Pleistocene

Source: Wikipedia, the free encyclopedia.

Pleistocene
2.58 – 0.0117 Ma
Epoch
Stratigraphic unitSeries
Time span formalityFormal
Lower boundary definition
Lower boundary GSSPMonte San Nicola Section,
stadial
Upper boundary GSSPNGRIP2 ice core, Greenland
75°06′00″N 42°19′12″W / 75.1000°N 42.3200°W / 75.1000; -42.3200
Upper GSSP ratified2008 (as base of Holocene)[4]

The Pleistocene (

last glacial period and also with the end of the Paleolithic age used in archaeology. The name is a combination of Ancient Greek πλεῖστος (pleîstos), meaning "most", and καινός (kainós; Latinized
as cænus), meaning "new".

At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by the

the extinction of most large-bodied animals
in these regions.

The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres (390 ft) lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by the Laurentide Ice Sheet.

Etymology

Evolution of temperature in the Post-Glacial period at the very end of the Pleistocene, according to Greenland ice cores[7]
Temperature rise marking the end of the Pleistocene, as derived from Antarctic ice core data.

Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene 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").[8][9][10] This contrasts with the immediately preceding Pliocene ("newer", from πλείων (pleíōn, "more") and kainós) and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος (hólos, "whole") and kainós) epoch, which extends to the present time.

Dating

The Pleistocene has been dated from 2.580 million (±0.005) to 11,650 years BP

ages, the Gelasian, Calabrian, Chibanian (previously the unofficial "Middle Pleistocene"), and Upper Pleistocene (unofficially the "Tarantian").[14][15][note 1]
In addition to these international subdivisions, various regional subdivisions are often used.

In 2009 the

type section, Global Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary (i.e. the upper boundary). The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W.[18] The lower boundary of the Pleistocene Series 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 nannofossils: Discoaster pentaradiatus and Discoaster surculus.[19][20]
The Pleistocene covers the recent period of repeated glaciations.

The name Plio-Pleistocene has, in the past, been used to mean the last ice age. Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species Hyalinea baltica first appeared in the marine section at La Castella, Calabria, Italy.[21] However, the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene.

Radiocarbon dating is considered to be inaccurate beyond around 50,000 years ago.

Marine isotope stages
(MIS) derived from Oxygen isotopes are often used for giving approximate dates.

Deposits

Pleistocene non-marine

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 kilometres of the modern shoreline. In a few geologically active areas such as the Southern California
coast, Pleistocene marine deposits may be found at elevations of several hundred metres.

Paleogeography and climate

The maximum extent of glacial ice in the north polar area during the Pleistocene Period

The modern

plates upon which they sit probably having moved no more than 100 km (62 mi) relative to each other since the beginning of the period. In glacial periods, the sea level would drop by up to 120 m (390 ft) lower than today[22] during peak glaciation, exposing large areas of the present continental shelf
as dry land.

According to

El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers.[23]

Glacial features

Pleistocene climate was marked by repeated glacial cycles in which

parallel in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, and several hundred in Eurasia
. The mean annual temperature at the edge of the ice was −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.

Atlas Mountains
.

In the northern hemisphere, many glaciers fused into one. The

Fenno-Scandian ice sheet rested on northern Europe, including much of Great Britain; the Alpine ice sheet on the Alps. Scattered domes stretched across Siberia
and the Arctic shelf. The northern seas were ice-covered.

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

It has been estimated that during the Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, and that thinning since the Last Glacial Maximum is less than 50 meters and probably started after ca 14 ka.[24]

Major events

Ice ages as reflected in atmospheric CO2, stored in the bubbles from glacial ice of Antarctica

During the 2.5 million years of the Pleistocene, numerous cold phases called

last glacial period ended about 10,000 years ago.[25] Over 11 major glacial events have been identified, as well as many minor glacial events.[26]
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 favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since the historical terminology was established.[26][27][28]

Historical names of the "four major" glacials in four regions.
Region Glacial 1 Glacial 2 Glacial 3 Glacial 4
Alps
Günz
Mindel Riss Würm
North Europe Eburonian
Elsterian
Saalian
Weichselian
British Isles Beestonian
Anglian
Wolstonian
Devensian
Midwest U.S. Nebraskan Kansan Illinoian
Wisconsinan
Historical names of interglacials.
Region Interglacial 1 Interglacial 2 Interglacial 3
Alps Günz-Mindel Mindel-Riss
Riss-Würm
North Europe Waalian Holsteinian
Eemian
British Isles Cromerian Hoxnian
Ipswichian
Midwest U.S. Aftonian
Yarmouthian
Sangamonian

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

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

Palaeocycles

The sum of transient factors acting at the Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors.

The Mid-Pleistocene Transition, approximately one million years ago, saw a change from low-amplitude glacial cycles with a dominant periodicity of 41,000 years to asymmetric high-amplitude cycles dominated by a periodicity of 100,000 years.[29]

However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere.[30]

Milankovitch cycles

Glaciation in the Pleistocene was a series of glacials and interglacials, stadials and interstadials, mirroring periodic climate changes. The main factor at work in climate cycling is now believed to be Milankovitch cycles. These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion. The effects of Milankovitch cycles were enhanced by various positive feedbacks related to increases in atmospheric carbon dioxide concentrations and Earth's albedo.[31]

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

Oxygen isotope ratio cycles

In

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 seawater, 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 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

Marine isotopic stage
(MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials.

According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588

Ma BP in the Early Pleistocene Gelasian
. Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced.

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

Fauna

Both marine and continental faunas were essentially modern but with many more large land mammals such as

giant sloths, species within Gigantopithecus and others. Isolated landmasses such as Australia, Madagascar, New Zealand and islands in the Pacific saw the evolution of large birds and even reptiles such as the Elephant bird, moa, Haast's eagle, Quinkana, Megalania and Meiolania
.

The severe climatic changes during the Ice Age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major

whitetail deer had replaced the megafauna and migrated north. Late Pleistocene bighorn sheep were more slender and had longer legs than their descendants today. Scientists believe that the change in predator fauna after the late Pleistocene extinctions resulted in a change of body shape as the species adapted for increased power rather than speed.[32]

The extinctions hardly affected Africa but were especially severe in North America where native horses and camels were wiped out.

Various schemes for subdividing the Pleistocene

In July 2018, a team of

nematodes frozen in permafrost, from around 42,000 years ago, back to life. The two nematodes, at the time, were the oldest confirmed living animals on the planet.[33][34]

Humans

The

Homo sapiens about 300,000 years ago.[37]

According to mitochondrial timing techniques,

archaic human forms already outside of Africa by the late Pleistocene, incorporating archaic human genetic material into the modern human gene pool.[41]


Hominin species during Pleistocene
Homo (genus)AustralopithecusAustralopithecus sedibaAustralopithecus africanusHomo floresiensisHomo neanderthalensisHomo sapiensHomo heidelbergensisHomo erectusHomo nalediHomo habilisHolocenePleistocenePliocene


See also

Explanatory notes

  1. IUGS decided that it will be replaced with a stage/age (currently unofficially/informally named the Tarantian).[16]

References

  1. ^ Cohen, K. M.; Finney, S. C.; Gibbard, P. L.; Fan, J.-X. (January 2020). "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. Retrieved 23 February 2020.
  2. . Retrieved 11 November 2019.
  3. . Retrieved 8 December 2020.
  4. .
  5. .
  6. ^ "Pleistocene". Dictionary.com Unabridged (Online). n.d.
  7. PMID 28059138
    .
  8. ^ Lyell, Charles (1839). Nouveaux éléments de géologie (in French). Paris, France: Pitois-Levranet. p. 621. From p. 621: "Toutefois, en même temps … et de substituer à la dénomination de Nouveau Pliocène celle plus abrégée de Pleistocène, tirée du grec pleiston, plus, et kainos, récent." (However, at the same time that it became necessary to subdivide the two periods mentioned above, I found that the terms intended to designate these subdivisions were of an inconvenient length, and I have proposed to use in the future the word "Pliocene" for "old Pliocene", and to substitute for the name "new Pliocene" this shorter "Pleistocene", drawn from the Greek pleiston (most) and kainos (recent).)
  9. ^ Wilmarth, Mary Grace (1925). Bulletin 769: The Geologic Time Classification of the United States Geological Survey Compared With Other Classifications, accompanied by the original definitions of era, period and epoch terms. Washington, D.C., U.S.: U.S. Government Printing Office. p. 47.
  10. ^ "Pleistocene". Online Etymology Dictionary.
  11. ^ a b "Major Divisions". Subcommission on Quaternary Stratigraphy. International Commission on Stratigraphy. Retrieved 25 September 2019.
  12. .
  13. .
  14. ^ "International Chronostratigraphic Chart v2017/02". International Commission on Stratigraphy. 2017. Retrieved 17 March 2018.
  15. ^ "Japan-based name 'Chibanian' set to represent geologic age of last magnetic shift". The Japan Times. 14 November 2017. Retrieved 17 March 2018.
  16. ^ "Formal subdivision of the Pleistocene Series/Epoch". Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy). 4 January 2016. Retrieved 17 March 2018.
  17. ^ Riccardi, Alberto C. (30 June 2009). "IUGS ratified ICS Recommendation on redefinition of Pleistocene and formal definition of base of Quaternary" International Union of Geological Sciences
  18. .
  19. .
  20. .
  21. . Retrieved 16 August 2023.
  22. National Geographic Channel
    , Six Degrees Could Change The World, Mark Lynas interview. Retrieved 14 February 2008.
  23. .
  24. ^ "Quaternary Period". National Geographic. 6 January 2017. Archived from the original on 20 March 2017.
  25. ^ .
  26. (PDF) on 28 September 2018. Retrieved 20 March 2010.
  27. . (contains a summary of how and why the Nebraskan, Aftonian, Kansan, and Yarmouthian stages were abandoned by modern stratigraphers).
  28. .
  29. .
  30. .
  31. ^ Valdez, Raul. Mountain Sheep of North America.
  32. ^ "Worms frozen in permafrost for up to 42,000 years come back to life". The Siberian Times. 26 July 2018. Retrieved 25 August 2021.
  33. S2CID 49743808
    .
  34. .
  35. .
  36. .
  37. .
  38. , pp. 241–251.
  39. S2CID 4397398. Archived from the original
    (PDF) on 12 April 2020. Retrieved 17 November 2017.
  40. .

External links