That diamond on your wedding ring isn't as rare as you might think.
Using sound waves, scientists uncovered a cache of diamonds distributed deep below the Earth's surface, and it amounts to over a quadrillion tons of the precious mineral (you read that right).
That's according to a new study published by a team of researchers from MIT, Harvard, and the University of California at Berkeley, among other top-tier institutions.
"This shows that diamond is not perhaps this exotic mineral, but on the [geological] scale of things, it's relatively common," Ulrich Faul, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences and one of the author's on the study, said. "We can’t get at them, but still, there is much more diamond there than we have ever thought before."
The diamonds are located in underground rock formations called cratons. These formations — which are shaped like inverted mountains and lie at the centre of the planet's tectonic plates, according to MIT News — stretch up to 320km into the Earth.
The researchers estimate that the roots, or bottom sections, of these cratons may be composed of 1-2% diamond.
You might be most familiar with how records of seismic activity — sound waves travelling through the Earth — is used to record earthquakes.
Scientists also use seismic data to reveal what the deepest parts of the Earth are composed of, and paint a picture of what the inside of the planet looks like.
Sound waves travel at different speeds depending on the composition, temperature, and density of the rocks and minerals they travel through, giving scientists a method to estimate what types of rocks are found below the Earth's surface by comparing the velocities of these sound waves, according to MIT News.
The researchers found that these sound waves tend to speed up when passing through the bottom, or roots, of cratons — much faster than they had previously thought.
After conducting a series of experiments in the lab where they sent sound waves through different rocks, the researchers found that only rock containing 1-2% diamond, among other components, could produce the velocities recorded in the craton roots.
To estimate the total mass of diamonds in the Earth, the researchers assumed cratonic roots contained 1-2% diamond and combined that with the total volume of cratonic roots distributed throughout the Earth. The number they came up with: 1016 tons of diamond, or over 1,000 times more than previously thought.
"We went through all the different possibilities, from every angle, and this is the only one that’s left as a reasonable explanation," Faul said.
The diamonds, however, are impossible to mine. They're located between 160- and 240km below the Earth's surface, which is far deeper than any drills are capable of reaching.
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