Mars may have had seas or oceans in the distant past. Proving or disproving that hypothesis is high on the scientific agenda. The possibility of life may hinge on whether there were indeed long-lasting bodies of water on a warm, wet early Mars. Life might have taken hold in an ancient Mars sea. On the other hand, if Mars was always dry and cold, then it's much less likely that life could have begun there.

See "Hunting For Martians" - it has my name in the image credits

See "Life on Mars - a definite possibility"