Editing Cryogenian (section)

== Cryogenian biota and fossils ==
Between the Sturtian and Marinoan glaciations, global biodiversity was very low.<ref name="Xu-2019" />

Fossils of [[test (biology)|testate]] amoeba (or [[Arcellinida]]) first appear during the Cryogenian Period.<ref>{{cite journal |title = Testate amoeba in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon |author1=Porter, S.A. |author2=Knoll, A.H.  |name-list-style=amp |year = 2000 |journal = Paleobiology |volume = 26 |issue = 3 |pages = 360–385 |doi = 10.1666/0094-8373(2000)026<0360:TAITNE>2.0.CO;2 |bibcode=2000Pbio...26..360P |s2cid=54636062 |issn = 0094-8373|url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:3708936 |url-access = subscription }}</ref> Since 2009, some researchers have argued that during the Cryogenian Period, potentially the oldest known fossils of [[sponges]], and therefore [[animals]], were formed.<ref>{{cite journal |title = Fossil steroids record the appearance of Demospongiae during the Cryogenian period |url = http://eaps.mit.edu/geobiology/recent%20pubs/Love%20et%20al%202009.pdf |author = Love |year = 2009 |journal = Nature |doi = 10.1038/nature07673 |last2 = Grosjean |first2 = Emmanuelle |last3 = Stalvies |first3 = Charlotte |last4 = Fike |first4 = David A. |last5 = Grotzinger |first5 = John P. |last6 = Bradley |first6 = Alexander S. |last7 = Kelly |first7 = Amy E. |last8 = Bhatia |first8 = Maya |last9 = Meredith |first9 = William |volume = 457 |issue = 7230 |pages = 718–721 |pmid = 19194449 |bibcode = 2009Natur.457..718L |s2cid = 4314662 |display-authors = etal |access-date = 2009-04-15 |archive-date = 2018-05-08 |archive-url = https://web.archive.org/web/20180508132248/http://eaps.mit.edu/geobiology/recent%20pubs/Love%20et%20al%202009.pdf |url-status = dead }}</ref><ref>{{cite journal|last1=Maloof|first1=Adam C.|first2=Catherine V.|last2=Rose|first3=Robert|last3=Beach|first4=Bradley M.| last4=Samuels|first5=Claire C.|last5=Calmet|first6=Douglas H.|last6=Erwin|first7=Gerald R.|last7=Poirier|first8=Nan|last8=Yao|first9=Frederik J.|last9=Simons|title=Possible animal-body fossils in pre-Marinoan limestones from South Australia|journal=Nature Geoscience|date=17 August 2010|volume=3|pages=653–659|doi=10.1038/ngeo934|issue=9|bibcode = 2010NatGe...3..653M}}</ref><ref>{{cite web |title = Discovery of possible earliest animal life pushes back fossil record |date = 2010-08-17 |url = http://www.physorg.com/news201273825.html}}</ref> However, it is unclear whether these fossils actually belong to sponges, though the authors do not rule out the possibility of such fossils to represent proto-sponges or complex microbial precursors to sponge-grade organisms.<ref>{{cite journal|author1=Wallace, M.W.|author2=Hood, A.v.S.|author3=Woon, E.M.S.|author4=Hoffman, K.-H.|author5=Reed, C.P.|year=2014|title=Enigmatic chambered structures in Cryogenian reefs: The oldest sponge-grade organisms?|journal=Precambrian Research|volume=255|pages=653–659|doi=10.1016/j.precamres.2014.09.020|bibcode=2014PreR..255..109W |hdl=11343/52679|hdl-access=free}}</ref> The issue of whether or not biology was impacted by this event has not been settled, for example Porter (2000) suggests that new groups of life evolved during this period, including the [[red algae]] and [[green algae]], [[stramenopile]]s, [[ciliate]]s, [[dinoflagellate]]s, and testate amoeba.<ref>{{Cite web|url=http://palaeos.com/proterozoic/neoproterozoic/cryogenian/cryogenian2.html|title = Palaeos Proterozoic: Neoproterozoic: Cryogenian}}</ref>

The end of the period also saw the origin of [[heterotroph]]ic [[plankton]], which would feed on [[Unicellular organism|unicellular]] [[algae]] and [[prokaryote]]s, ending the [[bacteria]]l dominance of the oceans.<ref>[https://newatlas.com/fossil-fats-snowball-earth/58292/ Fossil fats reveal how complex life kicked off after Snowball Earth phase]</ref> The unicellular algae ([[Archaeplastida]]) went through a big bang of diversification, and their population went up by a factor of a hundred to a thousand.<ref>[https://www.sciencealert.com/this-groundbreaking-period-in-earth-s-history-gave-rise-to-the-first-animals We Finally Know Which Groundbreaking Period in Earth's History Gave Rise to The First Animals]</ref><ref>[https://www.bbc.com/news/science-environment-40948972 The algae that terraformed Earth]</ref>