Holocene
The
Holocene epoch is a
geological period that extends from the present day to back about 10,000
radiocarbon years, approximately 11,430 ± 130 calendar years
BP (between 9560 and 9300
BC). It has been assigned to
MIS 1, which is an interglacial. The next glacial is yet to occur.
Human civilization dates entirely to the Holocene. More precise dating is provided by the
Blytt-Sernander classification of climatic periods defined by the pollen in peat moss. The scheme was defined for north Europe, but the climate changes are known somewhat more widely. The periods of the scheme include a few of the final oscillations of the glacier and then go on to classify the climates of recent prehistory.
The beginning of the Holocene was punctuated by the
Younger Dryas cold period, the final part of the
Pleistocene epoch. The end of the Younger Dryas has been dated to about 11600 calendar years BP (9600 BCE). However, evidence for the Younger Dryas is not clear cut anywhere other than in the Northern Hemisphere.
The Holocene starts late in the retreat of the
Pleistocene glaciers. The Holocene is the fourth and last epoch of the
Neogene period (second epoch of the unofficial
Quaternary sub-era). The name is derived from the Greek ὄλος (entire(ly)) and καινός (new). It has also been called the "Alluvium Epoch".
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.
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.
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 human-induced
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."
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.
*Neil Roberts
The Holocene: an environmental history (Blackwell Publishing)
*
Holocene extinction event*
Holocene calendar*
Geologic timescale*
Centuries*
10th millennium BC*
The Great Story* Ogg, Jim; June, 2004,
Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
