Time scales of erosion and deposition recorded in the residual south polar cap of Mars

► The residual south polar cap of Mars fluctuates in area yet is eroding within its cover of CO2 ice. ► Different morphologic units in the cap have different rates of scarp retreat. ► The oldest units suggest both deposition and erosion over more than 100 Mars years. ► Thinner units show changing erosional periods of Mars decades.