View source for End-Ediacaran extinction

{{Short description|Mass extinction event at the end of the Ediacaran period, 539 million years ago}}
The end-Ediacaran extinction is a mass extinction believed to have occurred near the end of the [[Ediacaran]] period, the final period of the Proterozoic eon. Evidence suggesting that such a [[mass extinction]] occurred includes a massive reduction in diversity of [[acritarch]]s, the sudden disappearance of the [[Ediacara biota]] and calcifying organisms, and the time gap before [[Cambrian]] organisms "replaced" them. Some lines of evidence suggests that there may have been two distinct pulses of the extinction event, one occurring {{Ma|550}} and the other {{Ma|539}}.<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 |volume=282 |issue=1814 |pages=1–10 |doi=10.1098/rspb.2015.1003 |pmid=26336166 |pmc=4571692 |bibcode=2015RSPSB.28251003D }}</ref>
==Evidence==
===Biotic evidence===
====Ediacaran organisms====
[[File:Life_in_the_Ediacaran_sea.jpg|thumb|Most of the Ediacaran organisms featured in this image went extinct because of the extinction event. Note: this is an outdated reconstruction, and the "[[jellyfish]]" in the image likely did not exist]]
During the Ediacaran period, two main groups of organisms are found in the fossil record: the "[[Ediacaran biota]]" of soft-bodied organisms, preserved by [[microbial mat]]s; and calcifying organisms such as ''[[Cloudina]]'' and ''[[Namacalathus]]'', which had a carbonate skeleton.<ref name=Amthor2003>{{cite journal|title=Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian Boundary in Oman|year=2003|journal=Geology|volume=31|pages=431–434|doi=10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2 |author = Amthor, Joachim E.|last2=Grotzinger|first2=John P.|last3=Schröder|first3=Stefan|last4=Bowring|first4=Samuel A.|last5=Ramezani|first5=Jahandar|last6=Martin|first6=Mark W.|last7=Matter|first7=Albert|issn=0091-7613|issue=5|bibcode = 2003Geo....31..431A }}</ref>  Because ''both ''these groups disappear abruptly at the end of the Ediacaran period, {{Ma|538.8|error=0.2}},<ref>{{cite web |title=Stratigraphic Chart 2022 |url=https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |publisher=International Stratigraphic Commission | date=February 2022  |access-date=25 April 2022}}</ref> their disappearance cannot simply represent the closure of a preservational window,<ref name=Marshall2006>{{cite journal|year=2006|doi=10.1146/annurev.earth.33.031504.103001|title=Explaining The Cambrian "Explosion" Of Animals|author=Marshall, Charles R.|s2cid=85623607|journal=Annual Review of Earth and Planetary Sciences|volume=34|pages=355–384|bibcode=2006AREPS..34..355M}}</ref> as had previously been suspected.<ref name=Amthor2003/>

Additionally, the late Ediacaran saw a faunal turnover between the [[White Sea assemblage|White Sea biota]], which lived between 560 and 550 million years ago, and the [[Nama assemblage|Nama biota]], which lived between 550 and 539 million years ago.<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 |journal=[[Proceedings of the National Academy of Sciences]] |volume=119 |issue=46 |pages=e2207475119 |doi=10.1073/pnas.2207475119 |doi-access=free |pmid=36343248 |pmc=9674242 |bibcode=2022PNAS..11907475E |hdl=10919/112639 }}</ref> The transition from the White Sea to the Nama biota saw a major reduction in diversity that was not recovered during the interval of the depauperate Nama biota, which has been attributed to either increased biological competition<ref name="DarrochEtAl2015" /> or an anoxic event<ref name="EvansEtAl2022" /> and in either case suggests that large-scale extinction began well before the boundary between the Ediacaran and Cambrian.{{Citation needed|date=October 2024}}

====Post-Ediacaran survivors====
The fossil record of the earliest Cambrian, just after the Ediacaran period, shows a [[Cambrian substrate revolution|sudden increase in burrowing activity and diversity]].  However, the [[Cambrian explosion]] of animals that gave rise to body fossils did not happen instantaneously.  This implies that the "explosion" did not represent animals "replacing" the incumbent organisms, and pushing them gradually to extinction; rather, the data are more consistent with a [[adaptive radiation|radiation]] of animals to fill in vacant [[ecological niche|niches]], left empty as an extinction cleared out the pre-existing fauna.<ref name=Wille2008>{{cite journal|doi=10.1038/nature07072|date=June 2008|author=Wille, M|author2=Nägler, T.F.|author3=Lehmann, B|author4=Schröder, S|author5=Kramers, J.D|title=Hydrogen sulphide release to surface waters at the Precambrian/Cambrian boundary|volume=453|issue=7196|pages=767–9|pmid=18509331|journal=Nature|bibcode = 2008Natur.453..767W |s2cid=4425120}}</ref>

The theory that all Ediacarans became extinct at the start of the Cambrian is disproven if any post-Ediacaran survivors are found.  Organisms from the lower Cambrian, such as ''[[Thaumaptilon]]'', were once thought to be Ediacarans, but this hypothesis no longer has many adherents.<ref name=Antcliffe2007>{{cite journal|author1=Antcliffe, Jonathan B. |author2=Brasier, Martin D. |year=2007|title=Charnia and sea pens are poles apart|journal=Journal of the Geological Society|volume=164|issue=1|pages=49–51|doi=10.1144/0016-76492006-080|url=http://jgs.geoscienceworld.org/cgi/content/abstract/164/1/49|bibcode=2007JGSoc.164...49A |s2cid=130602154 |url-access=subscription}}</ref>  One possible Ediacaran survivor whose status is still open to scrutiny is ''[[Ediacaria booleyi]]'', a purported [[holdfast (biology)|holdfast]] structure known from the ''upper'' Cambrian. If this does turn out to be a true Ediacaran, the biota cannot have disappeared completely.  Disbelievers have claimed that the fossils don't actually have a biological origin, which doesn't seem to be the case—evidence is mounting to suggest that it ''is'' an organism (or at least of biological origin, perhaps a microbial colony),<ref>See [[Ediacaria]]</ref> just not one that is related to the Ediacara biota.<ref name=MacGabhann2007>{{The Rise and Fall of the Ediacaran Biota |author=MacGabhann, B. A. |author2=Murray, J. |author3=Nicholas, C. |chapter=''Ediacaria booleyi'': weeded from the Garden of Ediacara? |pages=277=295|doi=10.1144/SP286.20}}</ref>

Some organisms clearly survived the extinction since life on Earth has continued. However, very few organisms are known from both sides of the Ediacaran-Cambrian boundary.{{Citation needed|date=October 2024}} One such organism is the agglutinated [[foraminifera]] ''[[Platysolenites]]''.<ref>{{cite journal|doi=10.1016/j.rgg.2008.06.012|title=A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)|year=2008|author=Kontorovich, A|journal=Russian Geology and Geophysics|volume=49|pages=932|last2=Varlamov|first2=A|last3=Grazhdankin|first3=D|last4=Karlova|first4=G|last5=Klets|first5=A|last6=Kontorovich|first6=V|last7=Saraev|first7=S|last8=Terleev|first8=A|last9=Belyaev|first9=S|issue=12|bibcode = 2008RuGG...49..932K |display-authors=9|last10=Varaksina|first10=I.}}</ref> ''[[Swartpuntia]]'' is one well known late Ediacaran vendobiont, which survived into the earliest Cambrian.<ref name="Jensen1998">{{cite journal| journal=Nature| title=Ediacara-type fossils in Cambrian sediments |author=Jensen, Sören |author2=James G. Gehling |author3=Mary L. Droser| volume=393| issue=6685| year=1998| pages=567–569| doi=10.1038/31215| bibcode=1998Natur.393..567J| s2cid=205001064}}</ref> Cambrian ''[[Erytholus]]'' is a similar sandstone cast to Ediacaran ''[[Ventogyrus]]''.<ref name="Retallack2011">{{cite journal| journal=Palaeontology| title= Problematic megafossils in Cambrian palaeosols of South Australia| author=Retallack, G.J.| volume=54| issue= 6| year=2011| pages=1223–1242| doi=10.1111/j.1475-4983.2011.01099.x| bibcode= 2011Palgy..54.1223R| s2cid= 130692406| doi-access=free}}</ref> Ordovician and Silurian ''[[Rutgersella]]''<ref name="Retallack2015">{{cite journal| journal=Alcheringa| title= Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont.| author=Retallack, G.J.| volume=39| issue= 4| year=2015| pages=573–588| doi=10.1080/03115518.2015.1069483| bibcode= 2015Alch...39..573R| s2cid= 54780312}}</ref> and Devonian ''[[Protonympha]]<ref name="Retallack2018">{{cite journal| journal=Lethaia| title=Reassessment of the Devonian Problematicum ''Protonympha'' as another post-Ediacaran vendobiont| author=Retallack, G.J.| volume=50| year=2018| doi=10.1111/let12253| doi-broken-date=1 November 2024}}</ref>'' have been interpreted as surviving vendobionts, comparable with Ediacaran ''[[Dickinsonia]]'' and ''[[Spriggina]]'', respectively.

===Geochemical evidence===
Negative {{delta|13|C|link}} excursions—geochemical signals often associated with mass extinctions—are observed during the Late Ediacaran. The [[Shuram excursion]] occurred around the same time as the boundary between the White Sea and Nama assemblages.<ref>{{cite journal |display-authors=etal|last1=Erwan Le Guerroué |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 |date=Apr 2006 |volume=146 |issue=1–2 |pages=68–92 |doi=10.1016/j.precamres.2006.01.007|bibcode=2006PreR..146...68L }}</ref> Another major negative carbon isotope excursion is known to have occurred at the end of the Ediacaran period and the beginning of the Cambrian.<ref name=Zhu2006>{{cite journal|author=Zhu|year=2006|doi=10.1016/j.palwor.2006.10.016|title=Advances in Cambrian stratigraphy and paleontology: Integrating correlation techniques, paleobiology, taphonomy and paleoenvironmental reconstruction|journal=[[Palaeoworld]]|volume=15|pages=217|last2=Babcock|first2=L|last3=Peng|first3=S|issue=3–4}}</ref>

===Sedimentary evidence===
The transition between the White Sea and Nama biotas near the end of the Ediacaran is reflected in the geological record by an increase in [[black shale]] deposition,<ref name=Schroder2007>{{cite journal|title=Evidence for anoxia at the Ediacaran-Cambrian boundary: the record of redox-sensitive trace elements and rare earth elements in Oman|year=2007|journal=Journal of the Geological Society|volume=164|issue=1|pages=175–187|doi=10.1144/0016-76492005-022|author1=Schroder, S. |author2=Grotzinger, J.P. |s2cid=18376742|bibcode=2007JGSoc.164..175S}}</ref> representing global anoxia.<ref name=Fike2006>{{cite journal|doi=10.1016/j.gca.2006.06.347|author=Fike, D.A.|author2=Grotzinger, J.P.|author3=Pratt, L.M.|author4=Summons, R.E.|journal=Geochimica et Cosmochimica Acta|volume=70|issue=18S|pages=173|year=2006|title=Multi-Stage Ediacaran Ocean Oxidation and Its Impact on Evolutionary Radiation|bibcode=2006GeCAS..70Q.173F}}</ref> This may be related to global changes in [[ocean circulation|oceanic circulation]] and may have been the worst marine [[anoxic event]] of the last 550 million years,<ref name=Wille2008/><ref name=Schroder2007/><ref>{{Cite web|url=https://www.sciencedaily.com/releases/2018/06/180627160543.htm|title=What caused the mass extinction of Earth's first animals? Unravelling mystery of the Ediacaran-Cambrian transition|website=ScienceDaily|access-date=20 February 2020}}</ref> although its causal relationship with the White Sea-Nama biotic turnover is controversial and has been challenged by studies concluding that this expansion of anoxia postdated the turnover.<ref>{{cite journal |last1=Tostevin |first1=Rosalie |last2=Clarkson |first2=Matthew O. |last3=Gangl |first3=Sophie |last4=Shields |first4=Graham A. |last5=Wood |first5=Rachel A. |last6=Bowyer |first6=Fred |last7=Penny |first7=Amelia M. |last8=Stirling |first8=Claudine H. |date=15 January 2019 |title=Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X18306472 |journal=[[Earth and Planetary Science Letters]] |volume=506 |pages=104–112 |doi=10.1016/j.epsl.2018.10.045 |bibcode=2019E&PSL.506..104T |s2cid=134663328 |access-date=17 December 2022|hdl=20.500.11820/25fe1837-1045-4698-bdb8-4516c7b26a38 |hdl-access=free }}</ref>

==References==
{{reflist}}

{{Extinction events}}

[[Category:Extinction events]]
[[Category:Proterozoic]]
[[Category:Ediacaran life]]
[[Category:Anoxic events]]