Shiny Rock Coating May Hold Key To Martian Life

By Aussiegirl

A very interesting article on one more method by which science could determine whether or not life has ever existed on our neighbor Mars. (You can see in the accompanying illustration how beautiful desert varnish is.)

Shiny Rock Coating May Hold Key To Martian Life

Shiny Rock Coating May Hold Key To Martian Life

by Staff Writers
London, England (SPX) Jul 06, 2006

A mysterious shiny coating found on rocks in many of Earth's most arid environments could reveal whether life once existed on Mars. Research published in the July edition of the journal Geology suggests the dark coating known as desert varnish creates a record of life around it by binding traces of DNA, amino acids and other organic compounds to desert rocks. Therefore, samples of Martian desert varnish could show whether there has been life on the red planet at any stage over the last 4.5 billion years.

The researchers said they hope their findings will encourage planners of future Mars sample-return missions to include desert varnish to their list of target substances.

The source of the varnish, which looks like it has been painted onto the rocks, has intrigued scientists since the mid-19th century. British biologist Charles Darwin became so fascinated with the material he asked Swedish geochemist Jons Berzelius to investigate it.

Previous research had suggested its dark color resulted from the presence of manganese oxide, and any traces of life found within the varnish probably originated from biological processes caused by microbes in the mineral.

The new research, however, used a battery of techniques - including high resolution electron microscopy - to show that any traces of life in the varnish do not come from microbes in MnO.

Instead, the research reveals, the most important mineral in the varnish is silica, which means biological processes are not significant in the coating's formation. On desert rock surfaces, silica is dissolved from other minerals and then gels together to form a glaze, trapping organic traces from its surroundings.

Randall Perry of Imperial College London, the lead author of the research, explained that because life is not involved in desert varnish formation, it can serve as an indicator of whether life was present or absent in the local environment.

"If silica exists in varnish-like coatings in Martian deserts or caves, then it may entomb ancient microbes or chemical signatures of previous life there, too," Perry said. "Desert varnish forms over tens of thousands of years and the deepest, oldest layers in the varnish may have formed in very different conditions than the shallowest, youngest layer."

"These lustrous chroniclers of the local surroundings can provide a window back in time," he added. "Martian desert varnish would contain a fascinating chronology of the Martian setting." [...]