The red planet was once awash in water, say scientists – not boiling water, but benign seas that may have been suitable for life.

"There was apparently pervasive water present during the first 600 to 700 million years," said Brown University geologist John Mustard, co-author of a paper scheduled to be published today in Nature.

Mustard's team studied data returned by the Compact Reconnaisance Imaging Spectrometer for Mars, an instrument designed to find traces of minerals that interact with water.

Earlier studies have found evidence of ancient gushers, and the Mars Phoenix Lander recently found ice. But Mustard's analysis provides the clearest picture yet of planet-wide hydrological impacts – and, most tantalizingly, CRISM showed widespread deposits of clay-like minerals that form only at relatively low temperatures.

Ancient Martian oceans may have been salty, but at least they weren't boiling. And perhaps, said Mustard, they weren't dead.

"I think the prospects for present life were dim, but for past life, during this habitable era, they were really quite good," he said.

As for whether evidence of life will remain after four billion years, Mustard said that "it's probably better-preserved on Mars than on the Earth, where plate tectonics has recycled the crust."

He continued, "On Mars, many more elements from that early history are still present. And we do think whiffs of life are preserved in the Earth record, so I think Mars stands a good chance of preserving signatures, if they ever existed."

Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument [Nature] [not yet online]

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Images: Courtesy of John Mustard and Nature; deposits of clay-like phyllosilicates, which preserve a record of past interactions between water and rock, appear in color.*

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