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
Paleozoic era (pā´lēəzō´Ĭk), a major division (era) of geologic time (see Geologic Timescale, table) occurring between 570 to 240 million years ago. It is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (see each listed individually). During the hiatus between the late Precambrian and the Paleozoic era most of the evidence of the earth's early history was destroyed by erosion. From the beginning of the Paleozoic, shallow seas began to encroach on the continents. In North America, the era began with submerged geosynclines, or downward thrusts of the earth's crust, along the eastern, southeastern, and western sides of the continent, while the interior was dry land. As the era proceeded, the marginal seas periodically washed over the stable interior, leaving sedimentary deposits to mark their incursions. During the early part of the era, the area of exposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the geosynclines from the interior. Beginning in the Ordovician period, mountain building intermittently proceeded in the eastern part of the Appalachian geosyncline throughout the rest of the era, bringing in new sediments. Sediments washing from the Acadian Mts. filled the western part of the Appalachian geosyncline to form the famous coal swamps of the Carboniferous period. Uplift of the Appalachians caused the region to be never again inundated by vast marginal seas. Paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwanaland had either formed or was forming. By mid-Paleozoic, the collision of N America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By late Paleozoic, continental collisions formed the supercontinent Pangaea and resulted in some of the great mountain chains, including the Appalachians, Urals, and Tasmans. The most noteworthy feature of Paleozoic life is the sudden appearance of nearly all of the invertebrate animal phyla in great abundance at the beginning of the Cambrian. A few primitive fishlike invertebrates, and then vertebrates, appeared in the Cambrian and Ordovician, scorpions in the Silurian period, land invertebrates and amphibians in the Devonian, land reptiles in the Carboniferous, and marine reptiles in the Permian. All reptiles increased in number and in variety by the late Permian. The plant life of the Paleozoic era reached its climax in the Carboniferous and was much contracted in the Permian.