So, I've just been reading a recent ScienceDaily article, and came across this interesting quote
"Clays form in more neutral, less acidic conditions than the sulfate-rich sandstones we've been looking at," Arvidson says. "Our hypothesis is that if there are clay minerals, the water was less acidic and therefore more conducive to life. The presence of zinc, bromine, phosphorus, chlorine, and sulfur in the Tisdale rock is exciting in that it points toward water moving through and altering the rock, although we have no evidence for clay minerals in Tisdale. Further, the Tisdale surfaces were very rough and we were unable to make use of the Rock Abrasion Tool (RAT) to clean off the surfaces to expose fresh materials.
"Thus, we moved on and are now in the thick of the hunt to find these elusive clay minerals by traversing to other rock targets and making detailed measurements, including making chemical and mineralogical observations of natural, brushed, and ground surfaces. The rock Opportunity is sitting over currently is called Chester Lake and will be our first target in which we will use the RAT to progressively expose deeper and deeper surfaces," Arvidson says.
Here's the thing: we know that liquid water once existed on the Martian surface - that's for sure. But could we tell right away once we found sedimentary rocks on the Martian surface, or could Martian sedimentary rocks form through some other process? (like maybe Martian's dust storms)