Lakes on Mars

The Mars Global Surveyor spacecraft has photographed layered structures
similar to sedimentary rocks that may have been formed by ancient lakes between
4.3 and 3.5 billion years ago. If any life existed on Mars at the time, these
rocks might contain fossil remains. Mike Malin and Kenneth Edgett of Malin Space
Science Systems in San Diego suspect that they formed as sediment settled out
from lakes inside early craters and chasms (Science, vol 290, p1927).