But don’t get your hopes up on mining them: According to the study, the deposits are located in “cratonic roots” between 90 and 150 miles below the Earth’s surface (much further than any drill has gone).

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

But what is a “cratonic root”? MIT News describes cratons as “the oldest and most immovable sections of rock that lie beneath the center of most continental tectonic plates.” These stable chunks of the Earth’s crust are shaped like “inverted mountains.” The deepest parts of cratons are known as their “roots” and can reach all the way to the Earth’s mantle. It is here where the study’s authors believe that diamonds are.

But if they are over 100 miles below the Earth’s surface, how did scientists find them? The answer comes from seismic data—or recorded sound waves from seismic activity like earthquakes and tsunamis.

Seismic data can be used to measure what the Earth is made of, because the speed of sound waves changes depending on the temperature, density and composition of the earth they travel through.

In looking at the seismic data, scientists realized there was an issue—sound waves were moving through cratonic roots “faster than what we think we can reproduce with reasonable assumptions about what is there,” Faul told MIT News.

So using 3D modeling to create virtual rocks, scientists set out to figure out what substances could compose the roots of cratons, allowing sound to pass through that that speed. Diamonds fit the bill, and to match the velocity of the sound traveling through the roots, the scientists estimated that the roots must be made of 1 to 2% diamond (in addition to peridotite and eclogite).

Using that estimate, and the number of known craton roots, the scientists arrived at their quadrillion ton estimate — 1,000 times more than originally thought, according to CNN.

Diamonds are created under high-temperature, high-pressure scenarios and make their way to the surface through volcanic activity.

The researchers involved were from the University of California, Santa Barbara, the University of California, Berkeley, the Ecole Polytechnique, the Institut de Physique du Globe de Paris, the Carnegie Institution of Washington, Harvard University, the University of Science and Technology of China, the University of Bayreuth, the University of Melbourne, the Massachusetts Institute of Technology, and University College London.