View source for Pleistocene

{{Short description|First epoch of the Quaternary Period}}
{{Distinguish|Plasticine}}
{{EngvarB|date=December 2022}}
{{Use dmy dates|date=December 2022}}
{{Infobox geologic timespan
| name                         = Pleistocene
| color                        = Pleistocene
| time_start                   = 2.58
| time_start_uncertainty       = 
| time_end                     = 0.0117
| time_end_uncertainty         = 
| image_map                    = File:Mollweide Paleographic Map of Earth, 21 Ka (Late Pleistocene Age).png
| caption_map                  = A map of Earth as it appeared approximately 21,000 years ago at the peak of the [[Last Glacial Maximum]] during the [[Late Pleistocene]]
| image_outcrop                =
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<!--Chronology-->  
| timeline                     = Quaternary
| former_subdivisions          =
| formerly_part_of             =
| partially_contained_in       =
| partially_contains           =
<!--Etymology-->
| name_formality               = Formal
| name_accept_date             =
| alternate_spellings          =
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<!--Usage Information--> 
| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = 
| formerly_used_by             =
| not_used_by                  =
<!--Definition-->
| chrono_unit                  = Epoch
| strat_unit                   = Series
| proposed_by                  =
| timespan_formality           = Formal
| lower_boundary_def           = 
* Base of magnetic polarity chronozone C2r (Matuyama).
* Extinction of the [[haptophyte]]s ''[[Discoaster|Discoaster pentaradiatus]]'' and ''[[Discoaster|Discoaster surculus]]''
| lower_gssp_location          = Monte San Nicola Section, [[Gela]], Sicily, Italy
| lower_gssp_coords            = {{Coord|37.1469|N|14.2035|E|type:landmark_region:IT-82|display=inline}}
| lower_gssp_accept_date       = 2009 (as base of Quaternary and Pleistocene)<ref>{{cite journal |last1=Gibbard |first1=Philip |last2=Head |first2=Martin |title=The newly-ratified definition of the Quaternary System/Period and redefinition of the Pleistocene Series/Epoch, and comparison of proposals advanced prior to formal ratification |journal=Episodes |date=September 2010 |volume=33 |issue=3 |pages=152–158 |doi=10.18814/epiiugs/2010/v33i3/002 |doi-access=free |url=https://stratigraphy.org/gssps/files/quaternary-pleistocene.pdf |access-date=8 December 2020}}</ref>
| upper_boundary_def           = End of the [[Younger Dryas]] [[stadial]]
| upper_gssp_location          = [[North Greenland Ice Core Project|NGRIP2]] ice core, [[Greenland]]
| upper_gssp_coords            = {{Coord|75.1000|N|42.3200|W|display=inline}}
| upper_gssp_accept_date       = 2008 (as base of Holocene)<ref>{{cite journal |last1=Walker |first1=Mike |last2=Johnse |first2=Sigfus |last3=Rasmussen |first3=Sune |last4=Steffensen |first4=Jørgen-Peder |last5=Popp |first5=Trevor |last6=Gibbard |first6=Phillip |last7=Hoek |first7=Wilm |last8=Lowe |first8=John |last9=Andrews |first9=John |last10=Björck |first10=Svante |last11=Cwynar |first11=Les |last12=Hughen |first12=Konrad |last13=Kershaw |first13=Peter |last14=Kromer |first14=Bernd |last15=Litt |first15=Thomas |last16=Lowe |first16=David |last17=Nakagawa |first17=Takeshi |last18=Newnham |first18=Rewi |last19=Schwande |first19=Jakob |display-authors=6 |title=The Global Stratotype Section and Point (GSSP) for the base of the Holocene Series/Epoch (Quaternary System/Period) in the NGRIP ice core |journal=Episodes |date=June 2008 |volume=31 |issue=2 |pages=264–267 |doi=10.18814/epiiugs/2008/v31i2/016 |doi-access=free |hdl=10289/920 |hdl-access=free }}</ref>
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}}
{{Human history and prehistory}}

The '''Pleistocene''' ({{IPAc-en|ˈ|p|l|aɪ|s|t|ə|ˌ|s|iː|n|,_|-|s|t|oʊ|-}} {{respell|PLY|stə|seen|,_|-|stoh|-}};<ref>{{cite encyclopedia |last=Jones|first=Daniel |author-link=Daniel Jones (phonetician) |title=Pleistocene |encyclopedia=[[English Pronouncing Dictionary]] |editor=Peter Roach |editor2=James Hartman|editor3=Jane Setter |location=Cambridge |publisher=[[Cambridge University Press]] |orig-date=1917 |year=2003 |isbn=3-12-539683-2}}</ref><ref>{{cite Dictionary.com|Pleistocene}}</ref> referred to colloquially as the ''[[ice age|Ice Age]]'') is the geological [[epoch (geology)|epoch]] that lasted from {{circa|2.58&nbsp;million}} to 11,700 years ago, spanning the Earth's most recent period of repeated [[glaciation]]s. Before a change was finally confirmed in 2009 by the [[International Union of Geological Sciences]], the cutoff of the Pleistocene and the preceding [[Pliocene]] was regarded as being 1.806&nbsp;million years [[Before Present]] (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the [[last glacial period]] and also with the end of the [[Paleolithic]] age used in [[archaeology]]. The name comes from [[Ancient Greek]] πλεῖστος (''pleîstos''), meaning "most", and καινός (''kainós''), meaning "new, recent".

The [[aridification]] and cooling trends of the preceding [[Neogene]] were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, oscillating between cold [[Glacial period|glacial periods]] and warmer [[Interglacial|interglacials]], with the sea levels being up to {{Convert|120|m|ft}} lower than present at peak glaciation, allowing the periodic connection of Asia and North America via the [[Beringia]] land bridge, and the covering of most of northern North America by the large [[Laurentide Ice Sheet]].

At the end of the preceding Pliocene, the previously isolated North and [[South American]] continents were joined by the [[Isthmus of Panama]], causing [[Great American Interchange|a faunal interchange]] between the two regions and changing [[ocean current|ocean circulation]] patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7&nbsp;million years ago. During the Early Pleistocene (2.58–0.8 Ma), [[archaic humans]] of the genus ''[[Homo]]'' originated in Africa and spread throughout [[Afro-Eurasia]]. The end of the Early Pleistocene is marked by the [[Mid-Pleistocene Transition]], with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme. The [[Late Pleistocene]] witnessed the spread of [[early modern human|modern humans]] outside Africa as well as the extinction of all other human species. Humans also [[History of Indigenous Australians#Migration|spread to the Australian continent]] and [[Settlement of the Americas|the Americas]] for the first time.

The Late Pleistocene from around 50,000 years ago onwards was marked by [[Late Pleistocene extinctions|the extinction of most large terrestrial animals outside of Africa]], an extinction event otherwise unprecedented in the geological record due to its extreme size bias. Most authors suggest that climate change, the expansion of modern humans, or the combination of both were the likely causes of the extinctions.

[[File:Evolution of temperature in the Post-Glacial period according to Greenland ice cores.jpg|thumb|upright=2|Evolution of temperature in the Post-Glacial period at the very end of the Pleistocene, according to Greenland ice cores<ref>{{cite journal |last1=Zalloua |first1=Pierre A. |last2=Matisoo-Smith |first2=Elizabeth |title=Mapping Post-Glacial expansions: The Peopling of Southwest Asia |journal=Scientific Reports |date=6 January 2017 |volume=7 |article-number=40338 |doi=10.1038/srep40338 |language=en |issn=2045-2322|pmc=5216412 |pmid=28059138 |bibcode=2017NatSR...740338P }}</ref>]]
[[File:20191021 Temperature from 20,000 to 10,000 years ago - recovery from ice age.png|thumb|upright=1.5 |right |Temperature rise marking the end of the Pleistocene, as derived from Antarctic ice core data.]]

==Etymology==
[[Charles Lyell]] introduced the term "Pleistocene" in 1839 to describe strata in [[Sicily]] that had at least 70% of their molluscan fauna still living today. This distinguished it from the older [[Pliocene|Pliocene Epoch]], which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" ('most new' or 'newest') from the [[Greek language|Greek]] ''πλεῖστος'' (''pleīstos'') 'most' and ''καινός'' (''kainós'' ([[Latin]]ized as ''cænus'') 'new').<ref>{{cite book |last1=Lyell |first1=Charles |title=Nouveaux éléments de géologie |date=1839 |publisher=Pitois-Levranet |location=Paris, France |page=621 |url=https://archive.org/stream/elmentsdegologi00meulgoog#page/n657/mode/2up |language=fr}} From p. 621:  ''"Toutefois, en même temps … et de substituer à la dénomination de Nouveau Pliocène celle plus abrégée de ''Pleistocène'', tirée du grec pleiston, ''plus'', et kainos, ''récent''."'' (However, at the same time that it became necessary to subdivide the two periods mentioned above, I found that the terms intended to designate these subdivisions were of an inconvenient length, and I have proposed to use in the future the word "Pliocene" for "old Pliocene", and to substitute for the name "new Pliocene" this shorter "Pleistocene", drawn from the Greek ''pleiston'' (most) and ''kainos'' (recent).)</ref><ref>{{cite book |last1=Wilmarth |first1=Mary Grace |title=Bulletin 769: The Geologic Time Classification of the United States Geological Survey Compared With Other Classifications, accompanied by the original definitions of era, period and epoch terms |date=1925 |publisher=U.S. Government Printing Office |location=Washington, D.C., U.S. |page=47 |url=https://books.google.com/books?id=my7x_PBkpm4C&pg=PA47}}</ref><ref name=OnlineEtDict>{{cite dictionary|title=Pleistocene|url=http://www.etymonline.com/index.php?term=Pleistocene&allowed_in_frame=0|dictionary=[[Online Etymology Dictionary]]}}</ref> This contrasts with the immediately preceding [[Pliocene]] ("newer", from ''πλείων'' (''pleíōn'', "more") and ''kainós'') and the immediately subsequent [[Holocene]] ("wholly new" or "entirely new", from ''ὅλος'' (''hólos'', "whole") and ''kainós'') [[Geologic time scale|epoch]], which extends to the present time.

==Dating==
{{Human timeline}}

The Pleistocene has been dated from 2.580 million (±0.005) to 11,700 years BP<ref name=ICS_majordiv>{{cite web|url=https://quaternary.stratigraphy.org/major-divisions|title=Major Divisions|website=Subcommission on Quaternary Stratigraphy|publisher=International Commission on Stratigraphy|access-date=17 December 2024}}</ref> with the end date expressed in [[radiocarbon year]]s as 10,000 [[carbon-14]] years BP.<ref>For the top of the series, see: {{cite book |last1=Lourens |first1=L. |last2=Hilgen |first2=F. |last3=Shackleton |first3=N. J. |last4=Laskar |first4=J. |last5=Wilson |first5=D. |year=2004 |chapter=The Neogene Period |editor-last=Gradstein |editor-first=F. |editor2-last=Ogg |editor2-first=J. |editor3-last=Smith |editor3-first=A. G. |title=A Geologic Time Scale 2004 |location=Cambridge |publisher=Cambridge University Press |isbn=0-521-78142-6 }}</ref> It covers most of the latest period of repeated [[glaciation]], up to and including the [[Younger Dryas]] cold spell. The end of the Younger Dryas has been dated to about 9700 BCE (11,700 years before present).  The end of the Younger Dryas is the official start of the current [[Holocene|Holocene Epoch]]. Although it is considered an epoch, the Holocene was not significantly different in terms of temperature change than previous Pleistocene interglacial intervals, although the rapid onset of the [[Anthropocene]] is unprecedented.<ref name="deBlij2012">{{cite book | url=https://books.google.com/books?id=7P0_sWIcBNsC | title=Why Geography Matters: More Than Ever | publisher=Oxford University Press | last=de Blij | first=Harm | year=2012 | location=Oxford | chapter=Holocene Humanity | isbn=978-0-19-991374-9| edition=2nd }}</ref> In the [[International Commission on Stratigraphy|ICS]] timescale, the Pleistocene is divided into four [[stage (stratigraphy)|stages]] or [[age (geology)|ages]], the [[Gelasian]], [[Calabrian (stage)|Calabrian]], [[Chibanian]] (previously the unofficial "Middle Pleistocene"), and [[Late Pleistocene|Upper Pleistocene]] (unofficially the "Tarantian").<ref name="ICSChart1">{{cite web|year=2017|title=International Chronostratigraphic Chart v2017/02|url=http://www.stratigraphy.org/ICSchart/ChronostratChart2017-02.jpg|access-date=17 March 2018|publisher=[[International Commission on Stratigraphy]]}}</ref><ref name="Chiba1">{{cite news|date=14 November 2017|title=Japan-based name 'Chibanian' set to represent geologic age of last magnetic shift|newspaper=The Japan Times|url=https://www.japantimes.co.jp/news/2017/11/14/national/science-health/japan-based-name-chibanian-set-represent-geologic-age-last-magnetic-shift|access-date=17 March 2018}}</ref>{{refn|name=note A|group=note|The Upper Pleistocene is a subseries/subepoch rather than a stage/age but, in 2009, the [[IUGS]] decided that it will be replaced with a stage/age (currently unofficially/informally named the ''Tarantian'').<ref name="ICSSQS">{{cite web | url=http://quaternary.stratigraphy.org/definitions/pleistocenesubdivision/ | title=Formal subdivision of the Pleistocene Series/Epoch | publisher=Subcommission on Quaternary Stratigraphy ([[International Commission on Stratigraphy]]) | date=4 January 2016 | access-date=17 March 2018}}</ref>}} In addition to these international subdivisions, various regional subdivisions are often used.

In 2009 the [[International Union of Geological Sciences]] (IUGS) confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the [[Gelasian]] as the base of the Pleistocene, namely the base of the Monte San Nicola [[Global Boundary Stratotype Section and Point|GSSP]].<ref>Riccardi, Alberto C. (30 June 2009). [http://www.stratigraphy.org/upload/IUGS%20Ratification_Q%20&%20Pleistocene.pdf "IUGS ratified ICS Recommendation on redefinition of Pleistocene and formal definition of base of Quaternary"] International Union of Geological Sciences</ref> The start date has now been rounded down to 2.580 million years BP.<ref name=ICS_majordiv/> The IUGS has yet to approve a [[type section]], [[Global Boundary Stratotype Section and Point]] (GSSP), for the upper Pleistocene/Holocene boundary (''i.e.'' the upper boundary). The proposed section is the ''[[North Greenland Ice Core Project]]'' ice core 75° 06' N 42° 18' W.<ref>{{cite journal | last1 = Svensson | first1 = A. | last2 = Nielsen | first2 = S. W. | last3 = Kipfstuhl | first3 = S. | last4 = Johnsen | first4 = S. J. | last5 = Steffensen | first5 = J. P. | last6 = Bigler | first6 = M. | last7 = Ruth | first7 = U. | last8 = Röthlisberger | first8 = R. | year = 2005 | title = Visual stratigraphy of the North Greenland Ice Core Project (NorthGRIP) ice core during the last glacial period | journal = Journal of Geophysical Research | volume = 110 | issue = D2| page = D02108 | doi=10.1029/2004jd005134 | bibcode=2005JGRD..110.2108S| url = http://epic.awi.de/12321/1/Sve2005a.pdf | doi-access = free }}</ref> The lower boundary of the Pleistocene Series is formally defined [[Magnetostratigraphy|magnetostratigraphically]] as the base of the Matuyama (C2r) [[chronozone]], isotopic stage 103. Above this point there are notable extinctions of the [[calcareous nannofossils]]: [[Discoaster|''Discoaster pentaradiatus'' and ''Discoaster surculus'']].<ref name="Gradstein-28">Gradstein, Felix M.; Ogg, James G. and Smith, A. Gilbert (eds.) (2005) ''A Geologic Time Scale 2004'' Cambridge University Press, Cambridge, UK, p. 28, {{ISBN|0-521-78142-6}}</ref><ref name="Rio">{{cite journal | last1 = Rio | first1 = D. | last2 = Sprovieri | first2 = R. | last3 = Castradori | first3 = D. | last4 = Di Stefano | first4 = E. | year = 1998 | title = The Gelasian Stage (Upper Pliocene): a new unit of the global standard chronostratigraphic scale | journal = Episodes | volume = 21 | issue = 2| pages = 82–87 | doi = 10.18814/epiiugs/1998/v21i2/002 |url=http://www.stratigraphy.org/GSSP/Gelasian7.pdf | doi-access = free }}</ref> The Pleistocene covers the recent period of repeated glaciations. 

The name [[Plio-Pleistocene]] has, in the past, been used to mean the last ice age. Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species ''Hyalinea baltica'' first appeared in the marine section at La Castella, Calabria, Italy.<ref>{{Cite book|last=Coles|first=J. M. |title=The archaeology of early man|date=1975|publisher=Penguin|others=E. S. Higgs|isbn=0-14-055107-7|location=Harmondsworth|oclc=2966860}}</ref> However, the revised definition of the [[Quaternary]], by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene.

While [[radiocarbon dating]] is well-suited for dates in the Holocene, its half life is too short for practical use in Pleistocene dating. Instead geologists use [[marine isotope stage]]s derived from oxygen isotopes to date materials deposited in the Pleistocene.

==Deposits==
Pleistocene non-marine [[sediment]]s are found primarily in fluvial [[deposit (geology)|deposit]]s, lakebeds, slope and [[loess]] deposits as well as in the large amounts of material moved about by glaciers. Less common are [[cave]] deposits, [[travertine]]s and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometres of the modern shoreline. In a few geologically active areas such as the [[Southern California]] coast, Pleistocene marine deposits may be found at elevations of several hundred metres.

==Paleogeography and climate==
[[File:Pleistocene north ice map.jpg|thumb|left|The maximum extent of [[ice age|glacial ice]] in the north polar area during the Pleistocene Period]]

The modern [[continent]]s were essentially at their present positions during the Pleistocene, the [[tectonic plate|plates]] upon which they sit probably having moved no more than {{convert|100|km|abbr=on}} relative to each other since the beginning of the period. In glacial periods, the sea level would drop by up to {{convert|120|m|abbr=on}} lower than today<ref>{{cite journal |last1=von der Heyden |first1=Sophie |title=Disentangling population structure in marine species |journal=Nature Reviews Genetics |date=17 Apr 2023 |volume=24 |issue=Sep 2023 |page=589 |doi=10.1038/s41576-023-00606-9 |pmid=37069255 |s2cid=258189561 |url=https://www.nature.com/articles/s41576-023-00606-9 |access-date=16 Aug 2023|url-access=subscription }}</ref> during peak glaciation, exposing large areas of the present [[continental shelf]] as dry land.

According to [[Mark Lynas]] (through collected data), the Pleistocene's overall climate could be characterised as a continuous [[El Niño]] with [[trade winds]] in the south [[Pacific Ocean|Pacific]] weakening or heading east, warm air rising near [[Peru]], warm water spreading from the west Pacific and the [[Indian Ocean]] to the east Pacific, and other El Niño markers.<ref>[[National Geographic Channel]], ''Six Degrees Could Change The World,'' Mark Lynas interview. Retrieved 14 February 2008.</ref>

===Glacial features===
{{More citations needed section|date=September 2018}}

Pleistocene climate was marked by repeated glacial cycles in which [[continental glacier]]s pushed to the 40th [[parallel (latitude)|parallel]] in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of [[permafrost]] stretched southward from the edge of the glacial sheet, a few hundred kilometres in [[North America]], and several hundred in [[Eurasia]]. The mean annual temperature at the edge of the ice was {{convert|-6|°C|0}}; at the edge of the permafrost, {{convert|0|°C|0}}.

Each glacial advance tied up huge volumes of water in continental ice sheets {{convert|1500|to(-)|3000|m}} thick, resulting in temporary sea-level drops of {{convert|100|m|sigfig=1}} or more over the entire surface of the Earth. During interglacial times, such as at present, [[drowned coastline]]s were common, mitigated by isostatic or other emergent motion of some regions.

The effects of glaciation were global. [[Antarctica]] was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The [[Andes]] were covered in the south by the [[Patagonia]]n ice cap. There were glaciers in [[New Zealand]] and [[Tasmania]]. The current decaying glaciers of [[Mount Kenya]], [[Mount Kilimanjaro]], and the [[Ruwenzori Range]] in east and central Africa were larger. Glaciers existed in the mountains of [[Ethiopia]] and to the west in the [[Atlas Mountains]].

In the northern hemisphere, many glaciers fused into one. The [[Cordilleran Ice Sheet]] covered the North American northwest; the east was covered by the [[Laurentide]]. The [[Fenno-Scandian ice sheet]] rested on [[northern Europe]], including much of Great Britain; the [[Alpine ice sheet]] on the [[Alps]]. Scattered domes stretched across [[Siberia]] and the Arctic shelf. The northern seas were ice-covered.

South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation. When the Laurentide Ice Sheet retreated, north-central North America was completely covered by [[Lake Agassiz]]. Over a hundred basins, now dry or nearly so, were overflowing in the North American west. [[Lake Bonneville]], for example, stood where [[Great Salt Lake]] now does. In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were [[Braided river|braided]]. African lakes were fuller, apparently from decreased evaporation. Deserts, on the other hand, were drier and more extensive. Rainfall was lower because of the decreases in oceanic and other evaporation.

It has been estimated that during the Pleistocene, the [[East Antarctic Ice Sheet]] thinned by at least 500 meters, and that thinning since the [[Last Glacial Maximum]] is less than 50 meters and probably started after c. 14 ka.<ref>{{cite journal|doi=10.1016/j.quascirev.2014.05.007|journal=Quaternary Science Reviews|first1=Yusuke |last1=Suganuma |first2=Hideki |last2=Miura |first3=Albert |last3=Zondervan |first4=Jun'ichi |last4=Okuno |date=August 2014|volume=97|title=East Antarctic deglaciation and the link to global cooling during the Quaternary: evidence from glacial geomorphology and 10Be surface exposure dating of the Sør Rondane Mountains, Dronning Maud Land|pages=102–120|bibcode=2014QSRv...97..102S|doi-access=free}}</ref>

===Major events===
{{Further|Timeline of glaciation}}
[[File:Co2 glacial cycles 800k.png|upright=1.15|thumb|Ice ages as reflected in [[Carbon dioxide in Earth's atmosphere|atmospheric CO<sub>2</sub>]], stored in the bubbles from glacial ice of [[Antarctica]]]]

During the 2.5&nbsp;million years of the Pleistocene, numerous cold phases called [[Glacial period|glacials]] ([[Quaternary glaciation|Quaternary ice age]]), or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter [[interglacial]]s which lasted about 10,000–15,000 years. The last cold episode of the [[last glacial period]] ended about 10,000 years ago.<ref>{{cite magazine|url=https://www.nationalgeographic.com/science/prehistoric-world/quaternary|archive-url=https://web.archive.org/web/20170320053318/http://www.nationalgeographic.com/science/prehistoric-world/quaternary/|archive-date=20 March 2017|title=Quaternary Period|magazine=National Geographic|date=6 January 2017}}</ref> Over 11 major glacial events have been identified, as well as many minor glacial events.<ref name="RichmondOther1">{{cite journal | last1 = Richmond | first1 = G.M. | last2 = Fullerton | first2 = D.S. | year = 1986 | title = Summation of Quaternary glaciations in the United States of America | journal = Quaternary Science Reviews | volume = 5 | pages = 183–196 | doi=10.1016/0277-3791(86)90184-8| bibcode = 1986QSRv....5..183R }}</ref> A major glacial event is a general glacial excursion, termed a "glacial". Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials".

These events are defined differently in different regions of the glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another.

For most of the 20th century, only a few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from the study of cyclical climate changes.

The glacials in the following tables show ''historical'' usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used. The headings "Glacial 1" to "Glacial 4" are designations indicating the four most recent glacials, with "Glacial 4" being the most recent. These names have been abandoned in favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since the historical terminology was established.<ref name="RichmondOther1"/><ref name="RoyOther20041">{{cite journal | last1 = Roy | first1 = M. | last2 = Clark | first2 = P.U. | last3 = Barendregt | first3 = R.W. | last4 = Glasmann | last5 = Enkin | first5 = R.J. | year = 2004 | title = Glacial stratigraphy and paleomagnetism of late Cenozoic deposits of the north-central United States | url = http://geo.oregonstate.edu/files/geo/Royetal-GSAB-2004.pdf | journal = Geological Society of America Bulletin | volume = 116 | issue = 1–2 | pages = 30–41 | doi = 10.1130/B25325.1 | access-date = 20 March 2010 | archive-url = https://web.archive.org/web/20180928051015/http://geo.oregonstate.edu/files/geo/Royetal-GSAB-2004.pdf | archive-date = 28 September 2018  | bibcode = 2004GSAB..116...30R }}</ref><ref>{{cite journal |last=Aber |first=J. S. |date=December 1991 |title=The Glaciation of Northeastern Kansas |journal=Boreas |volume=20 |issue=4 |pages=297–314 |doi=10.1111/j.1502-3885.1991.tb00282.x |bibcode=1991Borea..20..297A }} (contains a summary of how and why the Nebraskan, Aftonian, Kansan, and Yarmouthian stages were abandoned by modern stratigraphers).</ref>

{| class="wikitable"
|+ Historical names of the "four major" glacials in four regions.
! Region
! Glacial 1
! Glacial 2
! Glacial 3
! Glacial 4
|-
| '''Alps'''
| [[Gunz glaciation|Günz]]
| [[Mindel glaciation|Mindel]]
| [[Riss glaciation|Riss]]
| [[Würm glaciation|Würm]]
|-
| '''North Europe'''
| [[Eburonian]]
| [[Elsterian]]
| [[Saalian]]
| [[Weichselian]]
|-
| '''British Isles'''
| [[Beestonian stage|Beestonian]]
| [[Anglian Stage|Anglian]]
| [[Wolstonian Stage|Wolstonian]]
| [[Devensian]]
|-
| '''Midwest U.S.'''
| [[Pre-Illinoian|Nebraskan]]
| [[Kansan glaciation|Kansan]]
| [[Illinoian (stage)|Illinoian]]
| [[Wisconsinian Glaciation|Wisconsinan]]
|}

{| class="wikitable"
|+ Historical names of interglacials.
! Region
! Interglacial 1
! Interglacial 2
! Interglacial 3
|-
| '''Alps'''
| [[Cromerian Stage|Günz-Mindel]]
| [[Hoxnian Stage|Mindel-Riss]]
| [[Eemian Stage|Riss-Würm]]
|-
| '''North Europe'''
| Waalian
| Holsteinian
| [[Eemian Stage|Eemian]]
|-
| '''British Isles'''
| [[Cromerian Stage|Cromerian]]
| [[Hoxnian Stage|Hoxnian]]
| [[Eemian Stage|Ipswichian]]
|-
| '''Midwest U.S.'''
| [[Pre-Illinoian|Aftonian]]
| [[Yarmouthian Interglacial (Stage)|Yarmouthian]]
| [[Sangamonian]]
|}

Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use (Latin: ''pluvia'', rain). A pluvial is a warmer period of increased rainfall; an interpluvial is of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread.

There is no systematic correspondence between pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been stratigraphically defined.

===Palaeocycles===
[[File:Earth 1.00Ma.png|thumb|right|Map of Earth as it appeared 1 million years ago during the Pleistocene epoch, Calabrian stage]]
The sum of transient factors acting at the Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors.

The [[Mid-Pleistocene Transition]], approximately one million years ago, saw a change from low-amplitude glacial cycles with a dominant periodicity of 41,000 years to asymmetric high-amplitude cycles dominated by a periodicity of 100,000 years.<ref name="Willeit">{{cite journal|title=Mid-Pleistocene transition in glacial cycles explained by declining CO2 and regolith removal &#124; Science Advances|journal=Science Advances|volume=5|issue=4|article-number=eaav7337|doi=10.1126/sciadv.aav7337|last1=Willeit|first1=M.|last2=Ganopolski|first2=A.|last3=Calov|first3=R.|last4=Brovkin|first4=V.|year=2019|pmid=30949580|pmc=6447376}}</ref>

However, a 2020 study concluded that ice age terminations might have been influenced by [[Axial tilt|obliquity]] since the Mid-Pleistocene Transition, which caused stronger summers in the [[Northern Hemisphere]].<ref>{{cite news<!--|author=Petra Bajo |author2=Russell N. Drysdale |author3=Jon D. Woodhead |author4=John C. Hellstrom |author5=David Hodell |author6=Patrizia Ferretti |author7=Antje H. L. Voelker |author8=Giovanni Zanchetta |author9=Teresa Rodrigues |author10=Eric Wolff |author11=Jonathan Tyler |author12=Silvia Frisia |author13=Christoph Spötl |author14=Anthony E. Fallick--> |author=Petra Bajo|display-authors=etal|title=Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition|work=Science|year=2020|volume=367|issue=6483|pages=1235–1239|doi=10.1126/science.aaw1114}}</ref>

====Milankovitch cycles====
{{Main|Milankovitch cycles}}

Glaciation in the Pleistocene was a series of glacials and interglacials, stadials and interstadials, mirroring periodic climate changes. The main factor at work in climate cycling is now believed to be [[Milankovitch cycles]]. These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion. The effects of Milankovitch cycles were enhanced by various positive feedbacks related to increases in atmospheric carbon dioxide concentrations and Earth's [[albedo]].<ref>{{cite journal |last1=Lee |first1=Kyung Eun |last2=Clemens |first2=Steven C. |last3=Kubota |first3=Yoshimi |last4=Timmermann |first4=Axel |last5=Holbourn |first5=Ann |last6=Yeh |first6=Sang-Wook |last7=Bae |first7=Si Woong |last8=Ko |first8=Tae Wook |date=30 September 2021 |title=Roles of insolation forcing and CO2 forcing on Late Pleistocene seasonal sea surface temperatures |journal=[[Nature Communications]] |volume=12 |issue=1 |page=5742 |doi=10.1038/s41467-021-26051-y |pmc=8484283 |pmid=34593821 |bibcode=2021NatCo..12.5742L }}</ref>

Milankovitch cycles cannot be the sole factor responsible for the variations in climate since they explain neither the long-term cooling trend over the Plio-Pleistocene nor the millennial variations in the Greenland Ice Cores known as [[Dansgaard-Oeschger event]]s and [[Heinrich event]]s. Milankovitch pacing seems to best explain glaciation events with periodicity of 100,000, 40,000, and 20,000 years. Such a pattern seems to fit the information on climate change found in oxygen isotope cores.

====Oxygen isotope ratio cycles====
{{Main|Oxygen isotope ratio cycle}}

In [[Oxygen isotope ratio cycle|oxygen isotope ratio]] analysis, variations in the ratio of {{chem|18|O}} to {{chem|16|O}} (two [[isotopes]] of [[oxygen]]) by [[mass]] (measured by a [[mass spectrometer]]) present in the [[calcite]] of oceanic [[core sample]]s is used as a diagnostic of ancient ocean temperature change and therefore of climate change. Cold oceans are richer in {{chem|18|O}}, which is included in the tests of the microorganisms ([[foraminifera]]) contributing the calcite.

A more recent version of the sampling process makes use of modern glacial ice cores. Although less rich in {{chem|18|O}} than seawater, the snow that fell on the glacier year by year nevertheless contained {{chem|18|O}} and {{chem|16|O}} in a ratio that depended on the mean annual temperature.

Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of a deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another isotope ratio versus time. Ratios are converted to a percentage difference <!--(d)--> from the ratio found in standard mean ocean water (SMOW).

The graph in either form appears as a [[waveform]] with [[overtones]]. One half of a period is a [[Marine isotopic stage]] (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials.

According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 [[megaannum|Ma]] [[Before Present|BP]] in the Early Pleistocene [[Gelasian]]. Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced.

By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number and interglacials receive an odd number. The first major glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were 2, 6, 12, and 16. The warmest interglacials were 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under the articles for those names.

==Fauna==
{{See also|Quaternary extinction event}}
Both marine and continental faunas were essentially modern but with many more large land mammals such as [[Mammoth]]s, [[Mastodon]]s, ''[[Diprotodon]]s'', ''[[Smilodon]]s'', [[tiger]]s, [[lion]]s, [[Aurochs]], [[Arctodus|short-faced]] [[Arctotherium|bears]], [[giant sloth]]s, species within ''[[Gigantopithecus]]'' and others. Isolated landmasses such as [[Australia]], [[Madagascar]], [[New Zealand]] and islands in the Pacific saw the evolution of large birds and even reptiles such as the [[Elephant bird]], [[moa]], [[Haast's eagle]], ''[[Quinkana]]'', ''[[Megalania]]'' and ''[[Meiolania]]''.

The severe climatic changes during the Ice Age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major [[extinction event]] of large [[mammal]]s ([[megafauna]]), which included [[mammoth]]s, [[mastodon]]s, [[Machairodontinae|saber-toothed cats]], ''[[glyptodon]]s'', the [[woolly rhinoceros]], various [[giraffid]]s, such as the [[Sivatherium]]; [[ground sloth]]s, [[Irish elk]], [[Panthera spelaea|cave lions]], [[cave bear]]s, [[Gomphothere]]s, [[American lion]]s, [[dire wolves]], and [[Arctodus|short-faced bears]], began late in the Pleistocene and continued into the Holocene. [[Neanderthal]]s also became extinct during this period. At the end of the last ice age, [[Poikilotherm|cold-blooded]] animals, smaller mammals like [[wood mouse|wood mice]], migratory birds, and swifter animals like [[whitetail deer]] had replaced the megafauna and migrated north. Late Pleistocene [[bighorn sheep]] were more slender and had longer legs than their descendants today. Scientists believe that the change in predator fauna after the late Pleistocene extinctions resulted in a change of body shape as the species adapted for increased power rather than speed.<ref>{{cite book |last1=Valdez |first1=Raul |title=Mountain Sheep of North America}}</ref>

The extinctions hardly affected Africa but were especially severe in [[North America]] where native [[horse]]s and [[camel]]s were wiped out.

[[File:Pleistocene Chart.jpg|thumb|upright=1.5|Various schemes for subdividing the Pleistocene]]

* [[Asian land mammal ages]] (ALMA) include [[Zhoukoudianian]], [[Nihewanian]], and [[Yushean]].
* [[European land mammal ages]] (ELMA) include the [[Villafranchian]], [[Galerian Mammal Age|Galerian]], and [[Aurelian Mammal Age|Aurelian]]
*[[North American land mammal ages]] (NALMA) include [[Blancan]] (4.75–1.8), [[Irvingtonian]] (1.8–0.24) and [[Rancholabrean]] (0.24–0.01) in millions of years. The Blancan extends significantly back into the Pliocene.
* [[South American land mammal ages]] (SALMA) include [[Uquian]] (2.5–1.5), [[Ensenadan]] (1.5–0.3) and [[Lujanian]] (0.3–0.01) in millions of years. The Uquian previously extended significantly back into the Pliocene, although the new definition places it entirely within the Pleistocene.

In July 2018, a team of [[Russians|Russian]] scientists in collaboration with [[Princeton University]] announced that they had brought two female [[nematodes]] frozen in [[permafrost]], from around 42,000 years ago, back to life. The two nematodes, at the time, were the oldest confirmed living animals on the planet.<ref>{{cite web |url=http://siberiantimes.com/science/casestudy/news/worms-frozen-in-permafrost-for-up-to-42000-years-come-back-to-life |title=Worms frozen in permafrost for up to 42,000 years come back to life |work=The Siberian Times |date=26 July 2018 |access-date=25 August 2021 }}{{Dead link|date=August 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite journal |last1=Shatilovich |first1=A. V. |last2=Tchesunov |first2=A. V. |last3=Neretina |first3=T. V. |last4=Grabarnik |first4=I. P. |last5=Gubin |first5=S. V. |last6=Vishnivetskaya |first6=T. A. |last7=Onstott |first7=T. C. |last8=Rivkina |first8=E. M. |title=Viable Nematodes from Late Pleistocene Permafrost of the Kolyma River Lowland |journal=Doklady Biological Sciences |date=16 July 2018 |volume=480 |issue=1 |pages=100–102 |doi=10.1134/S0012496618030079 |pmid=30009350 |s2cid=49743808 }}</ref>

<gallery widths="200px" heights="150px">
File:Ice age fauna of northern Spain - Mauricio Antón.jpg|Pleistocene of [[Northern Spain]], including [[woolly mammoth]], [[Panthera leo fossilis|cave lion]]s eating a [[reindeer]], [[Equus ferus|horses]], and [[woolly rhinoceros]]
File:Pleistocene SA.jpg|Pleistocene of [[South America]], including ''[[Megatherium]]'' and two ''[[Glyptodon]]''
</gallery>

===Humans===
{{Main|Human evolution|Paleolithic|Settlement of the Americas}}
{{multiple image|perrow=2|total_width=500|caption_align=center
| align    = right
| direction =horizontal
| image1   = Superimposed structures within Trench E showing Neolithic 2A (10,600-9,300 cal BP) rectilinear structure atop Epipalaeolithic 1A (13,300-12,800 cal BP) pit dwellings in the foreground. Abu Hureyra, Syria.jpg
| image2   = Reconstruction of phase 1A (13,300-12,800 cal BP) pit dwellings showing a person seated on the open bench area in the foreground. Abu Hureyra, Syria.jpg
| footer=Remain of [[Epipalaeolithic Near East|Epipalaeolithic]] 1A (13,300-12,800 cal BP) [[Pit-house]] dwellings in the foreground, and reconstruction of phase 1A pit dwellings of [[Abu Hureyra]].<ref>{{cite journal |last1=Smith |first1=Alexia |last2=Oechsner |first2=Amy |last3=Rowley-Conwy |first3=Peter |last4=Moore |first4=Andrew M. T. |title=Epipalaeolithic animal tending to Neolithic herding at Abu Hureyra, Syria (12,800–7,800 calBP): Deciphering dung spherulites |journal=PLOS ONE |date=14 September 2022 |volume=17 |issue=9 |article-number=e0272947 |doi=10.1371/journal.pone.0272947 |bibcode=2022PLoSO..1772947S |doi-access=free |language=en |issn=1932-6203|pmc=9473395 }}</ref>
}}
The [[human evolution|evolution]] of [[anatomically modern humans]] took place during the Pleistocene.<ref>{{cite journal | last1 = Rogers | first1 = A.R. | last2 = Jorde | first2 = L.B. | year = 1995 | title = Genetic evidence on modern human origins | journal = Human Biology | volume = 67 | issue = 1| pages = 1–36 |jstor=41465052 | pmid = 7721272 }}</ref><ref>{{cite journal | last1 = Wall | first1 = J.D. | last2 = Przeworski | first2 = M. | year = 2000 | title = When did the human population start increasing? | pmc =1461207 |pmid=10924481 | journal = [[Genetics (journal)|Genetics]] | volume = 155 | issue = 4| pages = 1865–1874 | doi = 10.1093/genetics/155.4.1865 }}</ref> At the beginning of the Pleistocene ''[[Paranthropus]]'' species were still present, as well as early human ancestors, but during the lower Palaeolithic they disappeared, and the only [[hominin]] species found in fossilic records is ''[[Homo erectus]]'' for much of the Pleistocene. [[Acheulean]] [[Lithic analysis|lithics]] appear along with ''Homo erectus'', some 1.8&nbsp;million years ago, replacing the more primitive [[Oldowan]] industry used by ''[[Australopithecus garhi]]'' and by the earliest species of ''Homo''. The [[Middle Paleolithic]] saw more varied speciation within ''Homo'', including the appearance of ''[[Homo sapiens]]'' about 300,000 years ago.<ref>{{cite journal |last1=Hublin |first1=Jean-Jacques |last2=Ben-Ncer |first2=Abdelouahed |last3=Bailey |first3=Shara E. |last4=Freidline |first4=Sarah E. |last5=Neubauer |first5=Simon |last6=Skinner |first6=Matthew M. |last7=Bergmann |first7=Inga |last8=Le Cabec |first8=Adeline |last9=Benazzi |first9=Stefano |last10=Harvati |first10=Katerina |last11=Gunz |first11=Philipp |title=New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens |journal=Nature |date=8 June 2017 |volume=546 |issue=7657 |pages=289–292 |doi=10.1038/nature22336|pmid=28593953 |bibcode=2017Natur.546..289H |hdl=1887/74734 |s2cid=256771372 |url=https://kar.kent.ac.uk/62267/1/Submission_288356_1_art_file_2637492_j96j1b.pdf }}</ref> Artifacts associated with [[Behavioral modernity|modern human behavior]] are unambiguously attested starting 40,000–50,000 years ago.<ref name="Klein 1995">{{cite journal |last= Klein |first= Richard |title= Anatomy, behavior, and modern human origins |journal= Journal of World Prehistory |date= 1995 |volume= 9 |issue= 2 |pages= 167–198 |doi= 10.1007/bf02221838|s2cid= 10402296 }}</ref>

According to mitochondrial timing techniques, [[anatomically modern humans|modern humans]] migrated from Africa after the [[Riss glaciation]] in the Middle Palaeolithic during the [[Eemian Stage]], spreading all over the ice-free world during the late Pleistocene.<ref>{{cite journal | last1 = Cann | first1 = R.L. | last2 = Stoneking | first2 = M. | last3 = Wilson | first3 = A.C. | date = 1 January 1987 | title = Mitochondrial DNA and human evolution | journal = Nature | volume = 325 | issue = 6099 | pages = 31–36 | doi=10.1038/325031a0 | pmid=3025745| bibcode = 1987Natur.325...31C | s2cid = 4285418 }}</ref><ref>Stringer, C.B. (1992) "Evolution of early modern humans" ''In'': Jones, Steve; Martin, R. and Pilbeam, David R. (eds.) (1992) ''The Cambridge encyclopedia of human evolution'' Cambridge University Press, Cambridge, {{ISBN|0-521-32370-3}}, pp. 241–251.</ref><ref>{{cite journal |author=Templeton, A. R. |date=7 March 2002 |url=http://www.bioguider.com/ebook/biology/pdf/Templeton_n2002.pdf |title=Out of Africa again and again |journal=[[Nature (journal)|Nature]] |volume=416 |pages=45–51 |doi=10.1038/416045a |pmid=11882887 |issue=6876 |bibcode=2002Natur.416...45T |s2cid=4397398 |access-date=17 November 2017 |archive-date=12 April 2020 |archive-url=https://web.archive.org/web/20200412024836/http://www.bioguider.com/ebook/biology/pdf/Templeton_n2002.pdf  }}</ref> A 2005 study posits that humans in this migration interbred with [[archaic human]] forms already outside of Africa by the late Pleistocene, incorporating archaic human genetic material into the modern human gene pool.<ref>{{cite journal | last1 = Eswarana | first1 = Vinayak | last2 = Harpendingb | first2 = Henry | last3 = Rogers | first3 = Alan R | date = July 2005 | title = Genomics refutes an exclusively African origin of humans | doi = 10.1016/j.jhevol.2005.02.006 | journal = Journal of Human Evolution | volume = 49 | issue = 1| pages = 1–18 | pmid=15878780| bibcode = 2005JHumE..49....1E }}</ref>

{{Hominin species during Pleistocene}}

==See also==
{{portal|Earth sciences|Evolutionary biology|Geology|Paleontology}}
* [[Climate change]]
* [[Pleistocene megafauna]]
* [[Pleistocene Park]]
* [[Quaternary glaciation]]
{{Clear}}

== Explanatory notes ==
{{Reflist|group=note}}

==References==
{{Reflist}}
* Ogg, Jim (June 2004). [https://web.archive.org/web/20081218224452/http://www.stratigraphy.org/gssp.htm "Overview of Global Boundary Stratotype Sections and Points (GSSP's)"]. International Commission on Stratigraphy. Retrieved 20 March 2019.

==External links==
{{Commons category}}
{{Wikisource portal|Cenozoic#Quaternary}}
* [http://digitalcollections.smu.edu/cdm/ref/collection/sit/id/23 Late Pleistocene environments of the southern high plains], 1975, edited by Wendorf and Hester.
* [http://www.foraminifera.eu/querydb.php?age=Pleistocene&aktion=suche Pleistocene Microfossils: 50+ images of Foraminifera]
* [https://www.academia.edu/13755024/%D0%9F%D1%80%D0%B8%D1%80%D0%BE%D0%B4%D0%B0_%D1%96_%D0%BB%D1%8E%D0%B4%D0%B8%D0%BD%D0%B0_%D0%B2_%D0%BF%D0%BB%D0%B5%D0%B9%D1%81%D1%82%D0%BE%D1%86%D0%B5%D0%BD%D1%96_%D0%A3%D0%BA%D1%80%D0%B0%D1%97%D0%BD%D0%B8_Nature_and_man_in_the_pleistocene_of_Ukraine_._2010 Stepanchuk V.N., Sapozhnykov I.V. Nature and man in the pleistocene of Ukraine. 2010]
* [http://humanorigins.si.edu/evidence/human-evolution-timeline-interactive Human Timeline (Interactive)] – [[Smithsonian Institution|Smithsonian]], [[National Museum of Natural History]] (August 2016).
* [https://pleistocenepark.ru Pleistocene Park: Conservation Project to Restore a Pleistocene Ecology and Protect Permafrost Soils in Northern Siberia]
* [https://theclimatechronicles.com The Climate Chronicles], a multimedia production on the history of climate change in the Pleistocene, Holocene, and Anthropocene. 

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