"We're trying to systematically characterize the stratigraphy of the crater as we drive down, analyzing each unit chemically and mineralogically with all the instruments available," said Nicholas Tosca, a science-team affiliate from the State University of New York, Stony Brook. The first two newly accessed layers resemble the upper layer in having sulfate salts and spherical concretions; both are signs of formation of the rocks under wet conditions.

Squyres said, "I had thought we might see just basalt below the top salty layer, but instead it's salty as far as we've been able to see so far. Every time we see more sulfates as we work down this stack, it adds to the amount of water that was necessary to make this happen."