Mythos 2 – Pleistocene Epoch

 

The Pleistocene is the geological epoch which lasted from about 2.6 million to 11,700 years ago, spanning the world’s recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period. It also corresponds with the end of the Paleolithic age used in archaeology. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9,640 BC (11,750 years ago).

Earth 20,000 years ago a the height of the last ice age.

Earth 20,000 years ago a the height of the last ice age.

The modern continents were essentially at their present positions during the Pleistocene, the plates upon which they sit probably having moved no more than 100 km relative to each other since the beginning of the period. The Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th 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 kilometers in North America and Eurasia.

Each glacial advance tied up huge volumes of water in continental ice sheets 1.5 to 3 km (0.9 to 1.9 miles) thick, resulting in temporary sea-level drops of 100 meters (300 feet) or more over the entire surface of the world ocean. During interglacial times, such as at present, drown coastlines were common. The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania. The current decaying glaciers of Mount Kenya, Mount Kilimanjaro, and the Ruwenzori Range in east and central Africa were larger. Glaciers existed in the mountains of Ethiopia and in the Atlas mountains of Northwest Africa.

Lake Agassiz

Lake Agassiz

In the northern hemisphere, many glaciers fused into one. The Cordilleran and Laurentide ice-sheet covered the northern half of North America. The Fenno-Scandian ice-sheet rested on northern Europe, including Great Britain, while the Alpine ice-sheet covered the Alps. 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, Lake Agassiz covered most of Manitoba, and large sections of Ontario, Saskatchewan, Minnesota, and North Dakota. Over a hundred basins, now dry or nearly dry, were overflowing in the North American west, including Lake Bonneville, which filled the basin that Great Salt Lake now lays in. In Eurasia, large lakes developed as a result of the runoff from the glaciers. African lakes were fuller, apparently from decreased evaporation. Deserts on the other hand were drier and more extensive. Rainfall was lower because of the decrease in oceanic and other evaporation.

Over 11 major glacial events have been identified, as well as many minor glacial events.(1)G. M. Richmond and D. S. Fullerton (1986) “Summation of Quaternary glaciations in the United States of America” Quaternary Science Reviews, Volume 5, Pages 183-196 A major glacial event is a general glacial expansion, termed a glacial. Glacials are separated by inter-glacials. 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. Both oceanic and continental animals were essentially modern and many animals, specifically, mammals were much larger in body form than their modern relatives. The severe climatic changes during the ice age had major impacts on the animals and plants. With each advance of the ice, large areas of the continents became totally depopulated. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply.

A major extinction event of large mammals, which included mammoths, mastodons, sabre-toothed cats, glyptodons, ground sloths, Irish elk, cave bears, and short-faced bears, began late in the Pleistocene and continued into the Holocene. Neanderthals and other archaic-humans also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice, migratory birds, and swifter animals like whitetail deer had replaced the large animals and migrated north.

References   [ + ]

1. G. M. Richmond and D. S. Fullerton (1986) “Summation of Quaternary glaciations in the United States of America” Quaternary Science Reviews, Volume 5, Pages 183-196