Scientists have discovered that Earth has an ocean floor recycling system which transforms sediment into diamonds. There is a high chance that the diamond on your ring is made of recycled seabed as a result of intense chemical processes deep beneath the surface.
Scientists at Macquarie University in Sydney, Australia found traces of salt trapped in many diamonds. These traces indicate that the diamonds were formed in ancient seabeds deep beneath the Earth’s crust. While the vast majority of diamonds were formed this way, some were formed as a result of crystallization.
Researchers conducted experiments to recreate the extreme pressures and temperatures of more than 125 miles beneath the Earth’s crust. Dr. Michael Förster, Professor Stephen Foley, Dr. Olivier Alard and colleagues at Goethe Universität and Johannes Gutenberg Universität in Germany found that seawater in the sediment on the ocean floor produces the balance of salts which are found in diamonds. Their findings were published in the journal Science Advances.
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“There was a theory that the salts trapped inside diamonds came from marine seawater, but couldn’t be tested,” lead author Förster said in a statement. “Our research showed that they came from marine sediment.”
Diamonds are crystals made of carbon, and they form in the Earth’s crust. Due to volcanic activity, they are brought up to the surface by eruptions of kimberlite, a kind of magma. Gem diamonds are mostly made of pure carbon, but there are also fibrous diamonds which have a cloudy appearance and are less attractive to jewelers. They also contain traces of sodium, potassium and other minerals which tell scientists a lot about where they originate from.
“We knew that some sort of salty fluid must be around while the diamonds are growing, and now we have confirmed that marine sediment fits the bill,” Förster said.
For the ocean floor recycling system to work, a slab of sea floor must drop to a depth of more than 125 miles below the surface in a short amount of time. It occurs as part of a process called subduction, in which one tectonic plate drops beneath another.
The researchers created a model to test these processes beneath the surface to replicate the ocean floor recycling system. They tested it at pressures between four and six gigapascals and at extreme temperatures between 800 and 1,100 degrees Celsius. Their results showed evidence of their prediction, The salts formed in a balance with sodium and other minerals, matching the traces found in diamonds.
“We demonstrated that the processes that lead to diamond growth are driven by the recycling of oceanic sediments in subduction zones,” Förster said. “The products of our experiments also resulted in the formation of minerals that are necessary ingredients for the formation of kimberlite magmas, which transport diamonds to the Earth’s surface.”