Think of how much money could yield more than a quadrillion tons of diamond. Now stop dreaming about it, because it’s impossible to get those diamonds. Scientists at MIT and other universities have teamed up to estimate how many of these precious minerals are under the Earth’s surface. Unfortunately for any drilling possibilities, this diamond cache is 100 miles under the surface of our planet.
To be more exact, the diamonds are in the oldest sections of rock under the tectonic plates, rocks known as cratonic roots. The roots look like inverted mountains, and they can be as deep as 200 miles under the crust of our planet, reaching towards the mantle. Geologists call the deepest sections “roots.”
In their new study, scientists have estimated that inside the cratonic roots there is 1-2% diamond, and considering the volume of the cratonic roots, the team determined that the ancient rocks contain a quadrillion tons of diamonds at 90-150 miles under the surface.
Ulrich Faul is a research scientist at the Department of Earth, Atmospheric, and Planetary Sciences (MIT), explaining that, according to their findings, diamonds are not an exotic material, and it’s common:
“We can’t get at them, but still, there is much more diamond there than we have ever thought before.”
An Anomaly in Seismic Data
But how did the researchers conclude that there are diamonds in the cratonic roots? It all started with an anomaly in seismic data. Agencies like the United States Geological Survey kept records of seismic activity from the entire planet. It consisted of sound waves that travel through the Earth and are triggered by ground-shaking sources like earthquakes, tsunamis and so on. Sound waves are different as they pass through different compositions of rock, they depend on temperatures and the density of the rocks too.
But one thing that sounded suspicious was that sound waves passed very fast through the roots of ancient cratons. Even if cratons are colder and with a smaller density, allowing sound waves to pass easy, the speed was even faster:
“The velocities that are measured are faster than what we think we can reproduce with reasonable assumptions about what is their ground-shaking sources. Then we have to say, ‘There is a problem.’ That’s how this project started,” said Faul.
Using data from different sources (USGS and others), scientists created a 3D model of the velocities of seismic waves that traveled through the major cratons. Then, Faul and other researchers created virtual rocks from different minerals to see how fast sound traveled through each type of rock, and which one is close to the speed seismologists measured. In their scenario, scientists used a rock which contains: 1-2% diamond, peridotite, and eclogite, the single type of rock that matched the speed discovered in seismic data.
According to the scenario, this means that inside Earth, there are over 1,000 times more diamonds than people expected.
Geologic Pipes Reveal Diamonds in Kimberlite
Faul explains that it makes sense for the cratonic roots to contain diamonds, as they are forged in an environment that has high pressure and a high temperature. Then, when volcanoes erupt, diamonds have a chance to get close to the surface, being found in geologic “pipes” made from rocks called kimberlite.
In certain parts in Canada, Siberia, Australia and South Africa, kimberlite pipes were found at the edge of cratonic roots. Faul explains that they’ve pieced all the evidence together and “went through all the different possibilities, from every angle, and this is the only one that’s left as a reasonable explanation.”
Andre Blair s is the lead editor for Advocator.ca. He holds a B.A. in Psychology from the University of Toronto, and a Master of Science in Public Health (M.S.P.H.) from the School of Public Health, Department of Health Administration, at the University of North Carolina at Chapel Hill. Andre specializes in environmental health, but writes on a variety of issues.