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More than a quadrillion tons of diamonds are under your feet, new study proposes

A staff member sorted diamonds at the new Diamond Trading Company Botswana in Gaborone.ALEXANDER JOE/AFP/GettyImages/File

More than a quadrillion tons of diamonds are lying in the earth beneath our feet, but we’re not going to be digging them up any time soon, according to new research from MIT and other universities.

The gems are in the upper mantle, about 90 to 150 miles below the earth’s surface, far deeper than any drill has ever reached.

“This shows that diamond is not perhaps this exotic mineral, but on the [geological] scale of things, it’s relatively common,” said Ulrich Faul, a research scientist from MIT’s Department of Earth, Atmospheric, and Planetary Sciences, who is the lead senior author of the study. “We can’t get at them, but still, there is much more diamond there than we have ever thought before.”

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The deepest hole that has ever been drilled is only 7 1/2 miles deep, he said.

The study was first published in June in the journal Geochemistry, Geophysics, Geosystems.

Researchers came to this conclusion after they found in global records over the past few decades a “glitch” in seismic wave activity. Seismic waves are the waves of energy that travel through earth that come from earthquakes, tsunamis, explosions, or other ground-shaking sources.

The waves have been found to travel at various speeds depending on the temperature, density, and composition of the rocks through which they travel.

Researchers noted that there were unusually fast speeds for seismic waves within the roots of cratons, the most stiff and stable pieces of the upper mantle.

The team generated a 3-D model of the way seismic waves travel through earth’s major cratons. Then they created virtual rocks made from different combinations of minerals to see how that would affect seismic wave velocities.

After several calculations, researchers found only one type of rock in their model that produced the velocities that matched the actual measurements.

This rock contained 1 to 2 percent diamond. That may sound like a small percentage, but it’s far greater than people previously thought.

“This scenario represents at least one thousand times more diamond than people had previously expected,” researchers said.

Researchers considered the total volume of rocks in the cratonic roots in the earth and calculated that a quadrillion tons of diamonds are scattered within the ancient rocks beneath our feet.

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The results were further supported by tests involving electromagnetic waves, and the density and carbon content of rocks, lead author Joshua M. Garber said. Diamond was the answer that made the most sense.

People have tested upper mantle rock before, said Garber, “but they have not seen as much diamonds as we were proposing.”

He said the diamonds might be on the microscopic level, which would account for the missing proof.

“There is hesitation in the community to accept this answer, but we have excluded every answer that was not diamond,” said Garber, a postdoctoral scholar at Pennsylvania State University.

The next step to confirm the study’s results is to wait for Nature to bring diamonds up from the mantle by volcanic eruptions, he said.


Katie Camero can be reached at katie.camero@globe.com. Follow her Twitter @camerokt_