Climate history over the past 500 million years, with the last three major ice ages indicated, Andean-Saharan (450 Ma), Karoo (300 Ma) and Late Cenozoic. 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 Late Cenozoic 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 conditions, 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 is known as the Holocene epoch.[1]
Based on climate proxies, paleoclimatologists study the different climate states originating from glaciation.
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", i.e. a period during which Earth was completely covered in ice. It has also been suggested that the end of that second cold period[4] was responsible for the subsequent Cambrian explosion, a time of rapid diversification of multi-cellular life during the Cambrian Period. The hypothesis is still controversial,[5][6] though is gaining credence among researchers, as evidence in its favour has mounted.[7]
A minor series of glaciations occurred from 460 to 430 Ma, and there were extensive glaciations from 350 to 289 Ma.
The Late Cenozoic 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. That phase is known as the Quaternary glaciation, and was marked by more or less extensive glaciation. They first appeared with a dominant frequency of 41,000 years, but after the Mid-Pleistocene Transition that changed to high-amplitude cycles, with an average period of 100,000 years.[8]
Nomenclature of Quaternary glacial cycles
Whereas the first 30 million years of the Late Cenozoic 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. 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.[9] The names system has mostly been phased out by professionals. It is now more common for researchers to refer to the periods by their marine isotopic stage number.[10] For example, there are five Pleistocene glacial/interglacial cycles recorded in marine sediments during the last half million years, but only three classic glacials were originally recognized on land during that period (Mindel, Riss and Würm).[11]
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.[9]
It has proved difficult to correlate the traditional regional names with the global marine and ice core sequences. The indexes of MIS often identify several distinct glaciations that overlap in time with a single traditional regional glaciation. Some modern authors use the traditional regional glacial names to identify such a sequence of glaciations, whereas others replace the word "glaciation" with "complex" to refer to a continuous period of time that also includes warmer stages. As shown in the table below, it is only during the last 200-300 thousand years that the time resolution of the traditional nomenclature allow for clear correspondence with MIS indexes. In particular there has been a lot of controversy regarding the glaciations MIS 10 and MIS 12, and their correspondence to the Elster and Mindel glaciations of Europe.[14]
^"Chart". International Commission on Stratigraphy. Archived from the original on 2017-01-13. Retrieved 2017-02-14.
^ abMiracle Planet: Snowball Earth, (2005) documentary, Canadian Film Board, rebroadcast 25 April 2009 on the Science Channel (HD).
^van Andel, Tjeerd H. (1994). New Views on an Old Planet: A History of Global Change (2nd ed.). Cambridge UK: Cambridge University Press. ISBN978-0-521-44755-3.
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)
