Many places on Mars show rocks arranged in layers. Sometimes the layers are of different colors. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates. The Mars rover Opportunity examined such layers close-up with several instruments. Some layers are probably made up of fine particles because they seem to break up into find dust. Other layers break up into large boulders so they are probably much harder. Basalt, a volcanic rock, is thought to in the layers that form boulders. Basalt has been identified on Mars in many places. Instruments on orbiting spacecraft have detected clay (also called phyllosilicate) in some layers. Recent research with an orbiting near-infrared spectrometer, which reveals the types of minerals present based on the wavelengths of light they absorb, found evidence of layers of both clay and sulfates in Columbus crater.Cabrol, N. and E. Grin (eds.). 2010. Lakes on Mars. Elsevier.NY. This is exactly what would appear if a large lake had slowly evaporated.Wray, J. et al. 2009. Columbus Crater and other possible paleolakes in Terra Sirenum, Mars. Lunar and Planetary Science Conference. 40: 1896. Moreover, because some layers contained gypsum, a sulfate which forms in relatively fresh water, life could have formed in the crater.
