What Diamonds Tell Us About the Center of the Earth

Type IIa diamonds give us clues to what’s going on way down below

When Evan Smith talks about the deep Earth, he makes it clear he is talking about the deep Earth—way underground, beneath the tectonic plates, below where any human has traveled, as “far under our feet as the International Space Station is above our head,” in the words of NPR.

“Even the deepest mines only go down a couple of miles,” says Smith, a postdoctoral research fellow at the Gemological Institute of America. “If you want to go deeper than that, you are pretty limited.”

Which is why Smith has spent the last few years studying diamonds—they are one of the few objects we have up here that have also been down there.

“Diamonds have an unusual set of physical characteristics that are interesting for geologists,” he says. “They give you a window into the deep Earth.”

Because of their purity, Type IIa diamonds are some of the best specimens—but they are hard to find and expensive. Which is one benefit of doing research at GIA; it has access to a (relatively) plentiful supply.

Smith’s studies have led to what GIA is calling a major breakthrough in research on the Earth’s core (which we’ll have to take its word for). According to GIA, Type IIas often evidence small metallic inclusions, a solidified mixture of iron, nickel, carbon, and sulfur, with traces of fluid methane and hydrogen. These inclusions are generally cut away during cutting and polishing.

However, by studying these inclusions, Smith and his team believe they have proven that metals exist in the deep Earth. The findings were recently published in the journal Science.

“This has been talked about for over a decade,” he says. “The diamonds are confirming this.”

He admits his discovery is “not something that is going to revolutionize our day-to-day life. But it changes the way we think about the deep Earth.”

Granted, the geological studies Smith is engaged in are very different than the work that generally comprises GIA’s mission: protecting the gem and jewelry industry. But Smith says it might ultimately improve the mystique of diamonds.

“Diamonds are this pristine sample of the deep Earth,” he says. “They are really scientifically valuable. They carry information that otherwise we have no way of accessing.”

JCK News Director