Quaternary Period

Quaternary Period

In geologic time , the Quaternary Period (also termed the Anthropogene Period), the second geologic period in the Cenozoic Era , spans the time between roughly 2.6 million years ago (mya) and present day. On the geologic time scale, Earth is currently in the Quaternary Period of the Cenezoic Era of the Phanerozoic Eon .

The Quaternary Period contains two geologic epochs. The earliest epoch, the Pleistocene Epoch ranges from approximately 2.6 mya to 10,000 years ago. 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. The latest, most recent, and current epoch, the Holocene Epoch ranges from approximately 10,000 years ago until present day. According to geologic time, Earth is currently in the Holocene Epoch.

During the Quaternary Period, Earth's continents assumed their modern configuration. The Pacific Ocean separated Asia and Australia from North America and South America ; the Atlantic Ocean separated North and South America from Europe (Euro-Asia) and Africa . The Indian Ocean filled the basin between Africa, India, Asia, and Australia. The Arabian Plate wedged between the Eurasian and African plates continues to provide high levels of tectonic activity (e.g., earthquakes) in the area of modern day Turkey. The Indian plate driving against and under the Eurasian plate uplifts both in rapid mountain building. As a result of the ongoing collision, ancient oceanic crust bearing marine fossils was uplifted into the Himalayan chain. The collision between the Indian and Eurasian plate continues with a resulting slow—but measurable—increase in the altitude of the highest Himalayan mountains (e.g., Mt. Everest) each year.

Glaciation (e.g., ice ages ), and fluctuating climatic conditions—possibly at least partially explainable by Milankovitch cycles—during both the Tertiary and Quaternary Periods brought about sweeping changes in the landscape evident in modern topographical features.

The fossil record provides evidence that by the end of the Tertiary Period (also known as the Neogene period), the species Ardipithecus ramidus walked upright in an area now encompassing modern Ethiopa. Near the start of the Quaternary Period, a number of species lived and became extinct before modern humankind (Homo sapiens ) appeared. Many of these species, including Australopithecus anamensis, Australopithecus afarensis, Australopithecus garhi, and Australopithecus africanus were only collateral rungs on the ladder of evolution to Homo sapiens, and do not provide a direct evolutionary link to humans. Although these species became extinct near the start of the Quaternary Period, they at least co-existed with the direct ancestors of humans. Early in the Quaternary Period 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, Homo heidelbergensis, Homo neanderthalensis, and 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 Pliocene Epoch and Pleistocene Epoch geologic time boundary that established the start of the Quaternary Period.

See also Archean; Cambrian Period; Cretaceous Period; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Fossil record; Fossils and fossilization; Historical geology; Jurassic Period; Mesozoic Era; Miocene Epoch; Mississippian Period; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Paleozoic Era; Pennsylvanian Period; Precambrian; Proterozoic Era; Silurian Period; Supercontinents; Triassic Period