▁structures . ▁ ▁With ▁the ▁passage ▁of ▁time , ▁surrounding ▁material ▁was ▁er oded ▁away , ▁thereby ▁leaving ▁hard ▁rid ges ▁behind . ▁Since ▁the ▁rid ges ▁occur ▁in ▁locations ▁with ▁cl ay , ▁these ▁form ations ▁could ▁serve ▁as ▁a ▁marker ▁for ▁cl ay ▁which ▁requires ▁water ▁for ▁its ▁formation . ▁ ▁Water ▁here ▁could ▁have ▁supported ▁life . ▁ ▁F ract ured ▁ground ▁Some ▁places ▁on ▁Mars ▁break ▁up ▁with ▁large ▁f ract ures ▁that ▁created ▁a ▁terrain ▁with ▁mes as ▁and ▁valle ys . ▁ ▁Some ▁of ▁these ▁can ▁be ▁quite ▁pretty . ▁ ▁Mes as ▁ ▁Mes as ▁formed ▁by ▁ground ▁collapse ▁ ▁Vol cano es ▁under ▁ice ▁ ▁There ▁is ▁evidence ▁that ▁vol cano es ▁sometimes ▁er upt ▁under ▁ice , ▁as ▁they ▁do ▁on ▁Earth ▁at ▁times . ▁ ▁What ▁seems ▁to ▁happen ▁it ▁that ▁much ▁ice ▁mel ts , ▁the ▁water ▁esc apes , ▁and ▁then ▁the ▁surface ▁cra cks ▁and ▁col laps es . ▁ ▁These ▁exhib it ▁concent ric ▁f ract ures ▁and ▁large ▁pieces ▁of ▁ground ▁that ▁seemed ▁to ▁have ▁been ▁pulled ▁apart . ▁ ▁S ites ▁like ▁this ▁may ▁have ▁recently ▁had ▁held ▁liquid ▁water , ▁hence ▁they ▁may ▁be ▁fruit ful ▁places ▁to ▁search ▁for ▁evidence ▁of ▁life . ▁ ▁F ract ures ▁forming ▁blocks ▁In ▁places ▁large ▁f ract ures ▁break ▁up ▁surfaces . ▁ ▁Sometimes ▁straight ▁edges ▁are ▁formed ▁and ▁large ▁cub es ▁are ▁created ▁by ▁the ▁f ract ures . ▁ ▁L ava ▁flows ▁ ▁Root less ▁Con