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[[File:ICS Ordovician.jpg|thumb|right|Figure 1. ICS Ordovician timeline.<ref name=ICS12>International Commission on Stratigraphy."International Chronostratigraphic Chart v2015" Accessed Nov.8, 2018 [Online]. Available: https://www.britannica.com/science/Fortunian-Stage/media/1554753/133054</ref> ]]
<onlyinclude>The '''Ordovician''' was the second geological [[Geologic time scale|period]] of the [[Paleozoic]] era, extending from approximately 485.4 million to 443.8 million years ago.</onlyinclude> It is divided into Upper, Middle, and Lower [[Geologic epoch|epochs]](Figure 1).<ref name=ICS>International Commission on Stratigraphy."International Chronostratigraphic Chart v2018" Accessed Nov.8, 2018 [Online]. Available: http://www.stratigraphy.org/index.php/ics-chart-timescale</ref> This period is named after a northern Welsh tribe, the Ordovices. The name was first used by Dr. Charles Lapworth, an English geologist, in 1879.<ref name=GTS>Gradstein, F. M. "The Geologic Time Scale 2012". Volume 2. 1st ed. Amsterdam ; Boston: Elsevier, 2012.</ref>

Rapid and sustained [[biodiversity|biodiversification]] occurred throughout the Ordovician. The biodiversification during this period is sometimes referred to as the "Great Ordovician Biodiversification Event".<ref name=GTS/> Marine fauna and flora became more varied (Figure 2). Invertebrates were especially successful at diversifying at this time, particularly trilobites. There is some evidence that the first terrestrial plants may have developed in the Ordovician and the first mixed aquatic and land fauna may have also occurred. The oldest, fully vertebrate fossils in the geologic record appear at this time. The end of the Ordovician was marked by the Ordovician-Silurian extinction event, a [[mass extinction]] where a large number of species died off (Figure 3).<ref name=UCB>University of California, Museum of Paleontology."The Ordovician Period" Accessed Nov.12, 2018 [Online]. Available: http://www.ucmp.berkeley.edu/ordovician/ordovician.php</ref>

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File:Ordo dio.jpg|Figure 2. Ordovician diorama at Washington's National Museum of Natural History.<ref>WikiMedia Commons."File:Nmnh fg09.jpg" Accessed Nov.16, 2018 [Online]. Available: https://en.wikipedia.org/wiki/File:Nmnh_fg09.jpg</ref>
File:LibertyFormationSlab092313.jpg|Figure 3. Fossiliferous limestone slab from the Liberty Formation (Upper Ordovician) of Caesar Creek State Park.<ref>WikiMedia Commons."File:LibertyFormationSlab092313.jpg" Accessed Nov.16, 2018 [Online]. Available: https://en.wikipedia.org/wiki/File:LibertyFormationSlab092313.jpg</ref>
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[[Plate tectonics|Tectonic shifts]] during the Ordovician led to the [[supercontinent]] of Gondwana, the largest landmass at the time, moving towards the South Pole. Sea level fluctuated greatly during the Ordovician, rising and dropping throughout the period, occasionally flooding land areas and creating shallow inland seas. Gondwana moved far enough south by the Upper, or late, Ordovician, that a major [[glaciation]] occurred.<ref name=UCB/> The glaciation led to sea level dropping, as the forming land ice took up ocean water, and also led to [[climate]] fluctuations. This glaciation is thought to be a major contributing cause to the Ordovican-Silurian extinction event.<ref name=GTS/>

[[File:ChronostratChart2018-08.jpg|800px|thumb|center|Figure 4. The ICS Chronostratigraphic Chart<ref name=ICS/>]]

==For Further Reading==
*[[Geologic time scale]]
*[[Geologic period]]
*[[Glaciation]]
*[[Plate tectonics]]
*[[Stratigraphy]]
*Or explore a [[Special:Random|random page]]

==References==
{{reflist}}
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Ordovician - Revision history

Jmdonev: 1 revision imported

2dev>Jmdonev at 17:40, 19 November 2018