One hundred miles inside the earth lies a massive haul of diamonds that would be worth an eyewatering amount at today's prices - if only they could be mined.
According to experts, an area of the Earth's mantle beneath the joins of the tectonic plates contains over a quadrillion tonnes of diamonds worth an approximate £68.6 septillion (£68,600,000,000,000,000,000,000,000) at current prices. Anyone who could extract those diamonds would easily be the richest person to have ever lived, but they are 100 miles under the Earth's surface, much further than the reach of any drill. Even if you could drill through the earth's crust (about 18 miles), you would hit the mantle - which is a mix of rocks and hot magma.
The diamonds appear to be embedded in cratonic rocks, the oldest sections of mantle rock found underneath the planet's tectonic plates, which move around with the magma. Individual rocks have lengths of up to 200 miles and Dr Ulrich Faul, co-author of the diamond study and researcher at Massachusetts Institute of Technology (MIT), and his colleagues suggest that diamonds make up one to two per cent of their volume.
"We can't get at them, but still, there is much more diamond there than we have ever thought before," Dr Faul said.
The scientists discovered the diamonds through studying natural tectonic movement (e.g. earthquakes and tsunamis) which send enormous sound waves through the earth. A separate experiment conducted before the discovery showed that sound wave speeds change depending on the composition, temperature and density of the rocks and minerals they're travelling through. Through the tectonic activity, they saw the sound waves speed up, in a way that indicated the presence of diamonds.
"Diamond in many ways is special. The sound velocity in diamond is more than twice as fast as in the dominant mineral in upper mantle rocks, olivine," said Dr Faul.
It may be hundreds of years until we develop technology capable of mining the diamonds, but it's nice to know there's a jackpot hidden in the earth.
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