Diamonds are a girl's best friend, but where exactly do they come from?

Small amounts of salt trapped inside diamonds show the precious stones are produced from ancient seabeds that were buried deep within Earth's crust, according to new research from a team of scientists in Australia.

Researchers were able to conduct experiments demonstrating that seawater in sediment from the ocean's bottom reacts in the right way to produce the balance of salts found in diamonds.

They had to recreate the extreme pressure and temperatures found more than 124 miles underground.

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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 Michael Förster, who works at Goethe Universität and Johannes Gutenberg Universität in Germany, said in a statement. "Our research showed that they came from marine sediment."

In order for the process to work, a large chunk of seafloor would have to slip down to a depth of more than 124 miles below the surface very quickly in a process that's known as subduction, scientists said.

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According to researchers, the speedy descent is necessary because the sediment must be compressed to more than 40,000 times atmospheric pressure before it can melt in temperatures of over 800 degrees Celsius, or 1,472 °Fahrenheit.

The study, published in Science Advances, settles a long-standing question about the formation of diamonds.