Editing Photosynthesis (section)

===Cyanobacteria and the evolution of photosynthesis===
The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a [[common ancestor]] of extant [[cyanobacteria]] (formerly called blue-green algae). The geological record indicates that this transforming event took place early in Earth's history, at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier.<ref>{{cite journal |vauthors= Tomitani A, Knoll AH, Cavanaugh CM, Ohno T |date= April 2006 |title= The evolutionary diversification of cyanobacteria: molecular-phylogenetic and paleontological perspectives |journal= Proceedings of the National Academy of Sciences of the United States of America |volume= 103 |issue= 14 |pages= 5442–5447 |bibcode= 2006PNAS..103.5442T |doi= 10.1073/pnas.0600999103 |doi-access= free |pmc= 1459374 |pmid= 16569695 }}</ref><ref>{{cite web |url= http://www.ucmp.berkeley.edu/bacteria/cyanofr.html |title= Cyanobacteria: Fossil Record |website= ucmp.berkeley.edu |access-date= 2010-08-26 |archive-url= https://web.archive.org/web/20100824004835/http://www.ucmp.berkeley.edu/bacteria/cyanofr.html |archive-date= 2010-08-24 |url-status= dead }}</ref> Because the Earth's atmosphere contained almost no oxygen during the estimated development of photosynthesis, it is believed that the first photosynthetic cyanobacteria did not generate oxygen.<ref>{{cite book |vauthors= Smith A |year= 2010 |title= Plant biology |publisher= Garland Science |location= New York |isbn= 978-0-8153-4025-6 |url= https://books.google.com/books?id=eC0WBAAAQBAJ&pg=PA5 |page= 5 |access-date= 2019-04-17 |archive-date= 2023-01-19 |archive-url= https://web.archive.org/web/20230119181851/https://books.google.com/books?id=eC0WBAAAQBAJ&pg=PA5 |url-status= live }}</ref> Available evidence from geobiological studies of [[Archean]] (>2500 Ma) [[sedimentary rock]]s indicates that life existed 3500 Ma, but the question of when oxygenic photosynthesis evolved is still unanswered. A clear paleontological window on cyanobacterial [[evolution]] opened about 2000 Ma, revealing an already-diverse biota of cyanobacteria. Cyanobacteria remained the principal [[primary producers]] of oxygen throughout the [[Proterozoic Eon]] (2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of [[nitrogen fixation]].<ref>{{Cite journal |last1= Olson |first1= Stephanie L. |last2= Reinhard |first2= Christopher T. |last3= Lyons |first3= Timothy W. |date=2016 |title=Cyanobacterial Diazotrophy and Earth's Delayed Oxygenation |journal= Frontiers in Microbiology |volume= 7 |pages= 1526 |doi= 10.3389/fmicb.2016.01526 |doi-access= free |issn= 1664-302X |pmc= 5033965 |pmid= 27721813 }}</ref><ref>{{Cite journal |last1= Sánchez-Baracaldo |first1= Patricia |last2=Bianchini |first2= Giorgio |last3= Wilson |first3= Jamie D. |last4= Knoll |first4= Andrew H. |date= 2022 |title= Cyanobacteria and biogeochemical cycles through Earth history |url= https://www.cell.com/trends/microbiology/fulltext/S0966-842X(21)00131-1 |journal= Trends in Microbiology |volume= 30 |issue= 2 |pages= 143–157 |doi= 10.1016/j.tim.2021.05.008 |issn= 1878-4380 |pmid= 34229911 }}</ref> [[Green algae]] joined cyanobacteria as the major primary producers of oxygen on [[continental shelves]] near the end of the [[Proterozoic]], but only with the [[Mesozoic]] (251–66 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did the [[primary production]] of oxygen in marine shelf waters take modern form. Cyanobacteria remain critical to [[marine ecosystem]]s as [[Oxygen cycle|primary producers of oxygen]] in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the [[plastid]]s of marine algae.<ref>{{cite book |vauthors= Herrero A, Flores E |year= 2008 |title= The Cyanobacteria: Molecular Biology, Genomics and Evolution |edition= 1st |publisher= Caister Academic Press |isbn= 978-1-904455-15-8 |url= https://books.google.com/books?id=xgMahO1BXrQC |access-date= 2019-04-17 |archive-date= 2023-01-19 |archive-url= https://web.archive.org/web/20230119181852/https://books.google.com/books?id=xgMahO1BXrQC |url-status= live }}</ref>