The Ringwoodite Ocean

  Far below the Earth's surface, there is a gemstone ocean that lies on top of the mantle. It circulates water, carrying it from subduction zones to the great magma chambers where it erupts as lava and steam. This ocean is thought to contain three times as much water as all the surface oceans combined. But it is not a typically liquid ocean. Ringwoodite, the mineral that transports it, only consists of 1.5% water. Thus it is more like a fluid gemstone ocean that passes water between its crystals. 

 I can't imagine how remarkably beautiful it must be. Of all the wondrous things I have learned in my life, this is among the greatest. And to think it came from a children's magazine (National Geographic for Kids). The biggest mystery to me is how this ringwoodite transports water, and what the forces are keeping it buoyant. Ringwoodite is thought to be a grade of olivine which gets harder the farther down into the mantle you go, due to increased pressure. The relatively light pressure of the ringwoodite layer allows it to be flexible enough to act as a liquid. It's like being able to see gold as a rolling river. Truly remarkable.

 This has awesome implications for the water cycle. A subducted water molecule could spend ages in a subterranean sea before finally getting out. The long journey wouldn't be made by every water molecule, as many are content to return to the atmosphere by quickly evaporating once they reach the ocean. But the more adventurous ones, the ones who find their way to the deep blue abyss, by any manner of underwater travel, may eventually buy that riskiest of tickets, who dared to make that potentially infinite ride down the slope of a sinking crust to meet that dazzling layer of ringwoodite, their courage increasing with each exponential jump in pressure, sinking through the darkness to a boling soup, not knowing it may spend the rest of its eternal life there. Until one day when extinctions have passed and the ice ages have come and gone, and when the Earth is ready again to release its bladder on the surface above, the patient molecules will finally have their day as the pressure gets too great, the earth erupts in many locations, releasing them from the prison below, a boiling riot of H20 and C02, obscuring the sun to complete the cycle, to rain down and fill up the oceans again.

This is ringwoodite. An ocean of it is thought to encompass the earth, where the bottom of subduction zones draining ocean water intercept the upper mantle.