Editing Stromatolite (section)

===Fossil record ===
Some Archean rock formations show macroscopic similarity to modern microbial structures, leading to the inference that these structures represent evidence of ancient life, namely stromatolites. However, others regard these patterns as being the result of natural material [[Deposition (geology)|deposition]] or some other abiogenic mechanism. Scientists have argued for a biological origin of stromatolites due to the presence of organic globule clusters within the thin layers of the stromatolites, of [[aragonite]] nanocrystals (both features of current stromatolites),<ref name=Lepot2008>{{Cite journal | doi = 10.1038/ngeo107 | volume = 1 | pages = 118–21 | last = Lepot | first = Kevin |author2=Karim Benzerara |author3=Gordon E. Brown |author4=Pascal Philippot
 | title = Microbially influenced formation of 2.7 billion-year-old stromatolites | journal = Nature Geoscience | year = 2008 | issue=2 |bibcode = 2008NatGe...1..118L }}</ref> and of other microstructures in older stromatolites that parallel those in younger stromatolites that show strong indications of biological origin.<ref name=Allwood2009>{{Cite journal | last1 = Allwood | first1 = Abigail | last2 = Grotzinger |last3=Knoll |last4=Burch |last5=Anderson |last6=Coleman |last7=Kanik | title = Controls on development and diversity of Early Archean stromatolites | journal = Proceedings of the National Academy of Sciences | year = 2009 | doi = 10.1073/pnas.0903323106 | volume = 106 | pages = 9548–9555 | issue = 24 |bibcode = 2009PNAS..106.9548A | pmid=19515817 | pmc=2700989| doi-access = free }}</ref><ref>{{cite book|title=Cradle of life: the discovery of earth's earliest fossils |url=https://archive.org/details/cradlelifediscov00scho_554 |url-access=registration |publisher=Princeton University Press |location=Princeton, N.J |year=1999 |pages=[https://archive.org/details/cradlelifediscov00scho_554/page/n97 87]–89 |isbn=978-0-691-08864-8 }}</ref>

[[File:Stromatolites hoyt mcr1.JPG|thumb|Fossilized stromatolites in the [[Hoyt Limestone]] ([[Cambrian]]) exposed at Lester Park, near [[Saratoga Springs, New York|Saratoga Springs]], New York]]

[[File:Stromatolites.jpg|thumb|[[Precambrian]] fossilized stromatolites in the [[Siyeh Formation]], [[Glacier National Park (U.S.)|Glacier National Park]]]]

[[File:CambrianStromatolites.jpg|thumb|Fossilized stromatolites (Pika Formation, middle Cambrian) near Helen Lake, [[Banff National Park]], Canada]]

Stromatolites are a major constituent of the fossil record of the [[Earliest known life forms|first forms of life]] on Earth.<ref name="PiP">{{cite journal |title=Patterns in Palaeontology: The first 3 billion years of evolution |first=Russell J. |last=Garwood |year=2012 |journal=Palaeontology Online |volume=2 |issue=11 |pages=1–14 |url=http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/ |access-date=25 June 2015 |archive-url=https://web.archive.org/web/20150626104131/http://www.palaeontologyonline.com/articles/2012/patterns-in-palaeontology-the-first-3-billion-years-of-evolution/ |archive-date=26 June 2015 |url-status=live}}</ref> They peaked about 1.25 billion years ago (Ga)<ref name=Allwood2009/> and subsequently declined in abundance and diversity,<ref>{{cite journal| year=1982 | title=Precambrian conical stromatolites from California and Sonora | author=McMenamin, M. A. S. | journal=Bulletin of the Southern California Paleontological Society | volume=14 | issue=9&10 | pages=103–105 }}</ref> so that by the start of the Cambrian they had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victim to grazing creatures (the [[Cambrian substrate revolution]]); this theory implies that sufficiently complex organisms were common around 1 Ga.<ref name="McNamara1996DatingOriginAnimals">{{cite journal | author = McNamara, K.J. | title = Dating the Origin of Animals | journal = Science | volume = 274 | pages = 1993–1997 | date = 20 December 1996 | doi = 10.1126/science.274.5295.1993f | issue = 5295 | bibcode = 1996Sci...274.1993M | doi-access = free }}</ref><ref name="AwramikStromatoliteDiversityMetazoanAppearance">{{cite journal | author = Awramik, S.M. | title = Precambrian columnar stromatolite diversity: Reflection of metazoan appearance | journal = Science | volume = 174 | pages = 825–827 | date = 19 November 1971 | doi = 10.1126/science.174.4011.825 | pmid = 17759393 | issue = 4011 | bibcode = 1971Sci...174..825A| s2cid = 2302113 }}</ref><ref name="Bengtson2002OriginsOfPredation">{{Cite encyclopedia | author=Bengtson, S. | year=2002 | chapter=Origins and early evolution of predation | encyclopedia=The Paleontological Society Papers | volume=8 | title=The fossil record of predation | editor=Kowalewski, M. | editor2=Kelley, P.H. | pages=289–317 | publisher=The Paleontological Society | chapter-url=http://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf | access-date=29 December 2014 }}</ref> Another hypothesis is that [[protozoa]] such as [[foraminifera]] were responsible for the decline, favoring formation of [[Thrombolite|thrombolites]] over stromatolites through microscopic [[bioturbation]].<ref name="Bernhard Edgcomb Visscher McIntyre-Wressnig pp. 9830–9834">{{cite journal | last1=Bernhard | first1=J. M. | last2=Edgcomb | first2=V. P. | last3=Visscher | first3=P. T. | last4=McIntyre-Wressnig | first4=A. | last5=Summons | first5=R. E. | last6=Bouxsein | first6=M. L. | last7=Louis | first7=L. | last8=Jeglinski | first8=M. | title=Insights into foraminiferal influences on microfabrics of microbialites at Highborne Cay, Bahamas | journal=Proceedings of the National Academy of Sciences | volume=110 | issue=24 | date=28 May 2013 | doi=10.1073/pnas.1221721110 | pmid=23716649 | pmc=3683713 | pages=9830–9834| bibcode=2013PNAS..110.9830B | doi-access=free }}</ref>

[[Proterozoic]] stromatolite microfossils (preserved by [[permineralization]] in silica) include cyanobacteria and possibly some forms of the [[Eukaryota|eukaryote]] [[Chlorophyta|chlorophytes]] (that is, [[green algae]]). One [[genus]] of stromatolite very common in the [[geologic time scale|geologic record]] is ''[[Collenia]]''.

The connection between grazer and stromatolite abundance is well documented in the younger [[Ordovician]] [[evolutionary radiation]]; stromatolite abundance also increased after the [[Late Ordovician mass extinction]] and [[Permian–Triassic extinction event]] decimated marine animals, falling back to earlier levels as marine animals recovered.<ref name="SheehanHarris2004ResurgenceAfterOrdovicianExtinction">{{cite journal | title=Microbialite resurgence after the Late Ordovician extinction | journal=Nature | volume=430 | pages=75–78 | year=2004 | doi=10.1038/nature02654 | author1=Sheehan, P.M. | author2=Harris, M.T. | pmid=15229600 | issue=6995 | bibcode=2004Natur.430...75S| s2cid=4423149 }}</ref> Fluctuations in [[metazoan]] population and diversity may not have been the only factor in the reduction in stromatolite abundance. Factors such as the chemistry of the environment may have been responsible for changes.<ref name="Riding2006">{{cite journal | url=http://www.robertriding.com/pdf/riding2006mc.pdf | title=Microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time | author=Riding, R. | journal=Sedimentary Geology | date=March 2006 | volume=185 | issue=3–4 | pages=229–38 | doi=10.1016/j.sedgeo.2005.12.015 | bibcode=2006SedG..185..229R | access-date=9 December 2011 | archive-url=https://web.archive.org/web/20120426041343/http://www.robertriding.com/pdf/riding2006mc.pdf | archive-date=26 April 2012 | url-status=live}}</ref><ref name="phw2017"/>

While [[prokaryote|prokaryotic]] cyanobacteria reproduce asexually through cell division, they were instrumental in priming the environment for the [[timeline of evolution|evolutionary development]] of more complex eukaryotic organisms.<ref name="PiP" /> They are thought to be largely responsible for increasing the amount of oxygen in the primeval Earth's atmosphere through their continuing photosynthesis (see [[Great Oxygenation Event]]). They use water, carbon dioxide, and sunlight to create their food. A layer of [[polysaccharides]] often forms over mats of cyanobacterial cells.<ref>{{cite journal |last1=Kawaguchi |first1=Tomohiro |last2=Decho |first2=Alan W. |title=Biochemical Characterization of Cyanobacterial Extracellular Polymers (EPS) from Modern Marine Stromatolites (Bahamas) |journal=Preparative Biochemistry and Biotechnology |date=January 2000 |volume=30 |issue=4 |pages=321–330 |doi=10.1080/10826060008544971|pmid=11065277 |s2cid=37979265 }}</ref> In modern microbial mats, debris from the surrounding habitat can become trapped within the polysaccharide layer, which can be cemented together by the calcium carbonate to grow thin laminations of [[limestone]]. These laminations can accrete over time, resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight to the organisms for photosynthesis. Layered spherical growth structures termed [[oncolite]]s are similar to stromatolites and are also known from the fossil record. Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria, common in the fossil record and in modern sediments.<ref name=Lepot2008/> There is evidence that thrombolites form in preference to stromatolites when [[foraminifera]] are part of the biological community.<ref name="Nuwer2020">{{cite news |last1=Nuwer |first1=Rachel |author-link=Rachel Nuwer |title=What Happened to the Stromatolites, the Most Ancient Visible Lifeforms on Earth? |url=https://www.smithsonianmag.com/smart-news/what-happened-to-the-stromatolites-the-most-ancient-visible-lifeforms-on-earth-84714880/ |access-date=18 April 2020 |work=Smithsonian Magazine |agency=Smithsonian Institution |date=30 May 2013}}</ref>

The Zebra River Canyon area of the Kubis platform in the deeply dissected Zaris Mountains of southwestern [[Namibia]] provides a well-exposed example of the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, the stromatolites here being better developed in updip locations under conditions of higher current velocities and greater sediment influx.<ref>{{cite journal |author1=Adams, E. W. |author2=Grotzinger, J. P. |author3=Watters, W. A. |author4=Schröder, S. |author5=McCormick, D. S. |author6=Al-Siyabi, H. A. |year=2005 |title=Digital characterization of thrombolite-stromatolite reef distribution in a carbonate ramp system (terminal Proterozoic, Nama Group, Namibia) |journal=AAPG Bulletin |volume=89 |issue=10 |pages=1293–1318 |doi=10.1306/06160505005 |url=http://www.wellesley.edu/Astronomy/Wwatters/adams%20etal%20-%20digital%20models%20nama%20reefs%20-%20aapg%20bull%202005.pdf |access-date=9 December 2011 |archive-url=https://web.archive.org/web/20160307215400/http://wellesley.edu/Astronomy/wwatters/adams%20etal%20-%20digital%20models%20nama%20reefs%20-%20aapg%20bull%202005.pdf |archive-date=7 March 2016 |url-status=live}}</ref>