DEFINITION OF PERMIAN

The last period in the Paleozoic era, lasting from

290 million to 248 million years ago, and the corresponding

system of rocks. Sir Roderick Murchison named it in 1841

after the Perm region of northern Russia where rocks of this

age were first studied in detail. The supercontinent of Pangea

included most of the planet’s landmasses during the Permian,

and this continental landmass extended from the South Pole,

across the equator to high northern latitudes, with a wide

Tethys Sea forming an open wedge of water near the equator.

The Siberian continental block collided with Laurasia in the

Permian, forming the Ural Mountains. Most of Pangea was

influenced by hot and dry climate conditions and saw the formation

of continental red-bed deposits and large-scale crossbedded

sandstones such as the Coconino sandstone of the

southwestern United States, and the New Red sandstone of

the United Kingdom. Ice sheets covered the south-polar

region, amplifying already low sea levels so they fell below

the continental shelves, causing widespread mass extinctions.

The glaciations continued to grow in intensity through the

Permian and, together with weathering of continental calcsilicates,

were able to draw enough CO2 out of the atmosphere

to drastically lower global temperatures. This dramatic

climate change enhanced the already widespread extinctions,

killing off many species of corals, brachiopods, ammonoids,

and foraminifers in one of history’s greatest mass extinctions,

in which about 70–90 percent of all marine invertebrate

species perished, as did large numbers of land mammals.

See also MASS EXTINCTIONS; PANGEA; STRATIGRAPHY;

SUPERCONTINENT CYCLE.

petrogenesis See PETROLOGY.

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