Inner Earth May Hold More Water Than the Seas

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In different trials, the scientists slightly varied the proportions of the ingredients they used, and added or removed trace quantities of certain metallic compounds that they suspect mix in small amounts with more abundant materials in the lower mantle.

The trials resulted in different amounts of water being absorbed into the mantle-like matter. But in each case, water made up at least 0.19 percent of the material's mass.

That doesn't sound like a lot, but for Murakami and his team, the finding was a watershed.

A Waveless Waterworld

Earth's oceans make up just 0.02 percent of the planet's total mass. This means the vast lower mantle could contain many times more water than floats on the planet's surface.

The Japanese experiments don't guarantee that that's the case, of course, because the researchers haven't actually measured the mantle. No one is ever likely to get a direct sample of material from the fiery mantle itself. But by simulating mantle-like conditions in the lab, Murakami and his colleagues have demonstrated that a water-rich inner Earth is plausible.

Just how water-rich it is depends on the amount of trace "impurities" in the minerals. Compounds such as aluminum and iron "could dramatically change the solubility of water in these minerals," Murakami explained.

Other research has suggested that a zone between the mantle and the crust also contain a great deal of water, the Japanese researchers noted. If so, there could be more than ten times the amount of water inside the planet as there is on its surface.

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