MIT and several other scientific institutions used seismic machinery to measure the speed of sound waves deep below the Earth’s surface. They believe they’ve nearly perfected the process of estimating rock composition using this method, which has led to a startling discovery.
These scientists observed a sudden spike in the speed of these waves just below the center of most continental tectonic plates. This means there is a reasonably good chance you’re standing hundreds of miles above tons of diamonds as you’re reading this. But how could this be? What does it mean for both geology and the global diamond industry?
In 2018, researchers from all over the world from a variety of different institutions converged within the Cooperative Institute for Dynamic Earth Research (CIDER). There were scientists from the Institut de Physique du Globe de Paris, the University of Science and Technology of China, University of California, Berkeley, Harvard, MIT, the Carnegie Institution for Science in Washington, and several other institutions.
The purpose of CIDER is to form an interdisciplinary research center studying geological mechanisms and how they impact other global systems, as well as guiding the next generation of researchers. Researchers believe the answers to many questions we have about the distant past can be found underground. In this case, researchers were curious about the composition of rocks hundreds of miles beneath the surface. The results were shocking.
The essence of the study is this: Observing the speed at which the sound waves travel through rocks hundreds of miles below the Earth’s surface allows scientists to interpret the data and form conclusions on the composition of the rocks.
The method allows researchers to ascertain the composition of underground rocks without having to dig hundreds of miles beneath the surface. The denser the rocks, the slower the sound waves are able to travel through them. Scientists were surprised to find an increase in speed as these sound waves moved through cratons. How were the scientists able to explain this mystery?
It was a puzzling question: What kind of rock could account for such a rapid increase in the velocity of sound waves passing hundreds of miles deep in the Earth? To solve it, they first needed to create a model to re-create the phenomenon.
Seismologists were tasked with creating a three-dimensional model by compiling data gathered from several different sources. Then the team created “virtual rocks” out of data gathered during previous experiments. There were also many variables the team needed to control for, including buoyancy, electromagnetism, and mineral composition, among other factors. This led them to the incredible conclusion.
Scientists believe they have found a quadrillion tons of diamonds at the bottom of 200-mile-deep cratons and just beneath the center of tectonic plates. The only rocks scientists were able to measure similar velocity in seismic waves in were made up of 1%-2% diamond as well as peridotite and trace amounts of eclogite — both of which are often observed in oceanic crust.
From these findings, scientists have concluded that the bottom of cratons are partially composed of diamonds. This means diamonds are much less rare than previously thought. But how can they be sure? The scientists at CIDER are convinced their tests have confirmed their findings because diamonds have a particularly unique sound velocity.
How do they know there were diamonds down there?
“We went through all the possibilities, from every angle, and this is the only one that’s left as a reasonable explanation,” said Ulrich Faul, a researcher from MIT’s Department of Earth, Atmospheric and Planetary Sciences. According to Faul, the sound velocity of diamond is more than double that of the rock composition of the Earth’s upper mantle.
Using the 1% to 2% figure and estimating the weight of the Earth’s cratons, the team concluded that there is likely 1 quadrillion tons of diamonds hidden inside the plates. While the amount of diamonds discovered is mind-blowing, the findings confirm much of what we know about the formation of diamonds.
What is a craton and do diamonds factor into their geology?
A craton is the term given by geologists to differentiate the stable part of continental crust and mantle from unstable and mobile portions. They are commonly found in the interior of tectonic plates. “Cratons are a tiny bit less dense than their surroundings, so they don’t get subducted back into the Earth but stay floating on the surface,” said Ulrich Faul.
They are composed of crystalline basement rock. Sedimentary rock and sediments make up the layers above the craton. CIDER scientists now believe that diamonds keep the cratons stable. The recent findings mean that diamonds are about 1,000 times more common than we thought.
The shape of cratons
If you were to slice open the Earth and observe a craton, you would see they look much like upside-down mountains. Instead of stretching into the sky, however, cratons float upon the underlying mantle and extend downward. Cratons are the oldest part of the geological plates — considerably older than oceanic lithosphere.
For comparison, the cratonic lithosphere is an estimated 4 billion years old and the oceanic lithosphere dates back 180 million years. That means the rocks that make up cratons are nearly as old as the Earth itself, which is believed to be around 4.6 billion years old. Now that’s a long time.
Diamonds commonly found on the edge of cratons
We’ve all heard the expression, “pressure turns coal into diamonds.” Technically this is untrue. It’s true that diamonds and coal are similar in chemical composition, but where coal is formed from decaying organic material that releases carbon that is then solidified, diamonds are formed in a variety of radically different ways.
The most common way (though even this hasn’t been observed for 400 years) is through underground eruptions that shoot through the Earth’s mantle through kimberlite pipes (named after Kimberley, the location where the Star of South Africa was found). The carbon that will form a diamond comes from deep within the upper mantle or lower crust of the Earth. The combination of magma flowing through the immense pressure of hundreds of miles of rocks forges diamonds out of the carbon.
Where are kimberlite pipes located?
Kimberlite pipes are most frequently found on the edge of cratons. This seems to align itself with the findings of the recent study. The carrot-shaped kimberlite structures are formed by deep-origin volcanic eruptions that eject material that do not create an aboveground volcano.
Instead, a tuff ring marked by tephra (rock fragments ejected by volcanic eruption) forms around craterlike depressions on the surface of the Earth. Kimberlite pipes have been found on every continent. Only 900 of the 6,400 kimberlite structures are known as diamondiferous (containing diamonds), and just 30 of these 900 have been mined. Companies will only mine for diamonds in a given location if they estimate the economic benefits will outweigh the cost.
Diamonds are also formed in other ways
Diamonds are sometimes created by the subduction of tectonic plates. In this method, diamonds do not require the immense heat or pressure that the kimberlite process demands. This makes it possible for diamonds to be formed as shallow as 80 kilometers beneath the surface and at temperatures of only 200 degrees Celsius.
Of course, the events that create these diamonds are incredibly rare. Most often, an oceanic plate will subduct (be pushed underneath) when it makes contact with a continental plate, and the pressure generated combined with the magma forms diamonds from the carbon left behind by rotting plant matter that sank to the bottom of the ocean.
Diamonds are formed by asteroid impacts
The Earth has been here for a very long time — 4.6 billion years is our best estimate. During that time it has endured frequent asteroid assaults, some of which have produced diamonds. The incredible heat and pressure emitted upon contact with carbon on the Earth’s surface have the capability of forming diamonds.
Until recently, this was just a theory, but geologists studying craters such as Chicxulub (the impact zone of the comet that wiped out the dinosaurs) have been able to confirm it. The closer you move toward the center of impact (where the pressure of the impact is greatest), the larger the diamonds become.
Diamonds have been found inside meteorites
These diamonds are incredibly small, but the process in which they form is fascinating. It’s similar to the way asteroids colliding with the Earth are formed. Once again, high heat and pressure is generated upon impact. But where does the carbon that acts as the source of these diamonds come from?
The carbon is left over either from the creation of the universe itself or from shattered ancient planets! The amount of carbon is minimal but still substantial enough to form tiny diamonds — only nanometers in size. The carbon that forms these particles is older than our whole solar system!
What’s so special about diamonds, anyway?
One reason diamonds are so valuable is because of their beauty. The crystalline structure of diamonds gives them incredibly high optical dispersion. When light hits a diamond, it refracts into multiple different colors. This is what gives diamonds the incredible sparkle that people love so much.
Their sheer age also factors into their appeal. Most diamonds are between 1.5 and 3.5 billion years old. For this reason, they have become a symbol of eternal love. But the appeal of diamonds extends beyond their aesthetic and symbolic beauty. Diamonds are incredibly valuable because of their industrial and utilitarian capabilities as well …
Diamonds have many practical uses
Diamonds are hard — a 10 out of 10 on the Mohs scale of mineral hardness. Only the recently discovered material wurtzite boron nitride (w-BN) is calculated to be harder than diamond. Because of their durability, diamonds have a number of valuable uses, particularly in polishing and cutting. They’re also incredibly good conductors of heat.
Scientists have mastered the ability to create synthetic diamonds in laboratories that can fulfill these purposes. However, the diamonds created in these labs are not nearly as valuable as those uncovered in diamond mines. Of course, much of what makes diamonds so valuable is their rarity. Though perhaps diamonds are not as incredibly rare as we once thought …
What’s the economic value of the diamonds recently discovered by scientists?
It is hard to calculate the sheer economic magnitude of the amount of diamonds. The incredible vastness of the discovery puts the weight of the diamonds at a quadrillion tons. Although it’s impossible to predict the financial impact if they were to be mined, it would likely be devastating to the diamond industry.
It has long been known that diamond sellers engage in the unscrupulous practice of hoarding diamonds to reduce the supply in the market and keep prices high. If diamonds were to become more common, these business practices would become ineffective and the whole global industry might crumble.
The economic potential
So, say the market was able to remain static after these diamonds were mined — what would their value be? At recent market value, diamonds cost $3,800 per ton, which put the value of a quadrillion tons at $191,000,000,000,000,000,000,000,000 (191 septillion dollars).
This is well above the estimated value of the entire world economy. Of course, the price of diamonds would not remain static — their value would plummet drastically. In fact, prices already fluctuate constantly based on a variety of factors — an increase of a quadrillion tons of diamonds to the market’s supply would likely make them incredibly cheap.
The economic history of diamonds
The first diamonds were discovered by humans in India, sometime during the fourth century B.C. These gems had likely formed 900 million years ago. The Silk Road — the trade route between India and China — hosted the transportation of these precious stones. For over 2,000 years, humans thought that India was the only place diamonds could be found.
It wasn’t until the 18th century that humans found diamonds elsewhere. After India’s diamond mines were sucked dry, humans began looking for alternative sources. In 1725, diamonds were discovered in Brazil, though it was such a small amount it could not keep up with the world’s demand for the valuable gems.
Diamonds in South Africa
The first diamond in South Africa was discovered purely by chance. In 1866, a 15-year-old boy named Erasmus Jacobs found a strange pebble that turned out to be a 21.25-carat diamond. The discovery set off a chain of events that would begin the diamond rush and the rapid industrialization of South Africa that came to be known as the mineral rush.
Migrant workers flocked to the region in an effort to find diamonds, forcing South Africa to rapidly transform from a rural network of undeveloped states to a full-blown industrialized powerhouse. The metamorphosis had a disastrous impact on race relations that eventually led to apartheid.
The diamond trade is ruthless and rife with human suffering
Diamonds are one of the most valuable materials known to man, and they often come from the most economically depressed sectors of the world. This fact has led to an explosion of horrific exploitation and violence. Despite the creation of a system which regulates the import and export of diamonds, known as the Kimberley Process Certification Scheme, the violence continues.
Sadly, residents near the Marange diamond fields in Zimbabwe and other diamond-rich locations are still subjected to horrendous abuse and oppression. The laws have proven unable to curb diamonds tainted by violence from reaching the global market. Would a sudden influx of diamonds into the market end the exploitative nature of the diamond trade? While we can’t say what the future will hold, we do know the radical effect this recent discovery is having on our geological understanding.
So, can we mine these diamonds?
Put your shovel away. Unfortunately, these gems are far beyond our reach, at least for the time being. The deepest we’ve gone so far is the Kola Superdeep Borehole, which is 9 inches wide and 40,230 feet deep — about 192 miles short of the diamonds … and that took us 20 years to dig.
“We can’t get at them, but still, there is much more diamond there than we have ever thought before,” Faul said in a statement on behalf of MIT. Even without being able to reap the economic benefits of a quadrillion tons of diamonds, the discovery has sent shock waves through the scientific community. But not everyone is convinced yet …
The findings have their doubters
“I’m taking the conclusions, personally, with a grain of salt,” Suzan van der Lee, a seismic expert at Northwestern University, told National Geographic. But how does Dr. Suzan van der Lee explain the speed of the sound waves? She says that further research is needed to confirm or disprove the conclusions of the CIDER experiment.
According to her, the sound velocity could be explained by an unidentified rock composition, not just diamonds. Perhaps we simply have not yet discovered another rock compound that could explain the phenomena. Inevitably, we’ll see more proof of the findings or counterevidence in the future.
Why were scientists performing these studies?
You may be surprised to know how little we knew about our planet and the solar system until fairly recently. The first pictures taken of the Earth from space via satellite in the 1960s gave rise to the Gaia hypothesis of the Earth as one being in a certain sense — the complex relationship of living organisms and inorganic elements leads to simultaneous evolution and the regulation of conditions that maintain life.
While the Gaia principle has largely been challenged and discredited since its genesis, evidence gathered between the 1950s and 1970s helped form our modern understanding of plate tectonics, which essentially updated and explained the 1912 theory of continental drift. However, the process of discovery is ever-ongoing …
What have we learned and what don’t we know?
Our understanding of tectonic plates and how they move and collide led to our understanding of how mountains, continents, and volcanoes were formed. It also explains earthquakes, tidal waves, and other natural disasters and phenomena. These things have enabled people to prepare for the worst. But there are so many things that still puzzle scientists.
For example, how did water come to exist on our planet? Did it come from ice that melted when asteroids impacted the Earth? It’s a popular theory, but so far the search for evidence has left scientists empty-handed … And what about what’s under the tectonic plates?
What material makes up the Earth’s core?
One thing that’s been puzzling scientists for centuries is the core of the Earth. Scientists are now fairly certain that the Earth’s core is an alloy made up of nickel and iron, similar to the chemical composition of meteorites. They arrived at this conclusion by analyzing the velocity of seismic waves and the magnetic field.
However, there’s still some mystery. What other elements make up the core besides iron and nickel? Is it oxygen, silicon, or something else? Also, how did the world maintain its magnetic field as it cooled from a fiery state when it first began 4.6 billion years ago?
The answers to life’s greatest mysteries may be underground
It’s the question that has plagued mankind since the beginning of time — how did life begin? We’ve never been able to trace back that far. The earliest record of living things come from fossils of microorganisms that date back 3.47 billion years.
But how did these organisms come to inhabit the Earth? Did they somehow materialize on Earth or did they arrive via meteor? Both are popular theories with their own supporting evidence. We may never know the answers to these questions, but with each discovery, we arrive one step closer and learn more about the history of our planet.