Steve Squyres Water Quotations

One possibility is that it's the last layer to form. It speaks to yet another water episode.

We've got some evidence, I think, of water flowing through the rocks, and changes in chemistry, I don't think we have what any of us would consider compelling evidence for surface water yet.

When we first touched down at Gusev Crater on the night of January 4, 2004, the Columbia Hills seemed impossibly far away. It was a necessary place for us to get to, though, because as we looked across the plains we quickly realized these plains were made of basaltic lava. This was stuff that was interesting but did not tell us what we really sought to know about Gusev Crater, and that is whether there had been water here. So in order to find something, in order to find something different, we had to make that mile-and-a-half drive.

It was a hot, violent place with volcanic explosions and impacts. Water was around, perhaps localized hot springs in some cases and trace amounts of water in other cases.

They provide a wonderful glimpse into what Mars was like in the earliest part of its history, ... It was a violent place. It was a place where meteorite impacts were happening frequently. It was a place where there volcanic explosions happening frequently. Hot stuff was raining from the skies. There was water. When rocks were deposited, water would flow through those rocks and change their chemistry. This is a glimpse into the ancient past of Mars.

We have concluded that the rocks here were once soaked in liquid water. It changed their texture, and it changed their chemistry. We've been able to read the tell-tale clues the water left behind, giving us confidence in that conclusion.