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{{Ediacaran_biota timeline}}
The '''Ediacaran''' Period ({{IPAEng|ˌiːdɪˈækərən}}, named after the [[Ediacara Hills]] of [[South Australia]]) is the last [[geological period]] of the [[Neoproterozoic]] Era, just preceding the [[Cambrian]] Period of the [[Paleozoic]] Era. Its status as an official geological period was ratified in March [[2004]] by the [[International Union of Geological Sciences]] (IUGS) and announced on [[May 13]] [[2004]], the first new geological period declared in 120 years.<ref name=Knoll2004>{{cite journal
 | author = Knoll, A.H.
 | coauthors = Walter, M.R., Narbonne, G.M., Christie-blick, N.
 | year = 2004
 | title = A new period for the geologic time scale
 | journal = Science(Washington)
 | volume = 305
 | issue = 5684
 | pages = 621-622
 | issn = 
 | doi = 
 | url = http://www.stratigraphy.org/ediacaran/Knoll_et_al_2004b.pdf 
 | accessdate = 
 }}</ref><ref name=Ogg2004>{{cite journal
 | author = Ogg, J.G.
 | year = 2004
 | title = Status of Divisions of the International Geologic Time Scale
 | journal = Lethaia
 | volume = 37
 | issue = 2
 | pages = 183-199
 | issn = 
 | doi = 
 | url = http://taylorandfrancis.metapress.com/index/PUNM6BQLNW1BJMFN.pdf 
 | accessdate = 2007-05-05
 }}</ref> The [[type section]] is in the [[Flinders Ranges]] in South Australia. It overlaps, but is shorter than the '''Vendian''' period, a name that was earlier proposed in [[Russia]].

==Base of the Ediacaran==
Although the Ediacaran Period does contain soft bodied [[fossil]]s, it is unusual in comparison to later periods because its beginning is not defined by a change in the [[fossil record]]. Rather, the beginning is defined at the base of a chemically distinctive [[carbonate]] layer, referred to as a "[[cap carbonate]]", because it caps glacial deposits and indicates a sudden climatic change at the end of an [[ice age]]. This bed is characterized by an unusual depletion of <sup>13</sup>C, and is considered by many scientists to be of global extent, although this is controversial. 

==Dating==
No [[Absolute dating|dating]] has been possible at the type section of the Ediacaran Period in South Australia. Therefore the age range of 635 to 542 million years before the present is based on correlations to other countries where dating has been possible. The base age of approximately 635 million years ago is based on U-Pb ([[uranium]]-[[lead]]) [[isochron dating]] from [[Namibia]].<ref name=Hoffmann2004>{{cite journal
 | author = Hoffmann, K.H.
 | coauthors = Condon, D.J., Bowring, S.A., Crowley, J.L.
 | year = 2004
 | date = [[2004-09-01]]
 | title = U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation
 | journal = Geology
 | volume = 32
 | issue = 9
 | pages = 817-820
 | issn = 
 | doi = 10.1130/G20519.1
 | url = http://geology.geoscienceworld.org/cgi/content/abstract/32/9/817 
 | accessdate =
 }}</ref> Applying this age to the base of the Ediacaran assumes that individual cap carbonates are synchronous around the world and that the correct cap carbonate layers have been correlated between Australian and Namibia. This is controversial because an age of about 580 million years has been obtained in association with glacial rocks in [[Tasmania]] which some scientists tentatively correlate with those just beneath the Ediacaran rocks of the Flinders Ranges.<ref name=Calver2004>{{cite journal
 | author = Calver, C.R.
 | coauthors = Black, L.P., Everard, J.L., Seymour, D.B.
 | year = 2004
 | date = [[2004-10-01]]
 | title = U-Pb zircon age constraints on late Neoproterozoic glaciation in Tasmania
 | journal = Geology
 | volume = 32
 | issue = 10
 | pages = 893-896
 | issn = 
 | doi = 10.1130/G20713.1
 | url = http://geology.geoscienceworld.org/cgi/content/abstract/32/10/893 
 | accessdate = 
 }}</ref> The age of the top is the same as the widely recognised age for the base of the [[Cambrian]] Period.<ref name=Ogg2004> </ref>  

==Biota==
{{main|Ediacaran biota}}

The animal fossil record from this period is sparse, possibly because animals had yet to evolve hard shells, which make for easier fossilization. The Ediacaran biota include the oldest definite [[multicellular organism]]s, and the most common types resemble segmented worms, fronds, disks, or immobile bags. They bear little resemblance to modern lifeforms, and their [[scientific classification|relationship]] even with the later lifeforms of the [[Cambrian explosion]] is difficult to interpret. More than 100 [[genus|genera]] have been described, and well known forms include ''[[Arkarua]]'', ''[[Charnia]]'', ''[[Dickinsonia]]'', ''[[Ediacaria]]'', ''[[Marywadea]]'', ''[[Onega (fossil)|Onega]]'', ''[[Pteridinium]]'', and ''[[Yorgia]]''.

==See also==
* [[List of fossil sites]] ''(with link directory)''

==References==
{{reflist|2}}

==External links==
* {{cite news
 | url = http://news.bbc.co.uk/1/hi/sci/tech/3721481.stm
 | title = Geological time gets a new period: Geologists have added a new period to their official calendar of Earth's history—the first in 120 years
 | publisher = BBC
 | date = 17 May, 2004
 }}
* {{cite web
 | title = Ediacaran Period
 | work = GeoWhen Database
 | url = http://www.stratigraphy.org/geowhen/stages/Ediacaran.html
 | accessdate = January 5
 | accessyear = 2006
 }}
* [http://www.ucmp.berkeley.edu/vendian/vendian.html Introduction to the Vendian Period]
* [http://members.tripod.com/~Cambrian/IntrotoEdiacaran  Introduction to the Ediacaran Fauna]
* [http://www.abc.net.au/catalyst/stories/s1785092.htm#transcript transcript] - ''[[Catalyst (TV series)|Catalyst]]'' ([[Australian Broadcasting Corporation]])
* [http://members.rediff.com/mistakenpoint/ Mistaken Point Fauna : The Discovery]

{{Proterozoic Footer}}

{{Commonscat|Ediacaran}}

[[Category:Proterozoic]]
[[Category:Fossils]]

[[br:Ediakareg]]
[[ca:Ediacarià]]
[[da:Ediacara]]
[[de:Ediacarium]]
[[et:Ediacara]]
[[fr:Édiacarien]]
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[[ja:エディアカラ紀]]
[[no:Ediacara]]
[[pl:Ediakaran]]
[[pt:Ediacarano]]
[[ru:Эдиакарий]]
[[fi:Ediacarakausi]]
[[sv:Edicara]]
[[vi:Kỷ Ediacara]]
[[zh:埃迪卡拉纪]]
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