Earth's Pleistocene Epoch

The Pleistocene Epoch is arguably one of the most important Epochs of the Cenozoic, if not all the geologic time periods. This period that ran from around 1.8 million years ago until 11,000 years ago marked the evolution of mankind, thrust the world into a global ice age, and saw the extinction of many of the species that had dominated the Age of Mammals.

The Pleistocene was characterized by a number of glacial cycles that at some points in the period covered nearly 30% of Earth's surface. When two thirds of the Earth's surface is ocean which does not freeze as easily as dry land, that figure encompasses a giant land mass. Scientists have accumulated evidence suggesting four distinct glacial periods in the Pleistocene Epoch. Continental glaciers crept inward from the poles over the continents, particularly from the Arctic Circle. Antarctica at this point was completely glaciated and all remnants of vegetation on the continent were wiped clean. The presence of such large ice sheets caused subsequent drops in global sea levels, which devastated many coastal marine ecosystems. Many large lakes formed in the interior of continents due to the colder air temperatures and reduced evaporation rates for standing water.

In addition to the glacial cycles, referred to often as "The Ice Age," there were two very important developments on Earth during the Pleistocene. The first was that hominids evolved into the modern form of homo sapiens over the course of the Epoch. The lowly savannah-dwelling Australopithecus evolved into larger, and more human-like forms. Homo erectus and homo habilis were prototype humans who had grown into a more permanently upright posture and had an increased brain size. With this larger brain came the development of complex tool-making skills as well as the development of further social bonding and language. Two hominids, the Neanderthals and Cro Magnons, which are known in popular culture as cavemen, formed the direct foundation for modern humans.