But the new results are unlikely to set off a diamond rush.
The diamonds, however, are impossible to mine - they're 90 to 150 miles below the Earth's surface, far deeper than any drills are capable of reaching.
To be more exact, the diamonds are in the oldest sections of rock under the tectonic plates, rocks known as cratonic roots.
But how did the researchers conclude that there are diamonds in the cratonic roots?
"We can't get at them, but still, there is much more diamond there than we have ever thought before".
Faul and his colleagues came to their conclusion after puzzling over an anomaly in seismic data.
The study was detailed by MIT, which explains that seismic activity data gathered by entities like the USGS essentially involves sound waves that pass through the Earth. There are certain areas in which the seismic waves tend to speed up without explanation.
Sound waves travel at different speeds depending on the composition, temperature, and density of the rocks and minerals they travel through, giving scientists a method to estimate what types of rocks are below the Earth's surface by comparing the velocities of these sound waves, according to MIT. Analyzing seismic waves is a fairly standard way of determining the composition of our planet's interior, for the simple reason that they're one of the few things that we can detect actually traveling through it. Vibrations from earthquakes don't just travel along the surface, they move down through the body of our planet as well - and a network of seismographs around the world is listening in to every shake and shudder our planet makes.
Scientists also use seismic data to reveal what the deepest parts of the Earth are composed of and paint a picture of what the inside of the planet looks like.
"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". In terms of sheer mass, that works out to around a quadrillion, or thousand trillion, tons of diamond. Parts of Earth's mantle may be up to two percent diamond by composition, far more than previously suspected. 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. "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".
The scientists reckon there's a quadrillion tonnes of diamond buried in the "cratonic roots" in continents.
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. Diamond, along with magma from deep in the Earth, can spew out through kimberlite pipes, onto the surface of the Earth.
"It's circumstantial evidence, but we've pieced it all together", Faul says.