The first clue was the abandoned beach umbrella?

Several studies in recent years have claimed evidence for shorelines and other features that suggest ancient lakes on Mars. Firm evidence has remained elusive.

Now a University of Colorado at Boulder research team claims "the first definitive evidence of shorelines on Mars" in a statement released today.

The scientists see signs of "a deep, ancient lake," which would have implications for the potential for past life on Mars. Life as we know it requires water, and while Mars is dry now, if there was abundant water in the past -- as many studies have suggested -- then life would have been a possibility. There is, however, no firm evidence that life does or ever did exist on the red planet.

Researchers estimate the lake existed more than 3 billion years ago. It covered as much as 80 square miles and was up to 1,500 feet deep -- roughly the equivalent of Lake Champlain bordering the United States and Canada, said Gaetano Di Achille, who led the study out of the University of Colorado at Boulder.

The shoreline evidence, found along a broad delta, included a series of alternating ridges and troughs thought to be surviving remnants of beach deposits.

"This is the first unambiguous evidence of shorelines on the surface of Mars," Di Achille said. "The identification of the shorelines and accompanying geological evidence allows us to calculate the size and volume of the lake, which appears to have formed about 3.4 billion years ago."