Water from within the Earth:--"When we look into the origins of water on Earth, what we're really asking is, why are we so different than all the other planets?" Panero said. "In this solar system, Earth is unique because we have liquid water on the surface. We're also the only planet with active plate tectonics. Maybe this water in the mantle is key to plate tectonics, and that's part of what makes Earth habitable."- Read more at: http://phys.org/news/2014-12-hints-ancient-earth-watergeologically.html#jCp