In geologic time , the Pliocene Epoch occurs during the Tertiary Period (65 million years ago [mya] to 2.6 mya) of the Cenozoic Era of the Phanerozoic Eon . The Tertiary Period is sometimes divided into—or referred to in terms of—a Paleogene Period (65 mya to 23 mya) and a Neogene Period (23 mya to 2.6 mya). The Pliocene Epoch is the last epoch on the Tertiary Period or, in the alternative, the last epoch in the Neogene Period.
The Pliocene Epoch spans the time 5 mya to 2.6 mya.
The Pliocene Epoch is further subdivided into Zanclian (5 mya to 3.9 mya) and Placenzian (3.9 mya to 2.6 mya) stages.
By the end Pliocene Epoch, 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 (Eurasian plate) and Africa . The Indian Ocean filled the basin between Africa, India, Asia, and Australia. The Indian plate driving against and under the Eurasian plate uplifted both and resulted 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. The reemergence of the land bridge between North America and South America at the isthmus of Panama about 3 mya allowed migration of species and mixing of gene pools in subspecies.
Climatic cooling increased during Pliocene Epoch, and grasslands continued the rapid development found in the Miocene Epoch . Eventually, glaciation became well established and a general glacier advance started that continued into the subsequent Pleistocene Epoch of the Quaternary Period .
The Pliocene Epoch spanned that period of geologic time during which the evolution of humans becomes increasingly well documented in the fossil record . Notable in the development of primates and human evolution, are fossilized remains of Ardipithecus ramidus, Australopithecus anamensis, Australopithecus afarensis, Australopithecus garhi, and Australopithecus africanus that date to the Pliocene Epoch. Although these species became extinct during the Pliocene Epoch, they at a minimum co-existed with the ancestors of humans (Homo sapiens ); analysis of remains indicate that these species walked upright. Anthropologists argue that apes and humans diverged six to eight mya from a common ancestor that lived during the Miocene Epoch. By the end of the Pliocene Epoch, the subsequent extinctions of Homo habilis and Homo rudolfensis were almost contemporaneous with the appearance of Homo ergaster, a species some anthropologists argue is one of the earliest identifiable direct ancestors of 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.
See also Archean; Cambrian Period; Cretaceous Period; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Evolutionary mechanisms; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Mesozoic Era; Mississippian Period; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Paleozoic Era; Pennsylvanian Period; Precambrian; Proterozoic Era; Silurian Period; Triassic Period
Pliocene epoch (plī´əsēn), fifth epoch of the Cenozoic era of geologic time (see Geologic Timescale, table), from 5.1 to 2 million years ago. By the beginning of the Pliocene, the outlines of North America were almost the same as in recent time. Encroachments by the sea were limited to a narrow strip along the coasts of the Carolinas, Georgia, Florida, and the Gulf Coast states, and an embayment, smaller than that of the preceding Miocene epoch, in California. The Pliocene formations on the Atlantic coast are chiefly marine marls; on the Gulf they are nonmarine sediments resulting from erosion. In California they contain much volcanic ash and some are oil-bearing. The Pliocene formations of the western interior are small and scattered. In western interior North America and on the west coast, volcanic activity continued into the Pliocene from the Miocene. The close of the Pliocene was marked in North America by the Cascadian revolution, in the course of which the Sierra Nevada was elevated and tilted to the west. The Cascades, Rockies, Appalachians, and the Colorado plateau were uplifted, and there was activity in the mountains of Alaska and in the Great Basin ranges of Nevada and Utah. In Europe the Pliocene sea covered small parts of the northwest of the continent and a large area around the present Mediterranean; a number of volcanoes were active, among them Vesuvius and Etna. There was considerable mountain building, including the folding and thrusting of the Alps. The climate of the Pliocene was markedly cooler and drier than that of the Miocene and foreshadowed the glacial climates of the Pleistocene epoch. The life of the Pliocene was notable for its modern appearance; the Pliocene marked the climax, and perhaps the initial decline, of the supremacy of the mammals.