These rare superdeep diamonds exposed Earth’s primordial secrets

Chris Davies - Aug 15, 2019, 4:59 pm CDT
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These rare superdeep diamonds exposed Earth’s primordial secrets

A priceless haul of superdeep diamonds has seemingly confirmed the existence of an ancient reservoir of raw magma, a time capsule of the Earth’s most inaccessible secrets. The discovery could lead to breakthroughs in understanding how our planet formed, and what geological changes it may still be undergoing.

Although liquid magma regularly changes the Earth’s crust, a slow-moving shift in the tectonic plates, scientists have long held suspicions about what might be locked away far beneath the surface. Sandwiched somewhere between the core and the crust, this reservoir of rock is special because it is relatively undisturbed.

That hasn’t stopped theories abounding, mind. One widespread belief is that this cache of ancient rock could date back to before the creation of the Moon, a section of the planet that represents materials from the very earliest stages of its history.

It’s freshly-discovered superdeep diamonds that have cast new light on that possibility. Typically, diamonds form between roughly 90 and and 140 miles beneath the Earth’s crust, and are then carried by lava melts to the surface. However superdeep diamonds are created by vast forces far further down: anything up to 500 miles below the crust.

They’re rare to emerge at depths where human researchers can retrieve them, but when that does occur it’s effectively like finding a sampling tube of those incredibly deep regions. Gases trapped in tiny pockets in the diamonds can be extracted and analyzed, which is just what researchers at the Australian National University did.

“Diamonds are the hardest, most indestructible natural substance known, so they form a perfect time capsule that provides us a window into the deep Earth,” research leader Dr Suzette Timmerman explains. “We were able to extract helium gas from twenty-three super-deep diamonds from the Juina area of Brazil. These showed the characteristic isotopic composition that we would expect from a very ancient reservoir, confirming that the gases are remnants of a time at or even before the Moon and Earth collided.”

That dates the reservoir at potentially more than four billion years old. The diamonds’ geochemistry suggest they formed in the so-called “transition zone” between 255 and 410 miles under the Earth’s surface. It indicates the ancient reservoir is located either around there or below it.

Although these new insights would seem to confirm theories of the reservoir’s existence, there are still plenty of questions left unanswered. For a start, it’s unclear whether this is one, large body of ancient rock, or if that cache is split into several, smaller sections. The exact chemical make-up of the rock is also unknown.

Still, as historical features of our home planet go, what Timemrman describes as “probably the oldest remaining comparatively undisturbed material on Earth” is definitely worth getting excited over. We’re a long way from being able to dig down to such a primordial reservoir, but analysis of the sources of deep lavas such as those which form islands like Iceland and Hawaii is one step closer to figuring out some of Earth’s oldest secrets.


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