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Project Progress

It has been proposed that rocks on Mars are sometimes covered with a coating that may be the equivalent of desert varnish found on many rocks on earth. It has further been proposed that this desert varnish on Mars may have developed with the assistance of microbial activity and may even contain extant life. To prepare for more detailed study of varnish on Mars’s rocks, either by robotic investigation or on returned samples, we have undertaken a study of rock varnish from terrestrial locations. Initial work has been with varnish from southwestern Arizona and surface rocks from the Pilbara formation of western Australia. Samples are thin sectioned, examined with a petrographic microscope, selected areas are microtomed for transmission electron microscopy (TEM) imaging and analysis, and samples are analyzed by a SEM and electron microprobe. Results on both the Arizona and Australian samples show clear evidence of microbial activity. The Arizona varnish contains biomorphs, biofilms, and carbon-rich areas. The relationship between microbial activity and the precipitation of the Fe and Mn phases, which comprise the varnish, is being investigated. The Australian desert varnish samples show clear evidence for microbial activity, but we have not yet extensively documented its occurance.

In the coming year we will characterize the phases that make up the varnish on the Arizona and Western Australian rocks and compare them to rocks from other localities including desert regions, permafrost regions, and Antarctica. In each case we will document the extent of microbial activity, if any.

We will also attempt to culture some of the microorganisms found in the rock varnish and use biosignature techniques to identify the microbial population. We will attempt to determine the role of microbes in desert varnish. To what degree do they cause the precipitation of the varnish minerals and phases? Are they necessary for the formation of the varnish, or are they simply incorporated into it as it forms by inorganic chemical processes? Do the organic compounds generated by the microbes influence the nucleation and crystallization of the varnish mineral phases?