Mars Covered in Water?

It sure seems like it was the case a few billion years ago.

The ocean -- which likely covered about 36 percent of the planet and contained 30 million cubic miles of water, about ten times less than Earth's oceans -- was fed by at least 52 river deltas which were in turn fed by countless river valleys and tributaries. Half of those deltas were at similar elevations, most likely marking the ocean's boundaries.

The next questions to answer are where did the water go and if that ocean had any life living in it.