The 'Holocene'
epoch is a
geological period, which began approximately 11,550 calendar years
BP (about 9600
BC) and continues to the present. The Holocene is part of the
Neogene and
Quaternary periods. Its name comes from the Greek words (''holos'', whole or entire) and (''kainos'', new), meaning "entirely recent". It has been identified with
MIS 1 and can be considered an
interglacial in the current
ice age.
The Holocene has also been called the "Alluvium Epoch", but this name has fallen into disuse.
Overview
The Holocene starts late in the retreat of the
Pleistocene glaciers.
Human civilization dates entirely within the Holocene. The
Blytt-Sernander classification of climatic periods defined, initially, by plant remains in peat mosses, is now of purely historical interest. The scheme was defined for north Europe, but the climate changes have been claimed to occur more widely. The periods of the scheme include a few of the final, pre-Holocene, oscillations of the last glacial period and then classify climates of more recent prehistory.
The Holocene was preceded by the
Younger Dryas cold period, the final part of the
Pleistocene epoch. However, evidence for the Younger Dryas is not clear cut anywhere other than in the Northern Hemisphere.
Paleontologists have defined no
faunal stages for Holocene. If subdivision is necessary, periods of human technological development such as the
Mesolithic,
Neolithic, and
Bronze Age are usually used.
Climatically, the Holocene may be divided evenly into the
Hypsithermal and
Neoglacial periods; the boundary coincides with the start of the Bronze Age in western civilisation. According to some scholars, a third division, the
Anthropocene began in the 18th Century
[1]. It is debatable whether this is an age within, or follows, the Holocene
epoch.
Geology
Continental motions are less than a kilometre over a span of only 10 ka. However, ice melt caused world
sea levels to rise about 35 m (110 ft) in the early part of the Holocene. In addition, many areas above about 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as 180 m (600 ft) over the late Pleistocene and Holocene, and are still rising today.
The sea level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea. Holocene marine fossils are known from
Vermont,
Quebec,
Ontario, and
Michigan. Other than higher latitude temporary marine incursions associated with glacial depression, Holocene fossils are found primarily in lakebed, floodplain, and cave deposits. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any likely upthrusting of non-glacial origin.
Post-glacial rebound in the
Scandinavia region resulted in the formation of the
Baltic Sea. The region continues to rise, still causing weak
earthquakes across
Northern Europe. The equivalent event in North America was the rebound of
Hudson Bay, as it shrank from its larger, immediate post-glacial
Tyrrell Sea phase, to near its present boundaries.
Climate
Although geographic shifts in the Holocene were minor, climatic shifts were very large.
Ice core records show that before the Holocene there were global warming and cooling periods, but climate changes became more regional at the start of the Younger Dryas. However, the
Huelmo/Mascardi Cold Reversal in the Southern Hemisphere began before the Younger Dryas, and the maximum warmth flowed south to north from 11,000 to 7,000 years ago. It appears that this was influenced by the residual glacial ice remaining in the Northern Hemisphere until the latter date.
The
hypsithermal was a period of warming in which the global climate became 0.5–2°C warmer than today. However, the warming was probably not uniform across the world. This period ended about 5,500 years ago, when the earliest human civilizations in
Asia and
Africa were flourishing. This period of warmth ended with the descent into the Neoglacial. At that time, the climate was not unlike today's, but there was a slightly warmer period from the 10th–14th centuries known as the
Medieval Warm Period. This was followed by the
Little Ice Age, from the 13th or 14th century to the mid 19th century, which was a period of significant cooling, though not everywhere as severe as previous times during neoglaciation.
The Holocene warming is an interglacial period and there is no reason to believe that it represents a permanent end to the Pleistocene
glaciation. However, the current
global warming may result in the Earth becoming warmer than the
Eemian Interglacial, which peaked at roughly 125,000 years ago and was warmer than the Holocene. This prediction is sometimes referred to as a ''super-interglacial''.
Compared to glacial conditions, habitable zones have expanded northwards, reaching their northernmost point during the hypsithermal. Greater moisture in the polar regions has caused the disappearance of
steppe-tundra.
Ecological developments
Animal and plant life have not evolved much during the relatively short Holocene, but there have been major shifts in the distributions of plants and animals. A number of large animals including
mammoths and
mastodons,
saber-toothed cats like ''
Smilodon'' and ''
Homotherium'', and
giant sloths disappeared in the late Pleistocene and early Holocene—especially in North America, where animals that survived elsewhere (including horses and camels) became extinct. This extinction of American
megafauna has been explained as caused by the arrival of the ancestors of
Amerindians; though most scholars assert that climatic change also contributed.
Throughout the world, ecosystems in cooler climates that were previously regional have been isolated in higher altitude ecological "islands."
The ''
8.2 ka event'', an abrupt cold spell recorded as a negative excursion in the record lasting 400 years, is the most prominent climatic event occurring in the Holocene epoch, and may have marked a resurgence of ice cover. It is thought that this event was caused by the final drainage of
Lake Agassiz which had been confined by the glaciers, disrupting the
thermohaline circulation of the Atlantic
[1].
Human developments
The beginning of the Holocene corresponds with the beginning of the
Mesolithic age in most of Europe; but in regions such as the
Middle East and
Anatolia with a very early
neolithisation,
Epipaleolithic is preferred in place of Mesolithic. Cultures in this period include:
Hamburgian,
Federmesser, and the
Natufian culture.
Both are followed by the aceramic Neolithic (
Pre-Pottery Neolithic A and
Pre-Pottery Neolithic B) and the pottery
Neolithic.
Further reading
★ Neil Roberts ''The Holocene: an environmental history'' (Blackwell Publishing)
★ Mackay, A.W., Battarbee, R.W., Birks, H.J.B. & Oldfield, F. (2003) Editors. ''Global change in the Holocene''. Publisher: Arnold, London. 528 pp (29 chapters)
See also
★
8.2 kiloyear event
★
Anthropocene
★
Blytt-Sernander
★
Geologic timescale
★
Holocene calendar
★
Holocene extinction event
★
Neolithic Subpluvial
★
Older Peron
★
Piora Oscillation
★
10th millennium BC
References
★ Ogg, Jim; June, 2004, ''Overview of Global Boundary Stratotype Sections and Points (GSSP's)'' http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006
External links
★ http://extinctanimals.petermaas.nl/
★
The 8.2 ka event
★
Detecting Holocene changes in thermohaline circulation
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