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The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of
glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age#REDIRECT Ice age {{Redirect category shell, 1= {{R from move {{R from ambiguous term {{R from other capitalisation {{R unprintwor ...
and interglacial periods during the
Quaternary The Quaternary ( ) is the current and most recent of the three period (geology), periods of the Cenozoic era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans ...
period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe the entire time period up to the present as an "
ice age An ice age is a long period of reduction in the temperature of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents an ...

ice age
", in
popular culture Popular culture (also called mass culture or pop culture) is generally recognized by members of a society A society is a group A group is a number A number is a mathematical object used to counting, count, measurement, measure, and ...
the term "ice age" is usually associated with just the most recent glacial period during the
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally ...
or the Pleistocene
epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-E ...
in general. Since planet
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
still has ice sheets, geologists consider the Quaternary glaciation to be ongoing, with the Earth now experiencing an interglacial period. During the Quaternary glaciation,
ice sheets In glaciology Lateral moraine on a glacier joining the Gorner Glacier, Zermatt">Gorner_Glacier.html" ;"title="moraine on a glacier joining the Gorner Glacier">moraine on a glacier joining the Gorner Glacier, Zermatt, Swiss Alps. The moraine is ...
appeared. During
glacial periods A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( or ) is a persistent body of dense ice that is constantly movi ...
they expanded, and during interglacial periods they contracted. Since the end of the last glacial period, the only surviving ice sheets are the
Antarctic The Antarctic (US English or , UK English or and or ) is a around 's , opposite the region around the . The Antarctic comprises the continent of , the and other located on the or south of the . The Antarctic region includes the , wa ...
and
Greenland ice sheet The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice Ice is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of wate ...

Greenland ice sheet
s. Other ice sheets, such as the
Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three ...
, formed during glacial periods, had completely melted and disappeared during interglacials. The major effects of the Quaternary glaciation have been the
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
of land and the
deposition Deposition may refer to: * Deposition (law), taking testimony outside of court * List of deposed politicians, Deposition (politics), the removal of a person of authority from political power * Deposition (university), a widespread initiation ritual ...
of material, both over large parts of the continents; the modification of
river systems In geomorphology, drainage systems, also known as river systems, are the patterns formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by h ...
; the creation of millions of
lake A lake is an area filled with water, localized in a basin, surrounded by land Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable ove ...

lake
s, including the development of
pluvial lake Image:LakeManixSediments.JPG, Pluvial Lake Manix sediments (Pleistocene) in the Mojave Desert near Barstow, California. A pluvial lake is a body of water that accumulated in a basin because of a greater moisture availability resulting from change ...
s far from the ice margins; changes in
sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of the numbers divided by how many numbers are in th ...

sea level
; the
isostatic adjustment
isostatic adjustment
of the Earth's crust; flooding; and abnormal winds. The ice sheets themselves, by raising the
albedo Albedo (prounounced ; la, albedo, meaning 'whiteness') is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiat ...

albedo
(the extent to which the
radiant energy In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Ph ...
of the Sun is reflected from Earth) created significant
feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain Image:Kettenvergleich.jpg, Roller chains A chain is a wikt:series#Noun, serial assembly of connected pieces, called links, typically made of metal, with ...

feedback
to further cool the
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a la ...

climate
. These effects have shaped entire environments on land and in the oceans, and in their associated biological communities. Before the Quaternary glaciation, land-based ice appeared, and then disappeared, during at least four other ice ages.


Discovery

Evidence for the quaternary glaciation was first understood in the 18th and 19th centuries as part of the
scientific revolution The Scientific Revolution was a series of events that marked the emergence of modern science during the early modern period, when developments in History of mathematics#Mathematics during the Scientific Revolution, mathematics, History of phys ...

scientific revolution
. Over the last century, extensive field observations have provided evidence that continental glaciers covered large parts of
Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered ...

Europe
,
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
, and
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...

Siberia
. Maps of glacial features were compiled after many years of fieldwork by hundreds of geologists who mapped the location and orientation of
drumlin Elongate and forested drumlins south of Chile.html"_;"title="Puerto_Williams,_Chile">Puerto_Williams,_Chile._Flow_direction_here_was_at_time_of_formation_from_west_to_east_(left_to_right_on_picture). A_drumlin,_from_the_Irish_Gaelic.html" "ti ...
s,
esker An esker, eskar, eschar, or os, sometimes called an ''asar'', ''osar'', or ''serpent kame'', is a long, winding ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a contin ...
s,
moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glac ...

moraine
s,
striations Striations means a series of ridges, furrows or linear marks, and is used in several ways: * Glacial striation * Striation (fatigue), in material * Striation (geology), a ''striation'' as a result of a geological Fault (geology), fault * Striation ...
, and
glacial stream A glacier stream is a channelized area that is formed by a glacier A glacier ( or ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciolo ...
channels in order to reveal the extent of the
ice sheet In , an ice sheet, also known as a continental glacier, is a mass of that covers surrounding terrain and is greater than . The only current ice sheets are in and ; during the at (LGM) the covered much of , the ice sheet covered and the c ...

ice sheet
s, the direction of their flow, and the locations of systems of 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

To geologists, an
ice age An ice age is a long period of reduction in the temperature of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents an ...

ice age
is marked 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
Karoo The Karoo ( ; from the South Khoekhoe Khoekhoen (singular Khoekhoe) (or Khoikhoi in the former orthography; formerly also '' Hottentots''"Hottentot, n. and adj." ''OED Online'', Oxford University Press, March 2018, www.oed.com/view/Entry/ ...

Karoo
(360–260 Ma), Andean-Saharan (450–420 Ma),
Cryogenian The Cryogenian (, from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic era (geology), Era, preceded by the Tonian Perio ...
(720–635 Ma) and
Huronian The Huronian glaciation (or Makganyene glaciation) was a glaciation that extended from 2.4 billion years ago (Gya) to 2.1 Gya, during the Siderian and Rhyacian periods of the Paleoproterozoic era. The Huronian glaciation followed the Great Oxyge ...
(2,400–2,100 Ma). Within the Quaternary Period, or 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
glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( or ) is a persistent body of dense ice that is constantly movi ...
s, or simply glacials) large ice sheets at least thick at their maximum existed in
Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered ...

Europe
,
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
, and
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...

Siberia
. The shorter and warmer intervals between glacials, when continental glaciers retreated, are referred to as
interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial period A glacial period (alternatively glacial or ...
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 fluctuation period was about 41,000 years, but following the
Mid-Pleistocene Transition The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary Quaternary ( ) is the current and most recent of the three Period (geology ...
it has slowed to about 100,000 years, as evidenced most clearly by
ice core An ice core is a core sample . A pied butcherbird The pied butcherbird (''Cracticus nigrogularis'') is a songbird native to Australia. Described by John Gould in 1837, it is a black and white bird long with a long hooked bill. Its head an ...
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. The entire Quaternary Period, starting 2.58 Ma, is referred to as an ice age because at least one permanent large ice sheet—the
Antarctic ice sheet , showing glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( or ) is a persistent body of dense ice ...
—has existed continuously. There is uncertainty over how much of
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an autonomous territory An autonomous administrative division (also referred to as an autonomous area, entity, unit, region, subdivision, or territory) is a subnational administra ...

Greenland
was covered by ice during each interglacial. Currently, Earth is in an interglacial period, which marked the beginning of the
Holocene The Holocene ( ) is the current geological epoch In geochronology, an epoch is a subdivision of the geologic timescale that is longer than an age (geology), age but shorter than a period (geology), period. The current epoch is the Holocene E ...
epoch. The current interglacial began between 15,000 and 10,000 years ago; this caused the ice sheets from the last glacial period to begin to disappear. Remnants of these last glaciers, now occupying about 10% of the world's land surface, still exist in 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. Due to the volume of ice on land, sea level was about lower than present.


Causes

Earth's history of glaciation is a product of the ''internal variability'' of Earth's
climate system Earth's climate arises from the interaction of five major climate system components: the Atmosphere of Earth, atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosp ...
(e.g.,
ocean currents An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, wave breaking, breaking waves, cabbeling, and temperature and salinity differences. Dep ...
,
carbon cycle The carbon cycle is the biogeochemical cycle In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physi ...

carbon cycle
), interacting with ''external forcing'' by phenomena outside the climate system (e.g., changes in earth's orbit,
volcanism Volcanism (or volcanicity) is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called ...
, and changes in
solar output
solar output
).


Astronomical cycles

The role of Earth's orbital changes in controlling climate was first advanced by
James Croll James Croll, FRS, (2 January 1821 – 15 December 1890) was a 19th-century Scottish scientist who developed a theory of climate variability Climate variability includes all the variations in the climate that last longer than individual wea ...

James Croll
in the late 19th century. Later,
Milutin Milanković Milutin Milanković ( sr-cyr, Милутин Миланковић , sometimes anglicised Linguistic anglicisation (or anglicization, occasionally anglification, anglifying, or Englishing) is the practice of modifying foreign words, names, and ph ...

Milutin Milanković
, a Serbian
geophysicist Geophysics () is a subject of natural science concerned with the physical processes and Physical property, physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ' ...

geophysicist
, elaborated on the theory and calculated that these irregularities in Earth's orbit could cause the climatic cycles now known as
Milankovitch cycles Milankovitch cycles describe the collective effects of changes in the 's movements on its over thousands of years. The term is named for n and . In the 1920s, he hypothesized that variations in , , and resulted in cyclical variation in the r ...

Milankovitch cycles
. They are the result of the additive behavior of several types of cyclical changes in Earth's orbital properties. Changes in the
orbital eccentricity In astrodynamics Orbital mechanics or astrodynamics is the application of ballistics Ballistics is the field of mechanics Mechanics (Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ε ...
of Earth occur on a cycle of about 100,000 years.Why do glaciations occur?
/ref> The
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object. ...

inclination
, or tilt, of Earth's axis varies periodically between 22° and 24.5° in a cycle 41,000 years long. The tilt of Earth's axis is responsible for the
season A season is a division of the year based on changes in weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most ...

season
s; the greater the tilt, the greater the contrast between summer and winter temperatures.
Precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's Rotation around a fixed axis, rotational axis. In particular, it can refer to the gradual shift in the orientation of E ...
, or wobbles of 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 overall amount of solar heat Earth receives. The result is less ice melting than accumulating, and
glacier A glacier (; ) is a persistent body of dense ice Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color. In the , ice is abunda ...

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. Studies of deep-sea cores, and the fossils contained in them, indicate that the fluctuation of climate during the last few hundred thousand years is remarkably close to that predicted by Milankovitch. A problem with the theory is that these astronomical cycles have been in existence for many millions of years, but glaciation is a rare occurrence. Astronomical cycles correlate with glacial and interglacial periods, and their transitions, ''within'' a long-term ice age but do not initiate these long-term ice ages.


Atmospheric composition

One theory holds that decreases in atmospheric , an important
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhou ...
, started the long-term cooling trend that eventually led to glaciation. Geological evidence indicates a decrease of more than 90% in atmospheric since the middle of the
Mesozoic Era The Mesozoic Era ( ), also called the Age of Reptiles and the Age of Conifers, is the second-to-last era An era is a span of time defined for the purposes of chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the mo ...
. An analysis of reconstructions from
alkenone α,β-Unsaturated carbonyl compounds refers to organic compounds with the general structure (O=CR)−Cα=Cβ-R. Examples would be enones and enals. In these compounds the carbonyl group is conjugated system, conjugated with an alkene (hence the adje ...
records shows that in the atmosphere declined before and during Antarctic glaciation, and supports a substantial decrease as the primary cause of Antarctic glaciation. levels also play an important role in the transitions between interglacials and glacials. High contents correspond to warm interglacial periods, and low to glacial periods. However, studies indicate that may not be the primary cause of the interglacial-glacial transitions, but instead acts as a
feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain Image:Kettenvergleich.jpg, Roller chains A chain is a wikt:series#Noun, serial assembly of connected pieces, called links, typically made of metal, with ...

feedback
. The explanation for this observed variation "remains a difficult attribution problem".


Plate tectonics and ocean currents

An important component in the development of long-term ice ages is the positions of the continents. These can control the circulation of the oceans and the atmosphere, affecting how
ocean currents An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, wave breaking, breaking waves, cabbeling, and temperature and salinity differences. Dep ...
carry heat to high latitudes. Throughout most of
geologic time Geology (from the Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). ...

geologic time
, the
North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere The Northern Hemisphere is the half of Earth Earth is the third planet from the Sun and the only ast ...
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
Cenozoic Era The Cenozoic Era ( ) meaning "new life" is the current and most recent of the three geological eras of the Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologic time scale (GTS) is a system of ch ...

Cenozoic Era
, the large
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
n and
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
n continental plates drifted westward from the
Eurasia Eurasia () is the largest continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a ...

Eurasia
n plate. This interlocked with the development of the , running north–south, with the North Pole in the small, nearly landlocked basin of the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major s. It spans an area of approximately and is also known as the coldest of all the oceans. The (IHO) recognizes it as an ocean, although some call it the Arctic Medit ...

Arctic Ocean
. The
Drake passage Image:Drake-Passage profile hg.png, Depth profile with salinity and temperature for surface The Drake Passage (referred to as Mar de Hoces Hoces Sea"in Spain and other Spanish speaking countries) is the body of water between South America's ...
opened 33.9 million years ago (the
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' ...
-
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define ...
transition), severing
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
from
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
. The
Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, ca ...

Antarctic Circumpolar Current
could then flow through it, isolating
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
from warm waters and triggering the formation of its huge
ice sheet In , an ice sheet, also known as a continental glacier, is a mass of that covers surrounding terrain and is greater than . The only current ice sheets are in and ; during the at (LGM) the covered much of , the ice sheet covered and the c ...

ice sheet
s. The
Isthmus of Panama The Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lamè Kara ...
developed at a convergent plate margin about 2.6 million years ago, and further separated oceanic circulation, closing the last strait, outside the polar regions, that had connected the
Pacific The Pacific Ocean is the largest and deepest of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. ...

Pacific
and Atlantic Oceans. This increased poleward salt and heat transport, strengthening the North Atlantic
thermohaline circulation 350px, A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents. Thermohaline circulation (THC) is a part of the large-scale Ocean current, ocean circulation that ...

thermohaline circulation
, which supplied enough moisture to arctic latitudes to create the northern glaciation.


Rise of mountains

The elevation of continents surface, often in the form of
mountain formation Mountain formation refers to the geological processes that underlie the formation of mountains. These processes are associated with large-scale movements of the Earth's crust (List of tectonic plates, tectonic plates). Fold (geology), Folding, ...
, is thought to have contributed to cause the Quaternary glaciation. Modern glaciers correlate often to mountainous areas. The gradual movement of the bulk of Earth's landmasses away from the
Tropics The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% i ...

Tropics
in connection with increased mountain formation in the Late Cenozoic meant more surfaces at high altitude and latitudes favouring the formation of glaciers. For example, the
Greenland Ice Sheet The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice Ice is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of wate ...

Greenland Ice Sheet
formed in connection to the uplift of the West Greenland and East Greenland uplands. The Western and Eastern Greenland mountains constitute that were uplifted in two phases, 10 and 5
million years ago One million (1,000,000), or one thousand thousand, is the natural number In mathematics, the natural numbers are those used for counting (as in "there are ''six'' coins on the table") and total order, ordering (as in "this is the ''third'' l ...
, in the
Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; its name comes from the Greek words (', "less") and (', "new") and mean ...
epoch.
Computer modelling Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of or the outcome of a real-world or physical system. Since they allow to check the reliability of chosen mathemat ...
shows that the uplift would have enabled glaciation by producing increased
orographic precipitation Orography (from the Greek , hill, , to write) is the study of the topographic relief File:Maps-for-free Sierra Nevada.png, Relief map of Sierra Nevada (Spain), Sierra Nevada, Spain Terrain or relief (also topography, topographical relief) ...
and cooling the surface temperatures. For the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sou ...

Andes
it is known that the Principal Cordillera had risen to heights that allowed for the development of
valley glacier in New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and more than 700 List of islands of New Zealand, smaller ...
s about 1 million years ago.


Effects

The presence of so much ice upon the continents had a profound effect upon almost every aspect of Earth's hydrologic system. The most obvious effects 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

The Quaternary glaciation created more lakes than all other geologic processes combined. The reason is that a continental
glacier A glacier (; ) is a persistent body of dense ice Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color. In the , ice is abunda ...

glacier
completely disrupts the preglacial drainage system. The surface over which the glacier moved was scoured and
eroded In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

eroded
by the ice, leaving many closed, undrained depressions in the bedrock. These depressions filled with water and became lakes. Very large lakes were created along the glacial margins. The ice on both
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
and
Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered ...

Europe
was about 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, 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
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean, enclosed by Denmark Denmark ( da, Danmark, ) is a Nordic country The Nordic countries, or the Nordics, are a geographical and cultural region In geography, regions are areas that a ...

Baltic Sea
and the
Great Lakes The Great Lakes also called the Great Lakes of North America or the Laurentian Great Lakes, is a series of large interconnected freshwater lake A lake is an area filled with water, localized in a basin, surrounded by land Land ...

Great Lakes
of North America were formed primarily in this way. The numerous lakes of the
Canadian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a large area of exposed Precambrian igneous and high-grade metamorphic rocks ( geologic shield) that forms the ancient geologic core of the North American ...

Canadian Shield
, Sweden, and
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the west, Russia to the east, Norway to the north, and is defined by the Gulf of B ...

Finland
are thought to have originated at least partly from glaciers' selective erosion of
weathered ''Weathered'' is the third studio album by American Rock music, rock band Creed (band), Creed, released on November 20, 2001. It was the last Creed album to be released until ''Full Circle (Creed album), Full Circle'' came out in October 2009, wit ...
bedrock Bedrock in geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they cha ...

bedrock
.


Pluvial lakes

The climatic conditions that cause glaciation had an indirect effect on arid and semiarid regions far removed from the large
ice sheet In , an ice sheet, also known as a continental glacier, is a mass of that covers surrounding terrain and is greater than . The only current ice sheets are in and ; during the at (LGM) the covered much of , the ice sheet covered and the c ...

ice sheet
s. The increased precipitation that fed the
glacier A glacier (; ) is a persistent body of dense ice Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color. In the , ice is abunda ...

glacier
s 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 lake A dry lake, also known as a playa, is either a basin or depression that formerly contained a standing surface water body, which disappeared when evaporation processes exceeded recharge. If the floor of a dry lake is covered by deposits of alkali ...
s. 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

Major isostatic adjustments of the
lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
during the Quaternary glaciation were caused by the weight of the ice, which depressed the continents. In
Canada Canada is a country in the northern part of North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...

Canada
, a large area around
Hudson Bay Hudson Bay ( iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: baie d'Hudson), sometimes called Hudson's Bay (usually historically), is a large body of sal ...
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
earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth Earth is the third planet from the Sun and the only astronomical object known ...

earthquake
s in Scandinavia about 9,000 years ago. These earthquakes are unique in that they are not associated with
plate tectonics upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the la, label=Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written L ...
. Studies have shown that the uplift has taken place in two distinct stages. The initial uplift following
deglaciationDeglaciation describes the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming Climate change includes both global warming driven by human emissions of greenhouse gases and the ...
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 decreased after that. Today, typical uplift rates are of the order of 1 cm per year or less. In northern Europe, this is clearly shown by the
GPS The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government The federal government of the United States (U.S. federal government) is the national ...

GPS
data obtained by the BIFROST GPS network. Studies suggest that rebound will continue for about 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
loess Loess (, ; from German ''Löss'' ) is a clastic, predominantly silt-sized sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by ...
(wind-blown silt), forming irregular blankets over much of the
Missouri River The Missouri River is the longest river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its ...
valley, central Europe, and northern China. Sand
dune A dune is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the sc ...

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 Nebraska () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Nebraska
, USA, which covers an area of about . This region was a large, active dune field during the
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally ...
epoch, but today is largely stabilized by grass cover.


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
placer deposit Placer may refer to one of the following: * Placer deposit * Placer sheep * Placer mining * Placer (geography), a submerged bank or reef. * Placer, rugby league football role. * Placer, a job title in the Pottery industry. Geographical names: * P ...
s of gold. This is the case of southernmost Chile where reworking of Quaternary moraines have concentrated gold offshore.


Records of prior glaciation

Glaciation has been a rare event in Earth's history, but there is evidence of widespread glaciation during the late
Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popula ...
Era (300 to 200 Ma) and the late Precambrian (i.e. the
Neoproterozoic The Neoproterozoic Era is the unit of geologic time The geologic time scale (GTS) is a system of chronological datingChronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such ob ...
Era, 800 to 600 Ma). Before the current
ice age An ice age is a long period of reduction in the temperature of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents an ...

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
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
plants and animals and by the characteristics of sediments preserved in the
stratigraphic through Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approxi ...
record. 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 The late Paleozoic icehouse, formerly known as the Karoo ice age, was between 360–260 million years ago (Mya) during which large land-based ice-sheets were present on Earth's surface. It was the second major glacial period of the Phanerozoic. I ...
, is found in the late Paleozoic rocks in South Africa, India,
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
, Antarctica, and 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 Snowball Earth during the
Cryogenian The Cryogenian (, from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic era (geology), Era, preceded by the Tonian Perio ...
Period.


Next glacial period

The warming trend following the Last Glacial Maximum, since about 20,000 years ago, has resulted in a Early Holocene sea level rise, sea level rise by about . This warming trend subsided about 6,000 years ago, and sea level has been comparatively stable since the Neolithic. The present interglacial period (the Holocene climatic optimum) has been fairly stable and warm, but the previous one was interrupted by numerous cold spells lasting hundreds of years. If the previous period was more typical than the present one, the period of stable climate, which allowed the Neolithic Revolution and by extension human civilization, may have been possible only because of a highly unusual period of stable temperature. Based on Milankovitch cycles, orbital models, the cooling trend initiated about 6,000 years ago will continue for another 23,000 years. 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. "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." It is possible that the current cooling trend may be interrupted by an stadial, interstadial phase (a warmer period) in about 60,000 years, with the next glacial maximum reached only in about 100,000 years. Based on past estimates for interglacial durations of about 10,000 years, in the 1970s there was some concern that 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. Additionally, Human impact on the environment, 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 Carbon dioxide in Earth's atmosphere, the amount of in the atmosphere. Models assuming increased levels at 750 parts per million (Parts per million, ppm; current levels are at 407 ppm) have estimated the persistence of the current interglacial period for another 50,000 years. 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.


References


External links


Glaciers and Glaciation
* *

* (the last 2 million years)
IPCC's Palaeoclimate(pdf)
;Causes
Milutin Milankovitch and Milankovitch cycles
{{DEFAULTSORT:Quaternary Glaciation Ice ages Pleistocene Pleistocene events Quaternary events, Glaciation