Massive Diamond Cache Detected Beneath Earth’s Surface

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Using seismic technology to analyze how sound waves pass through the Earth, scientists detected the treasure trove in rocks called cratonic roots, which are shaped like inverted mountains that stretch through the Earth’s crust and into the mantle. Massachusetts Institute of Technology (MIT) explained that these are “the oldest and most immovable sections of rock that lie beneath the center of most continental tectonic plates.

It’s diamonds all the way down. That’s according to new research suggesting more than a quadrillion tons of diamond is nestled within the Earth’s interior1000 times more than previously thought. But don’t expect a diamond rush. These naturally occurring precious minerals are located far deeper than any drilling expedition has ever reached, about 90 to 150 miles (145 to 240 kilometers) below the surface of our planet.

Diamonds are made from carbon, and are formed under high-pressure and extreme temperatures deep in the Earth. They emerge near the surface only through volcanic eruptions that occur rarely on the order of every few tens of millions of years.

Ulrich Faul, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences said, “We can’t get at them, but still, there is much more diamond there than we have ever thought before” and further added, “This shows that diamond is not perhaps this exotic mineral, but on the scale of things, it’s relatively common.” Faul called the results “circumstantial evidence,” but described them as the only logical conclusion to the various possibilities they tested.

The project to uncover deep Earth diamonds began because scientists were puzzled by observations that sound waves would speed up significantly when passing through the roots of ancient cratons. So they assembled virtual rocks, made from various combinations of minerals, to calculate how fast sound waves would travel through them.

One of the special properties of the diamond is the sound velocity diamond of it which is more than twice as fast as in the dominant mineral in upper mantle rocks, olivine. The team found that the only type of rock that matched the speeds they were detecting in craton would contain one to two percent diamond. Cratons are a tiny bit less dense than their surroundings.

The study was published in the journal Geochemistry, Geophysics, Geosystems, and led by Joshua Garber, an earth science professor at the University of California, Santa Barbara.