Permian

The Permian (/ˈpɜːrmi.ən/ PUR-mee-ən) is a geologic period and stratigraphic system which spans 47 million years, from the end of the Carboniferous Period 298.9 Ma (million years ago) to the beginning of the Triassic Period 251.902 Ma. It is the sixth and last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.

The Permian witnessed the diversification of the two groups of amniotes, the synapsids and the sauropsids (reptiles). The world at the time was dominated by the supercontinent Pangaea, which had formed due to the collision of Euramerica and Gondwana during the Carboniferous. Pangaea was surrounded by the superocean Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, which could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors.

Various authors have proposed at least three, and possibly four major extinction events in the Permian, though the validity of some of these extinctions has been disputed. The end of the Early Permian (Cisuralian) has a gap in the fossil record that may have constituted a major extinction, as most lineages of primitive "pelycosaur" synapsids becoming extinct, being replaced by more advanced therapsids. The end of the Capitanian Stage of the Permian was marked by the major Capitanian mass extinction event, associated with the eruption of the Emeishan Traps. The Permian (along with the Paleozoic) ended with the Permian–Triassic extinction event (colloquially known as the Great Dying), the largest mass extinction in Earth's history (which is the last of the three or four crises that occurred in the Permian), in which nearly 81% of marine species and 70% of terrestrial species died out, associated with the eruption of the Siberian Traps. It took well into the Triassic for life to recover from this catastrophe; on land, ecosystems took 30 million years to recover.

Prior to the introduction of the term Permian, rocks of equivalent age in Germany had been named the Rotliegend and Zechstein, and in Great Britain as the New Red Sandstone.

The term Permian was introduced into geology in 1841 by Sir Roderick Impey Murchison, president of the Geological Society of London, after extensive Russian explorations undertaken with Édouard de Verneuil in the vicinity of the Ural Mountains in the years 1840 and 1841. Murchison identified "vast series of beds of marl, schist, limestone, sandstone and conglomerate" that succeeded Carboniferous strata in the region. Murchison, in collaboration with Russian geologists, named the period after the surrounding Russian region of Perm, which takes its name from the medieval kingdom of Permia that occupied the same area hundreds of years prior, and which is now located in the Perm Krai administrative region. Between 1853 and 1867, Jules Marcou recognised Permian strata in a large area of North America from the Mississippi River to the Colorado River and proposed the name Dyassic, from Dyas and Trias, though Murchison rejected this in 1871. The Permian system was controversial for over a century after its original naming, with the United States Geological Survey until 1941 considering the Permian a subsystem of the Carboniferous equivalent to the Mississippian and Pennsylvanian.

The Permian Period is divided into three epochs, from oldest to youngest, the Cisuralian, Guadalupian, and Lopingian. Geologists divide the rocks of the Permian into a stratigraphic set of smaller units called stages, each formed during corresponding time intervals called ages. Stages can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratify global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the stage. The ages of the Permian, from youngest to oldest, are:

For most of the 20th century, the Permian was divided into the Early and Late Permian, with the Kungurian being the last stage of the Early Permian. Glenister and colleagues in 1992 proposed a tripartite scheme, advocating that the Roadian-Capitanian was distinct from the rest of the Late Permian, and should be regarded as a separate epoch. The tripartite split was adopted after a formal proposal by Glenister et al. (1999).

Historically, most marine biostratigraphy of the Permian was based on ammonoids; however, ammonoid localities are rare in Permian stratigraphic sections, and species characterise relatively long periods of time. All GSSPs for the Permian are based around the first appearance datum of specific species of conodont, an enigmatic group of jawless chordates with hard tooth-like oral elements. Conodonts are used as index fossils for most of the Palaeozoic and the Triassic.