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.[1] 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[2] "Snowball Earth" in which the earth iced over completely. It has been suggested also that the end of this second cold period[2] 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,[3][4] 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.[5] 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.[6] 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).[7]

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.[6]

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[8] interglacial 115 – 130[9] 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[10] 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.[5]

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

References

  1. ↑ Walker, M., Johnsen, S., Rasmussen, S. O., Popp, T., Steffensen, J.-P., Gibbard, P., Hoek, W., Lowe, J., Andrews, J., Bjo¨ rck, S., Cwynar, L. C., Hughen, K., Kershaw, P., Kromer, B., Litt, T., Lowe, D. J., Nakagawa, T., Newnham, R., and Schwander, J. 2009. Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records. J. Quaternary Sci., Vol. 24 pp. 3–17. ISSN 0267-8179.
  2. 1 2 Miracle Planet: Snowball Earth, (2005) documentary, Canadian Film Board, rebroadcast 25 April 2009 on the Science Channel (HD)
  3. ↑ van Andel, Tjeerd H. (1994). New Views on an Old Planet: A History of Global Change (2nd ed.). Cambridge UK: Cambridge University Press. ISBN 0-521-44755-0.
  4. ↑ Rieu, Ruben; et al. (2007). "Climatic cycles during a Neoproterozoic "snowball" glacial epoch". Geology 35 (4): 299–302. doi:10.1130/G23400A.1.
  5. 1 2 Gibbard, P.; van Kolfschoten, T. (2004). "Chapter 22: The Pleistocene and Holocene Epochs" (PDF). In Gradstein, F. M.; Ogg, James G.; Smith, A. Gilbert. A Geologic Time Scale 2004. Cambridge: Cambridge University Press. ISBN 0-521-78142-6.
  6. 1 2 Davis, Owen K. "Non-Marine Records: Correlatiuons withe the Marine Sequence". Introduction to Quaternary Ecology. University of Arizona.
  7. ↑ Kukla, George (August 2005). "Saalian supercycle, Mindel/Riss interglacial and Milankovitch's dating". Quaternary Science Reviews 24 (14-15): 1573–83. doi:10.1016/j.quascirev.2004.08.023.
  8. ↑ Astorga, G. and Pino, M.. 2011. Fossil leaves from the last interglacial in Central-Southern Chile: Inferences regarding the vegetation and paleoclimate. Geologica Acta.
  9. ↑ NEEM community members (2013). "Eemian interglacial reconstructed from a Greenland folded ice core". Nature 493: 489–94. doi:10.1038/nature11789. PMID 23344358.
  10. ↑ Lisiecki, Lorraine E.; Raymo, Maureen E. (2005). "A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records". doi:10.1029/2004PA001071.

External links

Look up glaciation in Wiktionary, the free dictionary.
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