Scientists from Curtin University (Perth, Australia) have published in the journal Nature's Scientific Reports a study on the origin of the rarest superdeep continental diamonds. Analysis of the carbon isotope level reveals that these gemstones were once living things.
All natural diamonds belong to one of three main types: lithospheric, oceanic and superdeep continental. The most common - they make up 99% of all diamonds mined in the world - are lithospheric rocks, which are formed at a depth of 130-200 km. Oceanic ones are found at the bottom of the ocean. Superdeep continental diamonds are the rarest, they are formed at a depth of more than 300 km under the continental crust, the outer layer of the lithosphere, the rocky shell of the Earth.
All three types of diamonds are formed at different levels of the mantle, so they have different levels of organic and inorganic carbon. This ratio can be determined by the signature of the carbon isotope δ13C. Organic carbon compounds are formed in living things, therefore diamonds formed from organic carbon are also the remains of a living organism. As Australian scientists have found out, superdeep continental diamonds contain an "astonishing" amount of δ13C, that is, they are of organic origin.
Such diamonds are formed at a depth of 400 to 600 km, and then are transported into the lithosphere by hot streams during volcanic eruptions. “We see how waste recycling is becoming increasingly necessary for the survival of humanity. It is all the more surprising that Mother Nature has shown us how to tastefully recycle waste for billions of years and return it to people in the form of jewelry”, - the researchers write.