anthemaniac writes "Seismic observations reveal a huge reservoir of water in Earth's mantle beneath Asia. It's actually rock saturated with water, but it's an ocean's worth of water ... as much as is in the whole Arctic Ocean. How did it get there? A slab of water-laden crust sank, and the water evaporated out when it was heated, and then it was trapped, the thinking goes. The discovery fits neatly with the region's heavy seismic activity and fits neatly with the idea that the planet's moving crustal plates are lubricated with water."