Despite being one of the most abundant minerals on the planet, scientists had never actually found calcium silicate perovskite on the surface of the Earth. That was until some geologists discovered a diamond from South Africa with a little nugget of it trapped inside.
Using both laboratory experiments and seismological data, scientists have created a picture of what they think is going on deep under the crust, allowing them to figure out what minerals should be the most abundant within the mantle.
But due to the obvious limitations of studying the inner workings of our planet, and the machinations that are occurring some 1,000 kilometers (620 miles) beneath our feet, confirming any of this is incredibly tricky.
Calcium silicate perovskite, which is a polymorph of the more common calcium silicate, is formed under intense pressure and heat within the lower mantle. Due to its inherent instability, however, it isn’t thought to be able to survive when it reaches the surface.
This means that even though the geologists expected that the high-pressure mineral existed, and that it was probably the fourth most common mineral on the planet, it had never actually been seen in nature.
This is where the diamonds come in. “The only possible way of preserving this mineral at the Earth's surface is when it's trapped in an unyielding container like a diamond,” explained Graham Pearson, who co-authored the paper published in Nature. It is thought that as the diamond formed deep within the mantle, something like 700 kilometers (430 miles) down, a small bit of calcium silicate perovskite got trapped inside.
As the diamond then migrated to the surface it took the mineral with it, and because the structure of the diamond maintained the pressure on the mineral it survived the long journey.
This is a great confirmation of what researchers have only really known about from experiments in the lab and workings out on paper. “It's a nice illustration of how science works," Pearson said. "That you build on theoretical predictions, in this case from seismology, and that once in a while you're able to make a clinching observation that really proves that the theory works.”
Only in recent years have we been able to get any real grasp of what is actually going on in the middle of our planet, and diamonds have played a large part in that. Minerals found within one a few years ago suggested that there may be an ocean’s worth of water under our feet, while another study published this week provided the first direct evidence that this water is in liquid form, despite the incredible temperatures and pressures experienced.