Editing Paleoproterozoic (section)

== Life ==
{{see|Symbiogenesis}}
At the beginning of the preceding [[Archean]] eon, almost all existing lifeforms were [[single-cell organism|single-cell]] [[prokaryotic]] [[anaerobic organism]]s whose [[metabolism]] was based on a form of [[cellular respiration]] that did not require oxygen, and [[autotroph]]s were either [[chemosynthetic]] or relied upon [[anoxygenic photosynthesis]]. After the Great Oxygenation Event, the then mainly [[archaea]]-dominated anaerobic [[microbial mat]]s were devastated as free oxygen is highly reactive and biologically toxic to cellular structures. This was compounded by a 300-[[million years|million-year]]-long [[icehouse Earth|global icehouse]] event known as the [[Huronian glaciation]] — at least partly due to the depletion of atmospheric methane, a powerful [[greenhouse gas]] — resulted in what is widely considered one of the first and most significant [[mass extinction]]s on Earth.<ref>{{cite journal |last1=Hodgskiss |first1=Malcolm S. W. |last2= Crockford |first2=Peter W. |last3=Peng |first3=Yongbo |last4=Wing |first4=Boswell A. |last5=Horner |first5= Tristan J. |date=27 August 2019 |title=A productivity collapse to end Earth's Great Oxidation |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |df=dmy-all |volume=116 |issue=35 |pages=17207–17212 |doi=10.1073/pnas.1900325116 |doi-access=free |pmid=31405980 |pmc=6717284 |bibcode=2019PNAS..11617207H}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=eo_sMMRxgAUC&q=oxygen+holocaust&pg=PA99 |title=Microcosmos: Four Billion Years of Microbial Evolution |last1=Margulis |first1=Lynn |author-link=Lynn Margulis |last2=Sagan |first2=Dorion |author2-link=Dorion Sagan |date=1997-05-29 |publisher=University of California Press |isbn=9780520210646 |language=en }}</ref> The organisms that thrived after the extinction were mainly [[aerobe]]s that evolved [[antioxidant#Oxidative challenge in biology|bioactive antioxidant]]s and eventually [[aerobic respiration]], and surviving anaerobes were forced to live [[symbiotic]]ally alongside aerobes in hybrid colonies, which enabled the evolution of [[mitochondria]] in [[eukaryotic organism]]s.

The Palaeoproterozoic represents the era from which the oldest cyanobacterial fossils, those of ''Eoentophysalis belcherensis'' from the Kasegalik Formation in the [[Belcher Islands]] of [[Nunavut]], are known.<ref>{{Cite journal |last1=Hodgskiss |first1=Malcolm S.W. |last2=Dagnaud |first2=Olivia M.J. |last3=Frost |first3=Jamie L. |last4=Halverson |first4=Galen P. |last5=Schmitz |first5=Mark D. |last6=Swanson-Hysell |first6=Nicholas L. |last7=Sperling |first7=Erik A. |date=15 August 2019 |title=New insights on the Orosirian carbon cycle, early Cyanobacteria, and the assembly of Laurentia from the Paleoproterozoic Belcher Group |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X19302936 |journal=[[Earth and Planetary Science Letters]] |language=en |volume=520 |pages=141–152 |doi=10.1016/j.epsl.2019.05.023 |access-date=18 May 2024 |via=Elsevier Science Direct}}</ref> By 1.75 Ga, thylakoid-bearing cyanobacteria had evolved, as evidenced by fossils from the McDermott Formation of Australia.<ref>{{Cite journal |last1=Demoulin |first1=Catherine F. |last2=Lara |first2=Yannick J. |last3=Lambion |first3=Alexandre |last4=Javaux |first4=Emmanuelle J. |date=18 January 2024 |title=Oldest thylakoids in fossil cells directly evidence oxygenic photosynthesis |url=https://www.nature.com/articles/s41586-023-06896-7 |journal=[[Nature (journal)|Nature]] |language=en |volume=625 |issue=7995 |pages=529–534 |doi=10.1038/s41586-023-06896-7 |issn=0028-0836 |access-date=24 June 2024}}</ref>

Many crown node eukaryotes (from which the modern-day eukaryotic lineages would have arisen) have been approximately dated to around the time of the Paleoproterozoic Era.<ref>{{cite journal |last1=Mänd |first1=Kaarel |last2=Planavsky |first2=Noah J. |last3=Porter |first3=Susannah M. |last4=Robbins |first4=Leslie J. |last5=Wang |first5=Changle |last6=Kraitsmann |first6=Timmu |last7=Paiste |first7=Kärt |last8=Paiste |first8=Päärn |last9=Romashkin |first9=Alexander E. |last10=Deines |first10=Yulia E. |last11=Kirsimäe |first11=Kalle |last12=Lepland |first12=Aivo |last13=Konhauser |first13=Kurt O. |date=15 April 2022 |title=Chromium evidence for protracted oxygenation during the Paleoproterozoic |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X22001376 |journal=[[Earth and Planetary Science Letters]] |volume=584 |page=117501 |doi=10.1016/j.epsl.2022.117501 |access-date=15 December 2022|hdl=10037/24808 |hdl-access=free }}</ref><ref name=":0">{{Cite journal|last1=Hedges|first1=S Blair|last2=Chen|first2=Hsiong|last3=Kumar|first3=Sudhir|last4=Wang|first4=Daniel YC|last5=Thompson|first5=Amanda S|last6=Watanabe|first6=Hidemi|date=2001-09-12|title=A genomic timescale for the origin of eukaryotes|journal=BMC Evolutionary Biology|volume=1|pages=4|doi=10.1186/1471-2148-1-4|issn=1471-2148|pmid=11580860|pmc=56995 |doi-access=free }}</ref><ref name=":2">{{Cite journal|last1=Hedges|first1=S Blair|last2=Blair|first2=Jaime E|last3=Venturi|first3=Maria L|last4=Shoe|first4=Jason L|date=2004-01-28|title=A molecular timescale of eukaryote evolution and the rise of complex multicellular life|journal=BMC Evolutionary Biology|volume=4|pages=2|doi=10.1186/1471-2148-4-2|issn=1471-2148|pmid=15005799|pmc=341452 |doi-access=free }}</ref>
While there is some debate as to the exact time at which eukaryotes evolved,<ref>{{Cite journal|last1=Rodríguez-Trelles|first1=Francisco|last2=Tarrío|first2=Rosa|last3=Ayala|first3=Francisco J.|date=2002-06-11|title=A methodological bias toward overestimation of molecular evolutionary time scales|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=99|issue=12|pages=8112–8115|doi=10.1073/pnas.122231299|issn=0027-8424|pmid=12060757|pmc=123029|bibcode=2002PNAS...99.8112R|doi-access=free}}</ref><ref>{{Cite journal|last1=Stechmann|first1=Alexandra|last2=Cavalier-Smith|first2=Thomas|date=2002-07-05|title=Rooting the eukaryote tree by using a derived gene fusion|journal=Science|volume=297|issue=5578|pages=89–91|doi=10.1126/science.1071196|issn=1095-9203|pmid=12098695|bibcode=2002Sci...297...89S|s2cid=21064445}}</ref>
current understanding places it somewhere in this era.<ref>{{Cite journal|last1=Ayala|first1=Francisco José|last2=Rzhetsky|first2=Andrey|last3=Ayala|first3=Francisco J.|date=1998-01-20|title=Origin of the metazoan phyla: Molecular clocks confirm paleontological estimates|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=95|issue=2|pages=606–611|issn=0027-8424|pmid=9435239|pmc=18467|doi=10.1073/pnas.95.2.606|bibcode=1998PNAS...95..606J|doi-access=free}}</ref><ref>{{Cite journal|last1=Wang|first1=D Y|last2=Kumar|first2=S|last3=Hedges|first3=S B|date=1999-01-22|title=Divergence time estimates for the early history of animal phyla and the origin of plants, animals and fungi.|journal=Proceedings of the Royal Society B: Biological Sciences|volume=266|issue=1415|pages=163–171|pmc=1689654|pmid=10097391|doi=10.1098/rspb.1999.0617}}</ref><ref>{{cite journal |last1=Javaux |first1=Emmanuelle J. |last2=Lepot |first2=Kevin |date=January 2018 |title=The Paleoproterozoic fossil record: Implications for the evolution of the biosphere during Earth's middle-age |journal=[[Earth-Science Reviews]] |volume=176 |pages=68–86 |doi=10.1016/j.earscirev.2017.10.001 |doi-access=free |hdl=20.500.12210/62416 |hdl-access=free }}</ref> Statherian [[fossils]] from the [[Changcheng System|Changcheng Group]] in [[North China]] provide evidence that eukaryotic life was already diverse by the late Palaeoproterozoic.<ref>{{cite journal |last1=Miao |first1=Lanyun |last2=Moczydłowska |first2=Małgorzata |last3=Zhu |first3=Shixing |last4=Zhu |first4=Maoyan |date=February 2019 |title=New record of organic-walled, morphologically distinct microfossils from the late Paleoproterozoic Changcheng Group in the Yanshan Range, North China |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926818301827 |journal=[[Precambrian Research]] |volume=321 |pages=172–198 |doi=10.1016/j.precamres.2018.11.019 |s2cid=134362289 |access-date=29 December 2022}}</ref>