Scientists have become increasingly convinced in recent years that Mars, which now appears mostly dry on the surface, was once warm and wet — the sort of place where life might have got a toehold and possibly even flourished. But looming questions have formed around this expectation: Where did the water come from, and for how long was the Red Planet wet? A new study points a finger at one of the most obvious features on Mars, a hulking, elevated region known as the Tharsis rise that may have released tremendous amounts of lava, along with water and carbon dioxide that combined to possibly create a habitable planet. The research also narrows the range of time, under this scenario, that Mars would have been wet.