Last glacial period
The last glacial period was the last glacial period within the current ice age. She followed in the Upper Pleistocene following the last interglacial. It began around 115000-110000 years ago and ended some 12,500 to 10,000 years ago before. In the last ice age came, as it did during cold periods not to a cooling of the climate all over the world to long-range glaciations, widespread flooding and sinking of the sea.
The last glacial period is colloquially referred to as the "last ice age ", but this often with the term ice age leads to confusion within the meaning of the Ice Age. Ice Age are long periods of Earth's history, in which the poles are glaciated, as it is currently still the case. Currently, the Cenozoic ice age there. The end of the last ice age therefore only marked the beginning of the current warm period, the Holocene, within the same ice age.
Within the last ice age 100,000 years or so comprehensive, there were cold phases ( stadials ) and short -term heat stages ( interstadials ). The glaciers moved repeatedly before and retreated again, and also the flora and fauna followed the fluctuations accordingly. The last glacial maximum ( Last Glacial Maximum, LGM ), there was about 21000-18000 years ago. Although the time profiles of the temperatures and glaciation are similar around the world, there are from one continent to differences in the details.
Width landscapes on earth are still permeated by the glaciations of this cold period.
Geologists have traditionally provided for regions and therefore do not call cold periods as global climate and time periods, but in relation to a particular region in which they are detected. This is particularly the case for the final cold period. The cold period has therefore different in the various regions of the world name. In the Alps it is called Würm, in Northern and Central Europe as the Vistula in Eastern Europe as Valdai, in Siberia as Zyryanka, in the British Isles as Devensian, in Ireland as Midlandian, in North America as Fraser, Pinedale, Wisconsinan or Wisconsin, Mérida, called in Venezuela than in Chile Llanquihue and in New Zealand as Otira glaciation. See also problems with the structure of Cenozoic ice age.
The respective regional characteristics of the glacial period are defined according to individual and dated and also be broken down into individual subsections and stadials and interstadials.
Substituting the end of the Pleistocene, or the beginning of the Holocene, with the end of the last ice age the same, so this b2k 11,700 years ( = before 2000 ) is set, with an uncertainty of 99 years, based on the stratigraphic reference profile GSSP Pleistocene / Holocene.
Global temperatures dropped in the last ice age by several Kelvin over the Eemian before. It is assumed that the cooling at high latitudes was stronger than near the equator. At the same time, the climate became drier, because the rainfall decrease when in the cold less water evaporates.
In the foothills of the Alps, the mean annual temperatures in the Würm glacial period about 10 K colder than today. The average global temperature was in LGM about 5-6 K lower than today. Because of the gas inclusions in polar ice, we know that the atmospheric concentration of the greenhouse gases carbon dioxide (CO2), only 70% and methane ( CH4), only 50% of the pre-industrial value was (CO2 LGM: 200 ppmv pre-industrial 288 ppmv today (2005 ): 381 ppmv, CH4 in the LGM: 350 ppbv preindustrial: 750 ppbv, today: 1750 ppbv ).
The hot and cold periods are defined differently than the isotope stages after the marine oxygen isotope stratigraphy (MIS). Therefore, the beginning of the last glacial period falls in the middle of the heat - isotope stage " MIS 5". It was followed by the cold - Isotope Stage " MIS 4", the beginning of which approximately 71,000 years ago (after Aitken & Stokes ) or 74,000 years ago (after Martinson et al. ) Is dated. Then the climate warmed slightly ( " MIS 3", beginning about 60,000 years ago), but this phase was not warm enough to be considered a warm period. Finally, an even stronger cooling followed ( " MIS 2 ", beginning about 24,000 years ago) in the then lies the last glacial maximum. The temperature rise at the end of the last ice age was significantly faster.
Abrupt climate fluctuations
Within the last ice age several abrupt climate changes are detectable. Through its causes and periodicities, and to what extent they affect not only northern but also the southern hemisphere, there are different theories but no consensus yet.
The In 1988, Heinrich events show up in sediment cores of the North Atlantic Ocean. Select heat events in which glaciers and icebergs melted and the sediment contained in this ice continental origin was deposited on the seabed. Six to seven of these Heinrich events are known.
The Dansgaard - Oeschger events are particularly evident in ice cores from Greenland. You were raised in the northern hemisphere as rapid heating periods ( within a few decades by several Kelvin) followed by a slow cooling (within a few centuries ) dar. 23 such events were found for the period 110000-23000 BP. Between these and the Heinrich events, a relationship seems to exist.
About 74,000 years ago, the last eruption of the volcano Toba Super led to a cooling of several Kelvin and a dramatic climate change ( Volcanic winter). According to the Toba catastrophe theory after the population of Homo sapiens should have reduced to a few thousand individuals. This could be the low genetic diversity of modern man declare ( "Genetic bottleneck" called ).
The vegetation on the earth changed climate change accordingly. Vast areas of the country were not covered by ice to steppe and tundra ( cold ) deserts and grasslands. The forests and the tropical rain forests declined.
A characteristic feature of the fauna of the last glacial period were large animals ( megafauna ), especially large mammals, but also birds that are now extinct.
In Eurasia lived mammoths, mastodons, saiga, giant deer, saber-toothed cats, cave lions, cave hyenas and cave bears. In North America, there were other species such as prairie mammoth, the American Mastodon, Helmet musk oxen, bullocks bush ( Euceratherium ), giant ground sloths and giant armadillos. In Australia, lived rhino large marsupials like the Diprotodon and Zygomaturus, the Beuteltapir Palorchestes, the marsupial lion Thylacoleo carnifex, the giant rat kangaroo Propleopus, giant wombats, up to three meters high giant kangaroo, the large flightless bird Genyornis and the huge monitor lizard Megalania.
During and especially at the end of the last ice age came it the extinction of many of these species. This can be explained either with the environmental changes, the overhunting by humans, or a combination of both causes.
The glaciation of the last glacial period covered the northern Eurasia and North America with huge ice sheets, which were several kilometers thick in some cases. While today about 10 % of the land surface of the earth is covered by glacial ice, it was in the last glacial period 32% of the land area.
The Fennoscandian ice sheet (also called Scandinavian ice sheet called ) covered Northern Europe, bordering the Barents - Kara ice sheet parts of northern Asia. The Laurentide ice sheet and the Cordillera Ice Sheet covered large parts of North America. In the southern hemisphere of the Patagonian Ice Sheet covered the south of South America. Antarctica remained under the Antarctic ice sheet, from which it is covered today.
Even the great mountains were glaciated, in particular the Alps, the Himalayas. and the Andean Your glacier tongues united in large glaciers and pushed their way far into the foreland. Glaciers also existed in the mountain ranges of Africa, Japan, Taiwan, Tasmania and New Zealand. Whether the Tibetan Plateau was glaciated, is controversial.
The enormous weight of the ice sheets pushed the lithosphere down. Due to the melting of glaciers these areas are raised again, a process that is referred to as post-glacial land uplift and continues today.
Today still visible remnants of glaciation are "flat -planed " terrains with marshes, great lakes, lake districts, shallow seas, moraines, gravel fields / Sander, glacial valleys and glacial lakes edge. See also glacial deposits.
The glaciation of the ice age led near the glacier margins to severe cold, dry case winds through the cold air masses flowing down from them. These winds transported large amounts of loose sediment away from areas with low vegetation cover, which elsewhere then piled to loess.
There were also more inland dunes and sand dunes today. A relic of this is for example the Sandhills region in what is now the U.S. state of Nebraska.
The last glacial period was characterized despite lower rainfall also of major flooding. Several rivers of northern Asia, which drain into the Arctic Ocean could not drain because of them oncoming ice sheet and formed huge Eisstauseen. The largest of these lakes, the West Siberian Glacial Lake, was built in the West Siberian lowland in the rivers Ob and Yenisei and extended over about 1500 km from north to south and as far from West to East. To the west of the Urals, there was a Ice Lake in the region of today's Republic of Komi and a white man in today's sea. With the decline of the Scandinavian glacier created and enlarged the Baltic Ice Lake. About three intermediate phases ( Yoldia Sea, Ancylus Lake, Littorinameer ) the current connection of this body of water was the ocean, salt water flowed and there was today's Baltic Sea.
Also inland lakes such as the Caspian Sea and the Aral Sea rose significantly in the water mirror and enlarged to approximately twice its present area. It is thought that the Caspian Sea rose to such an extent that it is connected via the Aralo - Caspian lowlands to the Aral Sea and the Manytsch lowlands to the Black Sea (which was a freshwater lake with no connection to the Mediterranean during the cold period ) into a single huge water body had. Maybe even the West Siberian Glacial Lake of the chain Aral Sea dehydrated - Caspian Sea - Black Sea to the Mediterranean Sea. Like the Caspian seal and the Baikal Seal got into the lakes is unclear and could be explained by the hypothesis of a water connection between the Arctic Ocean and these lakes.
At the end of the cold period occurred in various regions of the earth catastrophic flooding. These are also called glacier runs when the dam breaks a Eisstausees. Among the largest of these events include the Missoula Floods in North America with the flow of the Eisstausees Lake Missoula. In Asia, there was a series of devastating glacier runs on a similar scale, the Altai floods in the present Republic of Altai. Other major floods were those of Lake Bonneville ( in present-day Utah ) in the Great Lakes, which are also cold temporal relics, and northeast of it, which has been previously depressed by the ice sheet in the Champlain Sea, where sea water penetrated far into the interior.
Due to the massive volume of water that were bound in the ice sheets, the sea level fell during the last glacial period to more than 100 meters below the present level off. Shelf seas like the North Sea were dry in many parts. As a result, increased the land area of the continents and islands and it created land bridges, which made it possible for animals and humans to reach areas that were later separated by rising sea levels from one another again.
The Beringia land bridge linking Asia with North America, and allowed the settlement of America. In Europe, there was a land bridge between Ireland, the British Isles and mainland Europe, which is called in the North Sea Doggerland. To the deepest sea level many of today's Mediterranean islands were connected to the mainland.
In Asia Pacific, there was a Southeast Asian land bridge to the western part of Indonesia ( Sunda ), and another land bridge that New Guinea, Australia and Tasmania to a land formations Association ( Sahul ). However, there was no land connection between Sunda and Sahul, but a separation that is still the basis of the Wallace Line recognizable. Therefore man must have found a way to cross the sea to get from Asia to Australia.
The Persian Gulf and the Gulf of Suez fell dry during the last glacial period. India and Sri Lanka were probably connected through the Adam's Bridge.
With the fall of the sea level also formed new islands in the ocean, such as the Mascarene Plateau east of Madagascar, which is now in 8-150 meters water depth.
Man in the last glacial period
The living as hunters and gatherers modern humans spread from Africa in this cold time coming across all continents of the earth ( with the exception of Antarctica ) from. In contrast, the Neanderthals died, who had colonized the European area in the Eemian, the last ice age about 30,000 years ago from. At the end of the glacial period, about 17000-12000 years ago, first sedentary societies, the agriculture and livestock farming ( Neolithic Revolution ) originated operated in Asia Minor.
From the perspective of human archeology the last cold period falls into the Paleolithic (Paleolithic ). The beginning of the cold time is approximately in the middle of the Mittelpaläolithikums. The period from about 40,000 years ago until the end of the last glacial period is referred to as the Upper Paleolithic. In the history of science, the prehistory and early history of cultural development of man in this era is concerned.
As the man was staying, especially near the coast, lie many of its settlements from this period now below sea level and are characterized archaeologically difficult to access.
From fossils and from genetic analyzes (molecular clock ) can be derived that anatomically modern humans before and at the beginning of the last ice age lived in Africa. Fossil sites from this period are Florisbad (South Africa = "Homo helmei " ), Eliye Springs (West Turkana, Kenya), Laetoli ( Tanzania) and Djebel Irhoud (Morocco ).
North Africa has undergone in the last cold period of strong vegetation changes. At the beginning of the cold period 120000-110000 years ago the Sahara was a verdant savannah; then it became a desert. 50000-45000 years ago, another savanna phase followed. During its peak in the last glacial period, the Sahara expanded again as a huge desert further south than today. After the cold period another and so far last fertile phase followed. Since then takes the Sahara again as the biggest dry desert on Earth.
Asia seems to have been in the last glacial period experienced two waves of colonization of man. From the first wave, it is believed that the man, coming from Africa, followed by about 60,000 years ago on the Middle East southern Asia to Australia. Of this there is virtually no trace.
In a second colonization wave that began about 40,000 years ago, humans spread throughout Asia. There are occupied, 30,000 years ago in China and 26,000 years ago in East Asia 40,000 years old traces inside Southeast Asia.
About 50,000 to 60,000 years ago, humans reached Australia. The oldest human remains in Australia are those of Mungo Man and Mungo Lady, both of which have been dated to about 40,000 years. Other finds are estimated at up to 60,000 years but this dating is disputed.
The oldest archaeological cultures in Europe are those of the Neanderthals.
Called The oldest culture of Homo sapiens in this era as Cro -Magnon man in Europe was the Aurignacian culture. It consisted of about 40,000 (possibly 45,000 ) years to about 31,000 years ago. They overlapped with the Châtelperronian culture, the culture of the last Neanderthal.
The most important cold temporal culture of Europe was the subsequent Gravettian culture. Their traces are detected in the areas of today's France, southern Germany, Austria, Czech Republic, Poland and Ukraine, and are at about the period of dated 28000-22000 years ago.
In Western Europe, followed thereafter, during the last cold maximum of about 24000-20000 years ago, the Solutrean culture. About 15,000 years ago, there was the Magdalenian culture. The last cultural groups before the Holocene were the hamburger culture about 15,000 to 14,000 years ago, the penknife groups, also referred to as Azilian culture, about 14000-13000 years ago, the Bromme culture and the Ahrensburg culture (about 12,000 years ago).
See also Frankokantabrische cave art.
According to the current state of research the colonization of America from Siberia was carried forth across the Beringia land bridge in at least three waves of immigration. The first and by far the most significant wave was about 15,500 years ago. The second wave brought the ancestors of the Na - Dene, the Diné and Apache Indians. With the third wave, the ancestors of the Inuit, Yupik and Unungun came.
The site of Monte Verde in Chile is one of the oldest traces of human settlement in the Americas. At the end of the cold period about 11000-10800 years ago there was the Clovis culture, the first area common American culture.