It Came From Within

hydrous ringwoodite                          Steve Jacobsen/Northwestern University

There have been many theories floated (pun intended) over the years about the source of Earth's water, probably the most prominent being that it came from comets that hit our planet. A new discovery of a huge water reservoir deep in Earth's mantle leads scientists to suggest that it seeped up from inside, instead: http://www.newscientist.com/article/dn25723-massive-ocean-discovered-towards-earths-core.html#.U5ufOS-5bgc