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Project Progress

Rock Varnish and Microbes (dm)

It has been proposed that rocks on Mars might be sometimes covered with a coating which may be 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 martian 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. Samples are thin sectioned, examined with petrographic microscope, selected areas are microtomed for TEM imaging and analysis, and samples are analyzed by SEM and electron microprobe. Results on the Arizona samples show clear evidence of microbial activity. The 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.