Ultra-deep continental diamonds are the rarest on Earth


If a diamond is eternal, could it come from things that have lived (almost) forever?

Although it is unlikely that your diamond necklace was a early cephalopod or dinosaur, there is a rare type of gem which began to form 500 million years ago and later (dinosaurs appeared about 230 million years ago). Ultra-deep continental diamonds were born from the immense pressure on carbon in the remains of ancient living things from about 186 to 621 miles below the surface.

Only diamonds found in rocks in the ocean were previously considered the sparkling remains of things that were once alive. Curtin University geologist Luc Doucet, who led a study recently published in Scientific reports, dug deeper to find an isotope that proved oceanic diamonds aren’t the only type made from things that used to swim, crawl, or walk around.

“Carbon has several isotopes, but organisms tend to prefer lighter carbon atoms,” Doucet told SYFY WIRE. “Therefore, organic matter tends to be made up of much lighter carbon than non-organic matter. This organic signature is kept in the mantle and can be used to identify the origin of diamonds.

All the diamonds in your jewelry are probably lithospheric diamonds, which form in much shallower soil, 93 to 155 miles deep. They are what you get from carbon under 725,000 pounds of pressure per square inch, at temperatures of 2,000 to 2,200 degrees Fahrenheit. Diamonds only appear because they are vomited up by volcanoes and pushed to the surface by other geological processes. No matter Journey to the Center of the Earth; humans have never been able to dive more than 12 km underground.

The Doucet isotope found in oceanic and ultra-deep diamonds is known as delta 13 carbon or δ13C. The problem is, unlike oceanic diamonds, very deep diamonds with this isotope have such inconsistent compositions. Previously, it was often difficult to tell whether the carbon it comes from is organic or not. Because very deep diamond cores with this isotope end up with crusts of inorganic carbon, they are often mistaken for lithospheric diamonds, so maybe you’re wearing what’s left of something off.

As to what this extinct thing might have been, at least depending on the diamond and how long it was formed, future advances in carbon dating might figure that out.

“Right now, deep diamonds are thought to be less than 500 million years old, but that’s because dating inclusions in diamonds is not an easy thing,” says Doucette. “Advances in microanalysis and the development of new instruments, such as the new SIMS CAMECA 1300 being installed at Curtin University, could help us cope with their age. “

The pressure and intense heat of the mantle aren’t the only things that create diamonds from prehistoric corpses. Oceanic and ultra-deep diamonds are believed to form in the mantle transition zone, the part of the mantle with the most volatile, or the substances that evaporate easily. Think of the transition zone as a partial boundary between the upper and lower mantle and a partial transition from the upper mantle to the lower mantle. This is where pieces of crust sink and plumes of magma rise, carrying diamonds from the depths to the surface.

It’s still unclear why diamonds that form beyond the lithosphere use carbon from what were once living creatures, but there are possibilities that Doucette and his team are considering. It could have something to do with the organic carbon in the mantle or certain processes that form diamonds using only the organic substance.

“It could be that only organic carbon is recycled deep into the mantle due to specific filters and / or processes needed to bring that carbon to depth while the other type of carbon remains at a shallower level,” says -he. “In addition, two types of carbon coexist in the mantle, but maybe some processes only use organic carbon to form deep diamonds.”

At least we now know that things that died hundreds of millions of years ago can find new life other than through gasoline.


About Lucille Thompson

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