The study also included researchers from various national and worldwide institutions, including the University of California at Berkeley, Harvard University, the University of Melbourne and the University of Science and Technology of China, among others.
"We can't get to them, but, nevertheless, there are more diamonds than we ever thought", said Ulrich Fowl (Ulrich Faul), researcher at Massachusetts Institute of technology. The cratons-which can stretch as deep as 200 miles through the Earth's crust and mantle- are shaped like inverted mountains.
In fact, it actually makes sense that their roots are partly made out of diamond, considering that these precious minerals - churned inside Earth's fiery interior and pushed upward by volcanic eruptions - generally come closer to the surface through channels forming at the edge of cratonic roots.
But other researchers have suggested some alternative explanations: Garber added perhaps, these cratonic are cooler than the suggestions of rock literature, which means that the rock will harden - and thus, seismic waves will travel more quickly through them - even without the diamonds or eclogite rock. The amount is huge and it gets up to over one quadrillion tons of diamonds.
Sound waves travel at different speeds depending on the composition, temperature, and density of the rocks and minerals they travel through, giving scientists a method to estimate what types of rocks are below the Earth's surface by comparing the velocities of these sound waves, according to MIT. They're located between 90 and 150 miles below the Earth's surface, which is far deeper than any drills are capable of reaching.
When the waves moved through the roots of the ancient cratons, the researchers noticed that they sped up considerably more than expected.
Garber said "Although we found that most of the data was explained by diamond best ... we certainly can not say anything".
Conducted by scientists from several universities in the U.S., the U.K., France, Germany, China, and Australia, the research initially began by following a completely different phenomenon - the odd propagation of sound waves through ancient cratonic roots.
Sound travels through diamond twice as fast as other rocks, so the team of researchers figured there had to be some of the material in the cratons. The anomaly in the data was that sound waves sped up as they went through the roots of old cratons.
"It's circumstantial evidence, but we've pieced it all together", said Faul. "So we found that you just need 1 to 2 percent diamond for cratons to be stable and not sink".
This research was supported, in part, by the National Science Foundation.