A new study in Geochemistry, Geophysics, Geosystems reveals that the value of diamonds would be very different if humans had better access to subterranean rock, reports Sarah Sloat for Inverse. Roberta Rudnick, an earth science professor at the University of California is part of an international team that discovered there may be more than a quadrillion tons of diamonds scattered throughout Earth. The diamonds lie about 90 to 150 miles below the Earth’s surface within immovable rocks known as cratonic roots.
In 2016, a team of seismologists—who study sound waves—revealed evidence of an anomaly deep within the Earth. This team picked up on sound waves that were moving unusually quickly as they passed through cratons, Sloat explains. To understand the reasons behind the strange seismic data, the team built a three-dimensional model of the velocities of the seismic waves moving through the Earth’s major cratons. Of all the explanations, says Harvard University postdoctoral fellow and co-author of the study, Li Zeng, “the most fascinating one was the possibility of diamonds—that there exists a sweet spot in terms of pressure, temperature, and redox conditions for the growth and retainment of diamonds at that depth.”
To test this theory, MIT research scientist Ulrich Faul tells Inverse that he began “calculating sound speeds expected for continental cratons.” He compared the experimental results to measurements made on actual rocks, and through the process of elimination, “ended up with diamonds as the only plausible and reasonable explanation as a solution to this puzzle.” Apparently, only one type of rock can produce the same velocity that the seismologists measured: one that is one to two percent diamond. This means that there is at least 1,000 times more diamond in the cratons than scientists had previously estimated. Still, getting to these diamonds will not be easily accessible—these diamonds are more than 10 times deeper than the deepest hole ever drilled.