View source for Neoproterozoic

{{short description|Third and last era of the Proterozoic Eon}}
{{Infobox geologic timespan
| name                         = Neoproterozoic
| color                        = Neoproterozoic
| top_bar                      = all time
| time_start                   = 1000
| time_end                     = 538.8
| time_end_uncertainty         = 0.2
| image_map                    =
| caption_map                  =
| image_outcrop                =
| caption_outcrop              =
| image_art                    = Neoproterozoic collage.png
| caption_art                  = Clockwise, from top left: ''[[Otavia]]'', a [[multicellular organism]] from [[Tonian]] period, [[Snowball Earth]] glaciations from [[Cryogenian]] period, [[Ediacaran biota]] from [[Ediacaran]] period
<!--Chronology-->
| timeline                     = Neoproterozoic
| proposed_boundaries1         = 850–541 Ma
| proposed_boundaries1_ref     = Gradstein et al., 2012
| proposed_subdivision1        = [[Cryogenian]] Period, 850–630 Ma
| proposed_subdivision1_coined = Gradstein et al., 2012
| proposed_subdivision2        = [[Ediacaran]] Period, 630–541.0 Ma
| proposed_subdivision2_coined = Gradstein et al., 2012
<!--Etymology-->
| name_formality               = Formal
| name_accept_date             =
<!--Usage Information-->
| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
<!--Definition-->
| chrono_unit                  = Era
| strat_unit                   = Erathem
| proposed_by                  =
| timespan_formality           = Formal
| lower_boundary_def           = Defined Chronometrically
| lower_gssa_accept_date       = 1991<ref name=Plumb1991>{{cite journal |last=Plumb |first=K. A. |date=June 1, 1991 |title=New Precambrian time scale |journal=Episodes |doi=10.18814/epiiugs/1991/v14i2/005 |volume=14 |issue=2 |pages=139–140|doi-access=free }}</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{{citation needed|date=February 2023|reason=Plumb 1991 says the upper boundary time will be determined later. This says 1992 but what's the source for that?}}
}}
The '''Neoproterozoic Era''' is the last of the three [[geologic era]]s of the [[Proterozoic]] [[geologic eon|eon]], spanning from 1 billion to 538.8 million years ago,<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=22 April 2022}}</ref> and is the last era of the [[Precambrian]] "supereon". It is preceded by the [[Mesoproterozoic]] era and succeeded by the [[Paleozoic]] era of the [[Phanerozoic]] eon, and is further subdivided into three [[geologic period|period]]s, the [[Tonian]], [[Cryogenian]] and [[Ediacaran]].
One of the most severe [[glaciation]] event known in the geologic record occurred during the Cryogenian period of the Neoproterozoic, when global [[ice sheet]]s may have reached the [[equator]] and created a "[[Snowball Earth]]" lasting about 100&nbsp;million years. The earliest fossils of [[complex life]] are found in the Tonian period in the form of ''[[Otavia]]'', a primitive [[sponge]], and the earliest fossil evidence of [[metazoan]] [[evolutionary radiation|radiation]] are found in the Ediacaran period, which included the namesaked [[Ediacaran biota]] as well as the oldest definitive [[cnidarian]]s and [[bilaterian]]s in the fossil record.
According to Rino and co-workers, the sum of the [[continental crust]] formed in the [[Pan-African orogeny]] and the [[Grenville orogeny]] makes the Neoproterozoic the period of Earth's history that has produced most continental crust.<ref name=Rinoetal2008>{{cite journal |last1=Rino |first1=S. |last2=Kon |first2=Y. |last3=Sato |first3=W. |last4=Maruyama |first4=S. |last5=Santosh |first5=M. |last6=Zhao |first6=D. |date=2008 |title=The Grenvillian and Pan-African orogens: World's largest orogenies through geologic time, and their implications on the origin of superplume |journal=[[Gondwana Research]] |volume=14 |issue=1–2 |pages=51–72 |doi=10.1016/j.gr.2008.01.001 |bibcode=2008GondR..14...51R }}</ref>
==Geology==
At the onset of the Neoproterozoic the supercontinent [[Rodinia]], which had assembled during the late Mesoproterozoic, straddled the equator. During the Tonian, rifting commenced which broke Rodinia into a number of individual land masses.
Possibly as a consequence of the low-latitude position of most continents, several large-scale glacial events occurred during the Neoproterozoic Era including the [[Sturtian]] and [[Marinoan]] glaciations of the Cryogenian Period.
These glaciations are believed to have been so severe that there were ice sheets at the equator—a state known as the "[[Snowball Earth]]".
==Subdivisions==
Neoproterozoic time is subdivided into the [[Tonian]] (1000–720 Ma), [[Cryogenian]] (720–635 Ma) and [[Ediacaran]] (635–538.8 Ma) periods.<ref name="StratChart 2022"/>
===Russian regional timescale===
In the regional timescale of Russia, the Tonian and Cryogenian correspond to the Late [[Riphean (stage)|Riphean]]; the Ediacaran corresponds to the Early to middle Vendian.<ref name="Craig2015">{{cite web | url=https://www.geosoc.fr/liens-docman/conferences/2015/les-roches-meres-petrolieres/1073-global-climate-the-dawn-of-life-and-the-world-s-oldest-petroleum-systems/file.html | title=Global Climate, the Dawn of Life and the Earth's Oldest Petroleum Systems | date=26 November 2015 | access-date=15 March 2019 | author=Craig, J.}}</ref> Russian geologists divide the Neoproterozoic of [[Siberia]] into the {{anchor|Mayanian}}'''Mayanian''' (from 1000 to 850 Ma) followed by the {{anchor|Baikalian}}'''Baikalian''' (from 850 to 650 Ma).<ref name='Khomentovsky2008'>{{cite journal
| doi = 10.1016/j.rgg.2007.12.001
| title = Mayanian (1100–850 Ma) – Prebaikalian Upper Riphean of Siberia
| year = 2008
| author = Khomentovsky, V
| journal = Russian Geology and Geophysics
| volume = 49
| issue = 1
| pages = 1
| last2 = Nagovitsin
| first2 = K
| last3 = Postnikov
| first3 = A
| bibcode=2008RuGG...49....1K}}</ref>
<gallery mode="packed" heights="60">
Proterozoic (Russian stratigraphic scale in English).png|Russian timescale for Proterozoic. Neoproterozoic is equivalent to the time span from Late Riphean to Late Vendian.
</gallery>
==Paleobiology==
{{main|Ediacaran biota}}
The idea of the Neoproterozoic Era was introduced in the 1960s. Nineteenth-century paleontologists set the start of [[metazoan|multicellular]] life at the first appearance of hard-shelled [[Arthropod | arthropods]] called [[trilobite]]s and [[Archaeocyatha|archeocyathid sponges]] at the beginning of the [[Cambrian]] Period. In the early 20th century, paleontologists started finding fossils of multicellular animals that predated the Cambrian. A complex fauna was found in South West [[Africa]] in the 1920s but was inaccurately dated. Another fauna was found in South Australia in the 1940s, but it was not thoroughly examined until the late 1950s. Other possible early animal fossils were found in Russia, England, Canada, and elsewhere (see [[Ediacaran biota]]). Some were determined to be [[pseudofossil]]s, but others were revealed to be members of rather complex biotas that remain poorly understood. At least 25 regions worldwide have yielded [[metazoan]] fossils older than the classical Precambrian–Cambrian boundary (which is currently dated at {{Ma|538.8}}).<ref>{{cite journal | first = A. H. | last = Knoll |author2=Walter, M. |author3=Narbonne, G. |author4=Christie-Blick, N. | title = The Ediacaran Period: a new addition to the geologic time scale | pages = 13–30 | journal = Lethaia | volume = 39 | issue =1| year = 2006 | url =https://academiccommons.columbia.edu/doi/10.7916/D8W38687/download | doi = 10.1080/00241160500409223| bibcode = 2006Letha..39...13K }}</ref><ref name="StratChart 2022"/>
A few of the early animals appear possibly to be ancestors of modern animals. Most fall into ambiguous groups of frond-like organisms; discoids that might be holdfasts for stalked organisms ("medusoids"); mattress-like forms; small calcareous tubes; and armored animals of unknown provenance.
These were most commonly known as [[Vendian biota]] until the formal naming of the Period, and are currently known as Ediacaran Period biota. Most were soft bodied. The relationships, if any, to modern forms are obscure. Some paleontologists relate many or most of these forms to modern animals. Others acknowledge a few possible or even likely relationships but feel that most of the Ediacaran forms are representatives of unknown animal types.
In addition to Ediacaran biota, two other types of biota were discovered in China. The [[Doushantuo Formation]] (of Ediacaran age) preserves fossils of microscopic marine organisms in great detail.<ref>{{cite journal |last1=Muscente |first1=A.D. |last2=Hawkins |first2=Andrew D. |last3=Xiao |first3=Shuhai |title=Fossil preservation through phosphatization and silicification in the Ediacaran Doushantuo Formation (South China): a comparative synthesis |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=September 2015 |volume=434 |pages=46–62 |doi=10.1016/j.palaeo.2014.10.013|bibcode=2015PPP...434...46M }}</ref>{{Contradictory inline|article=Doushantuo Formation|reason=The Doushantuo Formation is of Ediacaran age. This suggests it is part of the Ediacaran biota.|section=|date=May 2024}} The [[Huainan biota]] (of late Tonian age) consists of small worm-shaped organisms.<ref>{{cite journal |last1=Malenkov |first1=A. G. |title=13C, Ontogeny, and the Paradox of Evolution |journal=Biophysics |date=May 2018 |volume=63 |issue=3 |pages=477–484 |doi=10.1134/S0006350918030156}}</ref>
[[Molecular phylogeny]] suggests that animals may have emerged even earlier in the Neoproterozoic (early Tonian), but physical evidence for such animal life is lacking. Possible [[keratose sponge]] fossils have been reported in reefs dated to {{circa}} 890 million years before the present, but remain unconfirmed.<ref>{{cite journal |last1=Turner |first1=Elizabeth C. |title=Possible poriferan body fossils in early Neoproterozoic microbial reefs |journal=Nature |date=28 July 2021 |volume=596 |issue=7870 |pages=87–91 |doi=10.1038/s41586-021-03773-z|pmid=34321662 |pmc=8338550 |bibcode=2021Natur.596...87T |doi-access=free }}</ref>
==Terminal period==
{{main|Ediacaran}}
The nomenclature for the terminal period of the Neoproterozoic Era has been unstable. Russian and Nordic geologists referred to the last period of the Neoproterozoic as the [[Vendian]], while Chinese geologists referred to it as the [[Sinian]], and most Australians and North Americans used the name Ediacaran.
However, in 2004, the International Union of Geological Sciences ratified the Ediacaran Period to be a geological age of the Neoproterozoic, ranging from {{Period start|Ediacaran}} to {{Period end|Ediacaran}} (at the time to 542) million years ago.<ref name=Ogg2008>{{cite book | last = Ogg | first = James G. |author2=Ogg, Gabi |author3=Gradstein, Felix M. | title = The Concise Geologic Time Scale | publisher = Cambridge University Press | year = 2008 | pages = 184 | url = http://www.cambridge.org/catalogue/catalogue.asp?isbn=0521898498 | isbn = 978-0-521-89849-2}}</ref><ref name="USGS_2007">{{cite web | url=https://pubs.usgs.gov/fs/2007/3015/fs2007-3015.pdf | title=Divisions of Geologic Time— Major Chronostratigraphic and Geochronologic Units | publisher=[[USGS]] | work=USGS Fact Sheet 2007–3015 | date=March 2007 | accessdate=22 April 2022 | author=U.S. Geological Survey Geologic Names Committee}}</ref> The Ediacaran Period boundaries are the only Precambrian boundaries defined by biologic [[Global Boundary Stratotype Section and Point]]s, rather than the absolute [[Global Standard Stratigraphic Age]]s.
==See also==
*{{annotated link|Boring Billion}}
==References==
{{reflist}}
==External links==
* [https://ghkclass.com/ghkC.html?neoproterozoic Neoproterozoic (chronostratigraphy scale)]
{{Commons category|Neoproterozoic|position=left}}
{{Geological history|c|state=collapsed}}
{{Authority control}}
[[Category:Neoproterozoic| ]]
[[Category:Geological eras]]