The oceans of Mars teemed with life

... maybe.

Maybe there were vast oceans, and maybe they were occupied by microbes. This, according to reserearch being discussed in Natoial Geographic.

A vast ocean chock-full of microbes may have once covered more than a third of Mars's surface, scientists say.

The new evidence, from an analysis of dried-up Mars river deltas, adds to growing signs the red planet was once wet.

On Earth, river deltas all lie at more or less the same elevation and reflect the current sea level. In fact, by estimating the elevations of ancient deltas, scientists can reconstruct how sea levels have changed over time.

Details here.