Biological and organic constiuents of desert varnish: review and new hypotheses

Details Biological and organic constiuents of desert varnish: review and new hypotheses Biological and organic constiuents of desert varnish: review and new hypotheses

Feb 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004spie.5163..202p&link_type=abstract

Instruments, Methods, and Missions for Astrobiology VII. Edited by Hoover, Richard B.; Rozanov, Alexei Y. Proceedings of the

Biology

Scientific paper

Desert varnish coatings are found on rock surfaces throughout arid regions of the world. Rock varnishes may exist on Mars, as suggested by some observations on both Viking and Mars Pathfinder landing sites. There has long been a debate as to whether varnish coatings are microbially mediated or deposited by inorganic processes. Dozens of bacteria have been cultured from the surface of varnish coatings and recently the molecular ecology of varnish coatings have been characterized using 16S rRNA techniques. Colonies of micro colonial fungus are associated with varnish coatings but it is unclear whether bacteria or fungus are directly involved in varnish formation. Another alternative is the incorporation of microbial components into varnish coatings either by complexation with metals or in association with clays. For instance polysaccharides found in bacterial cell walls contain linear polymers of sugars that may be preserved in arid conditions when complexed with usual varnish components such as calcium, aluminum, silicon, iron and manganese. Understanding the organic components of desert varnish may help to resolve the question of the mechanism of formation of rock coatings, biomineralization processes and bacterial fossils and how to detect past microbially activity on planets.

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