NASA's many rovers and orbiters on and above Mars have discovered significant evidence that liquid water once flowed on the planet's surface. That much all space scientists agree upon. What is in dispute is how much water existed at any given time and how long did it last on the surface. Some scientists believe that ice melted when a volcano erupted or a meteorite struck the planet. But, they say, it gushed heavily, carving the many river beds on the red Planet, but evaporated rapidly and was lost to space. The water lasted at most a few years from each event before going away.

Others suggest that while it may have formed lakes and even an ocean, the water still went away in at most a few thousand years. That's not nearly a long enough time to for life to evolve. But a new study led by Michael Manga, a UC Berkeley professor of earth and planetary science, suggests that Mars' first of two, or even more, oceans came a few hundred million years earlier than generally believed.

The surface of Mars features the tallest volcano in the solar system, Olympus Mons, plus several other very large volcanoes in an area known as the Tharsis region of Mars. Rather than forming quickly, as had been assumed, the study led by Manga says the Tharsis area volcanoes formed over a long time, melting or releasing water from below the surface of the planet. The study says the Martian oceans existed for several hundred million years, perhaps intermittently. "Volcanoes may be important in creating the conditions for Mars to be wet," Manga said.

An ocean lasting for a few hundred million years is plenty long enough for life to come into existence and perhaps evolve into more complex microbial forms. Manga and his team only studied the geology associated with the formation of the Tharsis volcanoes and oceans on Mars. They did not address any biological implications of the processes they describe, but many biologists have claimed that with only short-lived oceans, life likely could never have formed. Now, they can frame that notion in more positive terms.