A study from Massachusetts Institute of Technology (MIT) and other universities has indicated that quadrillion tonnes of diamonds may be hidden deep beneath Earth’s surface.

Researchers used sound waves to determine that 1%-2% of Earth’s oldest mantle rocks are made from diamond.

However, it is not practically feasible to mine the diamonds as they are estimated to be buried more than 100 miles below the surface within rock formations known as cratonic roots that lie beneath the centre of most continental tectonic plates.

Cratons are inverted mountain-shaped structures that can stretch as deep as 200 miles into the Earth, the study noted.

MIT Department of Earth, Atmospheric, and Planetary Sciences researcher Ulrich Faul said: “This shows that diamond is not perhaps this exotic mineral, but on the [geological] scale of things, it’s relatively common.

“We can’t get at them, but still, there is much more diamond there than we have ever thought before.”

It all started when the scientists aimed to determine the composition of cratonic roots in order to understand the reason why sound waves tend to speed-up significantly when passing through the roots of ancient cratons.

“We can’t get at them, but still, there is much more diamond there than we have ever thought before.”

Faul added: “The velocities that are measured are faster than what we think we can reproduce with reasonable assumptions about what is there. Then we have to say: ‘There is a problem.’ That’s how this project started.”

The team used seismic data to generate a three-dimensional model of the velocities of seismic waves travelling through the Earth’s major cratons.

They then created virtual rocks, made from various combinations of minerals and calculated the speed of sound waves travelling through each virtual rock.

During this process, it was determined that only one type of rock produced the velocities as what the seismologists measured.

Faul added that the sound velocity in diamond is more than twice as fast as in the dominant mineral in upper mantle rocks, olivine.

Diamonds are present in the high-pressure, high-temperature environment deep inside the Earth and come close to the surface when volcanic eruptions take place.

Faul added that the study’s findings are based on circumstantial evidence and were arrived at after exploring all different possibilities, adding that the observations make sense.