Desert VarnishWhen Charles Darwin was a young man aboard the HMS Beagle, he explored a shore off the
Desert VarnishWhen Charles Darwin was a young man aboard the HMS Beagle, he explored a shore off the coast of South America, where he was intrigued by rock outcroppings that he said, “glittered in the sunlight”. He deducted that the rocks shone because of a coating of thin layers of metallic oxides, but could not explain how it might have been made.Geologists have since found the same coating that they now call “desert varnish”, in many locales and has even been proposed to exist on Mars based on data from various missions. Although they are no more certain of its provenance than Darwin was, there are several ideas that try to explain this “glittery rock”. These ideas have arisen by two observations that give reason to suspect that this substance may be a product of biology.The first observation is that the thin layers of minerals and chemicals that desert varnish reveals in cross sections resembles the layers found in “stromatolites.” These are the formations that in Shark Bay, Australia and in upstate New York. Strom’s, for short, are formed by many generations of bacteria that layer up, live and then die one atop another. So the thinking goes, the layering of desert varnish might result from a similar biological process.The second observation is that many of the chemicals in desert varnish layers, most notably manganese and iron, are not in the rocks (such as sandstone) that desert varnish typically varnishes, but are in fact produced by known organisms.These observations are a long way from a clear-cut case for life though as no laboratory microbiologist has been able to coax bacteria or algae to make desert varnish. Just as discouraging (to those who might wish it to be a product of organisms), bacteria found in ‘in situ’ desert varnish (the bacteria that might reasonably be expected to produce it) are of many varieties, too many, microbiologists think, to turn out the same product so consistently.It is possible that the stuff that intrigued Darwin and so many after him is the end result of some very complex chemistry. But no one has been able to reproduce that either. So it appears that at the moment, a natural phenomenon that exists for us to see, and after nearly two centuries of study remains a mystery. That’s the exciting part of science though, the try and solve these mysteries – some of which may never be solved, and I personally quite like the thought of that.~ JMPhoto Credit (Main): http://commons.wikimedia.org/wiki/File:Desert_Varnish_-_Horseshoe_Canyon.jpgPhoto Credit: My ownMore info:A close look at the mystery of desert varnish http://artsandsciences.colorado.edu/magazine/2011/06/a-close-look-at-the-mystery-of-desert-varnish/Perry, R. S., & Kolb, V. M. (2004, February). Biological and organic constituents of desert varnish: review and new hypotheses. In Optical Science and Technology, SPIE’s 48th Annual Meeting (pp. 202-217). International Society for Optics and Photonics.https://www.psi.edu/sites/default/files/imported/about/staff/rperry/perry/SPIE_DV.pdfDessert Varnish, Canyonlands:http://www.nps.gov/cany/learn/nature/desertvarnish.htm[__](https://www.facebook.com/TheEarthStory/photos/pcb.838332016227844/838331729561206/?type=3&theater#) -- source link
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