Pleistocene Epoch (World of Earth Science)
In geologic time, the Pleistocene Epoch represents the first epoch in current Quaternary Period (also termed the Anthropogene Period) of the Cenozoic Era of the Phanerozoic Eon. The Pleistocene Epoch spans the time between roughly 2.6 million years ago (mya) and onset of the current Holocene Epoch 10,000 to 11,000 years ago.
The Quaternary Period contains two geologic epochs. The earliest epoch, the Pleistocene Epoch is further subdivided into (from earliest to most recent) Gelasian and Calabrian stages. The Calabrian stage is also frequently replaced by a series of geologic stages, from earliest to most recent, including the Danau, Donau-Günz, Günzian, Günz-Mindel, Mindelian, Mindel-Riss, Rissian, Riss-Würm, and Würmian stages.
During the Pleistocene Epoch, Earth's continents almost completely assumed their modern configuration.
Glaciation cycles dominated the major climatic changes of the Pleistocene Epoch. There were at least four distinct glacial advances and recessions. In addition to tremendous landscape evolution, climatic cooling contributed to mass extinction in selective areas of the world, but not nearly on the scale as earlier mass extinctions.
The size of land mammals generally increased throughout the Pleistocene Epoch and the fossil record established that during the Pleistocene Epoch, hominid (human-like) species became established and evolved into humans (Homo sapiens).
Near the start of the Pleistocene Epoch, a number of related species (e.g., Australopithecus afarensis) lived and became extinct before modern humankind (Homo sapiens) appeared. Early in the Pleistocene Epoch, Homo habilis and Homo rudolfensis lived and became extinct. Their extinctions are dated to approximately the appearance of Homo ergaster, a species some anthropologists argue is one of the earliest identifiable direct ancestors of Homo erectus. Although often confused with Homo erectus, many scientists assert that Homo ergaster is a common ancestor that lead more directly to the subsequent development of Homo heidelbergensis, Homo neanderthalensis, and humans (Homo sapiens).
The last major impact crater with a diameter over 31 mi (50 km) struck Earth near what is now Kara-Kul, Tajikistan, at the start of the Pleistocene Epoch. The last major impacts producing craters greater than 6.2 mi (10 km) in diameter occurred during the Pleistocene Epoch about 1.2 million years ago in what are now Kazakhastan and Ghana.
See also Archean; Cambrian Period; Cretaceous Period; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Fossils and fossilization; Glacial landforms; Glaciers; Historical geology; Ice ages; Jurassic Period; Mesozoic Era; Miocene Epoch; Mississippian Period; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Paleozoic Era; Pennsylvanian Period; Precambrian; Proterozoic Era; Silurian Period; Triassic Period