First, you’ll need some ancient seabed that has been buried in the Earth’s crust, cooked up deep down, and then spat out onto the surface.
Macquarie University geoscientists studied how diamonds are formed. In experiments recreating the extreme pressures and temperatures found 200 kilometres underground, they demonstrated that seawater in sediment from the bottom of the ocean reacted in the right way to produce the balance of salts found in a diamond. Most diamonds found nearer the Earth’s surface are made this way.
“There was a theory that the salts trapped inside diamonds came from marine seawater, but couldn’t be tested,” says lead author Michael Förster. “Our research showed that they came from marine sediment.”