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The presence of eukaryotic biomarkers in archaea points towards an archaeal origin. The genomes of [[Asgard (archaea)|Asgard]] archaea have plenty of [[Eukaryotic signature protein]] genes, which play a crucial role in the development of the [[cytoskeleton]] and complex cellular structures characteristic of eukaryotes. In 2022, [[Cryo Electron Tomography|cryo-electron tomography]] demonstrated that Asgard archaea have a complex [[actin]]-based cytoskeleton, providing the first direct visual evidence of the archaeal ancestry of eukaryotes.<ref name="Rodrigues-Oliveira et al 2023">{{cite journal |vauthors=Rodrigues-Oliveira T, Wollweber F, Ponce-Toledo RI, etal. |title=Actin cytoskeleton and complex cell architecture in an Asgard archaean |journal=Nature |volume=613 |pages=332–339 |date=2023 |issue=7943 |doi=10.1038/s41586-022-05550-y|pmid=36544020 |pmc=9834061 |bibcode=2023Natur.613..332R |hdl=20.500.11850/589210 |hdl-access=free }}</ref>
=== Fossils ===
The timing of the origin of eukaryotes is hard to determine but the discovery of ''Qingshania magnificia'', the earliest multicelluar eukaryote from North China which lived during 1.635 billion years ago, suggests that the crown group eukaryotes would have originated from the late [[Paleoproterozoic]] ([[Statherian]]); the earliest unequivocal unicellular eukaryotes which lived during approximately 1.65 billion years ago are also discovered from North China: ''Tappania plana'', ''Shuiyousphaeridium macroreticulatum'', ''Dictyosphaera macroreticulata'', ''Germinosphaera alveolata'', and ''Valeria lophostriata''.<ref>{{Cite journal|last1=Miao |first1=L. |last2=Yin |first2=Z. |last3=Knoll |first3=A. H. |last4=Qu |first4=Y. |last5=Zhu |first5=M. |title=1.63-billion-year-old multicellular eukaryotes from the Chuanlinggou Formation in North China |year=2024 |journal=Science Advances |volume=10 |issue=4 |pages=eadk3208 |doi=10.1126/sciadv.adk3208 |doi-access=free |pmid=38266082 |pmc=10807817 |bibcode=2024SciA...10K3208M }}</ref>
Some [[acritarch]]s are known from at least 1.65 billion years ago, and a fossil, ''[[Grypania]]'', which may be an alga, is as much as 2.1 billion years old.<ref name="Han">{{cite journal |vauthors=Han TM, Runnegar B |title=Megascopic eukaryotic algae from the 2.1-billion-year-old negaunee iron-formation, Michigan |journal=Science |volume=257 |issue=5067 |pages=232–5 |date=July 1992 |pmid=1631544 |doi=10.1126/science.1631544 |bibcode=1992Sci...257..232H |url=}}</ref><ref>{{cite journal |vauthors=Knoll AH, Javaux EJ, Hewitt D, Cohen P |title=Eukaryotic organisms in Proterozoic oceans |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=361 |issue=1470 |pages=1023–1038 |date=June 2006 |pmid=16754612 |pmc=1578724 |doi=10.1098/rstb.2006.1843 }}</ref> The [[Incertae sedis|"problematic"]]<ref name="Retallack 2013"/><!--in case adj is challenged--> fossil ''[[Diskagma]]'' has been found in [[paleosol]]s 2.2 billion years old.<ref name="Retallack 2013">{{cite journal |vauthors=Retallack GJ, Krull ES, Thackray GD, Parkinson DH |title= Problematic urn-shaped fossils from a Paleoproterozoic (2.2 Ga) paleosol in South Africa. |journal=Precambrian Research |year=2013 |volume=235 |pages=71–87 |doi=10.1016/j.precamres.2013.05.015 |bibcode=2013PreR..235...71R }}</ref>
[[File:Diskagma butonii.jpg|thumb|left|Reconstruction of the problematic<ref name="Retallack 2013"/> ''[[Diskagma buttonii]]'', a terrestrial fossil less than 1mm high, from rocks around 2.2 billion years old]]
Structures proposed to represent "large colonial organisms" have been found in the [[black shale]]s of the [[Palaeoproterozoic]] such as the [[Francevillian B Formation]], in [[Gabon]], dubbed the "[[Francevillian biota]]" which is dated at 2.1 billion years old.<ref name="El Albani Bengtson Canfield 2010">{{cite journal |vauthors=El Albani A, Bengtson S, Canfield DE, Bekker A, Macchiarelli R, Mazurier A, Hammarlund EU, Boulvais P, Dupuy JJ, Fontaine C, Fürsich FT, Gauthier-Lafaye F, Janvier P, Javaux E, Ossa FO, Pierson-Wickmann AC, Riboulleau A, Sardini P, Vachard D, Whitehouse M, Meunier A |display-authors=3 |s2cid=4331375 |title=Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago |journal=Nature |volume=466 |issue=7302 |pages=100–104 |date=July 2010 |pmid=20596019 |doi=10.1038/nature09166 |bibcode=2010Natur.466..100A }}</ref><ref name="El Albani 2023">{{cite journal |title=A search for life in Palaeoproterozoic marine sediments using Zn isotopes and geochemistry |last=El Albani |first=Abderrazak |journal=Earth and Planetary Science Letters |year=2023 |volume=623 |page=118169 |doi=10.1016/j.epsl.2023.118169|bibcode=2023E&PSL.61218169E |s2cid=258360867 |doi-access=free |url=https://hal.science/hal-04095643/file/El%20Albani%20et%20al._EPSL_2023.pdf }}</ref> However, the status of these structures as fossils is contested, with other authors suggesting that they might represent [[pseudofossil]]s.<ref name="Ossa Ossa Pons Bekker Hofmann 2023">{{cite journal | last1=Ossa Ossa | first1=Frantz | last2=Pons | first2=Marie-Laure | last3=Bekker | first3=Andrey | last4=Hofmann | first4=Axel | last5=Poulton | first5=Simon W. | last6=Andersen | first6=Morten B. | last7=Agangi | first7=Andrea | last8=Gregory | first8=Daniel | last9=Reinke | first9=Christian | last10=Steinhilber | first10=Bernd | last11=Marin-Carbonne | first11=Johanna | last12=Schoenberg | first12=Ronny | display-authors=5 | title=Zinc enrichment and isotopic fractionation in a marine habitat of the c. 2.1 Ga Francevillian Group: A signature of zinc utilization by eukaryotes? | journal=Earth and Planetary Science Letters | volume=611 | date=2023 | doi=10.1016/j.epsl.2023.118147 | page=118147| doi-access=free | bibcode=2023E&PSL.61118147O | url=https://eprints.whiterose.ac.uk/197720/8/1-s2.0-S0012821X23001607-main.pdf }}</ref> The oldest fossils than can unambiguously be assigned to eukaryotes are from the Ruyang Group of China, dating to approximately 1.8-1.6 billion years ago.<ref>{{Cite journal |last1=Fakhraee |first1=Mojtaba |last2=Tarhan |first2=Lidya G. |last3=Reinhard |first3=Christopher T. |last4=Crowe |first4=Sean A. |last5=Lyons |first5=Timothy W. |last6=Planavsky |first6=Noah J. |date=May 2023 |title=Earth's surface oxygenation and the rise of eukaryotic life: Relationships to the Lomagundi positive carbon isotope excursion revisited |journal=Earth-Science Reviews |language=en |volume=240 |pages=104398 |doi=10.1016/j.earscirev.2023.104398 |bibcode=2023ESRv..24004398F |s2cid=257761993 |doi-access=free }}</ref> Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of [[red algae#Fossil record|red algae]], though recent work suggests the existence of fossilized [[filamentous algae]] in the [[Vindhya]] basin dating back perhaps to 1.6 to 1.7 billion years ago.<ref>{{cite journal |vauthors=Bengtson S, Belivanova V, Rasmussen B, Whitehouse M |title=The controversial "Cambrian" fossils of the Vindhyan are real but more than a billion years older |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=19 |pages=7729–7734 |date=May 2009 |pmid=19416859 |pmc=2683128 |doi=10.1073/pnas.0812460106 |bibcode=2009PNAS..106.7729B |doi-access=free }}</ref>
The presence of [[sterane]]s, eukaryotic-specific [[Biomarker (petroleum)|biomarkers]], in [[Australia]]n [[shale]]s previously indicated that eukaryotes were present in these rocks dated at 2.7 billion years old,<ref name=sterane>{{cite journal |vauthors=Brocks JJ, Logan GA, Buick R, Summons RE |title=Archean molecular fossils and the early rise of eukaryotes |journal=Science |volume=285 |issue=5430 |pages=1033–1036 |date=August 1999 |pmid=10446042 |doi=10.1126/science.285.5430.1033 |bibcode=1999Sci...285.1033B |citeseerx=10.1.1.516.9123 }}</ref><ref>{{cite magazine |vauthors=Ward P |title=Mass extinctions: the microbes strike back |magazine=[[New Scientist]] |pages=40–43 |date=9 February 2008 |url=https://www.newscientist.com/channel/life/mg19726421.900-mass-extinctions-the-microbes-strike-back.html |authorlink=Peter Ward (paleontologist) |access-date=27 August 2017 |archive-date=8 July 2008 |archive-url=https://web.archive.org/web/20080708222803/http://www.newscientist.com/channel/life/mg19726421.900-mass-extinctions-the-microbes-strike-back.html |url-status=live }}</ref> but these Archaean biomarkers have been rebutted as later contaminants.<ref>{{cite journal |vauthors=French KL, Hallmann C, Hope JM, Schoon PL, Zumberge JA, Hoshino Y, Peters CA, George SC, Love GD, Brocks JJ, Buick R, Summons RE |title=Reappraisal of hydrocarbon biomarkers in Archean rocks |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=112 |issue=19 |pages=5915–5920 |date=May 2015 |pmid=25918387 |doi=10.1073/pnas.1419563112 |pmc=4434754 |bibcode=2015PNAS..112.5915F |doi-access=free }}</ref> The oldest valid biomarker records are only around 800 million years old.<ref>{{cite journal |vauthors=Brocks JJ, Jarrett AJ, Sirantoine E, Hallmann C, Hoshino Y, Liyanage T |title=The rise of algae in Cryogenian oceans and the emergence of animals |journal=Nature |volume=548 |issue=7669 |pages=578–581 |date=August 2017 |pmid=28813409 |doi=10.1038/nature23457 |s2cid=205258987 |bibcode=2017Natur.548..578B }}</ref> In contrast, a molecular clock analysis suggests the emergence of sterol biosynthesis as early as 2.3 billion years ago.<ref>{{cite journal |vauthors=Gold DA, Caron A, Fournier GP, Summons RE |title=Paleoproterozoic sterol biosynthesis and the rise of oxygen |journal=Nature |volume=543 |issue=7645 |pages=420–423 |date=March 2017 |pmid=28264195 |doi=10.1038/nature21412 |hdl-access=free |s2cid=205254122 |bibcode=2017Natur.543..420G |hdl=1721.1/128450 |url=https://resolver.caltech.edu/CaltechAUTHORS:20170407-083556533 }}</ref> The nature of steranes as eukaryotic biomarkers is further complicated by the production of [[sterol]]s by some bacteria.<ref>{{cite journal |vauthors=Wei JH, Yin X, Welander PV |title=Sterol Synthesis in Diverse Bacteria |journal=Frontiers in Microbiology |volume=7 |pages=990 |date=2016-06-24 |pmid=27446030 |pmc=4919349 |doi=10.3389/fmicb.2016.00990 |doi-access=free |authorlink3=Paula V. Welander }}</ref><ref>{{cite journal |vauthors=Hoshino Y, Gaucher EA |title=Evolution of bacterial steroid biosynthesis and its impact on eukaryogenesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=118 |issue=25 |pages=e2101276118 |date=June 2021 |pmid=34131078 |pmc=8237579 |doi=10.1073/pnas.2101276118 |bibcode=2021PNAS..11801276H |doi-access=free }}</ref>
Whenever their origins, eukaryotes may not have become ecologically dominant until much later; a massive increase in the [[Abiogenesis#Zinc world|zinc composition]] of marine sediments {{Ma|800}} has been attributed to the rise of substantial populations of eukaryotes, which preferentially consume and incorporate [[zinc]] relative to prokaryotes, approximately a billion years after their origin (at the latest).<ref name="pmid29869832">{{cite journal |vauthors=Isson TT, Love GD, Dupont CL, Reinhard CT, Zumberge AJ, Asael D, Gueguen B, McCrow J, Gill BC, Owens J, Rainbird RH, Rooney AD, Zhao MY, Stueeken EE, Konhauser KO, John SG, Lyons TW, Planavsky NJ |display-authors=3 |title=Tracking the rise of eukaryotes to ecological dominance with zinc isotopes |journal=Geobiology |volume=16|issue=4|pages=341–352|date=June 2018 |pmid=29869832 |doi=10.1111/gbi.12289 |bibcode=2018Gbio...16..341I |doi-access=free }}</ref>
== See also ==
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