Ancient Mars ocean (IMAGE) University of Colorado at Boulder Caption This is an illustration of what Mars might have looked like some 3.5 billion years ago when an ocean likely covered one-third of the planet's surface, according to a new University of Colorado at Boulder study. (Illustration by University of Colorado) Credit University of Colorado Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.