Quadrillion tonnes of diamond discovered 100 miles below Earth's surface by MIT scientists
Scientists have found a quadrillion tonnes of diamonds about 150 km below the Earth's surface into the roots of our continents, ripe for the taking. However, a diamond-rush from this discovery is rather unlikely. Firstly, the depth of the resource and the heat surrounding it is rather prohibitive. Plus, once the commodity becomes commonplace, its value will suffer significant deflation. That being said, researchers at Massachusetts Institute of Technology (MIT) do not think their discovery is purposeless. They believe we can learn much about our planet's heart owing to the diamond's close proximity to some of the oldest known rocks.
“This shows that diamond is not perhaps this exotic mineral but, on the scale of things, it’s relatively common,” says Ulrich Faul, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “We can’t get at them, but still, there is much more diamond there than we have ever thought before.”
Researchers were examining seismic data via reflected sound waves from earthquakes and explosions that penetrate deep into the earth when they stumbled upon an anomaly. These reflected waves can be used to build an image of what our planet's interior would look like, similar to sonar and radar.
The picture constructed from this data shows that our continents have "roots" that go deep beneath the planet's surface, resembling huge inverted mountains extending to our core. The inverted mountains are cooler and less dense than the surrounding mantle and are called cratons.
However, when scientists reconstructed the data, the sound waves showed something unexpected.
“The velocities that are measured are faster than what we think we can reproduce with reasonable assumptions about what is there,” Faul says. “Then we have to say, ‘There is a problem.’ That’s how this project started.”
Researchers then went ahead and tested the speed of sound through every kind of rock with varying densities. They found that only one matched what they witnessed from the Earth's core.
Now, they believe that about 1 to 2 percent of these cratonic roots are made up of diamond and, given the size of these roots, the team concluded that over a quadrillion tonnes of the same are scattered about 150 km to 250 km below the surface of the Earth.
How the discovery unfolded
A natural diamond is synonymous with luxury and a coveted lifestyle, costing as much as $6,000 for an engagement ring. However, if he had better access to the subterranean world, it would have been a completely different story.
Roberta Rudnick, Ph.D., is an earth science professor at the University of California, Santa Barbara, and is part of the international team behind the new study. In a conversation with Inverse, Rudnick said, “Diamond is not a particularly rare mineral.”
Li Zeng, a Harvard University postdoctoral fellow, said that during the 2016 CIDER workshop, seismologists revealed the evidence of a strange anomaly deep within the planet. As mentioned above, the team picked up on sound waves that were moving much faster through cratons than other dense mantle rock.
There were quite a few explanations for this anomaly in seismic data previously, according to Zeng. To reach a solid conclusion, the team had to build a 3D model of the wave velocities moving through Earth's major cratons. They then introduced various virtual rocks to calculate the speed of these waves and matched them with their actual readings.
Zeng says that of all the original possibilities, “The most fascinating one was the possibility of diamonds — that there exists a sweet spot in terms of pressure, temperature, and redox conditions for the growth and retainment of diamonds at that depth.”
“With the experimental results in hand, I began calculating sound speeds expected for continental cratons,” Faul told Inverse.
By the process of elimination, Faul compared the experimental results to actual measurements, and “ended up with diamonds as the only plausible and reasonable explanation as a solution to this puzzle.”
Seismologists and researchers concluded that only one type of rock can produce the same velocity originally measured from the waves -- one that contains trace amounts of oceanic crust, minor amounts of a coarse-grained rock called peridotite, and is one to two percent diamond. That shows there is over 1,000 times more diamond in these cratons than previously estimated.
“While it is a higher concentration of diamonds than we would have expected based on the rocks that have come up from those depths, it is not more than the Earth can handle,” study co-author and geochemist Megan Duncan, Ph.D., told Inverse. “We’re not adding lots of extra carbon to the Earth’s overall budget. It does have some interesting implications for ancient Earth processes, like subduction, and how it may or may not have changed with time.”
Having said that, it is probably going to be a while before we get access to these diamonds with a drill. These diamonds are more than 10 times deeper than the deepest hole ever drilled, which a mere 7.5 miles in depth.