The PLEISTOCENE ( /ˈplaɪstəˌsiːn, -toʊ-/ , often colloquially
referred to as the ICE AGE) is the geological epoch which lasted from
about 2,588,000 to 11,700 years ago, spanning the world's most recent
period of repeated glaciations . The end of the Pleistocene
corresponds with the end of the last glacial period and also with the
end of the
Paleolithic age used in archaeology .
Pleistocene is the first epoch of the
Quaternary Period or sixth
epoch of the
Cenozoic Era . In the ICS timescale, the
divided into four stages or ages , the
Gelasian , Calabrian , Ionian
Tarantian . All of these stages were defined in southern Europe .
In addition to this international subdivision, various regional
subdivisions are often used.
Before a change finally confirmed in 2009 by the International Union
of Geological Sciences , the time boundary between the
Pliocene was regarded as being at 1.806 million years
Before Present (BP), as opposed to the currently accepted 2.588
million years BP: publications from the preceding years may use either
definition of the period.
* 1 Etymology
* 2 Dating
* 3 Paleogeography and climate
* 3.2 Major events
* 3.3 Palaeocycles
Oxygen isotope ratio cycles
* 4 Fauna
* 4.1 Humans
* 5 Deposits
* 6 See also
* 7 References
* 8 External links
Charles Lyell introduced the term "pleistocene" in 1839 to describe
Sicily that had at least 70% of their molluscan fauna still
living today. This distinguished it from the older
Pliocene Epoch ,
which Lyell had originally thought to be the youngest fossil rock
layer. He constructed the name "Pleistocene" ("Most New" or "Newest")
from the Greek πλεῖστος, _pleīstos_, "most", and
καινός, _kainós_ (latinized as _cænus_), "new"; this
contrasting with the immediately preceding
Pliocene ("More New" or
"Newer", from πλείων, _pleíōn_, "more", and _kainós_; usual
spelling: Pliocene), and the immediately subsequent
new" or "entirely new", from ὅλος, _hólos_, "whole", and
_kainós_) epoch , which extends to the present time.
Human timeline view • discuss • edit -10 — – -9 — –
-8 — – -7 — – -6 — – -5 — – -4 — – -3 — – -2
— – -1 — – 0 — Human-like
Nakalipithecus _ _
Ouranopithecus _ _
Orrorin _ _
Ardipithecus _ _
Australopithecus _ _HOMO HABILIS _
_HOMO ERECTUS _ _NEANDERTHAL _ _HOMO SAPIENS _
← Earlier apes ← Possibly bipedal ← Earliest
bipedal ← Earliest stone tools ← Earliest exit
from Africa ← Earliest fire use ← Earliest cooking
← Earliest clothes ← Modern humans
Axis scale : millions of years .
Also see: _Life timeline _ and _Nature timeline _
Pleistocene has been dated from 2.588 million (±.005) to 11,700
years BP with the end date expressed in radiocarbon years as 10,000
carbon-14 years BP. It covers most of the latest period of repeated
glaciation , up to and including the
Younger Dryas cold spell. The end
Younger Dryas has been dated to about 9640 BC (11,654 calendar
years BP). It was not until after the development of radiocarbon
dating, however, that
Pleistocene archaeological excavations shifted
to stratified caves and rock-shelters as opposed to open-air
In 2009 the
International Union of Geological Sciences (IUGS)
confirmed a change in time period for the Pleistocene, changing the
start date from 1.806 to 2.588 million years BP, and accepted the base
Gelasian as the base of the Pleistocene, namely the base of the
Monte San Nicola GSSP . The IUGS has yet to approve a type section ,
Global Boundary Stratotype Section and Point (GSSP), for the upper
Holocene boundary (_i.e._ the upper boundary). The
proposed section is the _North Greenland Ice Core Project_ ice core
75° 06' N 42° 18' W. The lower boundary of the
is formally defined magnetostratigraphically as the base of the
Matuyama (C2r) chronozone , isotopic stage 103. Above this point there
are notable extinctions of the calcareous nanofossils : _Discoaster
pentaradiatus_ and _
Discoaster surculus_ .
Pleistocene covers the recent period of repeated glaciations. The
Plio-Pleistocene has, in the past, been used to mean the last ice
age. The revised definition of the
Quaternary , by pushing back the
start date of the
Pleistocene to 2.58 Ma, results in the inclusion of
all the recent repeated glaciations within the Pleistocene.
PALEOGEOGRAPHY AND CLIMATE
The maximum extent of glacial ice in the north polar area during
The modern continents were essentially at their present positions
during the Pleistocene, the plates upon which they sit probably having
moved no more than 100 km relative to each other since the beginning
of the period.
Mark Lynas (through collected data), the Pleistocene's
overall climate could be characterized as a continuous
El Niño with
trade winds in the south Pacific weakening or heading east, warm air
Peru , warm water spreading from the west Pacific and the
Indian Ocean to the east Pacific, and other
El Niño markers.
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Pleistocene climate was marked by repeated glacial cycles in which
continental glaciers pushed to the 40th parallel in some places. It is
estimated that, at maximum glacial extent, 30% of the Earth's surface
was covered by ice. In addition, a zone of permafrost stretched
southward from the edge of the glacial sheet, a few hundred kilometres
North America , and several hundred in
Eurasia . The mean annual
temperature at the edge of the ice was −6 °C (21 °F); at the edge
of the permafrost, 0 °C (32 °F).
Each glacial advance tied up huge volumes of water in continental ice
sheets 1,500 to 3,000 metres (4,900–9,800 ft) thick, resulting in
temporary sea-level drops of 100 metres (300 ft) or more over the
entire surface of the Earth. During interglacial times, such as at
present, drowned coastlines were common, mitigated by isostatic or
other emergent motion of some regions.
The effects of glaciation were global.
Antarctica was ice-bound
Pleistocene as well as the preceding Pliocene. The
Andes were covered in the south by the Patagonian ice cap. There were
New Zealand and
Tasmania . The current decaying glaciers
Mount Kenya ,
Mount Kilimanjaro , and the
Ruwenzori Range in east
and central Africa were larger. Glaciers existed in the mountains of
Ethiopia and to the west in the
Atlas mountains .
In the northern hemisphere, many glaciers fused into one. The
Cordilleran ice sheet covered the North American northwest; the east
was covered by the
Laurentide . The Fenno-Scandian ice sheet rested on
northern Europe , including
Great Britain ; the Alpine ice sheet on
Alps . Scattered domes stretched across
Siberia and the Arctic
shelf. The northern seas were ice-covered.
South of the ice sheets large lakes accumulated because outlets were
blocked and the cooler air slowed evaporation. When the
sheet retreated, north central
North America was totally covered by
Lake Agassiz . Over a hundred basins, now dry or nearly so, were
overflowing in the North American west.
Lake Bonneville , for example,
Great Salt Lake now does. In Eurasia, large lakes
developed as a result of the runoff from the glaciers. Rivers were
larger, had a more copious flow, and were braided . African lakes were
fuller, apparently from decreased evaporation. Deserts on the other
hand were drier and more extensive. Rainfall was lower because of the
decreases in oceanic and other evaporation.
It has been estimated that during the Pleistocene, the East Antarctic
Ice Sheet thinned by at least 500 meters, and that thinning since the
Glacial Maximum is less than 50 meters and probably started after
ca 14 ka.
Timeline of glaciation Ice ages as
reflected in atmospheric CO2 , stored in bubbles from glacial ice of
Over 11 major glacial events have been identified, as well as many
minor glacial events. A major glacial event is a general glacial
excursion, termed a "glacial." Glacials are separated by
"interglacials". During a glacial, the glacier experiences minor
advances and retreats. The minor excursion is a "stadial"; times
between stadials are "interstadials".
These events are defined differently in different regions of the
glacial range, which have their own glacial history depending on
latitude, terrain and climate. There is a general correspondence
between glacials in different regions. Investigators often interchange
the names if the glacial geology of a region is in the process of
being defined. However, it is generally incorrect to apply the name of
a glacial in one region to another.
For most of the 20th century only a few regions had been studied and
the names were relatively few. Today the geologists of different
nations are taking more of an interest in
Pleistocene glaciology. As a
consequence, the number of names is expanding rapidly and will
continue to expand. Many of the advances and stadials remain unnamed.
Also, the terrestrial evidence for some of them has been erased or
obscured by larger ones, but evidence remains from the study of
cyclical climate changes.
The glacials in the following tables show _historical_ usages, are a
simplification of a much more complex cycle of variation in climate
and terrain, and are generally no longer used. These names have been
abandoned in favor of numeric data because many of the correlations
were found to be either inexact or incorrect and more than four major
glacials have been recognized since the historical terminology was
Historical names of the "four major" glacials in four regions.
Historical names of interglacials.
Corresponding to the terms glacial and interglacial, the terms
pluvial and interpluvial are in use (Latin: _pluvia_, rain). A pluvial
is a warmer period of increased rainfall; an interpluvial, of
decreased rainfall. Formerly a pluvial was thought to correspond to a
glacial in regions not iced, and in some cases it does. Rainfall is
cyclical also. Pluvials and interpluvials are widespread.
There is no systematic correspondence of pluvials to glacials,
however. Moreover, regional pluvials do not correspond to each other
globally. For example, some have used the term "Riss pluvial" in
Egyptian contexts. Any coincidence is an accident of regional factors.
Only a few of the names for pluvials in restricted regions have been
The sum of transient factors acting at the Earth's surface is
cyclical: climate, ocean currents and other movements, wind currents,
temperature, etc. The waveform response comes from the underlying
cyclical motions of the planet, which eventually drag all the
transients into harmony with them. The repeated glaciations of the
Pleistocene were caused by the same factors.
Glaciation in the
Pleistocene was a series of glacials and
interglacials, stadials and interstadials, mirroring periodic changes
in climate. The main factor at work in climate cycling is now believed
Milankovitch cycles . These are periodic variations in regional
and planetary solar radiation reaching the Earth caused by several
repeating changes in the Earth's motion.
Milankovitch cycles cannot be the sole factor responsible for the
variations in climate since they explain neither the long term cooling
trend over the Plio-Pleistocene, nor the millennial variations in the
Greenland Ice Cores. Milankovitch pacing seems to best explain
glaciation events with periodicity of 100,000, 40,000, and 20,000
years. Such a pattern seems to fit the information on climate change
found in oxygen isotope cores. The timing of our present interglacial
interval (known as the
Holocene , Postglacial, or the Present
Interglacial) to that of the previous interglacial, beginning about
130,000 years ago (The Eemian Interglacial), suggests that the next
glacial might begin in about 3,000 years.
Oxygen Isotope Ratio Cycles
Oxygen isotope ratio cycle
In oxygen isotope ratio analysis, variations in the ratio of 18
O to 16
O (two isotopes of oxygen ) by mass (measured by a mass spectrometer )
present in the calcite of oceanic core samples is used as a diagnostic
of ancient ocean temperature change and therefore of climate change.
Cold oceans are richer in 18
O, which is included in the tests of the microorganisms (foraminifera
) contributing the calcite.
A more recent version of the sampling process makes use of modern
glacial ice cores. Although less rich in 18
O than sea water, the snow that fell on the glacier year by year
nevertheless contained 18
O and 16
O in a ratio that depended on the mean annual temperature.
Temperature and climate change are cyclical when plotted on a graph
of temperature versus time. Temperature coordinates are given in the
form of a deviation from today's annual mean temperature, taken as
zero. This sort of graph is based on another of isotope ratio versus
time. Ratios are converted to a percentage difference from the ratio
found in standard mean ocean water (SMOW).
The graph in either form appears as a waveform with overtones . One
half of a period is a
Marine isotopic stage
Marine isotopic stage (MIS). It indicates a
glacial (below zero) or an interglacial (above zero).
stadials or interstadials.
According to this evidence, Earth experienced 102 MIS stages
beginning at about 2.588 Ma BP in the Early
Pleistocene stages were shallow and frequent. The latest were
the most intense and most widely spaced.
By convention, stages are numbered from the Holocene, which is MIS1.
Glacials receive an even number; interglacials, odd. The first major
glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were
2, 6, 12, and 16; the warmest interglacials, 1, 5, 9 and 11. For
matching of MIS numbers to named stages, see under the articles for
Quaternary extinction event
Both marine and continental faunas were essentially modern but with
many more large land mammals such as mammoths , mastodons ,
Diprotodon _, _
Short-faced bear ,
Gigantopithecus _ and others. In isolated places such as
New Zealand and islands in the Pacific saw the evolution
of large birds and even reptiles such as the elephant bird , moa ,
Haast\'s eagle , _
Quinkana _, _
Megalania _ and _
Meiolania _. _
Northern Spain showing woolly mammoth , cave lions
eating a reindeer , tarpans , and woolly rhinoceros .
South America showing
Megatherium _ and two _Glyptodon
The severe climatic changes during the ice age had major impacts on
the fauna and flora. With each advance of the ice, large areas of the
continents became totally depopulated, and plants and animals
retreating southward in front of the advancing glacier faced
tremendous stress. The most severe stress resulted from drastic
climatic changes, reduced living space, and curtailed food supply. A
major extinction event of large mammals (megafauna ), which included
mammoths , mastodons , saber-toothed cats , _glyptodon _s, ground
Irish elk , cave bears , and short-faced bears , began late
Pleistocene and continued into the Holocene. Neanderthals also
became extinct during this period. At the end of the last ice age,
cold-blooded animals, smaller mammals like wood mice , migratory
birds, and swifter animals like whitetail deer had replaced the
megafauna and migrated north.
The extinctions were especially severe in
North America where native
horses and camels were eliminated.
Asian land mammal ages (ALMA) include Zhoukoudianian , Nihewanian
, and Yushean .
European land mammal ages (ELMA) include
Gelasian (2.5—1.8 Ma ).
North American land mammal ages (NALMA) include Blancan
Irvingtonian (1.8–0.24) and Rancholabrean
(0.24–0.01) in millions of years. The
Blancan extends significantly
back into the Pliocene.
South American land mammal ages (SALMA) include Uquian
Ensenadan (1.5–0.3) and
Lujanian (0.3–0.01) in
millions of years. The
Uquian previously extended significantly back
into the Pliocene, although the new definition places it entirely
within the Pleistocene.
Human evolution ,
Paleolithic , and Models of
migration to the New World
The evolution of anatomically modern humans took place during the
Pleistocene. In the beginning of the
species are still present, as well as early human ancestors, but
during the lower Palaeolithic they disappeared, and the only hominin
species found in fossilic records is _
Homo erectus _ for much of the
Acheulean lithics appear along with _Homo erectus_, some
1.8 million years ago, replacing the more primitive
used by _A. garhi _ and by the earliest species of _Homo_. The Middle
Paleolithic saw more varied speciation within _Homo_, including the
appearance of _
Homo sapiens _ about 200,000 years ago.
According to mitochondrial timing techniques, modern humans migrated
from Africa after the
Riss glaciation in the Middle Palaeolithic
Eemian Stage , spreading all over the ice-free world during
the late Pleistocene. A 2005 study posits that humans in this
migration interbred with archaic human forms already outside of Africa
by the late Pleistocene, incorporating archaic human genetic material
into the modern human gene pool.
HOMININ SPECIES DURING PLEISTOCENE
Pleistocene non-marine sediments are found primarily in fluvial
deposits , lakebeds, slope and loess deposits as well as in the large
amounts of material moved about by glaciers. Less common are cave
deposits, travertines and volcanic deposits (lavas, ashes).
Pleistocene marine deposits are found primarily in shallow marine
basins mostly (but with important exceptions) in areas within a few
tens of kilometers of the modern shoreline. In a few geologically
active areas such as the
Southern California coast,
deposits may be found at elevations of several hundred meters.
Geologic time scale
Timeline of glaciation
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