss Illinoian Saale Wolstonian or Gipping glacial period 130 – 200 6
Mindel-Riss Yarmouth Holstein Hoxnian interglacial(s) 200 – 300/380 7,9,11
3rd – 5th Mindel Kansan Elster Anglian glacial period(s) 300/380 – 455 8,10,12
Günz-Mindel Aftonian Cromerian* interglacial(s) 455 – 620 13-15
7th Günz Nebraskan Menapian Beestonian glacial period 620 – 680 16

Older periods of the Pleistocene

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

**Table data is based on Gibbard Figure 22.1.[3]

[edit] 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.

[edit] References

  1. ^ van Andel, Tjeerd H. (1994) New Views on an Old Planet: A History of Global Change 2nd ed. Cambridge University Press, Cambridge, UK, ISBN 0521447550
  2. ^ Rieu, Ruben et al. (2007) "Climatic cycles during a Neoproterozoic “snowball” glacial epoch" Geology 35(4): pp. 299–302
  3. ^ a b Gibbard, P. and van Kolfschoten, T. (2004) "The Pleistocene and Holocene Epochs" Chapter 22 In Gradstein, F. M., Ogg, James G., and Smith, A. Gilbert (eds.), A Geologic Time Scale 2004 Cambridge University Press, Cambridge, ISBN 0521781426
  4. ^ a b Davis, Owen K. "Non-Marine Records: Correlatiuons withe the Marine Sequence" Introduction to Quaternary Ecology University of Arizona
  5. ^ Kukla, George (2005) "Saalian supercycle, Mindel/Riss interglacial and Milankovitch's dating" Quaternary Science Reviews 24(14/15): pp. 1573-1583

[edit] See also

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