Many places on Mars show rocks arranged in layers.
Rock can form layers in a variety of ways.
 Volcanoes, wind, or water can produce 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 fine 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 many places, especially craters.
 This is exactly what would appear if a large lake had slowly evaporated.
  Moreover, since some layers contain gypsum, a sulfate which forms in relatively fresh water, life could have formed in some craters.
Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways.  Volcanoes, wind, or water can produce 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 fine 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 many places, especially craters.  This is exactly what would appear if a large lake had slowly evaporated.   Moreover, since some layers contain gypsum, a sulfate which forms in relatively fresh water, life could have formed in some craters.
Flammarion (Martian crater)