If we keep looking ,we will eventually find evidence of internal combustion engine use that must have ruined their ozone layer and killed this poor planet and all the inhabitants. This will surely happen to us also.
LOL! I hate to be a buzz-kill, but I think it was a combination of Mars' lack of a significant planetary magnetic field (to deflect the solar wind, and its low gravity, that allowed the primorial Martian atmosphere to simply be blown away into space.
FRegrards!