Paleolithic - Paleogeography and Climate

Paleogeography and Climate

The climate of the Paleolithic Period spanned two geologic epochs known as the Pliocene and the Pleistocene. Both of these epochs experienced important geographic and climatic changes that affected human societies.

During the Pliocene, continents continued to drift from possibly as far as 250 km from their present locations to positions only 70 km from their current location. South America became linked to North America through the Isthmus of Panama, bringing a nearly complete end to South America's distinctive marsupial fauna. The formation of the Isthmus had major consequences on global temperatures, because warm equatorial ocean currents were cut off, and the cold Arctic and Antarctic waters lowered temperatures in the now-isolated Atlantic Ocean. Central America formed completely during the Pliocene, allowing fauna from North and South America to leave their native habitats and colonize new areas. Africa's collision with Asia created the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. During the Pleistocene, the modern continents were essentially at their present positions; the tectonic plates on which they sit have probably moved at most 100 km from each other since the beginning of the period.

Climates during the Pliocene became cooler and drier, and seasonal, similar to modern climates. Ice sheets grew on Antarctica. The formation of an Arctic ice cap around 3 Ma is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds. Mid-latitude glaciation probably began before the end of the epoch. The global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas.

The Pleistocene climate was characterized by repeated glacial cycles during which continental glaciers pushed to the 40th parallel in some places. Four major glacial events have been identified, as well as many minor intervening events. A major event is a general glacial excursion, termed a "glacial". Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials". Each glacial advance tied up huge volumes of water in continental ice sheets 1500–3000 m deep, resulting in temporary sea level drops of 100 m or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.

The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene and the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania. The now 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 to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one. The Cordilleran ice sheet covered the North American northwest; the Laurentide covered the east. The Fenno-Scandian ice sheet covered northern Europe, including Great Britain; the Alpine ice sheet covered the Alps. Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were frozen. During the late Upper Paleolithic (Latest Pleistocene) c. 18,000 BP, the Beringa land bridge between Asia and North America was blocked by ice, which may have prevented early Paleo-Indians such as the Clovis culture from directly crossing Beringa to reach the Americas.

According to Mark Lynas (through collected data), the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers.

The ice age ended with the end of the Paleolithic era (the end of the Pleistocene epoch), and Earth's climate became warmer. This may have caused or contributed to the extinction of the Pleistocene megafauna, although it is also possible that the late Pleistocene extinctions were (at least in part) caused by other factors such as disease and over hunting by humans. New research suggests that the extinction of the woolly mammoth may have been caused by the combined effect of climatic change and human hunting. Scientists suggest that climate change during the end of the Pleistocene caused the mammoths' habitat to shrink in size, resulting in a drop in population. The small populations were then hunted out by Paleolithic humans. The global warming that occurred during the end of the Pleistocene and the beginning of the Holocene may have made it easier for humans to reach mammoth habitats that were previously frozen and inaccessible. Small populations of wooly mammoths survived on isolated Arctic islands, Saint Paul Island and Wrangel Island, till circa 3700 and 1700 BCE respectively. The Wrangel Island population went extinct around the same time the island was settled by prehistoric humans. There's no evidence of prehistoric human presence on Saint Paul island (though early human settlements dating as far back as 6500 BCE were found on nearby Aleutian Islands).

Currently agreed upon classifications as Paleolithic geoclimatic episodes