Our planet could be hiding a massive wealth of diamonds deep under its surface — more than a quadrillion tons of diamonds, in fact, tucked away within Earth’s oldest mantle rocks.
The news comes from researchers at the Massachusetts Institute of Technology (MIT) in Cambridge, who have uncovered that Earth’s ancient mantle rocks may be made out of diamond.
These incredibly old rocks are found beneath the heart of most continental plates and are known as “the oldest and most immovable sections of rock,” notes MIT.
Called cratons, these mantle rocks look like inverted mountains that run through our planet’s crust and into its mantle, with their deepest sections — known as cratonic roots — going up to 200 miles (320 kilometers) deep into the Earth.
It’s within these cratonic roots that the diamond cache is though to be found, making up around 1-2 percent of their structure. Judging by the entire mass of cratonic roots found within the Earth, MIT scientists estimate that there could be more than a quadrillion tons of diamonds beneath our planet’s surface.
But don’t break out your mining gear just yet. This massive treasure trove lies buried far deeper than any drilling machine has ever ventured, some 90 to 150 miles (145 to 240 kilometers) below the surface.
“We can’t get at them, but still, there is much more diamond there than we have ever thought before,” said MIT’s Ulrich Faul, who recently co-authored a paper on this new discovery, published in the journal Geochemistry, Geophysics, Geosystems.
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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 strange propagation of sound waves through ancient cratonic roots.
Sound Waves Spot The Treasure
Researchers regularly listen in on what goes on under our planet’s surface in order to monitor seismic activity. Picking up the sound waves that zoom through the planet’s interior can help pinpoint the location of earthquakes, while also revealing an image of what the Earth looks like on the inside.
Because the speed of sound waves is largely determined by the type of material they travel through, meaning they speed up or slow down depending on the physical characteristics of the rock — such as temperature, density, and composition — sound waves can tell a lot about the type of rocks that make up our planet’s interior.
In the case of cratonic roots, sound waves had been found to speed up inexplicably when passing through them — a lot more than expected giving the temperature and density of these ancient rocks.
“Cratons are known to be colder and less dense than the surrounding mantle, which would in turn yield slightly faster sound waves, but not quite as fast as what has been measured,” explains MIT.
Puzzled by this anomaly, the team set out to uncover exactly what cratonic roots are made of, in order to find out what could be causing sound waves to zoom through them so fast.
The first step was to make a 3D model showing the speed of sound waves through the planet’s major cratons. Then came a fun experiment of building virtual rocks of different mineral compositions and calculating the velocity of sound waves in each separate case.
By combining both parts of the project, the team discovered that those particular velocities found at cratonic roots can only occur when sound waves travel through a specific type of rock — one that’s 1-2 percent made from diamond, while also containing peridotite and eclogite, rocks found in the Earth’s upper mantle and in the crust of subducted oceanic plates, respectively.
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“Diamond in many ways is special. One of its special properties is, the sound velocity in diamond is more than twice as fast as in the dominant mineral in upper mantle rocks, olivine,” said Faul, who does research at MIT’s Department of Earth, Atmospheric, and Planetary Sciences.
While this means that our planet is hiding 1,000 times more diamonds than we were aware, this revelation doesn’t change what we knew about cratons and their density.
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.
“It’s circumstantial evidence, but we’ve pieced it all together,” Faul says. “We went through all the different possibilities, from every angle, and this is the only one that’s left as a reasonable explanation.”