The intense heat and pressure at the Earth's core, deep beneath the surface, is enough to make diamonds out of carbon, scientists say.

Researchers from Arizona State University's School of Earth and Space Exploration investigated the conditions at the boundary between the Earth's metal core and the magma in the mantle, and according to their paper published in the journal Geophysical Research Letters, have found that the carbon in the core's liquid iron metal alloy can form diamonds.

"The stable form of carbon at the pressure-temperature conditions of the Earth's core-mantle boundary is diamond," Dan Shim, a professor at Arizona State University and a co-author on the paper, said in a statement.

The find was dubbed a "diamond factory" by Arizona State University.

The interior of the Earth is divided into several segments, all composed of different ingredients and states of matter. Underneath the thin rocky crust comes the mantle, a slow-moving layer of molten rocks making up 84% of the planet's total volume, according to National Geographic. It sits at between 1,832 degrees F and 6,692 degrees F. Further in comes the Earth's outer and inner core: the outer core is liquid iron and nickel, among other elements, and is around 9,000 degrees F, while the inner core is mostly made of solid iron, due to the intense pressures, and is about as hot as the surface of the sun.

The authors of the paper have measured how carbon in the liquid outer core comes out of the liquid iron metal alloy, reacts with water, and forms diamonds.

"Temperature at the boundary between the silicate mantle and the metallic core at [around 1,800 miles] depth reaches to [about 7,000 degrees Fahrenheit], which is sufficiently high for most minerals to lose H2O captured in their atomic-scale structures," Shim said.

"At the pressures expected for the Earth's core-mantle boundary, hydrogen alloying with iron metal liquid appears to reduce solubility of other light elements in the core. Therefore, solubility of carbon, which likely exists in the Earth's core, decreases locally where hydrogen enters into the core from the mantle (through dehydration)."

"So the carbon escaping from the liquid outer core would become diamond when it enters into the mantle."

Diamonds are made entirely from carbon atoms in a uniquely strong arrangement of chemical bonds. They can be found in the crust across the planet, but are incredibly rare and therefore expensive. Diamonds are thought to have been transported from their origins in the mantle to the Earth's surface via deep-source volcanic eruptions.

The hardest known substance, the diamond, is used in industry for cutting and abrasion, as well as being a revered and symbolic jewelry gemstone.

"Carbon is an essential element for life and plays an important role in many geological processes. The new discovery of a carbon transfer mechanism from the core to the mantle will shed light on the understanding of the carbon cycle in the Earth's deep interior," Byeongkwan Ko, a recent Arizona State University PhD graduate and co-author of the paper, said in a statement. "This is even more exciting given that the diamond formation at the core-mantle boundary might have been going on for billions of years since the initiation of subduction on the planet."

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