Paleozoic

The Paleozoic (or Palaeozoic) Era ( /ˌpeɪliəˈzoʊɪk, ˌpæ-/; from the Greek palaios (παλαιός), 'old' and zoe (ζωή), 'life', meaning 'ancient life') is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from 541 to 251.902 million years ago, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era. The Paleozoic (or Palaeozoic) Era ( /ˌpeɪliəˈzoʊɪk, ˌpæ-/; from the Greek palaios (παλαιός), 'old' and zoe (ζωή), 'life', meaning 'ancient life') is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from 541 to 251.902 million years ago, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era. The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Arthropods, molluscs, fish, amphibians, synapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, it was dominated by various forms of organisms. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsids and synapsids were dominant and the first modern plants (conifers) appeared. The Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover. Recovery of life in the sea may have been much faster. The Paleozoic era began and ended with supercontinents and in between were the rise of mountains along the continental margins, and flooding and draining of shallow seas between the mountain ranges, in the interior of the continents. At its start, the supercontinent Pannotia broke up. 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 Gondwana (510 million years ago) formed or was forming. By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent of Pangaea and resulted in some of the great mountain chains, including the Appalachians, Ural Mountains, and mountains of Tasmania. There are six periods in the Paleozoic Era: Cambrian, Ordovician, Silurian, Devonian, Carboniferous (alternatively subdivided into the Mississippian Period and the Pennsylvanian Period), and the Permian. The Cambrian spans from 541 million years to 485 million years and is the first period of the Paleozoic era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any single period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, like trilobites. Almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, most of which later became the supercontinent Gondwana. The Ordovician spanned from approximately 485 million years to approximately 443 million years ago. The Ordovician was a time in Earth's history in which many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods, and coral. The most common forms of life, however, were trilobites, snails and shellfish. More importantly, the first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovician, Gondwana was at the south pole, early North America had collided with Europe, closing the Atlantic Ocean. Glaciation of Africa resulted in a major drop in sea level, killing off all life that had established along coastal Gondwana. Glaciation may have caused the Ordovician–Silurian extinction events, in which 60% of marine invertebrates and 25% of families became extinct, and is considered the first mass extinction event and the second deadliest. The Silurian spanned from 443 to 416 million years ago. The Silurian saw the rejuvenation of life as the Earth recovered from the previous glaciation. This period saw the mass evolution of fish, as jawless fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as sea scorpions, were still apex predators. Fully terrestrial life evolved, including early arachnids, fungi, and centipedes. The evolution of vascular plants (Cooksonia) allowed plants to gain a foothold on land. These early plants were the forerunners of all plant life on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, Siberia), Laurentia (North America), Baltica (Northern Europe), and Avalonia (Western Europe). The recent rise in sea levels allowed many new species to thrive in water. The Devonian spanned from 416 million years to 359 million years ago. Also known as 'The Age of the Fish', the Devonian featured a huge diversification of fish, including armored fish like Dunkleosteus and lobe-finned fish which eventually evolved into the first tetrapods. On land, plant groups diversified incredibly in an event known as the Devonian Explosion when plants made lignin allowing taller growth and vascular tissue: the first trees evolved, as well as seeds. This event also diversified arthropod life, by providing them new habitats. The first amphibians also evolved, and the fish were now at the top of the food chain. Near the end of the Devonian, 70% of all species became extinct in an event known as the Late Devonian extinction, which was the Earth's second mass extinction event.