Rock varnish may hold clues to life on Mars

As NASA’s Curiosity rover prepares to search for signs that Mars may once have supported life, a team of researchers analyzing rocks in New York may have found a clue telling the rover where to look. By gazing through high-powered microscopes, the researchers discovered that the dark brownish/blackish coating on some rocks, called rock varnish, probably stems from large numbers of microorganisms that died on the rocks. Later, manganese in the microbes would have mixed with tiny clay minerals to adhere to the surface of the rocks and form the several-micrometers-thick layer of manganese-rich varnish.