Sedimentary deposits are places where our planet's fossil record is stored, so they are probably good places to hunt for fossils on Mars, too, added Nealson. Their small, soft bodies usually decompose before fossilization can occur. For now, the challenge facing scientists is to determine whether the sedimentary deposits seen on Mars are in fact the remnants of ancient lakebeds or seafloors. You have to be careful. Clues in the rocks themselves will help scientists determine whether the layered features on Mars were deposited by water or by some other agent.
Wind is a primary contender.
As these deposits became buried, pressure from the covering material's weight would begin the transformation to sedimentary rock. Because wind can carry only very small dust particles, while water can transport larger ones, geologists would expect wind-laid sedimentary rocks to contain relatively small grains. Measuring the sizes of grains in the Martian deposits will provide important clues about their origin. Some of these data will be gathered by upcoming missions to Mars. In December 2003, the European Space Agency's Beagle 2 lander is scheduled to land at Isidis Planitia, an area of the Martian surface near 10 degrees North latitude.