A small piece of ringwoodite from the bowels of the planet reveals: The mantle is wet.
Every kid and his dog knows the structure of the planet: thin crust, under which is the thicker molten mantle, and in the center is the red-hot core, like strawberry jelly in a doughnut. From crust to core, it's all rock in one state or another, with puddles of ocean riding on top. Or is it? A brownish, cracked, grim-looking diamond found by serendipity in a Brazil riverbed says otherwise.
Diamonds are created deep in the earth, under conditions of terrific pressure. They may rise close to the surface, where they are found, in any number of ways, such as through volcanic action. The gemstones come in a variety of colors depending on contaminants that coagulated with the carbon under pressure, or even wrapped up with another stone entirely.
This particular piece, which no woman would want to wear forever or otherwise, encompasses an extremely rare, dense mineral called ringwoodite, says a team of scientists headed by Graham Pearson of Alberta University in their paper published in Nature.
And inside that ringwoodite, a great deal of water – about 1.5% of its weight– is locked.
Since ringwoodite can only be created deep in the earth under terrific pressure, the conclusion is that water was there locked in the rocks of deep earth.
Their conclusion is that far from being dry as dust, the interior of the planet could well contain a great deal of water. How much? Oceans' worth, Pearson told the press.
Albeit it isn't the sort you could drink: it's locked up within the rocks, but it's there, they say in their paper "Hydrous mantle transition zone indicated by ringwoodite included within diamond". Doesn't that just say it all.
To be sure, the scientists qualify that one rock that you could lift with two fingers can't tell the whole story of the whole mantle; it can mainly show that the environment of its creation was hydrous. But they postulate that the theory of water arriving on the planet from outer space, through icy comets and asteroids, need not be true. "The ultimate origin of water in the Earth’s hydrosphere is in the deep Earth—the mantle," writes the team.
Ringwoodite, which is a dense form of the common greenish rock olivine, has been found in meteorites, by the way. Whether originating from the bowels of the planet or otherwise, any water it contains isn't sloshing about, it's in hydroxide form.
While it seems the Earth’s shallow mantle does not have much water, the transition zone, which lies between 400 and 660 kilometers deep, could be a major repository for water that gets recycled from the surface.
The deep core, on the other hand, is not believed to contain water.