In order to solve this conundrum, Faul and colleagues started assembling virtual rocks which could theoretically exist at the temperature and pressure conditions in those parts of the mantle. They then calculated how fast seismic waves would pass through these structures, to see if this would fit the observed seismic data.

They found that the data would be best explained by a craton rock composition of 1 to 2 percent diamond. This would translate to about quadrillion tons of diamond.

In a way, this makes a lot of sense. We know that diamonds are forged deep in the bowels of the Earth, in high-pressure, high-temperature environments. The only reason why we’re able to find diamonds is that they’re brought closer to the surface by volcanic eruptions which act like “pipes” — bringing them to the surface, where we at least have a chance of finding them.