What is Stromatolite?
[[File:Stromatolites in Sharkbay.jpg|right|thumb|220px|Modern stromatolites in [[Shark Bay]], [[Western Australia]]]] [[File:Stromatolithe_Paléoarchéen_-_MNHT.PAL.2009.10.1.jpg|thumb|Stromatolite from [[Strelley Pool]] [[chert]] (SPC) ([[Pilbara]] Craton) - Western Australia]] [[File:Stromatolites Cochabamba.jpg|thumb|right|220px| Lower [[Proterozoic]] stromatolites from [[Bolivia]], [[South America]] (polished vertical section through rock)]] '''Stromatolites''' <ref>from [[Greek language|Greek]] ''strōma'', mattress, bed, stratum, and ''lithos'', rock</ref> are special [[Rock (geology)|rock]]-like structures. They usually form in shallow water. They are formed by [[bacteria]] such as [[cyanobacteria]]. There may also be other types of bacteria and single-celled [[algae]]. The [[mucus]] [[Secretion|secreted]] by the bacteria collects grains of [[sediment]], and they are stuck together with [[calcium carbonate]], also from the bacteria. This builds up into the structures seen in certain sea-shore bays. Cyanobacteria use water, [[carbon dioxide]], and sunlight to create their food, and expel [[oxygen]] as a by-product. The real significance of stromatolites is that they are the earliest [[fossil]] evidence of [[life]] on Earth. The oldest known stromatolites have been dated between 3,710 million years and 3,695 million years old, and were discovered from an exposed outcrop of metacarbonate rocks in the Isua supracrustal belt (ISB) in Southwest [[Greenland]].<ref>{{Cite journal|last1=Nutman|first1=Allen P.|last2=Bennett|first2=Vickie C.|last3=Friend|first3=Clark R. L.|last4=Kranendonk|first4=Martin J. Van|last5=Chivas|first5=Allan R.|date=September 2016|title=Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures|url=http://www.nature.com/doifinder/10.1038/nature19355|journal=Nature|language=En|volume=537|issue=7621|pages=535–538|bibcode=2016Natur.537..535N|doi=10.1038/nature19355|issn=1476-4687|pmid=27580034|s2cid=205250494}}</ref> The ISB stromatolites predate by over 215