How do we know that conditions for earth-like life were never favorable on Mars? And for that matter, life could have evolved differently on Mars. Besides the evidence suggests there were at least periods of liquid water on Mars - the layered rock formed by a dry lake bed. I guess the questions is how long did life have a chance to take hold.

It's the possibility that life might, or may have existed on mars that I find most intriguing. Evidence of any life on Mars would indicate that it's not that hard for life to begin and the likelyhood of other civilizations even in our own galaxy goes up.

Admit it, while being able to look at the basic gelology of mars is amazing, I bet most people here have their eye's glued on the microscopic imager pics, looking for something like the "flake".