View source for Earth:Quaternary glaciation

{{Short description|Series of alternating glacial and interglacial periods}}

[[File:Iceage_north-glacial_hg.png|thumb|upright=1.15|right|Extent of maximum glaciation (in black) in the [[Earth:Northern Hemisphere|Northern Hemisphere]] during the Pleistocene. The formation of {{convert|3|to|4|km|mi|abbr=on}} thick ice sheets equate to a global sea level drop of about {{convert|120|m|ft|abbr=on}}]]

The '''Quaternary glaciation''', also known as the '''Pleistocene glaciation''', is an alternating series of [[Earth:Glacial period|glacial]] and [[Earth:Interglacial|interglacial periods]] during the [[Earth:Quaternary|Quaternary]] period that began 2.58 [[Year#SI prefix multipliers|Ma]] (million years ago) and is ongoing.<ref>{{Cite book |first1=L. |last1=Lorens |first2=F. |last2=Hilgen |first3=N.J. |last3=Shackelton |first4=J. |last4=Laskar |first5=D. |last5=Wilson |editor-last=Gradstein |editor-first=Felix M. |editor2-first=James G. |editor2-last=Ogg |editor3-first=Alan G. |editor3-last=Smith |chapter=Part III Geological Periods: 21 The Neogene Period | title = A Geologic Time Scale 2004 | publisher = Cambridge University Press | year = 2004 | pages = 412 | isbn = 978-0-521-78673-7 |chapter-url=https://books.google.com/books?id=rse4v1P-f9kC&pg=PA412}}</ref><ref>{{cite book|year=2011|doi=10.1007/978-90-481-2642-2_423|title=Encyclopedia of Snow, Ice and Glaciers|pages=873–882|series=Encyclopedia of Earth Sciences Series|last1=Ehlers|first1=Jürgen|last2=Gibbard|first2=Philip|chapter=Quaternary Glaciation |isbn=978-90-481-2641-5}}</ref><ref name="HarvCO2">{{cite book |chapter=CO2 And Astronomical Forcing of the Late Quaternary |last1=Berger |first1=A. |last2=Loutre |first2=M.F. |page=155 |isbn=9290926937 |year=2000 |bibcode=2000ESASP.463..155B |title=Proceedings of the 1st Solar and Space Weather Euroconference, 25-29 September 2000 <!--|journal = The Solar Cycle and Terrestrial Climate-->|publisher=ESA Publications Division |volume=463}}</ref> Although geologists describe this entire period up to the present as an "[[Earth:Ice age|ice age]]", in [[Social:Popular culture|popular culture]] this term usually refers to the [[Earth:Last Glacial Period|most recent glacial period]], or to the [[Earth:Pleistocene|Pleistocene]] epoch in general.<ref>{{cite web |title=Glossary of Technical Terms Related to the Ice Age Floods |url=https://iafi.org/resources/glossary/ |publisher=Ice Age Floods Institute |access-date=17 February 2019 |archive-date=18 February 2019 |archive-url=https://web.archive.org/web/20190218131914/https://iafi.org/resources/glossary/ |url-status=dead }}</ref> Since [[Astronomy:Earth|Earth]] still has polar [[Earth:Ice sheet|ice sheets]], geologists consider the Quaternary glaciation to be ongoing, though currently in an interglacial period.

During the Quaternary glaciation, ice sheets appeared, expanding during glacial periods and contracting during interglacial periods. Since the end of the last glacial period, only the [[Earth:Antarctic ice sheet|Antarctic]] and [[Earth:Greenland ice sheet|Greenland ice sheet]]s have survived, while other sheets formed during glacial periods, such as the [[Earth:Laurentide Ice Sheet|Laurentide Ice Sheet]], have completely melted. 

The major effects of the Quaternary glaciation have been the continental [[Earth:Erosion|erosion]] of land and the [[Earth:Deposition (geology)|deposition]] of material; the modification of [[Earth:Drainage system (geomorphology)|river systems]]; the formation of millions of [[Earth:Lake|lake]]s, including the development of pluvial lakes far from the ice margins; changes in [[Sea level|sea level]]; the [[Earth:Isostasy|isostatic adjustment]] of the Earth's [[Earth:Crust (geology)|crust]]; flooding; and abnormal winds. The ice sheets, by raising the [[Earth:Albedo|albedo]] (the ratio of solar [[Physics:Radiant energy|radiant energy]] reflected from Earth back into space), generated significant [[Feedback|feedback]] to further cool the [[Earth:Climate|climate]]. These effects have shaped land and ocean environments and biological communities.

Long before the Quaternary glaciation, land-based ice appeared and then disappeared during at least four other ice ages. The Quaternary glaciation can be considered a part of a [[Earth:Late Cenozoic Ice Age|Late Cenozoic Ice Age]] that began 33.9 Ma and is ongoing.

==Discovery==
Evidence for the [[Earth:Quaternary|Quaternary]] glaciation was first understood in the 18th and 19th centuries as part of the scientific revolution. Over the last century, extensive field observations have provided evidence that continental glaciers covered large parts of [[Earth:Europe|Europe]], [[Earth:North America|North America]], and Siberia. Maps of glacial features were compiled after many years of fieldwork by hundreds of geologists who mapped the location and orientation of [[Earth:Drumlin|drumlin]]s, [[Earth:Esker|esker]]s, [[Earth:Moraine|moraine]]s, [[Earth:Striation (geology)|striations]], and [[Earth:Glacial stream|glacial stream]] channels to reveal the extent of the [[Earth:Ice sheet|ice sheet]]s, the direction of their flow, and the systems of [[Earth:Meltwater|meltwater]] channels. They also allowed scientists to decipher a history of multiple advances and retreats of the ice. Even before the theory of worldwide glaciation was generally accepted, many observers recognized that more than a single advance and retreat of the ice had occurred.

==Description==
{{see|Marine isotope stages}}
[[File:Vostok Petit data.svg|thumb|upright=1.35|Graph of reconstructed temperature (blue), CO<sub>2</sub> (green), and dust (red) from the Vostok Station ice core for the past 420,000 years]]
To geologists, an [[Earth:Ice age|ice age]] is defined by the presence of large amounts of land-based ice. Prior to the Quaternary glaciation, land-based ice formed during at least four earlier geologic periods: the [[Earth:Late Paleozoic icehouse|late Paleozoic]] (360–260 Ma), [[Earth:Andean-Saharan glaciation|Andean-Saharan]] (450–420 Ma), [[Earth:Cryogenian|Cryogenian]] (720–635 Ma) and [[Earth:Huronian glaciation|Huronian]] (2,400–2,100 Ma).<ref>{{cite journal |author=Lockwood, J.G. |title=The Antarctic Ice-Sheet: Regulator of Global Climates?: Review |journal=The Geographical Journal |volume=145 |issue=3 |pages=469–471 |date=November 1979 |jstor=633219 |doi=10.2307/633219 |last2=van Zinderen-Bakker |first2=E. M.|author-link2=Eduard Meine van Zinderen-Bakker}}</ref><ref>{{cite book |url=https://books.google.com/books?id=ihny39BvVhIC&pg=PA289 |title=Evaporites: sediments, resources and hydrocarbons |first=John K. |last=Warren |publisher=Birkhäuser |year=2006 |isbn=978-3-540-26011-0 |page=289}}</ref>

Within the Quaternary ice age, there were also periodic fluctuations of the total volume of land ice, the sea level, and global temperatures. During the colder episodes (referred to as [[Earth:Glacial period|glacial period]]s or glacials) large ice sheets at least {{convert|4|km|mi|1|abbr=on}} thick at their maximum covered parts of Europe, North America, and Siberia. The shorter warm intervals between glacials, when continental glaciers retreated, are referred to as [[Earth:Interglacial|interglacial]]s. These are evidenced by buried soil profiles, peat beds, and lake and stream deposits separating the unsorted, unstratified deposits of glacial debris.

Initially the glacial/interglacial cycle length was about 41,000 years, but following the [[Earth:Mid-Pleistocene Transition|Mid-Pleistocene Transition]] about 1 Ma, it slowed to about 100,000 years, as evidenced most clearly by [[Earth:Ice core|ice core]]s for the past 800,000 years and marine sediment cores for the earlier period. Over the past 740,000 years there have been eight glacial cycles.<ref>{{Cite journal
  | last = Augustin | first = Laurent | title = Eight glacial cycles from an Antarctic ice core
  | journal = Nature | volume = 429 | issue = 6992 | pages = 623–8
  | year = 2004 | doi = 10.1038/nature02599 
  | pmid = 15190344|display-authors=0| bibcode = 2004Natur.429..623A| doi-access = free}}</ref>

The entire Quaternary period, starting 2.58 Ma, is referred to as an ice age because at least one permanent large ice sheet—the [[Earth:Antarctic ice sheet|Antarctic ice sheet]]—has existed continuously. There is uncertainty over how much of [[Earth:Greenland ice sheet|Greenland was covered by ice]] during each interglacial. Currently, Earth is in an interglacial period, the [[Earth:Holocene|Holocene]] epoch beginning 15,000 to 10,000 years ago; this has caused the ice sheets from the [[Earth:Last Glacial Period|Last Glacial Period]] to [[Earth:Holocene glacial retreat|slowly melt]]. The remaining glaciers, now occupying about 10% of the world's land surface, cover Greenland, Antarctica and some mountainous regions. During the glacial periods, the present (i.e. interglacial) hydrologic system was completely interrupted throughout large areas of the world and was considerably modified in others. The volume of ice on land resulted in a sea level about {{convert|120|m|ft|0}} lower than present.

==Causes==
{{Further|Earth:Ice age}}
Earth's history of glaciation is a product of the ''internal variability'' of Earth's [[Earth:Climate system|climate system]] (e.g., ocean currents, [[Earth:Carbon cycle|carbon cycle]]), interacting with ''external forcing'' by phenomena outside the climate system (e.g., changes in Earth's orbit, volcanism, and changes in solar output).<ref>{{Cite web |url=http://exhibits.museum.state.il.us/exhibits/ice_ages/why_4_cool_periods.html |title=Why were there Ice Ages?<!-- Bot generated title --> |access-date=2019-12-11 |archive-date=2019-12-11 |archive-url=https://web.archive.org/web/20191211231311/http://exhibits.museum.state.il.us/exhibits/ice_ages/why_4_cool_periods.html |url-status=dead }}</ref>

===Astronomical cycles===
The role of Earth's orbital changes in controlling climate was first advanced by James Croll in the late 19th century.<ref>[http://earthguide.ucsd.edu/virtualmuseum/climatechange2/02_2.shtml Discovery of the Ice Age<!-- Bot generated title -->]</ref> Later, the Serbian [[Physics:Geophysics|geophysicist]] Milutin Milanković elaborated on the theory and calculated that these irregularities in Earth's orbit could cause the climatic cycles now known as [[Earth:Milankovitch cycles|Milankovitch cycles]].<ref>[http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/ EO Library: Milutin Milankovitch<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20031210132700/http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/ |date=December 10, 2003 }}</ref> They are the result of the additive behavior of several types of cyclical changes in Earth's orbital properties.
[[File:Milankovitch Variations.png|thumb|upright=1.35|Relationship of Earth's orbit to periods of glaciation]]
Firstly, changes in the [[Astronomy:Orbital eccentricity|orbital eccentricity]] of Earth occur on a cycle of about 100,000 years.<ref name="ilwhy">[http://iceage.museum.state.il.us/content/why-do-ice-ages-happen Why do glaciations occur?<!-- Bot generated title -->]</ref> Secondly, the [[Astronomy:Orbital inclination|inclination]] or tilt of Earth's axis varies between 22° and 24.5° in a cycle 41,000 years long.<ref name="ilwhy"/> The tilt of Earth's axis is responsible for the [[Physics:Season|season]]s; the greater the tilt, the greater the contrast between summer and winter temperatures. Thirdly, [[Physics:Precession|precession]] of the [[Astronomy:Equinox|equinoxes]], or wobbles in the [[Astronomy:Axial tilt|Earth's rotation axis]], have a periodicity of 26,000 years. According to the Milankovitch theory, these factors cause a periodic cooling of Earth, with the coldest part in the cycle occurring about every 40,000 years. The main effect of the Milankovitch cycles is to change the contrast between the seasons, not the annual amount of solar heat Earth receives. The result is less ice melting than accumulating, and [[Earth:Glacier|glacier]]s build up.

Milankovitch worked out the ideas of climatic cycles in the 1920s and 1930s, but it was not until the 1970s that a sufficiently long and detailed chronology of the Quaternary temperature changes was worked out to test the theory adequately.<ref>[https://web.archive.org/web/20000903012859/http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch_3.html EO Library: Milutin Milankovitch Page 3<!-- Bot generated title -->]</ref> Studies of deep-sea cores and their fossils indicate that the fluctuation of climate during the last few hundred thousand years is remarkably close to that predicted by Milankovitch.{{clear}}

===Atmospheric composition===
One theory holds that decreases in atmospheric {{chem|C|O|2|link=carbon dioxide}}, an important [[Chemistry:Greenhouse gas|greenhouse gas]], started the long-term cooling trend that eventually led to the formation of continental ice sheets in the Arctic.<ref name="BartoliHönischZeebe2011">{{cite journal |last1=Bartoli |first1=Greta |last2=Hönisch |first2=Bärbel |last3=Zeebe |first3=Richard E. |date=16 November 2011 |title=Atmospheric CO2 decline during the Pliocene intensification of Northern Hemisphere glaciations |journal=[[Earth:Paleoceanography and Paleoclimatology|Paleoceanography and Paleoclimatology]] |volume=26 |issue=4 |pages=1–14 |doi=10.1029/2010PA002055 |bibcode=2011PalOc..26.4213B |doi-access=free }}</ref> [[Earth:Carbon dioxide in Earth's atmosphere#Concentrations in the geologic past|Geological evidence]] indicates a decrease of more than 90% in atmospheric {{CO2}} since the middle of the [[Earth:Mesozoic|Mesozoic Era]].<ref>{{cite journal |last1=Fletcher |first1=Benjamin J. |last2=Brentnall |first2=Stuart J. |last3=Anderson |first3=Clive W.|last4=Berner |first4=Robert A.|last5=Beerling |first5=David J. |title=Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change |journal=[[Earth:Nature Geoscience|Nature Geoscience]] |volume=1 |issue=1 |pages=43–48 |year=2008 |doi=10.1038/ngeo.2007.29 |bibcode=2008NatGe...1...43F}}</ref> An analysis of {{CO2}} reconstructions from [[Earth:Alkenone|alkenone]] records shows that {{CO2}} in the atmosphere declined before and during Antarctic glaciation, and supports a substantial {{CO2}} decrease as the primary cause of Antarctic glaciation.<ref>{{cite journal |last1=Pagani |first1=Mark |first2=Matthew |last2=Huber |first3=Zhonghui |last3=Liu |first4=Steven M. |last4=Bohaty |first5=Jorijntje |last5=Henderiks |first6=Willem |last6=Sijp |first7=Srinath |last7=Krishnan |first8=Robert M. |last8=DeConto |year=2011 |title=The Role of Carbon Dioxide During the Onset of Antarctic Glaciation |journal=Science |volume=334 |issue=6060 |pages=1261–4 |pmid=22144622 |doi=10.1126/science.1203909 |bibcode=2011Sci...334.1261P |s2cid=206533232 }}</ref>

{{CO2}} levels also play an important role in the transitions between interglacials and glacials. High {{CO2}} contents correspond to warm interglacial periods, and low {{CO2}} to glacial periods. However, studies indicate that {{chem|C|O|2}} may not be the primary cause of the interglacial-glacial transitions, but instead acts as a [[Feedback|feedback]].<ref name="Joos">{{cite book |last=Joos |first=Fortunat |author2=Prentice, I. Colin |title=The Global Carbon Cycle: Integrating Humans, Climate, and the Natural World |chapter-url=http://www.climate.unibe.ch/~joos/OUTGOING/publications/joos03scope_proofs.pdf |access-date=2008-05-07 |series=Scope |volume=62 |year=2004 |publisher=Island Press |location=Washington D.C. |pages=165–186 |chapter=A Paleo-Perspective on Changes in Atmospheric CO2 and Climate |url-status=dead |archive-url=https://web.archive.org/web/20081217075154/http://www.climate.unibe.ch/~joos/OUTGOING/publications/joos03scope_proofs.pdf |archive-date=2008-12-17 }}</ref> The explanation for this observed {{chem|C|O|2}} variation "remains a difficult attribution problem".<ref name="Joos"/>

===Plate tectonics and ocean currents===
{{Further|Earth:Plate tectonics|Earth:Ocean current}}
An important component in the development of long-term ice ages is the positions of the continents.<ref>[http://www.geo.ua.edu/intro03/ice.html Glaciers and Glaciation<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20070805083920/http://www.geo.ua.edu/intro03/ice.html |date=August 5, 2007 }}</ref> These can control the circulation of the oceans and the atmosphere, affecting how ocean currents carry heat to high latitudes. Throughout most of [[Earth:Geologic time scale|geologic time]], the [[Earth:North Pole|North Pole]] appears to have been in a broad, open ocean that allowed major ocean currents to move unabated. Equatorial waters flowed into the polar regions, warming them. This produced mild, uniform climates that persisted throughout most of geologic time.

But during the [[Earth:Cenozoic|Cenozoic Era]], the large [[Earth:North American Plate|North American]] and [[Earth:South American Plate|South American]] continental plates drifted westward from the [[Earth:Eurasian Plate|Eurasian Plate]]. This interlocked with the development of the [[Earth:Atlantic Ocean|Atlantic Ocean]], running north–south, with the North Pole in the small, nearly landlocked basin of the [[Earth:Arctic Ocean|Arctic Ocean]]. The Drake Passage opened 33.9 million years ago (the [[Earth:Eocene|Eocene]]-[[Earth:Oligocene|Oligocene]] transition), severing [[Earth:Antarctic Plate|Antarctica]] from South America. The [[Earth:Antarctic Circumpolar Current|Antarctic Circumpolar Current]] could then flow through it, isolating Antarctica from warm waters and triggering the formation of its huge ice sheets. The weakening of the [[Earth:North Atlantic Current|North Atlantic Current]] around 3.65 to 3.5 million years ago resulted in cooling and freshening of the Arctic Ocean, nurturing the development of Arctic sea ice and preconditioning the formation of continental glaciers later in the Pliocene.<ref name="KalasEtAl2020">{{cite journal |last1=Kalas |first1=Cyrus |last2=Khélifi |first2=Nabil |last3=Bahr |first3=André |last4=Naafs |first4=B. D. A. |last5=Nürnberg |first5=Dirk |last6=Herrle |first6=Jens O. |date=January 2020 |title=Did North Atlantic cooling and freshening from 3.65–3.5 Ma precondition Northern Hemisphere ice sheet growth? |journal=[[Earth:Global and Planetary Change|Global and Planetary Change]] |volume=185 |page=103085 |doi=10.1016/j.gloplacha.2019.103085 |bibcode=2020GPC...18503085K |s2cid=213769471 |doi-access=free |hdl=1983/f1d7878d-a7cb-49b5-8e33-7bfc6fb3cb1c |hdl-access=free }}</ref> The Isthmus of Panama developed at a convergent plate margin about 2.6 million years ago and further separated oceanic circulation, closing [[Earth:Central American Seaway|the last strait]], outside the polar regions, that had connected the [[Earth:Pacific Ocean|Pacific]] and Atlantic Oceans.<ref>[http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16401 EO Newsroom: New Images – Panama: Isthmus that Changed the World<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20070802015424/http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16401 |date=August 2, 2007 }}</ref> This increased poleward salt and heat transport, strengthening the North Atlantic [[Earth:Thermohaline circulation|thermohaline circulation]], which supplied enough moisture to arctic latitudes to initiate the northern glaciation.<ref>{{cite journal |last1=Bartoli |first1=G. |last2=Sarnthein |first2=M. |last3=Weinelt |first3=M. |last4=Erlenkeuser |first4=H. |last5=Garbe-Schönberg |first5=D. |last6=Lea |first6=D. W. |title=Final closure of Panama and the onset of northern hemisphere glaciation |journal=[[Earth:Earth and Planetary Science Letters|Earth and Planetary Science Letters]] |date=30 August 2005 |volume=237 |issue=1 |pages=33–44 |doi=10.1016/j.epsl.2005.06.020 |bibcode=2005E&PSL.237...33B |issn=0012-821X|doi-access=free }}</ref>

===Rise of mountains===
The elevation of continental surface, often as [[Earth:Mountain formation|mountain formation]], is thought to have contributed to cause the Quaternary glaciation. The gradual movement of the bulk of Earth's landmasses away from the tropics in addition to increased mountain formation in the Late Cenozoic meant more land at high altitude and high latitude, favouring the formation of glaciers.<ref>{{Cite book|title=Glacial and Quaternary Geology|last=Flint|first=Richard Foster|publisher=John Wiley and Sons|year=1971|pages=22|author-link=Richard Foster Flint}}</ref> For example, the Greenland ice sheet formed in connection to the uplift of the west Greenland and east Greenland uplands in two phases, 10 and 5 Ma, respectively. These mountains constitute [[Earth:Passive margin|passive continental margins]].<ref name="Solgaardetal2013" /> Computer models show that the uplift would have enabled glaciation through increased orographic precipitation and [[Lapse rate|cooling of surface temperatures]].<ref name=Solgaardetal2013>{{cite journal |last1=Solgaard |first1=Anne M. |last2=Bonow |first2=Johan M. |last3=Langen |first3=Peter L.|last4=Japsen |first4=Peter|last5=Hvidberg |first5=Christine|date=2013 |title=Mountain building and the initiation of the Greenland Ice Sheet |journal=[[Earth:Palaeogeography, Palaeoclimatology, Palaeoecology|Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=392 |pages=161–176 |doi= 10.1016/j.palaeo.2013.09.019|bibcode=2013PPP...392..161S }}</ref> For the [[Place:Andes|Andes]] it is known that the Principal Cordillera had risen to heights that allowed for the development of [[Earth:Glacier morphology|valley glaciers]] about 1 Ma.<ref name=Charrieretal1019>{{cite journal |last1=Charrier |first1=Reynaldo |last2=Iturrizaga |first2=Lafasam|last3=Charretier |first3=Sebastién |last4=Regard |first4=Vincent |date=2019 |title=Geomorphologic and Glacial Evolution of the Cachapoal and southern Maipo catchments in the Andean Principal Cordillera, Central Chile (34°-35º S) |url=http://www.andeangeology.cl/index.php/revista1/article/view/V46n2-3108/pdf |journal=Andean Geology |author-link1=Reynaldo Charrier |volume=46 |issue=2 |pages=240–278 |doi=10.5027/andgeoV46n2-3108 |access-date=June 9, 2019|doi-access=free }}</ref>

==Effects==
The presence of so much ice upon the continents had a profound effect upon almost every aspect of Earth's hydrologic system. Most obvious are the spectacular mountain scenery and other continental landscapes fashioned both by glacial erosion and deposition instead of running water. Entirely new landscapes covering millions of square kilometers were formed in a relatively short period of geologic time. In addition, the vast bodies of glacial ice affected Earth well beyond the glacier margins. Directly or indirectly, the effects of glaciation were felt in every part of the world.

===Lakes===
{{Further|Earth:Glacial lake}}
The Quaternary glaciation produced more lakes than all other geologic processes combined. The reason is that a continental glacier completely disrupts the preglacial [[Earth:Drainage system (geomorphology)|drainage system]]. The surface over which the glacier moved was scoured and eroded by the ice, leaving many closed, undrained depressions in the bedrock. These depressions filled with water and became lakes.
[[File:Glacial lakes.jpg|thumb|right|A diagram of the formation of the Great Lakes]]
Very large lakes were formed along the glacial margins. The ice on both North America and Europe was about {{convert|3000|m|ft|-3|abbr=on}} thick near the centers of maximum accumulation, but it tapered toward the glacier margins. Ice weight caused crustal subsidence, which was greatest beneath the thickest accumulation of ice. As the ice melted, [[Earth:Post-glacial rebound|rebound of the crust]] lagged behind, producing a regional slope toward the ice. This slope formed basins that have lasted for thousands of years. These basins became lakes or were invaded by the ocean. The [[Place:Baltic Sea|Baltic Sea]]<ref>{{cite journal |last1=Tikkanen |first1=Matti |last2=Oksanen |first2=Juha |date=2002 |title=Late Weichselian and Holocene shore displacement history of the Baltic Sea in Finland |url=http://www.helsinki.fi/maantiede/geofi/fennia/demo/pages/oksanen.htm |journal=Fennia |volume=180 |issue=1–2 |access-date=December 22, 2017 }}</ref><ref>[http://www.pgi.gov.pl/pgi_en/index.php?option=articles&task=viewarticle&artid=514&Itemid=3 Polish Geological Institute<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20080315020229/http://www.pgi.gov.pl/pgi_en/index.php?option=articles&task=viewarticle&artid=514&Itemid=3 |date=March 15, 2008 }}</ref> and the Great Lakes of North America<ref>[http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_ice_sheets.html CVO Website – Glaciations and Ice Sheets<!-- Bot generated title -->]</ref> were formed primarily in this way.{{dubious|date=February 2018}}

The numerous lakes of the [[Place:Canadian Shield|Canadian Shield]], Sweden, and Finland are thought to have originated at least partly from glaciers' selective erosion of [[Earth:Weathering|weathered]] [[Earth:Bedrock|bedrock]].<ref name=Karnaetal1999>{{cite book |last1=Lidmar-Bergström |first1=K. |last2=Olsson |first2=S.|last3=Roaldset |first3=E.|date=1999 |chapter= Relief features and palaeoweathering remnants in formerly glaciated Scandinavian basement areas |title=Palaeoweathering, Palaeosurfaces and Related Continental Deposits |editor-last=Thiry |editor-first=Médard |editor-last2=Simon-Coinçon |editor-first2=Régine |publisher=Blackwell |pages= 275–301 |isbn=0-632-05311-9 |volume=27|series=Special publication of the International Association of Sedimentologists }}</ref><ref name=UppslagsFiBERG>{{cite web |url=http://uppslagsverket.fi/sv/sok/view-103684-BerggrundOchYtformer |title=berggrund och ytformer |last=Lindberg |first=Johan  |date=April 4, 2016 |website=[[Uppslagsverket Finland]] |access-date=November 30, 2017 |language=sv}}</ref>

====Pluvial lakes====
The climatic conditions that cause glaciation had an indirect effect on arid and semiarid regions far removed from the large ice sheets. The increased precipitation that fed the glaciers also increased the runoff of major rivers and intermittent streams, resulting in the growth and development of large pluvial lakes. Most pluvial lakes developed in relatively arid regions where there typically was insufficient rain to establish a drainage system leading to the sea. Instead, stream runoff flowed into closed basins and formed playa lakes. With increased rainfall, the playa lakes enlarged and overflowed. Pluvial lakes were most extensive during glacial periods. During interglacial stages, with less rain, the pluvial lakes shrank to form small salt flats.

===Isostatic adjustment===
{{Main|Earth:Post-glacial rebound}}
Major isostatic adjustments of the [[Earth:Lithosphere|lithosphere]] during the Quaternary glaciation were caused by the weight of the ice, which depressed the continents. In {{wipe|Canada}}, a large area around Hudson Bay was depressed below (modern) sea level, as was the area in Europe around the Baltic Sea. The land has been rebounding from these depressions since the ice melted. Some of these isostatic movements triggered large [[Earth:Earthquake|earthquake]]s in Scandinavia about 9,000 years ago. These earthquakes are unique in that they are not associated with plate tectonics.

Studies have shown that the uplift has taken place in two distinct stages.  The initial uplift following [[Earth:Deglaciation|deglaciation]] was rapid (called "elastic"), and took place as the ice was being unloaded. After this "elastic" phase, uplift proceed by "slow viscous flow" so the rate [[Exponential decay|decreased exponentially]] after that. Today, typical uplift rates are of the order of 1&nbsp;cm per year or less, except in areas of North America, especially Alaska, where the rate of uplift is 2.54&nbsp;cm per year (1 inch or more).<ref>Actual observations from Haines, Alaska</ref> In northern Europe, this is clearly shown by the [[Engineering:GPS|GPS]] data obtained by the BIFROST GPS network.<ref>{{cite journal |first1=J.M. |last1=Johansson |first2=J.L. |last2=Davis |first3=H.-G. |last3=Scherneck |first4=G.A. |last4=Milne |first5=M. |last5=Vermeer |first6=J.X. |last6=Mitrovica |first7=R.A. |last7=Bennett |first8=B. |last8=Jonsson |first9=G. |last9=Elgered |first10=P. |last10=Elósegui |first11=H. |last11=Koivula |first12=M. |last12=Poutanen |first13=B.O. |last13=Rönnäng |first14=I.I. |last14=Shapiro |title=Continuous GPS measurements of postglacial adjustment in Fennoscandia 1. Geodetic results |journal=Geodesy and Gravity/Tectonophysics |volume=107 |issue=B8 |pages=2157 |year=2002 |doi=10.1029/2001JB000400 |bibcode=2002JGRB..107.2157J |url=http://publications.lib.chalmers.se/publication/197898-continuous-gps-measurements-of-postglacial-adjustment-in-fennoscandia-1-geodetic-results |doi-access=free }}{{Dead link|date=May 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Studies suggest that rebound will continue for at least another 10,000 years. The total uplift from the end of deglaciation depends on the local ice load and could be several hundred meters near the center of rebound.

===Winds===
The presence of ice over so much of the continents greatly modified patterns of atmospheric circulation. Winds near the glacial margins were strong and persistent because of the abundance of dense, cold air coming off the glacier fields. These winds picked up and transported large quantities of loose, fine-grained sediment brought down by the glaciers. This dust accumulated as [[Earth:Loess|loess]] (wind-blown silt), forming irregular blankets over much of the Missouri River valley, central Europe, and northern China.

Sand [[Earth:Dune|dune]]s were much more widespread and active in many areas during the early Quaternary period. A good example is the Sand Hills region in Nebraska which covers an area of about {{convert|60000|km2|sqmi|0|sp=us|abbr=on}}.<ref>[http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17104 EO Newsroom: New Images – Sand Hills, Nebraska<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20070802015451/http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17104 |date=August 2, 2007 }}</ref> This region was a large, active dune field during the Pleistocene epoch but today is largely stabilized by grass cover.<ref>[http://www.livescience.com/imageoftheday/siod_051216.html LiveScience.com<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20081201125659/http://www.livescience.com/imageoftheday/siod_051216.html |date=December 1, 2008 }}</ref><ref>[http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/SandHills.HTM Nebraska Sand Hills<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20071221015154/http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/SandHills.HTM |date=2007-12-21 }}</ref>

===Ocean currents===
Thick glaciers were heavy enough to reach the sea bottom in several important areas, which blocked the passage of ocean water and affected ocean currents. In addition to these direct effects, it also caused feedback effects, as ocean currents contribute to global heat transfer.

===Gold deposits===
Moraines and till deposited by Quaternary glaciers have contributed to the formation of valuable [[Earth:Placer deposit|placer deposit]]s of gold. This is the case of [[Place:Magallanes Region|southernmost Chile]] where reworking of Quaternary moraines have concentrated gold offshore.<ref>{{Cite journal|title=Potential mineral resources of the Chilean offshore: an overview|journal=Andean Geology|url=http://www.andeangeology.cl/index.php/revista1/article/view/V47n1-3260/html|last1=García|first1=Marcelo|volume=47|pages=1–13|last2=Correa|first2=Jorge|issue=1|year=2020|last3=Maksaev|first3=Víctor|last4=Townley|first4=Brian|doi=10.5027/andgeov47n1-3260|doi-access=free}}</ref>

==Records of prior glaciation==
{{Main|Earth:Timeline of glaciation}}
[[File:Phanerozoic Climate Change.png|thumb|right|upright=1.15|500 million years of [[Earth:Climate change (general concept)|climate change]].]]
Glaciation has been a rare event in Earth's history,<ref>{{Cite web |url=http://exhibits.museum.state.il.us/exhibits/ice_ages/ |title=Ice Ages- Illinois State Museum<!-- Bot generated title --> |access-date=2019-12-11 |archive-date=2022-02-15 |archive-url=https://web.archive.org/web/20220215163148/http://exhibits.museum.state.il.us/exhibits/ice_ages/ |url-status=dead }}</ref> but there is evidence of widespread glaciation during the late [[Earth:Paleozoic|Paleozoic]] Era (300 to 200 Ma) and the late [[Earth:Precambrian|Precambrian]] (i.e. the [[Earth:Neoproterozoic|Neoproterozoic]] Era, 800 to 600 Ma).<ref>{{Cite web |url=http://exhibits.museum.state.il.us/exhibits/ice_ages/why_4_cool_periods.html |title=When have Ice Ages occurred?<!-- Bot generated title --> |access-date=2019-12-11 |archive-date=2019-12-11 |archive-url=https://web.archive.org/web/20191211231311/http://exhibits.museum.state.il.us/exhibits/ice_ages/why_4_cool_periods.html |url-status=dead }}</ref> Before the current ice age, which began 2 to 3 Ma, Earth's climate was typically mild and uniform for long periods of time. This climatic history is implied by the types of [[Biology:Fossil|fossil]] plants and animals and by the characteristics of sediments preserved in the [[Earth:Stratum|stratigraphic]] record.<ref>[http://pubs.usgs.gov/gip/continents/ Our Changing Continent<!-- Bot generated title -->]</ref> There are, however, widespread glacial deposits, recording several major periods of ancient glaciation in various parts of the geologic record. Such evidence suggests major periods of glaciation prior to the current Quaternary glaciation.

One of the best documented records of pre-Quaternary glaciation, called the Karoo Ice Age, is found in the late Paleozoic rocks in {{wipe|South Africa}}, {{wipe|India}}, South America, Antarctica, and {{wipe|Australia}}. Exposures of ancient glacial deposits are numerous in these areas. Deposits of even older glacial sediment exist on every continent except South America. These indicate that two other periods of widespread glaciation occurred during the late Precambrian, producing the [[Earth:Snowball Earth|Snowball Earth]] during the [[Earth:Cryogenian|Cryogenian]] period.<ref>[http://www.agiweb.org/geotimes/apr03/WebExtra041803.html Geotimes – April 2003 – Snowball Earth<!-- Bot generated title -->]</ref>

==Next glacial period==
{{See|Milankovitch cycles|Past sea level|Climate change|Human impact on the environment}}

[[File:Carbon History and Flux Rev.png|thumb|Increase in atmospheric {{chem|C|O|2}} since the [[History:Industrial Revolution|Industrial Revolution]]]]
The warming trend following the [[Earth:Last Glacial Maximum|Last Glacial Maximum]], since about 20,000 years ago, has resulted in a [[Earth:Early Holocene sea level rise|sea level rise]] by about {{convert|121|m|ft|0}}. This warming trend subsided about 6,000 years ago, and sea level has been comparatively stable since the [[History:Neolithic|Neolithic]]. The present interglacial period (the [[Earth:Holocene climatic optimum|Holocene climatic optimum]]) has been stable and warm compared to the preceding ones, which were interrupted by numerous cold spells lasting hundreds of years. This stability might have allowed the [[History:Neolithic Revolution|Neolithic Revolution]] and by extension human [[Social:Civilization|civilization]].<ref>{{cite journal | url=http://www.des.ucdavis.edu/faculty/Richerson/AgOrigins_2_12_01.pdf | title=Was agriculture impossible during the Pleistocene but mandatory during the Holocene? A climate change hypothesis | access-date=29 December 2015 | last=Richerson | first=Peter J. | author2=Robert Boyd | author3=Robert L. Bettinger | journal=[[History:American Antiquity|American Antiquity]] | year=2001 | volume=66 | issue=3 | pages=387–411 | doi=10.2307/2694241| jstor=2694241 | s2cid=163474968 }}</ref>

Based on [[Earth:Milankovitch cycles|orbital models]], the cooling trend initiated about 6,000 years ago will continue for another 23,000 years.<ref name="Imbriel1980">{{cite journal |author1=J Imbrie |author2=J Z Imbrie |title=Modeling the Climatic Response to Orbital Variations |journal=Science |volume=207 |issue=4434 |year=1980 |pages=943–953 |doi=10.1126/science.207.4434.943 |pmid=17830447 |bibcode=1980Sci...207..943I|s2cid=7317540 }}</ref> Slight changes in the Earth's orbital parameters may, however, indicate that, even without any human contribution, there will not be another glacial period for the next 50,000 years.<ref name="Berger2002">{{cite journal |vauthors=Berger A, Loutre MF |title=Climate: An exceptionally long interglacial ahead? |journal=Science |volume=297 |issue=5585 |year=2002 |pages=1287–8 |doi=10.1126/science.1076120 |pmid=12193773|s2cid=128923481 }} "Berger and Loutre argue in their Perspective that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth's orbit around the Sun."</ref>
It is possible that the current cooling trend might be interrupted by an [[Earth:Stadial|interstadial]] phase (a warmer period) in about 60,000 years, with the next glacial maximum reached only in about 100,000 years.<ref>{{cite web|url=http://www.ncdc.noaa.gov/paleo/milankovitch.html|title=NOAA Paleoclimatology Program – Orbital Variations and Milankovitch Theory}}
{{cite journal|author1=A. Ganopolski |author2=R. Winkelmann |author3=H. J. Schellnhuber |year=2016|title=Critical insolation–CO2 relation for diagnosing past and future glacial inception|journal=Nature|volume=529|issue=7585|pages=200–203|bibcode=2016Natur.529..200G|doi=10.1038/nature16494|pmid=26762457|s2cid=4466220}}
M. F. Loutre, A. Berger, "Future Climatic Changes: Are We Entering an Exceptionally Long Interglacial?", ''Climatic Change'' 46 (2000), 61-90.</ref>

Based on past estimates for interglacial durations of about 10,000 years, in the 1970s there was some concern that [[Earth:Global cooling|the next glacial period would be imminent]]. However, slight changes in the eccentricity of Earth's orbit around the Sun suggest a lengthy interglacial period lasting about another 50,000 years.<ref>{{cite journal |last1=Berger |first1=A. |last2=Loutre |first2=M.F.  |date=2002-08-23 |title=An Exceptionally Long Interglacial Ahead? |journal=Science |volume=297 |issue=5585 |pages=1287–8 |doi=10.1126/science.1076120 |pmid=12193773|s2cid=128923481 |url=ftp://ftp.soest.hawaii.edu/engels/Stanley/Textbook_update/Science_297/Berger-02.pdf}}</ref> Other models, based on periodic variations in solar output, give a different projection of the start of the next glacial period at around 10,000 years from now.<ref>{{Cite journal |last=Perry |first=Charles A. |last2=Hsu |first2=Kenneth J. |date=24 October 2000 |title=Geophysical, archaeological, and historical evidence support a solar-output model for climate change |url=https://pnas.org/doi/full/10.1073/pnas.230423297 |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=97 |issue=23 |pages=12433–12438 |doi=10.1073/pnas.230423297 |issn=0027-8424 |pmc=18780 |pmid=11050181 |access-date=11 November 2023}}</ref> Additionally, human impact is now seen as possibly extending what would already be an unusually long warm period. Projection of the timeline for the next glacial maximum depend crucially on [[Earth:Carbon dioxide in Earth's atmosphere|the amount of {{chem|C|O|2}} in the atmosphere]]. Models assuming increased {{chem|C|O|2}} levels at 750 parts per million ([[Parts per million|ppm]]; current levels are at 417 ppm<ref>{{cite web |title=Trends in Atmospheric Carbon Dioxide – Mauna Loa |last=Tans |first=Pieter |url=http://www.esrl.noaa.gov/gmd/ccgg/trends/ |publisher=[[Organization:National Oceanic and Atmospheric Administration|National Oceanic and Atmospheric Administration]] |access-date=2016-05-06}}</ref>) have estimated the persistence of the current interglacial period for another 50,000 years.<ref name="Dynamic Earth">{{cite book|last1=Christiansen|first1=Eric|title=Dynamic Earth|year=2014|isbn=9781449659028|pages=441|publisher=Jones & Bartlett Publishers |url=https://books.google.com/books?id=KEUoAwAAQBAJ&pg=PA441}}</ref> However, more recent studies concluded that the amount of heat trapping gases emitted into Earth's oceans and atmosphere will prevent the next glacial (ice age), which otherwise would begin in around 50,000 years, and likely more glacial cycles.<ref name="LiveScience2007">{{cite web |url=https://www.livescience.com/1846-global-warming-good-news-ice-ages.html |title=Global Warming Good News: No More Ice Ages |year=2007 |publisher=LiveScience |access-date=11 November 2023}}</ref><ref name="PIK2016">{{cite web|url=https://www.pik-potsdam.de/en/news/latest-news/human-made-climate-change-suppresses-the-next-ice-age|title=Human-made climate change suppresses the next ice age|year=2016|publisher=Potsdam Institute for Climate Impact Research in Germany}}</ref>

{{clear}}

==References==
{{reflist|30em}}

==External links==
<!--These should be used as references in the text -->
*[https://web.archive.org/web/20070805083920/http://www.geo.ua.edu/intro03/ice.html Glaciers and Glaciation]
*[http://maps.unomaha.edu/maher/2003MBfieldtrip/Moakreport/Pleistgeo.html Pleistocene Glaciation and Diversion of the Missouri River in Northern Montana] {{Webarchive|url=https://web.archive.org/web/20120415090611/http://maps.unomaha.edu/maher/2003mbfieldtrip/moakreport/pleistgeo.html |date=2012-04-15 }}
<!--Not available, dead link *http://jasonlowder.googlepages.com/Hewitt1996.pdf -->
*{{cite journal |volume=23 |issue=4 |pages=483–6 |title=Correlation of late Pleistocene glaciation in the western United States with North Atlantic Heinrich events |doi=10.1130/0091-7613(1995)023<0483:COLPGI>2.3.CO;2 |year=1995 |journal=Geology |first1=Peter U. |last1=Clark |first2=Patrick J. |last2=Bartlein|bibcode=1995Geo....23..483C }}
*{{cite book |first=E.C. |last=Pielou |title=After the Ice Age: The Return of Life to Glaciated North America |url=https://books.google.com/books?id=knEyjCYWEHQC&pg=PA1 |date=2008 |publisher=University of Chicago Press |isbn=978-0-226-66809-3}}
<!--Not available, dead link *http://jgs.geoscienceworld.org/cgi/content/abstract/142/3/417 -->
*[http://www.fs.fed.us/r10/tongass/forest_facts/resources/geology/icefields.htm Alaska's Glacier and Icefields]
*{{webarchive|url=https://web.archive.org/web/20120207032312/http://www.zoology.ubc.ca/~etaylor/413www/glaciation.html |date=7 February 2012 |title=Pleistocene glaciations}} (the last 2 million years)
*[http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter6.pdf IPCC's Palaeoclimate(pdf)] {{Webarchive|url=https://web.archive.org/web/20130319023153/http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter6.pdf |date=2013-03-19 }}
;Causes
*[http://www.ncdc.noaa.gov/paleo/milankovitch.html Astronomical Theory of Climate Change]
*[http://earthobservatory.nasa.gov/Features/Milankovitch/ Milutin Milankovitch and Milankovitch cycles]

{{Ice Ages}}
{{Quaternary Footer}}
{{Pleistocene Lakes and Seas}}

{{DEFAULTSORT:Quaternary Glaciation}}
[[Category:Pleistocene]]
[[Category:Pleistocene events]]

{{Sourceattribution|Quaternary glaciation}}