Sound waves reveal diamond cache deep in Earth’s interior

Study finds 1–2 percent of Earth’s oldest mantle rocks are made from diamond.

Study finds 1–2 percent of Earth’s oldest mantle rocks are made from diamond.
Study finds 1–2 percent of Earth’s oldest mantle rocks are made from diamond.

A new study by the MIT scientists suggests that there might be quadrillion tons of diamond hidden in the Earth’s interior. The outcomes are unlikely to set off a diamond rush.

The ultradeep cache might be scattered inside cratonic roots — the most established and most ardent segments of rock that lie underneath the center of most mainland structural plates. Molded like rearranged mountains, cratons can extend as profound as 200 miles through the Earth’s outside and into its mantle; geologists allude to their most profound areas as “roots.”

Scientists in the study demonstrated that cratonic roots may contain 1 to 2 percent diamond. Considering the aggregate volume of cratonic roots in the Earth, the group assumes that about a quadrillion (1016) tons of diamond are scattered inside these old rocks, 90 to 150 miles underneath the surface.

Ulrich Faul, a research scientist in MIT’s Department of Earth, Atmospheric said, “This shows that diamond is not perhaps this exotic mineral, but on the [geological] scale of things, it’s relatively common. We can’t get at them, but still, there is much more diamond there than we have ever thought before.”

Faul and his associates reached their decision subsequent to thinking about an abnormality in seismic information. For as far back as couple of decades, organizations, for example, the United States Geological Survey have kept worldwide records of seismic action — basically, solid waves going through the Earth that are activated by earthquakes, tsunamis, blasts, and other ground-shaking sources. Seismic receivers around the globe get sound waves from such sources, at different rates and powers, which seismologists can use to figure out where, for instance, a quake started.

Researchers can likewise utilize this seismic information to build a picture of what the Earth’s inside might resemble. Sound waves move at different speeds through the Earth, contingent upon the temperature, thickness, and organization of the stones through which they travel. Researchers have utilized this connection between seismic speed and rock structure to assess the kinds of rocks that make up the Earth’s hull and parts of the upper mantle, otherwise called the lithosphere.

Be that as it may, in utilizing seismic information to outline Earth’s inside, researchers have been notable clarify an inquisitive abnormality: Sound waves tend to accelerate fundamentally when going through the underlying foundations of antiquated cratons. Cratons are known to be colder and less thick than the encompassing mantle, which would thus yield marginally quicker stable waves, yet not exactly as quick as what has been estimated.

Faul’s co-authors include scientists from the University of California at Santa Barbara, the Institut de Physique du Globe de Paris, the University of California at Berkeley, Ecole Polytechnique, the Carnegie Institution of Washington, Harvard University, the University of Science and Technology of China, the University of Bayreuth, the University of Melbourne, and University College London.

Faul said, “The velocities that are measured are faster than what we think we can reproduce with reasonable assumptions about what is there. Then we have to say, ‘There is a problem.’ That’s how this project started.”

The team aimed to identify the composition of cratonic roots that might explain the spikes in seismic speeds. To do this, seismologists on the team first used seismic data from the USGS and other sources to generate a three-dimensional model of the velocities of seismic waves traveling through the Earth’s major cratons.

Scientists later used this knowledge to gather virtual rocks, produced using different blends of minerals. At that point the group computed how quick stable waves would go through each virtual shake, and discovered just a single kind of shake that delivered an indistinguishable speeds from what the seismologists estimated: one that contains 1 to 2 percent diamond, notwithstanding peridotite (the transcendent shake sort of the Earth’s upper mantle) and minor amounts of eclogite (speaking to subducted maritime hull). This situation speaks to no less than 1,000 times more jewel than individuals had beforehand anticipated.

Faul said, “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.”

The researchers found that a rock composition of 1 to 2 percent diamond would be just enough to produce the higher sound velocities that the seismologists measured. This small fraction of diamond would also not change the overall density of a craton, which is naturally less dense than the surrounding mantle.

“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.”