Paleozoic Era

In geologic time , the Paleozoic Era, the first era in the Phanerozoic Eon , covers the time between roughly 544 million years ago (mya) and until 245 mya.

The Paleozoic Era spans six geologic time periods including the Cambrian Period (544 to 500 mya); Ordovician Period (500 mya to 440 mya); Silurian (440 mya to 410 mya); Devonian (410 mya to 360 mya); and the Carboniferous Period (360 mya to 286 mya) (in many modern geological texts, especially those in the United States, the time of Carboniferous Period is covered by two alternate geologic periods, the Mississippian Period [360 mya to 325 mya] and the Pennsylvanian Period [325 mya to 286 mya]. The final geologic time period in the Paleozoic Era is the Permian Period (286 mya to 245 mya).

The onset of the Paleozoic Era is marked by the "Cambrian explosion," the sudden appearance of numerous fossils . Although life certainly started in Precambrian time, The start of the Paleozoic Era marks the point at which life developed to a variety or organisms capable of leaving fossils. Although fossilization is difficult under any circumstances, organisms with structures such as shells have a much greater chance of leaving fossilized remains than did single celled microorganisms.

The Paleozoic Era spanned that period of geologic time during which the evolution of the first invertebrates, vertebrates, terrestrial (land-based) plants, bony fish, reptiles, insects, etc. took place. The end of the Paleozoic Era (approximately 245 mya) marks the largest mass extinction of species in Earth's history. During this mass extinction an estimated 90% of all Earth's marine species suddenly became extinct.

Six major continental landmasses developed during the Paleozoic Era. Although not located in their present global positions, parts of the modern continents can be traced to these landmasses. For example, continental crust now located in the North American continent was located near the equator during the Paleozoic Era. The forces of plate tectonics were active, and not only moved the continents but helped shape the continental margins though uplift and subduction. Enormous changes on sea state relative to the continents meant extensive flooding, marine transgression , and marine regression that added large sedimentary deposits (e.g., large limestone deposits). The abundance of organic life provided the start for abundant coal formation during the Carboniferous Period (Pennsylvanian Period and Mississippian Period).

See also Archean; Cenozoic Era; Cretaceous Period; Dating methods; Eocene Epoch; Evolution, evidence of; Fossil record; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Mesozoic Era; Miocene Epoch; Oligocene Epoch; Paleocene Epoch; Pennsylvanian Period; Pleistocene Epoch; Pliocene Epoch; Quaternary Period; Tertiary Period; Triassic Period

Pa·le·o·zo·ic / ˌpālēəˈzōik/ • adj. Geol. of, relating to, or denoting the era between the Precambrian eon and the Mesozoic era. Formerly called primary. ∎  [as n.] (the Paleozoic) the Paleozoic era or the system of rocks deposited during it.

Paleozoic See PALAEOZOIC.