Quadrillion tonnes of diamond found hidden in centre of Earth

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

Josh Gabbatiss
Science Correspondent
@josh_gabbatiss
Tuesday 17 July 2018 16:43
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A huge cache of diamonds appears to be buried at least 100 miles below Earth's surface
A huge cache of diamonds appears to be buried at least 100 miles below Earth's surface

An enormous treasure trove of diamonds has been discovered deep inside our planet.

There may be more than a quadrillion tonnes of these precious minerals buried below Earth’s surface, according to new research by an international team of scientists.

They say despite its reputation for rarity and the value people have attributed to it, the discovery shows diamond is “perhaps not this exotic mineral” after all.

However, the discovery is not much use to any enterprising prospectors, as at 100 miles below the planet’s surface, the diamonds are far deeper than any drilling expedition has ever penetrated.

“We can’t get at them, but still, there is much more diamond there than we have ever thought before,” said Dr Ulrich Faul, a researcher at Massachusetts Institute of Technology (MIT) and a co-author of the study describing the diamond cache.

The diamonds appear to be embedded in cratonic rocks – the oldest sections of mantle rock found underneath the planet’s tectonic plates.

These inverted mounds of rock stretch up to 200 miles through the Earth’s crust, and the analysis conducted by Dr Faul and his colleagues suggested diamonds make up around 1 or 2 per cent of them.

The scientists were alerted to this phenomenon by an anomaly in data collected from ground-shaking events like earthquakes and tsunamis.

Such phenomena generate enormous sound waves that travel through the planet, and this information can be used to construct an image of what the planet looks like on the inside. This includes assessing the composition of rocks that make up Earth.

Scientists had previously noticed that sound waves sped up when passing through ancient cratons, a clear indication that diamonds were hiding within them.

“Diamond in many ways is special,” said Dr Faul.

"The sound velocity in diamond is more than twice as fast as in the dominant mineral in upper mantle rocks, olivine.”

In their study, published in the journal Geochemistry, Geophysics, Geosystems, the researchers estimated that if up to 2 per cent of the cratons were diamond, this would account for the seismic measurements they were observing.

“It’s circumstantial evidence, but we’ve pieced it all together,” said Dr Faul.

“We went through all the different possibilities, from every angle, and this is the only one that’s left as a reasonable explanation.”

Diamonds are formed in the incredibly hot and high-pressure environment of deep Earth, and only make their way onto the surface when volcanic eruptions eject them onto the surface. As these eruptions often take place at the edge of cratonic rocks, the researchers said it makes sense that the rocks themselves also contain high densities of diamonds.

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