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