Editing Microfossil (section)

===Archean cells===
{{see also|Archean life in the Barberton Greenstone Belt}}

Cells can be preserved in the [[rock record]] because their cell walls are made of proteins which convert to the organic material [[kerogen]] as the cell breaks down after death. Kerogen is [[insoluble]] in mineral [[acids]], [[base (chemistry)|base]]s, and [[organic solvents]].<ref>{{cite journal|last=Philp|first=R.P.|author2=Calvin, M. |title=Possible origin for insoluble organic (kerogen) debris in sediments from insoluble cell-wall materials of algae and bacteria|journal=Nature|year=1976|volume=262|pages=134–136 |doi=10.1038/262134a0|issue=5564|bibcode = 1976Natur.262..134P |s2cid=42212699}}</ref> Over time, it is mineralised into [[graphite]] or graphite-like [[carbon]], or degrades into oil and gas hydrocarbons.<ref>{{cite journal|last=Tegelaar|first=E.W.|author2=deLeeuw, J.W.|author3=Derenne, S.|author4=Largeau, C. |title=A reappraisal of kerogen formation|journal=Geochimica et Cosmochimica Acta|year=1989|volume=53|issue=11|pages=3103–3106 |doi=10.1016/0016-7037(89)90191-9|bibcode=1989GeCoA..53.3103T}}</ref> There are three main types of cell morphologies. Though there is no established range of sizes for each type, spheroid microfossils can be as small as about 8&nbsp;[[micrometre]]s, filamentous microfossils have diameters typically less than 5&nbsp;micrometres and have a length that can range from tens of micrometres to 100&nbsp;micrometres, and spindle-like microfossils can be as long as 50&nbsp;micrometres.<ref name=Walsh>{{cite journal|last=Walsh|first=M.|title=Microfossils and possible microfossils from the early Archean Onverwacht Group, Barberton mountain land, South Africa |journal=[[Precambrian Research]]|year=1991|volume=54|issue=2–4|pages=271–293 |pmid=11540926 |doi=10.1016/0301-9268(92)90074-X}}</ref><ref>{{cite journal|author=Oehler, D.Z. |author2=Robert, F. |author3=Mostefaoui, S. |author4=Meibom, A. |author5=Selo, M. |author6=McKay, D.S.|title=Chemical Mapping of Proterozoic Organic Matter at Submicron Spatial Resolution|journal=Astrobiology|year=2006|volume=6|issue=6|pages=838–850 |pmid=17155884 |doi=10.1089/ast.2006.6.838|bibcode = 2006AsBio...6..838O |hdl=2060/20060028086 |hdl-access=free }}</ref>

{{clear}}