Sinuous channels have characteristics of river beds, including channel islands .
Collapsed terrain shows evidence that saturated frozen crust was heated in places from below, producing catastrophic flooding. Mars probably outgassed a substantial amount of CO 2 like Venus and Earth. Initially this CO 2 produced a strong greenhouse effect and made Mars a temperate place. The weak gravity of Mars is only marginally capable of holding on to an atmosphere as well. Volcanism on Mars ended long ago.