Keith Cowing has a nice essay on the current state of our knowledge of Martian history.

From what I have seen of him, Steve Squyres won’t commit himself to a position until there is a lot of data, so when HE says there was a sea there at some point, I would say that is a near certainty. I’m not surprised, but it is nice to have the confirmation. Of course, it just makes me want see people there that much more - now that we have some of the preliminary information, people could discover so much, much more. Even better: Demonstrate people can live using the resources of another world.