The Paleozoic or Palaeozoic Era (from the Greek palaio, "old" and zoe, "life", meaning "ancient life") is the earliest of three geologic eras of the Phanerozoic eon. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed The Paleozoic spanned from roughly 542 mya to roughly 251 mya (ICS, 2004), and is subdivided into six geologic periods; from oldest to youngest they are: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 The Permian is a geologic period and system that extends from 299

Paleozoic life

Trilobites flourished throughout the lower Paleozoic era until becoming extinct in the Permian period

The Paleozoic covers the time from the first appearance of abundant, soft-shelled fossils to the time when the continents were beginning to be dominated by large, relatively sophisticated reptiles and relatively modern plants. Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. The Permian is a geologic period and system that extends from 299 FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. A continent is one of several large Landmasses on Earth. They are generally identified by Convention rather than any strict criteria with seven regions Plants are living Organisms belonging to the kingdom Plantae. The lower (oldest) boundary was classically set at the first appearance of creatures known as trilobites and archeocyathids. Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. The Archaeocyatha or archaeocyathids ("ancient cups" were Sessile The upper (youngest) boundary is set at a major extinction event 300 million years later, known as the Permian extinction. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial Modern practice sets the older boundary at the first appearance of a distinctive trace fossil called Trichophycus pedum. Trace fossils, also called ichnofossils (ˈɪknoʊfɒsɨl ιχνος or ikhnos meaning "trace" or "track" are geological records of biological Trichophycus pedum (or Treptichnus pedum; formerly Phycodes pedum) is regarded as the earliest widespread complex Trace fossil

At the start of the era, all life was confined to bacteria, algae, sponges and a variety of somewhat enigmatic forms known collectively as the Ediacaran fauna. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals The Ediacara (ˌiːdɪˈækərə formerly Vendian) biota are ancient lifeforms of the Ediacaran Period which represent the earliest known complex A large number of body plans appeared nearly simultaneously at the start of the era -- a phenomenon known as the Cambrian Explosion. The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex Animals around, as evidenced by the There is some evidence that simple life may already have invaded the land at the start of the Paleozoic, but substantial plants and animals did not take to the land until the Silurian and did not thrive until the Devonian. Although primitive vertebrates are known near the start of the Paleozoic, animal forms were dominated by invertebrates until the mid-Paleozoic. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate Fish populations exploded in the Devonian. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two During the late Paleozoic, great forests of primitive plants thrived on land forming the great coal beds of Europe and eastern North America. A forest is an area with a high density of Trees There are many definitions of a forest based on various criteria By the end of the era, the first large, sophisticated reptiles and the first modern plants (conifers) had developed.

Tectonics

Geologically, the Paleozoic starts shortly after the breakup of a supercontinent called Pannotia and at the end of a global ice age. In Geology, a supercontinent is a Landmass comprising more than one Continental core or Craton. Pannotia, first described by Ian W D Dalziel in 1997 is a hypothetical Supercontinent that existed from the Pan-African orogeny about 600 million years ago to the An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets (See Varanger glaciation and Snowball Earth). The Cryogenian (from Greek cryos "cold" and genesis "birth" is a Geologic period that lasted from. The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of Throughout the early Paleozoic, the Earth's landmass was broken up into a substantial number of relatively small continents. Toward the end of the era, the continents gathered together into a supercontinent called Pangaea, which included most of the Earth's land area. In Geology, a supercontinent is a Landmass comprising more than one Continental core or Craton. Pangaea, Pangæa or Pangea (pænˈdʒiːə from παν pan, meaning entire, and Γαῖα Gaea, meaning Earth in

Climate

The Early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway. However, as if to offset this trend, Gondwana moved south with considerable speed, so that, in Ordovician time, Most of West Gondwana (Africa and South America) lay directly over the South Pole. Gondwana (ɡɒnˈdwɑːnə originally Gondwanaland) was a southern Supercontinent that existed about 500 to 200 Ma ago The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. The Early Paleozoic climate was also strongly zonal, with the result that the "climate", in an abstract sense became warmer, but the living space of most organisms of the time -- the continental shelf marine environment -- became steadily colder. However, Baltica (Northern Europe and Russia) and Laurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate. Baltica redirects here For the Russian beer, see Baltika Breweries Baltica is a name applied by geologists to a late- Proterozoic, Laurentia (also known as the North American craton) like all Craton land was created as continents moved about the surface of the Earth The Early Paleozoic ended, rather abruptly, with the short, but apparently severe, Late Ordovician Ice Age. This cold spell caused the second-greatest mass extinction of Phanerozoic time. Over time, the warmer weather moved into the Paleozoic era.

The Middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the Ice Age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single The north-south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.

The Late Paleozoic was a time which has left us a good many unanswered questions. The Mississippian Epoch began with a spike in atmospheric oxygen, while carbon dioxide plummeted to unheard-of lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 These were far more severe than the brief Late Ordovician Ice; but, this time, the effects on world biota were inconsequential. By the Cisuralian, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangea created huge arid inland areas subject to temperature extremes. The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial

See also

• Geologic timescale

References and further reading

• British Palaeozoic Fossils, 1975, The Natural History Museum, London. The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other
• International Commission on Stratigraphy (ICS). Home Page. Retrieved on September 19, 2005.