Deep Earth has oceans’ worth of water, $10 diamond reveals

University of Alberta researchers find ‘meteorite mineral’ that formed naturally on our planet

A dirty, $10 diamond with a prize inside has helped reveal that there are vast quantities of water stored deep inside the Earth.

The diamond formed in the “transition zone” around 410 to 660 kilometres below our planet’s surface. Analysis of a mineral grain trapped inside it suggests that it came from surroundings that were about one per cent water, report researchers led by University of Alberta geochemist Graham Pearson. They published their  findings online in the journal Nature today.

If the sample is representative of that part of the deep Earth, the amount of water there could be “about the same as the mass of all the world’s oceans combined,” wrote Hans Keppler, a geophysicist at the University of Bayreuth in Germany, in an analysis article.

That, in turn, changes our understanding of the way water cycles through our planet, and has implications for the way tectonic plates andvolcanoes behave, Pearson notes.

Meteorite mineral from Earth

Previously, geophysicists had debated about whether there could be water in the transition zone. Geophysical measurements from the surface had provided conflicting results.

The new, hard evidence that there is water deep in the Earth comes from a tiny grain of rock — just four-hundredths of a millimetre in diameter — trapped inside the diamond.

That grain was made of ringwoodite — a form of the green mineral peridot that has never before been found on Earth, except in meteorites from space. That’s because, like a diamond itself, it can only be made under extremely high pressures like those found so deep inside the Earth that they are inaccessible to humans.

“You can’t run a field trip to those areas,” Pearson said in a phone interview. “No one’s ever even going to drill to those areas.”

Typically, the amount of water in peridot is “vanishingly small,” Pearson added.

But he and his colleagues probed the ringwoodite in the diamond with different kinds of light and looked for the signature of water. Their analysis showed the sample contained 1.5 per cent water by weight, suggesting that the transition zone where it formed is about one per cent water.

The layers of Earth above and below the transition zone, called the upper and lower mantles respectively, are each known to be “a desert for water,” Pearson said.

“What we’ve found is an oasis of water in the transition zone.”


CBC News has the full article

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