by THE DAILY TELEGRAPH BOULDER (Colorado)

A vast Earth-like ocean covered a third of the surface of Mars 3.5 billion years ago, new research suggests.

Scientists believe it stretched around the planet's northern hemisphere and held 10 times more water than all the Earth's oceans combined.

The water may have provided a cradle for the emergence of extraterrestrial life, researchers claim.

In new research published in the journal Nature Geoscience, scientists from the University of Colorado identified 52 delta regions on Mars fed by numerous river-like systems.

All lay at about the same height, suggesting that they marked the shoreline edge of a huge river-fed ocean, which they believe covered a third of the planet.

"Our findings lend credence to the hypothesis that an ocean formed on early Mars as part of a global and active hydrosphere," said the researchers, led by Dr Gaetano Di Achille and Professor Brian Hynek.