8/4/2014 Paleozoic - Wikipedia, the free encyclopedia

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  Phanerozoic

  Proterozoic

Paleozoic era

541 - 252.2 million years ago

Key events in the Paleozoic

An approximate timescale of

key Paleozoic events.

Axis scale: millions of years ago.

PaleozoicFrom Wikipedia, the free encyclopedia

The Paleozoic (or Palaeozoic) Era (/ˌpæliː ɵˈzoʊɪk/ or /ˌpeɪliː ɵˈzoʊɪk/; fromthe Greek palaios (παλαιός), "old" and zoe (ζωή), "life", meaning "ancient

life"[1]) is the earliest of three geologic eras of the Phanerozoic Eon, spanningfrom roughly 541 to 252.2 million years ago (ICS, 2004). It is the longest ofthe Phanerozoic eras, and is subdivided into six geologic periods (from oldestto youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous,and Permian. The Paleozoic comes after the Neoproterozoic Era of theProterozoic Eon, and is followed by the Mesozoic Era.

The Paleozoic was a time of dramatic geological, climatic, and evolutionarychange. The Cambrian Period witnessed the most rapid and widespreaddiversification of life in Earth's history, known as the Cambrian explosion, inwhich most modern phyla first appeared. Fish, arthropods, amphibians andreptiles all evolved during the Paleozoic. Life began in the ocean but eventuallytransitioned onto land, and by the late Paleozoic, it was dominated by variousforms 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 reptiles were dominant andthe first modern plants (conifers) appeared.

The Paleozoic Era ended with the largest mass extinction in Earth's history, thePermian–Triassic extinction event. The effects of this catastrophe were sodevastating that it took life on land 30 million years into the Mesozoic to

recover.[2] Recovery of life in the sea may have been much faster.[3]

Contents

1 Geology

1.1 Tectonic activity

2 Climate3 Flora

4 Fauna

5 See also

6 References and further reading

7 External links

Geology

In North America, the era began with deep sedimentary basins along the eastern, southeastern, and western sides ofthe continent, while the interior was dry land. As the era proceeded, the marginal seas periodically washed over thestable interior, leaving sedimentary deposits to mark their incursions. During the early part of the era, the area ofexposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the basins from theinterior. Beginning in the Ordovician Period, mountain building intermittently proceeded in the eastern part of theAppalachian region throughout the rest of the era, bringing in new sediments. Sediments washing from the AcadianMountains filled the western part of the Appalachian basins to form the famous coal swamps of the CarboniferousPeriod. In North America, carboniferous is not generally used. Instead, the time is divided between Mississippian and

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Neoproterozoic

Mesozoic

Cambrian

Ordovician

Silurian

Devonian

Carboniferous

Permian

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Land distribution early in the

Paleozoic, around 540 Ma

Pennsylvanian periods because of differences in the sedimentary rock deposited during that time. The Mississippian ischaracterized by limey sediments deposited in shallow seas, typically with abundant crinoidal fossils as in theBurlington fm. The Pennsylvanian typically is characterized by terrestrial sediments such as sands, shale and mostimportantly coal. Most of our oil and gas are obtained from Pennsylvanian sediments. Where this has been stripped,as in the Ozark domal region, oil is not typically available.

Paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions duringthe early Paleozoic. During the early Paleozoic, the huge continent Gondwanaland had either formed or was forming.By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and asubduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinentPangaea and resulted in some of the great mountain chains, including the Appalachians, Urals, and mountains ofTasmania.

Tectonic activity

Geologically, the Paleozoic starts shortly after the breakup of asupercontinent called Pannotia. Throughout the early Paleozoic, the Earth'slandmass was broken up into a substantial number of continents. Towardsthe end of the era, the continents gathered together into a supercontinentcalled Pangaea, which included most of the Earth's land area.

Climate

The Ordovician and Silurian periods were warm greenhouse periods, withthe highest sea levels of the Paleozoic (200 m above today's); the warmclimate was interrupted only by a 30 million years cool period, the Early Palaeozoic Icehouse, culminating in the

Hirnantian glaciation.[4]

The early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, asthe 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 andSouth America) lay directly over the South Pole. The early Paleozoic climate was also strongly zonal, with the resultthat the "climate", in an abstract sense became warmer, but the living space of most organisms of the time—thecontinental shelf marine environment—became steadily colder. However, Baltica (Northern Europe and Russia) andLaurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay inwaters which were at least temperate. The Early Paleozoic ended, rather abruptly, with the short, but apparentlysevere, late Ordovician ice age. This cold spell caused the second-greatest mass extinction of Phanerozoic time. Overtime, 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, butslowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and thenorthward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow seafloor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, althoughmuch less dramatically. The north–south temperature gradient also seems to have moderated, or metazoan life simplybecame hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwanabecame increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of MiddlePaleozoic 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 began with aspike in atmospheric oxygen, while carbon dioxide plummeted to unheard-of lows. This destabilized the climate andled to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief LateOrdovician Ice; but, this time, the effects on world biota were inconsequential. By the Cisuralian, both oxygen and

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An artist's impression of early land

plants

carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangaea created huge aridinland areas subject to temperature extremes. The Lopingian is associated with falling sea levels, increased carbondioxide and general climatic deterioration, culminating in the devastation of the Permian extinction.

Flora

While macroscopic plant life appeared early in the Paleozoic and possiblylate in the Neoproterozoic, it mostly remained aquatic until sometime in theSilurian and Devonian, when it began to transition onto dry land. Terrestrialflora reached its climax in the Carboniferous, when towering lycopsidrainforests dominated the tropical belt of Euramerica. Climate changecaused the Carboniferous Rainforest Collapse which fragmented thishabitat, diminishing the diversity of plant life in the late Carboniferous and

Permian.[5]

Fauna

A noteworthy feature of Paleozoic life is the sudden appearance of nearlyall of the invertebrate animal phyla in great abundance at the beginning of the Cambrian. The first vertebrates appearedin the form of primitive fish, which greatly diversified in the Silurian and Devonian. The first animals to venture onto dryland were the arthropods. Some fish had lungs and strong, bony fins and could crawl onto the land also. The bones intheir fins eventually evolved into legs and they became the first tetrapods. Amphibians were the dominant tetrapodsuntil the mid-Carboniferous, when climate change greatly reduced their diversity. Later, reptiles prospered and

continued to increase in number and variety by the late Permian.[5]

See also

Geologic timescalePrecambrianCenozoic

Mesozoic

References and further reading

1. ^ "Paleozoic" (http://www.etymonline.com/index.php?term=Paleozoic&allowed_in_frame=0). Online EtymologyDictionary.

2. ^ Sahney, S. and Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time"(http://journals.royalsociety.org/content/qq5un1810k7605h5/fulltext.pdf) (PDF). Proceedings of the Royal Society:

Biological 275 (1636): 759–65. doi:10.1098/rspb.2007.1370 (http://dx.doi.org/10.1098%2Frspb.2007.1370).PMC 2596898 (//www.ncbi.nlm.nih.gov/pmc/articles/PMC2596898). PMID 18198148(//www.ncbi.nlm.nih.gov/pubmed/18198148).

3. ^ url=http://www.economist.com/node/16524904

4. ^ Munnecke, A.; Calner, M.; Harper, D. A. T.; Servais, T. (2010). "Ordovician and Silurian sea-water chemistry, sea

level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology 296 (3–4): 389–413.doi:10.1016/j.palaeo.2010.08.001 (http://dx.doi.org/10.1016%2Fj.palaeo.2010.08.001).

5. ̂a b Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapoddiversification in Euramerica" (http://geology.geoscienceworld.org/cgi/content/abstract/38/12/1079) (PDF). Geology

38 (12): 1079–1082. doi:10.1130/G31182.1 (http://dx.doi.org/10.1130%2FG31182.1).

British Palaeozoic Fossils, 1975, The Natural History Museum, London.

"International Commission on Stratigraphy (ICS)" (http://www.stratigraphy.org/). Home Page. Retrieved

September 19, 2005.

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Preceded

by

ProterozoicEon

Phanerozoic Eon

Paleozoic Era Mesozoic Era Cenozoic Era

Cambrian O rdovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene 4ry

External links

60+ images of Paleozoic Foraminifera (http://www.foraminifera.eu/querydb.php?

&period=Carboniferous&aktion=suche)

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Categories: Geological history of Earth Paleozoic

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