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takyon writes:

Mars' oceans formed early, possibly aided by massive volcanic eruptions

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million years earlier and were not as deep as once thought.

[...] The new model proposes that the oceans formed before or at the same time as Mars' largest volcanic feature, Tharsis, instead of after Tharsis formed 3.7 billion years ago. Because Tharsis was smaller at that time, it did not distort the planet as much as it did later, in particular the plains that cover most of the northern hemisphere and are the presumed ancient seabed. The absence of crustal deformation from Tharsis means the seas would have been shallower, holding about half the water of earlier estimates.

"The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later," Manga said. "We're saying that the oceans predate and accompany the lava outpourings that made Tharsis."

It's likely, he added, that Tharsis spewed gases into the atmosphere that created a global warming or greenhouse effect that allowed liquid water to exist on the planet, and also that volcanic eruptions created channels that allowed underground water to reach the surface and fill the northern plains.

Timing of oceans on Mars from shoreline deformation (DOI: 10.1038/nature26144) (DX)

Related: Evidence of Giant Tsunami on Mars Suggests an Early Ocean
Evidence of Sea Floor Hydrothermal Deposits Found on Mars
Ceres May Have Had a Global Surface Ocean in the Past

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