Editing Ediacaran

{{Short description|Third and last period of the Neoproterozoic Era}}
{{Use dmy dates|date=July 2018}}
{{Infobox geologic timespan
| name                         = Ediacaran
| color                        = Ediacaran
| top_bar                      = all time
| time_start                   = 635
| time_start_prefix            = ~
| time_end                     = 538.8
| time_end_uncertainty         = 0.2
| image_map                    = Mollweide Paleographic Map of Earth, 600 Ma (Ediacaran Period).png
| caption_map                  = A map of Earth as it appeared during the mid-Ediacaran, {{circa}} 600 Ma
| image_outcrop                =
| caption_outcrop              =
| image_art                    =
| caption_art                  =
<!--Chronology-->  
| timeline                     = Ediacaran
<!--Etymology-->
| name_formality               = Formal
| name_accept_date             = 1990
| alternate_spellings          =
| synonym1                     =
| synonym1_coined              =
| synonym2                     =
| synonym2_coined              =
| synonym3                     =
| synonym3_coined              =
| nicknames                    =
| former_names                 =
| proposed_names               =
<!--Usage Information--> 
| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
| formerly_used_by             =
| not_used_by                  =
<!--Definition-->
| chrono_unit                  = Period
| strat_unit                   = System
| proposed_by                  =
| timespan_formality           = Formal
| lower_boundary_def           =
* Worldwide distinct cap carbonates.
* Beginning of a distinctive pattern of secular changes in [[carbon isotope]]s.
| lower_gssp_location          = Enorama Creek section, [[Flinders Ranges]], [[South Australia]]
| lower_gssp_coords            = {{Coord|31.3314|S|138.6334|E|display=inline}}
| lower_gssp_accept_date       = March 2004<ref>{{cite journal |last1=Knoll |first1=Andrew H. |last2=Walter |first2=Malcolm R. |last3=Narbonne |first3=Guy M. |last4=Christie-Black |first4=Nicholas |title=The Ediacaran Period: a new addition to the geologic time scale |journal=Lethaia |date=3 March 2006 |volume=39 |issue=1 |pages=13–30 |doi=10.1080/00241160500409223 |bibcode=2006Letha..39...13K |url=https://stratigraphy.org/gssps/files/ediacaran.pdf |access-date=6 December 2020}}</ref>
| upper_boundary_def           = Appearance of the [[Trace fossil|Ichnofossil]] ''[[Treptichnus pedum]]''
| upper_gssp_location          = [[Fortune Head|Fortune Head section]], [[Newfoundland]], [[Canada]]
| upper_gssp_coords            = {{Coord|47.0762|N|55.8310|W|display=inline}}
| upper_gssp_accept_date       = 1992<ref>{{cite journal |last1=Brasier |first1=Martin |last2=Cowie |first2=John |last3=Taylor |first3=Michael |title=Decision on the Precambrian-Cambrian boundary stratotype |journal=Episodes |volume=17 |url=https://stratigraphy.org/gssps/files/fortunian.pdf |access-date=6 December 2020}}</ref>
<!--Atmospheric and Climatic Data-->
| o2                           = 8
| co2                          = 4500
| temp                         = 17
| sea_level                    =
}}

The '''Ediacaran''' ({{IPAc-en|pron|ˌ|iː|d|i|ˈ|æ|k|ər|ə|n|,_|ˌ|ɛ|d|i|-}} {{respell|EE|dee|AK|ər|ən|,_|ED|ee|-}})<ref>{{dictionary.com|Ediacaran}}</ref> is a [[geological period]] of the [[Neoproterozoic]] [[geologic era|Era]] that spans 96 million years from the end of the [[Cryogenian]] Period at 635 [[Million years ago|Mya]] to the beginning of the [[Cambrian]] Period at 538.8 Mya.<ref name="StratChart 2022">{{cite web |title=Stratigraphic Chart 2022 |url=https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |publisher=International Stratigraphic Commission |date=February 2022 |access-date=20 April 2022}}</ref> It is the last period of the [[Proterozoic]] [[geologic eon|Eon]] as well as the last of the so-called "[[Precambrian]] supereon", before the beginning of the subsequent Cambrian Period marks the start of the [[Phanerozoic]] Eon, where recognizable [[fossil]] evidence of [[life]] becomes common.

The Ediacaran Period is named after the [[Ediacara Hills]] of [[South Australia]], where [[trace fossil]]s of a diverse community of previously unrecognized lifeforms (later named the [[Ediacaran biota]]) were first discovered by geologist [[Reg Sprigg]] in 1946.<ref>{{cite journal|last1=Sprigg|first1=Reg. C.|title=Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia|journal=Transactions of the Royal Society of South Australia|date=1947|volume=71|issue=2|pages=212–224|url=https://www.biodiversitylibrary.org/page/41347851#page/234/mode/1up}}</ref> Its status as an official geological period was ratified in 2004 by the [[International Union of Geological Sciences]] (IUGS), making it the first new geological period declared in 120 years.<ref name=Knoll2004a/><ref name=Knoll2004>{{cite journal
 | author = Knoll, A. H.
 | date = 30 July 2004
 | title = A new period for the geologic time scale
 | journal = Science
 | volume = 305
 | issue = 5684
 | pages = 621–622
 | doi = 10.1126/science.1098803
 | url = http://www.stratigraphy.org/bak/ediacaran/Knoll_et_al_2004b.pdf 
 | pmid = 15286353
 | last2 = Walter
 | first2 = MR
 | last3 = Narbonne
 | first3 = G. M
 | last4 = Christie-Blick
 | first4 = N 
 | s2cid = 32763298
 }}</ref><ref name=Knoll2006>{{cite journal
 |author1         = Knoll, A. H.
 |author2         = Walter, M. R.
 |author3         = Narbonne, G. M.
 |author4         = Christie-Blick, N.
 |name-list-style = amp
 |date            = March 2006
 |title           = The Ediacaran Period: A new addition to the geologic time scale
 |journal         = Lethaia
 |volume          = 39
 |issue = 1
 |pages           = 13–30
 |url             = http://geol.queensu.ca/people/narbonne/KnollWalterNarbonneChristieBlick_Lethaia_2006.pdf
 |doi             = 10.1080/00241160500409223
 |bibcode = 2006Letha..39...13K
 |url-status         = dead
 |archive-url      = https://web.archive.org/web/20070221084915/http://geol.queensu.ca/people/narbonne/KnollWalterNarbonneChristieBlick_Lethaia_2006.pdf
 |archive-date     = 2007-02-21
}}</ref> Although the period took [[namesake]] from the Ediacara Hills in the [[Nilpena Ediacara National Park]], the [[Global Boundary Stratotype Section and Point|type section]] is actually located in the bed of the Enorama Creek<ref>{{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 = 2004-05-17
 | location=London}} Accessed 27 December 2010.</ref> within the Brachina Gorge<ref>[http://www.samuseum.sa.gov.au/page/default.asp?site=1&page=Newsletter&id=876&fragPage=1 South Australian Museum Newsletter April 2005] {{Webarchive|url=https://web.archive.org/web/20110217013850/http://www.samuseum.sa.gov.au/page/default.asp?site=1&page=Newsletter&id=876&fragPage=1 |date=17 February 2011 }} Accessed 9 August 2010.</ref> in the [[Ikara-Flinders Ranges National Park]], at {{coord|31|19|53.8|S|138|38|0.1|E|display=inline}}, approximately {{cvt|55|km}} southeast of the Ediacara Hills fossil site.

The Ediacaran marks the first widespread appearance of complex [[multicellular]] [[fauna]] following the end of the Cryogenian global [[glaciation]] known as the [[Snowball Earth]]. The relatively sudden [[evolutionary radiation]] event, known as the [[Avalon Explosion]], is represented by now-extinct, relatively simple [[soft-bodied organism|soft-bodied]] [[animal]] [[Phylum|phyla]] such as [[Proarticulata]] ([[bilaterian]]s with simple [[joint|articulation]], e.g. ''[[Dickinsonia]]'' and ''[[Spriggina]]''), [[Petalonamae]] ([[sea pen]]-like animals, e.g. ''[[Charnia]]''), [[Aspidella]] (radial-shaped animals, e.g. ''[[Cyclomedusa]]'') and [[Trilobozoa]] (animals with [[Symmetry in biology#Subtypes of radial symmetry|tri-radial symmetry]], e.g. ''[[Tribrachidium]]''). Most of these organisms appeared during or after the Avalon explosion 575 million years ago and died out during the [[End-Ediacaran extinction]] event 539 million years ago. Forerunners of some modern animal phyla also appeared during this period, including [[cnidarian]]s and early [[bilaterian]]s, as well as [[mollusc]]-like ''[[Kimberella]]''. Hard-bodied organisms with [[mineralized tissue|mineralized]] [[exoskeleton|shell]]s also began their fossil record in the last few million years of the Ediacaran.<ref>{{cite journal | author = Grant, S.W. | year = 1990 | title = Shell structure and distribution of Cloudina, a potential index fossil for the terminal Proterozoic | journal = American Journal of Science | issue = 290–A | pages = 261–294 | url = http://lib.bioinfo.pl/pmid:11538690 | access-date = 2008-07-19 | pmid = 11538690 | volume = 290-A | archive-url = https://web.archive.org/web/20110522041703/http://lib.bioinfo.pl/pmid:11538690 | archive-date = 2011-05-22 }}</ref>

The supercontinent [[Pannotia]] formed and broke apart by the end of the period. The Ediacaran also witnessed several [[ice age|glaciation event]]s, such as the [[Gaskiers glaciation|Gaskiers]] and [[Baykonurian glaciation]]s. The [[Shuram excursion]] also occurred during this period, but its glacial origin is unlikely.

==Ediacaran vs. Vendian==
{{See also|Riphean (stage)|Jotnian}}
The Ediacaran Period overlaps but is shorter than the '''Vendian''' Period (650 to 543 million years ago), a name that was earlier, in 1952, proposed by Russian geologist and [[paleontologist]] [[Boris Sergeyevich Sokolov|Boris Sokolov]]. The Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian.<ref name= Sokolov1952>{{cite journal
 | author = B. M. Sokolov
 | year = 1952
 | title = On the age of the old sedimentary cover of the Russian Platform
 | journal = Izvestiya Akademii Nauk SSSR, Seriya Eologicheskaya
 | volume = 5
 | pages = 21–31
}}</ref><ref name="Sokolov1997">Sokolov, B.S. (1997). "Essays on the Advent of the Vendian System." 153 pp. [[KMK Scientific Press]], Moscow. (in Russian)</ref>

Paleontological substantiation of this boundary was worked out separately for the [[siliciclastic]] basin (base of the [[Baltic Sea|Baltic]] Stage of the [[East European craton|Eastern European Platform]]<ref name=Sokolov1965>Sokolov B. S. (1965) "Abstracts of All-Union Symposium on Paleontology of the Precambrian and Early Cambrian." Nauka, Novosibirsk.</ref>) and for the [[carbonate]] basin (base of the [[Tommotian]] stage of the [[Siberian Platform]]).<ref name=Rozanov1969>{{cite journal
 |author1=Rozanov, A.Y. |author2=Missarzhevskij, V.V. |author3=Volkova, N.A. |author4=Voronova, L.G. |author5=Krylov, I.N. |author6=Keller, B.M. |author7=Korolyuk, I.K. |author8=Lendzion, K. |author9=Michniak, R. |author10=Pykhova, N.G. |author11= Sidorov, A.D. |name-list-style=amp| year = 1969
 | title = The Tommotian Stage and the problem of the lower boundary of the Cambrian
 | journal = Trudy Geologičeskogo Instituta AN SSSR
 | volume = 206
 | pages = 1–380
}}</ref>
The lower boundary of the Vendian was suggested to be defined at the base of the [[Varanger Peninsula|Varanger]] (Laplandian [[Stage (stratigraphy)|stage]]) [[tillite]]s.<ref name= Sokolov1997/><ref name=Fedonkin2007>{{cite web |url=http://vendian.net76.net/Vendian_vs_Ediacaran.htm |title=Vendian versus Ediacaran: priorities, contents, prospectives |author1=M. A. Fedonkin |author2=B. S. Sokolov |author3=M. A. Semikhatov |author4=N. M. Chumakov |year=2007 |url-status=dead |archive-url=https://web.archive.org/web/20111004184527/http://vendian.net76.net/Vendian_vs_Ediacaran.htm |archive-date=October 4, 2011 }} In: {{cite web |url=http://www.geosci.monash.edu.au/precsite/docs/workshop/moscow07/transaction.pdf |title=The Rise and Fall of the Vendian (Ediacaran) Biota |date=August 20–31, 2007 |work=Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493n Moscow: GEOS |archive-url=https://web.archive.org/web/20121122062305/http://www.geosci.monash.edu.au/precsite/docs/workshop/moscow07/transaction.pdf |archive-date=22 November 2012 |url-status=dead }} (82mb)</ref>

The Vendian in its type area consists of large subdivisions such as Laplandian, [[Redkino]], [[Kotlin Island|Kotlin]] and [[Rovno]] regional stages with the globally traceable subdivisions and their boundaries, including its lower one.

The Redkino, Kotlin and Rovno regional stages have been substantiated in the type area of the Vendian on the basis of the abundant organic-walled [[microfossil]]s, megascopic algae, [[metazoan]] body fossils and [[ichnofossil]]s.<ref name=Sokolov1997/><ref name=SokolovFedonkin1984>{{Cite journal| doi = 10.1134/S0869593808060014| title = The Yudomian of Siberia, Vendian and Ediacaran systems of the International stratigraphic scale| year = 2008| last1 = Khomentovsky | first1 = V. V.| journal = Stratigraphy and Geological Correlation| volume = 16| issue = 6| pages = 581–598 |bibcode = 2008SGC....16..581K | s2cid = 128966206}}</ref>

The lower boundary of the Vendian could have a [[biostratigraphic]] substantiation as well taking into consideration the worldwide occurrence of the Pertatataka assemblage of giant acanthomorph [[acritarch]]s.<ref name=Fedonkin2007/>

==Upper and lower boundaries==
[[File:Ediacaran-GSSP-IMGP6652-.jpg|thumb|250px|The 'golden spike' (bronze disk in the lower section of the image) or 'type section' of the [[Global Boundary Stratotype Section and Point]] (GSSP) for the base of the Ediacaran System]]
[[File:Ediacaran GSSP - closeup.JPG|thumb|The 'golden spike' marking the GSSP]]
The Ediacaran Period (c. 635–538.8 Mya) represents the time from the end of global [[Marinoan glaciation]] to the first appearance worldwide of somewhat complicated trace fossils (''[[Treptichnus pedum]]'' (Seilacher, 1955)).<ref name=Knoll2004a>A. Knoll, M. Walter, G. Narbonne, and N. Christie-Blick (2004) "[http://www.stratigraphy.org/bak/ediacaran/Knoll_et_al_2004a.pdf The Ediacaran Period: A New Addition to the Geologic Time Scale.]" Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy.</ref>

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 that is referred to as a "[[cap carbonate]]", because it caps glacial deposits.

This bed is characterized by an unusual depletion of <sup>13</sup>[[Carbon|C]] that indicates a sudden climatic change at the end of the [[Marinoan]] [[ice age]]. The lower [[GSSP|global boundary stratotype section (GSSP)]] of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina [[diamictite]] in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia.

The [[GSSP]] of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the [[Tommotian]] Stage in [[Siberia]] which was selected on the basis of the ichnofossil ''[[Treptichnus pedum]]'' (Seilacher, 1955). In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition.

Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and [[ichnofossil]]s are disputable.<ref name=Fedonkin2007/><ref name=Comments2004>Comments By B. S. Sokolov, M. A. Semikhatov, And M. A. Fedonkin. (2004) Appendix 2 in: "[http://www.stratigraphy.org/bak/ediacaran/Knoll_et_al_2004a.pdf The Ediacaran Period: A New Addition to the Geologic Time Scale.]" Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy. pp. 32–34</ref>

Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation){{vague|date=June 2013}} and usually siliciclastic sediments laterally replace the cap carbonates in a rather short distance but cap carbonates do not occur above every tillite elsewhere{{clarify|reason=location not specified|date=May 2013}} in the world.

The C-isotope chemostratigraphic characteristics obtained for contemporaneous cap carbonates in different parts of the world may be variable in a wide range owing to different degrees of secondary alteration of carbonates, dissimilar criteria used for selection of the least altered samples, and, as far as the C-isotope data are concerned, due to primary lateral variations of δ <sup>l3</sup>C<sub>carb</sub> in the upper layer of the ocean.<ref name=Fedonkin2007/><ref name= Bristow2008>{{cite journal
 |author1      = Bristow, T. F.
 |author2      = Kennedy, M. J.
 |year         = 2008
 |title        = Carbon isotope excursions and the oxidant budget of the Ediacaran atmosphere and ocean
 |journal      = Geology
 |volume       = 36
 |issue        = 11
 |pages        = 863–866
 |url          = http://taylorandfrancis.metapress.com/index/PUNM6BQLNW1BJMFN.pdf
 |access-date  = 2007-05-05
 |doi          = 10.1130/G24968A.1
 |bibcode      = 2008Geo....36..863B
 |archive-date = 7 May 2020
 |archive-url  = https://web.archive.org/web/20200507214320/http://taylorandfrancis.metapress.com/index/PUNM6BQLNW1BJMFN.pdf
 |url-status   = dead
}}</ref>

Furthermore, [[Oman]] presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram<ref name="LeGuerroue2006a">{{cite journal
|author1=Le Guerroué, E. |author2=Allen, P. A. |author3=Cozzi, A. | year = 2006
| title =Chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in Earth history: The Neoproterozoic Shuram Formation (Nafun Group, Oman).
| journal = Precambrian Research
| volume = 146
| issue = 1–2
| pages = 68–92
| doi = 10.1016/j.precamres.2006.01.007
|bibcode=2006PreR..146...68L}}</ref> Formation that is clearly away from any glacial evidence<ref name=LeGuerroue2006b>{{cite journal
| author = Le Guerroué, E. |author2=Allen, P. A. |author3=Cozzi, A. |author4=Etienne, J. L. |author5=Fanning, C. M.
| year = 2006
| title =50 Myr recovery from the largest negative ''δ''<sup>13</sup>C excursion in the Ediacaran ocean
| journal = Terra Nova
| volume = 18
| issue = 2
| pages = 147–153
| doi = 10.1111/j.1365-3121.2006.00674.x
| url = http://www3.interscience.wiley.com/journal/118624047/abstract
| archive-url = https://archive.today/20130105074949/http://www3.interscience.wiley.com/journal/118624047/abstract
| url-status = dead
| archive-date = 2013-01-05
|bibcode=2006TeNov..18..147L|s2cid=140710102 }}</ref> strongly questioning systematic association of negative δ <sup>l3</sup>C<sub>carb</sub> excursion and glacial events.<ref name=LeGuerroue2006c>{{cite journal
| author = Le Guerroué, E.
|author2=Allen, P. A. |author3=Cozzi, A. 
| year = 2006
| title =Parasequence development in the Ediacaran Shuram Formation (Nafun Group, Oman): primary origin stratigraphic test of negative carbon isotopic ratios
| journal = Basin Research
| volume = 18
| pages = 205–220
| doi = 10.1111/j.1365-2117.2006.00292.x 
| url = http://www3.interscience.wiley.com/journal/118629748/abstract
| archive-url = https://archive.today/20130105102240/http://www3.interscience.wiley.com/journal/118629748/abstract
| url-status = dead
| archive-date = 2013-01-05
| issue = 2
| bibcode =2006BasR...18..205L|s2cid=128910191 }}</ref> Also, the [[Shuram excursion]] is prolonged and is estimated to last for ~9.0 Myrs.<ref>{{Cite journal|title=Rock magnetic cyclostratigraphy of the Doushantuo Formation, South China and its implications for the duration of the Shuram carbon isotope excursion|last1=Gong|first1=Zheng|last2=Kodama|first2=Kenneth|year=2017|last3=Li|first3=Yong-Xiang|doi=10.1016/j.precamres.2016.12.002|volume=289|journal=Precambrian Research|pages=62–74|bibcode=2017PreR..289...62G}}</ref>

As to the ''Treptichnus pedum'', a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky, because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the level of ''T. pedum'' in [[Namibia]], [[Spain]] and [[Newfoundland (island)|Newfoundland]], and possibly, in the [[western United States]]. The stratigraphic range of ''T. pedum'' overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.<ref name=Fedonkin2007/><ref name= Ragozina2007>A. Ragozina, D. Dorjnamjaa, A. Krayushkin, E. Serezhnikova (2008). "[http://vendian.net76.net/Treptichnus_pedum.htm ''Treptichnus pedum'' and the Vendian-Cambrian boundary] {{Webarchive|url=https://web.archive.org/web/20111004184532/http://vendian.net76.net/Treptichnus_pedum.htm |date=4 October 2011 }}". 33 Intern. Geol. Congr. August 6–14, 2008, Oslo, Norway. Abstracts. Section HPF 07 Rise and fall of the Ediacaran (Vendian) biota. P. 183.</ref>

== Subdivisions ==
[[File:Nou Fonts Ediacaran.jpg|thumb|
Outcrops of Ediacaran micaschists and marble (c. 600 Ma) in the eastern Pyrenees (commune of Fontpédrouse, France).<ref>B. Laumonier et al., [http://ficheinfoterre.brgm.fr/Notices/1099N.pdf ''Notice explicative de la feuille Prats-de-Mollo-La-preste (1099) à 1/50 000''], BRGM Éditions, Orléans, 2015, pages 22-23 (bC1 - « ...niveau de marbres calcaires et dolomitiques M1...(dans les) hautes vallées de la Ribérole et de la Carança M1 est formé de 2 ou 3 niveaux décamétriques très continus.  », ''ficheinfoterre.brgm.fr''.</ref>]]
The Ediacaran Period is not yet formally subdivided, but a proposed scheme<ref name="Xiao2016">{{cite journal | title=Towards an Ediacaran Time Scale: Problems, Protocols, and Prospects | first1=Shuhai | last1=Xiao | first2=Guy M. | last2=Narbonne | first3=Chuanming | last3=Zhou | first4=Marc | last4=Laflamme | first5=Dmitriy V. | last5=Grazhdankin | first6=Malgorzata | last6=Moczydlowska-Vidal | first7=Huan | last7=Cui | journal=Episodes | year=2016 | volume=39 | issue=4 | pages=540555 | doi=10.18814/epiiugs/2016/v39i4/103886 | doi-access=free }}</ref> recognises an Upper Ediacaran whose base corresponds with the [[Gaskiers glaciation]], a Terminal Ediacaran Stage starting around {{Ma|550}}, a preceding stage beginning around 575 Ma with the earliest widespread [[Ediacaran biota]] fossils; two proposed schemes differ on whether the lower strata should be divided into an Early and Middle Ediacaran or not, because it is not clear whether the Shuram excursion (which would divide the Early and Middle) is a separate event from the Gaskiers, or whether the two events are correlated.

==Absolute dating==
The [[Absolute dating|dating]] of the rock type section of the Ediacaran Period in South Australia has proven uncertain due to lack of overlying igneous material. Therefore, the age range of 635 to 538.8 million years is based on [[Stratigraphy|correlations]] to other countries where dating has been possible. The base age of approximately 635 million years is based on [[Uranium–lead dating|U–Pb]] ([[uranium]]–[[lead]]) and [[Rhenium–osmium dating|Re–Os]] ([[rhenium]]–[[osmium]]) dating from Africa, China, North America, and Tasmania.<ref>{{Cite journal |last1=Rooney |first1=Alan D. |last2=Strauss |first2=Justin V. |last3=Brandon |first3=Alan D. |last4=Macdonald |first4=Francis A. |date=2015 |title=A Cryogenian chronology: Two long-lasting synchronous Neoproterozoic glaciations |url=http://pubs.geoscienceworld.org/geology/article/43/5/459/131888/A-Cryogenian-chronology-Two-longlasting |journal=Geology |language=en |volume=43 |issue=5 |pages=459–462 |doi=10.1130/G36511.1 |bibcode=2015Geo....43..459R |issn=1943-2682}}</ref><ref>{{Cite journal |last1=Rooney |first1=Alan D. |last2=Yang |first2=Chuan |last3=Condon |first3=Daniel J. |last4=Zhu |first4=Maoyan |last5=Macdonald |first5=Francis A. |date=2020-06-01 |title=U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath |url=https://pubs.geoscienceworld.org/gsa/geology/article/48/6/625/583510/UPb-and-ReOs-geochronology-tracks-stratigraphic |journal=Geology |language=en |volume=48 |issue=6 |pages=625–629 |doi=10.1130/G47246.1 |bibcode=2020Geo....48..625R |s2cid=218815302 |issn=0091-7613}}</ref><ref>{{Cite journal |last1=Zhang |first1=Shihong |last2=Jiang |first2=Ganqing |last3=Zhang |first3=Junming |last4=Song |first4=Biao |last5=Kennedy |first5=Martin J. |last6=Christie-Blick |first6=Nicholas |date=2005 |title=U-Pb sensitive high-resolution ion microprobe ages from the Doushantuo Formation in south China: Constraints on late Neoproterozoic glaciations |url=https://pubs.geoscienceworld.org/geology/article/33/6/473-476/103786 |journal=Geology |language=en |volume=33 |issue=6 |pages=473 |doi=10.1130/G21418.1 |bibcode=2005Geo....33..473Z |issn=0091-7613}}</ref><ref>{{Citation |last=Schmitz |first=M.D. |title=Radiometric ages used in GTS2012 |date=2012 |url=https://linkinghub.elsevier.com/retrieve/pii/B9780444594259150024 |work=The Geologic Time Scale |pages=1045–1082 |publisher=Elsevier |language=en |doi=10.1016/b978-0-444-59425-9.15002-4 |isbn=978-0-444-59425-9 |access-date=2022-04-02}}</ref><ref>{{Cite journal |last1=Calver |first1=C.R. |last2=Crowley |first2=J.L. |last3=Wingate |first3=M.T.D. |last4=Evans |first4=D.A.D. |last5=Raub |first5=T.D. |last6=Schmitz |first6=M.D. |date=2013 |title=Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia |url=http://pubs.geoscienceworld.org/geology/article/41/10/1127/131079/Globally-synchronous-Marinoan-deglaciation |journal=Geology |language=en |volume=41 |issue=10 |pages=1127–1130 |doi=10.1130/G34568.1 |bibcode=2013Geo....41.1127C |issn=1943-2682}}</ref>

== Biota ==
{{Main|Ediacaran biota}}
[[File:Archaeaspinus_fedonkini.jpg|thumb|left|''[[Archaeaspinus]]'', a representative of [[phylum]] [[Proarticulata]] which also includes ''[[Dickinsonia]]'', ''[[Karakhtia]]'' and numerous other organisms. They are members of the [[Ediacaran biota]].<ref name="book1">{{Cite book|url=https://books.google.com/books?id=KsFFIrJ8IxEC&dq=Archaeaspinus&pg=PA261|title=The Rise of Animals: Evolution and Diversification of the Kingdom Animalia|first1=Mikhail A.|last1=Fedonkin |first2=James G.|last2=Gehling |first3=Kathleen|last3=Grey|first4=Guy M.|last4=Narbonne|first5=Patricia|last5=Vickers-Rich |date=Mar 16, 2007|publisher=JHU Press|isbn=9780801886799|access-date=August 7, 2022|via=Google Books}}</ref>]]

The fossil record from most of the Ediacaran Period is sparse, as more easily fossilized hard-shelled animals did not evolve until the latest Ediacaran. The Ediacaran biota include the oldest definite [[multicellular organism]]s (with specialized tissues), the most common types of which resemble segmented worms, fronds, disks, or immobile bags. Among largely undisputed animals, ''[[Auroralumina]]'' and ''[[Haootia]]'' were [[cnidarian|cnidarians]], while ''[[Yilingia]]'' represented the motile [[Bilateria|bilaterians]].<ref>{{cite journal |last1=Dunn |first1=F. S. |last2=Kenchington |first2=C. G. |last3=Parry |first3=L. A. |last4=Clark |first4=J. W. |last5=Kendall |first5=R. S. |last6=Wilby |first6=P. R. |title=A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK |journal=Nature Ecology & Evolution |date=25 July 2022 |volume=6 |issue=8 |pages=1095–1104 |doi=10.1038/s41559-022-01807-x |pmid=35879540 |pmc=9349040 |bibcode=2022NatEE...6.1095D }}</ref><ref>{{Cite journal |last1=McIlroy |first1=D. |last2=Pasinetti |first2=G. |last3=Pérez-Pinedo |first3=D. |last4=McKean |first4=C. |last5=Dufour |first5=S. C. |last6=Matthews |first6=J. J. |last7=Menon |first7=L. R. |last8=Nicholls |first8=R. |last9=Taylor |first9=R. S. |date=2024-08-30 |title=The Palaeobiology of Two Crown Group Cnidarians: Haootia quadriformis and Mamsetia manunis gen. et sp. nov. from the Ediacaran of Newfoundland, Canada |journal=Life |language=en |volume=14 |issue=9 |pages=1096 |doi=10.3390/life14091096 |doi-access=free |pmid=39337880 |bibcode=2024Life...14.1096M |issn=2075-1729 |pmc=11432848 }}</ref><ref>{{Cite journal |last1=Chen |first1=Zhe |last2=Zhou |first2=Chuanming |last3=Yuan |first3=Xunlai |last4=Xiao |first4=Shuhai |date=September 2019 |title=Death march of a segmented and trilobate bilaterian elucidates early animal evolution |url=https://www.nature.com/articles/s41586-019-1522-7 |journal=Nature |language=en |volume=573 |issue=7774 |pages=412–415 |doi=10.1038/s41586-019-1522-7 |pmid=31485079 |bibcode=2019Natur.573..412C |issn=1476-4687}}</ref> [[Sponge|Sponges]] recognisable as such also appeared, at latest, during the terminal Ediacaran, including ''[[Helicolocellus]]'', a likely non-biomineralizing sponge. <ref>{{Cite journal |last=Xiao |first=Shuhai |date=12 August 2020 |title=Ediacaran sponges, animal biomineralization, and skeletal reefs |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |language=en |volume=117 |issue=35 |pages=20997–20999 |bibcode=2020PNAS..11720997X |doi=10.1073/pnas.2014393117 |issn=0027-8424 |pmc=7474584 |pmid=32817471 |doi-access=free}}</ref><ref>{{Cite journal |last1=Wang |first1=Xiaopeng |last2=Liu |first2=Alexander G. |last3=Chen |first3=Zhe |last4=Wu |first4=Chengxi |last5=Liu |first5=Yarong |last6=Wan |first6=Bin |last7=Pang |first7=Ke |last8=Zhou |first8=Chuanming |last9=Yuan |first9=Xunlai |last10=Xiao |first10=Shuhai |date=June 2024 |title=A late-Ediacaran crown-group sponge animal |url=https://www.nature.com/articles/s41586-024-07520-y |journal=Nature |language=en |volume=630 |issue=8018 |pages=905–911 |doi=10.1038/s41586-024-07520-y |pmid=38839967 |bibcode=2024Natur.630..905W |issn=1476-4687}}</ref>

Other than these definitive animals, most members of the Ediacaran biota bear little resemblance to modern lifeforms, and their [[biological classification|relationship]] with even the immediately following lifeforms of the [[Cambrian explosion]] is rather difficult to interpret.<ref name="OnTheEveOfAnimalRadiation">{{cite journal |last1=Xiao |first1=Shuhai |last2=Laflamme |first2=Marc |date=January 2009 |title=On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota |url=https://www.sciencedirect.com/science/article/abs/pii/S0169534708003066 |journal=[[Trends in Ecology & Evolution]] |volume=24 |issue=1 |pages=31–40 |doi=10.1016/j.tree.2008.07.015 |pmid=18952316 |bibcode=2009TEcoE..24...31X |access-date=10 November 2022}}</ref><ref>{{cite journal |last1=Dunn |first1=Frances S. |last2=Liu |first2=Alexander G. |date=11 February 2019 |title=Viewing the Ediacaran biota as a failed experiment is unhelpful |url=https://www.nature.com/articles/s41559-019-0815-4#citeas |journal=[[Nature Ecology and Evolution]] |volume=3 |issue=4 |pages=512–514 |doi=10.1038/s41559-019-0815-4 |pmid=30742104 |bibcode=2019NatEE...3..512D |s2cid=59945361 |access-date=10 November 2022}}</ref> More than 100 [[List of Ediacaran genera|genera]] have been described, and well known forms include ''[[Arkarua]]'', ''[[Charnia]]'', ''[[Dickinsonia]]'', ''[[Ediacaria]]'', ''[[Marywadea]]'', ''[[Cephalonega]]'', ''[[Pteridinium]]'', and ''[[Yorgia]]''. However, despite the overall enigmaticness of most Ediacaran organisms, some fossils identifiable as hard-shelled agglutinated [[foraminifera]] (which are not classified as animals) are known from latest Ediacaran sediments of western Siberia.<ref>{{Cite journal|last1=Kontorovich|first1=A. E.|last2=Varlamov|first2=A. I.|last3=Grazhdankin|first3=D. V.|last4=Karlova|first4=G. A.|last5=Klets|first5=A. G.|last6=Kontorovich|first6=V. A.|last7=Saraev|first7=S. V.|last8=Terleev|first8=A. A.|last9=Belyaev|first9=S. Yu.|last10=Varaksina|first10=I. V.|last11=Efimov|first11=A. S.|date=2008-12-01|title=A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)|url=http://www.sciencedirect.com/science/article/pii/S106879710800206X|journal=Russian Geology and Geophysics|language=en|volume=49|issue=12|pages=932–939|doi=10.1016/j.rgg.2008.06.012|bibcode=2008RuGG...49..932K|issn=1068-7971}}</ref>

Four different biotic intervals are known in the Ediacaran, each being characterised by the prominence of a unique ecology and faunal assemblage. The first spanned from 635 to around 575 Ma and was dominated by acritarchs known as [[large ornamented Ediacaran microfossil]]s.<ref name=Cohen2009>{{Cite journal | first1=P. A.| last2= Knoll| last3= Kodner | first2=A. H.| last1 = Cohen | first3=R. B.| journal = Proceedings of the National Academy of Sciences of the United States of America| volume = 106| title = Large spinose microfossils in Ediacaran rocks as resting stages of early animals| issue = 16| pages = 6519–6524| date=Apr 2009 | issn = 0027-8424| pmid = 19366668| pmc = 2672526| doi = 10.1073/pnas.0902322106 |bibcode = 2009PNAS..106.6519C | doi-access= free}}</ref> The second spanned from around 575 to 560 Ma and was characterised by the Avalon biota. The third spanned from 560 to 550 Ma; its biota has been dubbed the White Sea biota due to many fossils from this time being found along the coasts of the [[White Sea]]. The fourth lasted from 550 to 539 Ma and is known as the interval of the Nama biotic assemblage.<ref name="EvansEtAl2022">{{cite journal |last1=Evans |first1=Scott D. |last2=Tu |first2=Chenyi |last3=Rizzo |first3=Adriana |last4=Surprenant |first4=Rachel L. |last5=Boan |first5=Phillip C. |last6=McCandless |first6=Heather |last7=Marshall |first7=Nathan |last8=Xiao |first8=Shuhai |last9=Droser |first9=Mary L. |date=7 November 2022 |title=Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition |url=https://www.researchgate.net/publication/365204103 |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=119 |issue=46 |pages=e2207475119 |bibcode=2022PNAS..11907475E |doi=10.1073/pnas.2207475119 |doi-access=free |pmc=9674242 |pmid=36343248 |access-date=24 November 2023 |hdl=10919/112639}}</ref>

There is evidence for [[End-Ediacaran extinction|a mass extinction]] during this period from early animals changing the environment,<ref>{{Cite journal |last1=Laflamme |first1=Marc |last2=Darroch |first2=Simon A. F. |last3=Tweedt |first3=Sarah M. |last4=Peterson |first4=Kevin J. |last5=Erwin |first5=Douglas H. |date=1 March 2013 |title=The end of the Ediacara biota: Extinction, biotic replacement, or Cheshire Cat? |url=https://www.sciencedirect.com/science/article/pii/S1342937X1200353X |journal=[[Gondwana Research]] |series=Geological processes in the Early Earth |volume=23 |issue=2 |pages=558–573 |doi=10.1016/j.gr.2012.11.004 |bibcode=2013GondR..23..558L |issn=1342-937X |access-date=24 November 2023}}</ref> dating to the same time as the transition between the White Sea and the Nama-type biotas.<ref name="DarrochEtAl2015">{{cite journal |last1=Darroch |first1=Simon A. F. |last2=Sperling |first2=Erik A. |last3=Boag |first3=Thomas H. |last4=Racicot |first4=Rachel A. |last5=Mason |first5=Sara J. |last6=Morgan |first6=Alex S. |last7=Tweedt |first7=Sarah |last8=Myrow |first8=Paul |last9=Johnston |first9=David T. |last10=Erwin |first10=Douglas H. |last11=Laflamme |first11=Marc |date=7 September 2015 |title=Biotic replacement and mass extinction of the Ediacara biota |journal=[[Proceedings of the Royal Society B: Biological Sciences]] |volume=282 |issue=1814 |pages=1–10 |doi=10.1098/rspb.2015.1003 |pmc=4571692 |pmid=26336166|bibcode=2015RSPSB.28251003D }}</ref><ref>[https://www.sciencedaily.com/releases/2015/09/150902123456.htm Evidence that Earth's first mass extinction was caused by critters not catastrophe], ''[[ScienceDaily]]''</ref> Alternatively, this mass extinction has also been theorised to have been the result of an [[anoxic event]].<ref name="EvansEtAl2022" />

== Astronomical factors ==
The relative proximity of the Moon at this time meant that [[Tidal acceleration|tides]] were stronger and more rapid than they are now. The day was 21.9 ± 0.4 hours, and there were 13.1 ± 0.1 synodic months/year and 400 ± 7 solar days/year.<ref>{{Cite journal | doi = 10.1029/1999RG900016 | last1 = Williams | first1 = George E. | date = 2000 | title = Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit | bibcode = 2000RvGeo..38...37W | journal = Reviews of Geophysics | volume = 38 | issue = 1| pages = 37–60 | citeseerx = 10.1.1.597.6421 | s2cid = 51948507 }}</ref>

== Documentaries ==
A few English language documentaries have featured the Ediacaran Period and biota:
* ''[[Australia: The Time Traveller's Guide]]'' (2012, [[ABC Science]]; Part 1 of 4).<ref>[https://www.abc.net.au/science/articles/2014/09/01/4076259.htm Celebrating 50 years of ABC Science] Retrieved 18 March 2023.</ref>
* ''The Geological History of Canada'', as part of [[The Nature of Things]] series, CBC-SRC; 2011; Eastern Canada.
* The first episode of a BBC documentary titled ''[[Life on Earth (TV series)|Life on Earth]]'', with [[David Attenborough]] as narrator.
* Another documentary narrated by David Attenborough titled ''[[First Life (TV series)|First Life]]'' featuring ''[[Charnia]]'', ''[[Dickinsonia]]'', ''[[Spriggina]]'', ''[[Funisia]]'', and ''[[Kimberella]]'' animated in [[Computer-generated imagery|CGI]].

==See also==
* {{Annotated link|List of fossil sites}} ''(with link directory)''
* [[Avalon explosion]]
* [[End-Ediacaran extinction]]

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Ediacaran}}
* {{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 = 2004-05-17
 | location=London}}
* {{cite web
 | title = Ediacaran Period
 | work = GeoWhen Database
 | url = http://www.stratigraphy.org/bak/geowhen/stages/Ediacaran.html
 | access-date = 5 January 2006
 | url-status = dead
 | archive-url = https://web.archive.org/web/20191016220407/http://www.stratigraphy.org/bak/geowhen/stages/Ediacaran.html
 | archive-date = 16 October 2019
 }}
* [http://www.ucmp.berkeley.edu/vendian/vendian.html Introduction to the Vendian Period]
* [http://www.abc.net.au/catalyst/stories/s1785092.htm#transcript transcript] – ''[[Catalyst (TV program)|Catalyst]]'' ([[Australian Broadcasting Corporation]])
* [https://web.archive.org/web/20061113031119/http://members.rediff.com/mistakenpoint/ Mistaken Point Fauna: The Discovery]
* [http://www.abc.net.au/news/2013-08-03/sa-pastoral-property-nilpena-holds-animal-fossils/4862432 Earth's oldest animal ecosystem held in fossils at Nilpena Station in SA outback] ''[[ABC News (Australia)|ABC News]]'', 5 August 2013. Accessed 6 August 2013.
*{{IMDb title|2380395|Australia: The Time Traveller's Guide (2012)}}
* [https://www.bbc.co.uk/programmes/b00lh2s3 ''In Our Time'' – Ediacara Biota], BBC Radio, 9 July 2009. Accessed 1 February 2025.


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