About a Quadrillion Tons of Diamonds May Be Hiding in Earth

Sound waves may have detected huge numbers of diamonds lying beneath Earth's surface.

An international team of scientists said that diamonds might be scattered in Earth's crust and mantle, according to a June 19 study published in the journal Geochemistry, Geophysics, Geosystems, MIT announced Monday. The scientists set out to research a seismic anomaly and found something surprising—and shiny.

The U.S. Geological Survey and other agencies keep global records of seismic data, which are sound waves that travel through the planet from tsunamis, earthquakes, explosions and other events that cause parts of Earth to shake. They use this data to track many things, including where an earthquake originated. In some spots of Earth's crust, called cratons, the sound waves traveled much faster than expected.

Cratons are stable parts of Earth's crust and mantle that are usually found in the interiors of tectonic plates, and are not part of the more active, unstable parts of the crust. Cratons are typically less dense and colder than the parts of Earth that surround them, so sound waves should travel through them slightly faster but not as fast as the seismic data showed.

To test which material causes the sound waves to travel that quickly through the cratons, the scientists created virtual rock models. Only one virtual rock showed the same velocity as the abnormal seismic waves that were traveling through the cratons. The rock contained a surprising 1 percent to 2 percent diamond, in addition to the more common rock peridotite and small amounts of eclogite, which is from the oceanic crust. The diamonds are beneficial to cratons—as they help them stay stable and keep them from sinking, preserving the planet's oldest rocks.

Ulrich Faul, a research scientist in MIT's Department of Earth, Atmospheric, and Planetary Sciences, said in a statement, "This shows that diamond is not perhaps this exotic mineral, but on the [geological] scale of things, it's relatively common." In fact, the scientists have estimated that there are 1,000 times more diamonds in Earth's surface than previously thought.

Volcanic eruptions bring diamonds to Earth's surface by creating kimberlite pipes, which can spew out magma and diamonds. The scientists say it makes sense that diamonds are found in cratons, because the kimberlite pipes are found on the edges of cratonic roots.

The diamonds are estimated to be about 90 to 150 miles beneath Earth's surface, much farther than any mining expedition has ever gone. Faul says: "We can't get at them, but still, there is much more diamond there than we have ever thought before."

A handful of 50-carat diamonds found in kimberlite pipes in Russia. Volcanic eruptions bring diamonds to Earth's surface by creating kimberlite pipes, which can spew out magma and diamonds. Diamonds might be scattered in Earth’s crust and mantle, according to an international team of scientists. SERGEI KARPUKHIN/REUTERS