Mars is a planet I've always been particularly interested in. In my own opinion on EE/GE, Mars represents things that could have been and things that may yet to come. Mars is much smaller then Earth, and has significantly less mass. It appears to me like a planet that may have started out much like Earth did. I can honestly say I think it used to be a lot smaller, it had a single joined thin crust that had a shallow ocean.
Valles Marineris: I honestly think the planet began to expand much like earth, and the Valles Marineris may be the planets earliest attempt at a massive tectonic spread like our own pacfic ocean. I don't know if it's the planets lack of mass, maybe even magnetic shielding, but it would seem the tectonic spreading subsided, it's shallow ocean was absorbed into it's upper mantle and it's massive shield volcano is but a grave stone to early planetary expansion.
I think the planet may serve as a warning sign for the future of Earth, Short Term the oceans may rise as the ice caps melt off. But long term, the planet may become less tectonically active, the mantle may re-absorb the oceans and gradually maybe loose the magnetic shielding resulting in a loss of atmosphere. I think Mars may end up looking like our moon in the distant future.