A huge trove of diamonds is discovered deep within the Earth

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. (Yes, 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," said Ulrich Faul, a research scientist in MIT's Department of Earth, Atmospheric, and Planetary Sciences who helped write 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 diamonds are in underground rock formations called cratons, which are shaped like inverted mountains, lie at the centre of the planet's tectonic plates, and can stretch up to 320 kilometres into the Earth, according to MIT.

The researchers estimate that the bottom sections of these cratons, or roots, may be composed of 1-2 per cent diamond.

LOOKING WITH SEISMIC DATA

You might be most familiar with how records of seismic activity – sound waves travelling through the Earth – are 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 below the Earth's surface by comparing the velocities of these sound waves, according to MIT.

The researchers found that these sound waves tend to speed up when passing through the cratons' roots – 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 per cent diamond, among other components, could produce the velocities recorded in the cratons' roots.

To estimate the total mass of diamonds in the Earth, the researchers assumed cratonic roots were 1-2 per cent diamond and combined that with the total volume of cratonic roots distributed throughout the Earth. The number they came up with was a quadrillion tons (1 with 15 zeros) of diamonds, or more than 1000 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 140 to 240 kilometres below the Earth's surface, far deeper than any drills are capable of reaching.

- Reference to an estimated 1016 tons of diamonds has been corrected

- This story first appeared at BusinessInsider.com.au