Soil minerals point to planet-wide ocean on Mars New Scientist

An ocean of water once wrapped around Mars, suggests the discovery of soil chemicals by NASA’s rovers. But the same chemicals also indicate that life was not widespread on the planet at the time the ocean was present.
Sulphates, which form most readily in liquid water, had already been detected by the Spirit and Opportunity rovers. The minerals have been interpreted as evidence for past bodies of water on the surface. But it has not been clear how large these bodies of water might have been.
Now, a new analysis of rover data suggests that the sulphates were once dissolved in a planet-wide ocean. The study was carried out by James Greenwood of Wesleyan University and Ruth Blake of Yale University, both in Connecticut, US.