Pay Dirt: Sound Waves Accidentally Found One Quadrillion Tons of Diamonds Buried Deep Within the Earth

Monday, 16 July 2018 - 1:45PM
Science News
Monday, 16 July 2018 - 1:45PM
Pay Dirt: Sound Waves Accidentally Found One Quadrillion Tons of Diamonds Buried Deep Within the Earth
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Image Credit: Ayswaryak/Wikimedia Commons (CC BY-SA 3.0)
The biggest payday in history is sitting one hundred miles beneath Earth's surface. Scientists from MIT – with scholars at ten research universities around the world – have discovered over one quadrillion tons of diamond.

That's fifteen zeroes, for those of you keeping score at home.

Like so many scientific discoveries, this one happened by accident. The researchers originally set out to investigate some bizarre seismic data that nobody could explain.

Seismic data – that is, information about anything pertaining to earthquakes and the Earth's crust – can be gathered by analyzing sound waves. Sound waves move through different materials at different speeds depending on a range of factors including density and temperature.

What nobody could explain was why sound waves suddenly accelerated when they passed through what is called a "cratonic root."

According to Ulrich Faul, a member of MIT's Department of Earth, Atmospheric, and Planetary Sciences:

Opening quote
"The velocities that are measured are faster than what we think we can reproduce with reasonable assumptions about what is there…Then we have to say, 'There is a problem.' That's how this project started."
Closing quote


Cratons are ancient, unmoving sections in the center of tectonic plates. The very deepest portions are known as the "root." Although they aren't as hot or dense as the surrounding rock – which would otherwise explain the increased speed of sound waves – it still didn't account for just how fast they were traveling.

The research team created a 3D model of the sound wave velocities, then used this information to model possible mineral compositions that would account for this anomaly. In the end, there was only one possible answer.

"Diamond in many ways is special," Faul explains. "One of its special properties is, the sound velocity in diamond is more than twice as fast as in the dominant mineral in upper mantle rocks…"

All told, the research revealed 1,000 times more diamond than any previous study had indicated. While the discovery does spark the popular imagination, these diamonds are locked out of reach one hundred miles underground. The deepest hole ever drilled took 20 years to reach its ultimate 7.5-mile depth – not even an irritated Elon Musk can mine them to fund his next PR move.

Image Credit: Ayswaryak/Wikimedia Commons (CC BY-SA 3.0) Resized for main image.
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