| Quaternary Period. |
Pleistocene
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Holocene
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The Holocene epoch is a geological period that extends from the present day back to about 10,000 radiocarbon years, approximately 11,430 ± 130 calendar years BP (between 9560 and 9300 BC). The Holocene is the fourth and last epoch of the Neogene period (second epoch of the unofficial Quaternary sub-era). Its name comes from the Greek words ὄλος ("holos") which means whole or entire and καινή ("kai-ne") which means new or recent. It has also been called the "Alluvium Epoch". It has been assigned to MIS 1, which is an interglacial. The next glacial is yet to occur.
The Holocene starts late in the retreat of the Pleistocene glaciers.
Human civilization dates entirely to 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. The end of the Younger Dryas has been dated to about 11,600 calendar years BP (9600 BC). 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 Paleolithic, Mesolithic and Neolithic are usually used.
Geology
Continental motions are negligible over a span of only 10,000 years -- less than a kilometer. However, world sea levels rose about 35 meters (110 feet) in the early part of the Holocene due to ice melt. In addition, many areas above about 40 degrees latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as 180 meters over the late Pleistocene and Holocene.
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.
Apart from temporary incursions, Post-glacial rebound in the Scandinavia region resulted in the evolution 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 by historic times.
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. There appears to be a south to north pattern, with southern latitudes displaying maximum warming a few millennia before the Northern Hemisphere regions.
The Holocene Climatic Optimum 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. It began roughly 9,000 years ago and ended about 5,000 years ago, when the earliest human civilizations in Asia and Africa were flourishing. This period of warmth ended with a cooler period with minor glaciation, which continued until about 2,000 years ago. 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 as severe as previous periods during the Holocene.
The Holocene warming is an interglacial period and there is no reason to believe that it represents a permanent end to the Pleistocene glaciation. It is thought that the planet could return to a new period of glaciation in as little as 3,000 years from now, although 19,000 years is also suggested. However, if the current global warming continues, a super-interglacial might occur, and become warmer and possibly longer than any past interglacial periods in the Pleistocene. A super-interglacial could become warmer than the Eemian Interglacial, which peaked at roughly 125,000 years ago and was warmer than the Holocene.
Habitable zones expanded northwards. Large mid-latitude area such as the Southwestern United States that were previously productive became deserts (see Lake Manly). The epoch started with large lakes in many areas of the world that are now quite arid.
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 also been explained by the arrival of the ancestors of Amerindians. Throughout the world, ecosystems in cooler climates that were previously regional have been isolated in higher altitude ecological "islands."
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
- Holocene extinction event
- Holocene calendar
- Geologic timescale
- Centuries
- 10th millennium BC
- 8.2 ka event
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
| Neogene period | ||
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| Quaternary | ||
| Pliocene | Pleistocene | Holocene |
| ← Neogene | Gelasian | Early | Middle | Late | |