Timeline of glaciation

Climate history over the past 500 million years, with the last three major ice ages indicated, Andean-Saharan (450 Ma), Karoo (300 Ma) and Current. A less severe cold period or ice age is shown during the Jurassic-Cretaceous (150 Ma).

There have been five or six major ice ages in the history of Earth over the past 3 billion years. The Current Ice Age began 34 million years ago, its latest phase being the Quaternary glaciation, in progress since 2.58 million years ago.

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 glaciation, with the last glacial period of the Quaternary having ended approximately 11,700 years ago, the current interglacial being known as the Holocene epoch.^[1] Based on climate proxies, paleoclimatologists study the different climate states originating from glaciation.

Known ice ages

10¹⁰

10⁹

10⁸

10⁷

10⁶

10⁵

10⁴

Descriptions

The third ice age, and possibly most severe, is estimated to have occurred from 720 to 635 Ma (million years) ago,^[3] in the Neoproterozoic Era, and it has been suggested that it produced a second^[4] "Snowball Earth", in which the Earth iced over completely. It has been suggested also that the end of this second cold period^[4] 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,^[5][6] 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 has seen extensive ice sheets in Antarctica for the last 34 Ma. During the last 3 Ma ice sheets have also developed on the northern hemisphere. This phase is known as the Quaternary glaciation, and has seen more or less extensive glaciation on 40,000 and later, 100,000 year cycles.

Nomenclature of Quaternary glacial cycles

Whereas the first 30 million years of the Current Ice Age mostly involved Antarctica, the Quaternary has seen numerous ice sheets extending over parts of Europe and North America that are currently populated and easily accessible. Early geologists therefore named apparent sequences of glacial and interglacial periods of the Quaternary Ice Age 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.^[7] 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.^[8] The names system has mostly been phased out by professionals, who instead use the marine isotopic stage indexes for all technical discussions. 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).^[9]

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.^[8]

Sources

For sources to the tables, see the individual linked articles.

See also

References

External links

The dictionary definition of glaciation at Wiktionary

• Aber, J.S. (2006). "Regional Glaciation of Kansas and Nebraska". Emporia KA: Emporia State University.
• Work Group on Geospatial Analysis of Glaciated Environments (GAGE) (2000). "Pre-Wisconsin Glaciation of Central North America". Emporia KA: INQUA Commission on Glaciation, Emporia State University. Archived from the original on May 13, 2008.
• Subcommission on Quaternary Stratigraphy (2011). "Global correlation tables for the Quaternary". Cambridge UK: Department of Geography, University of Cambridge.
• Gibbard, P.L.; Boreham, S.; Cohen, K.M.; Moscariello, A. (2011). "Global chronostratigraphical correlation table for the last 2.7 million years v. 2011". Cambridge UK: Subcommission on Quaternary Stratigraphy, Department of Geography, University of Cambridge.
• Hambrey, M.J.; Harland, W.B., eds. (1981). Earth's pre-Pleistocene glacial record. Cambridge University Press. Archived from the original on October 11, 2006. 1004 + xv pp. (book downloadable as series of PDF files)
• Silva, P.G.; Zazo,C; Bardají,T.; Baena, J.; Lario, J.; Rosas, A.; Van der Made (2009). "Tabla Cronoestratigráfica del Cuaternario AEQUA V.2" (PDF). Departamento de Geología, Universidad de Salamanca, Spain: Asociación Española para el Estudio del Cuaternario (AEQUA). Archived from the original (PDF 3.6 Mb) on 2012-06-26. (Correlation Chart of European Quaternary and cultural stages and fossils)