Earth’s rarest diamonds form from primordial carbon in the mantle
The planet’s carbon cycle may not go as deep as scientists have thought
![Hope Diamond](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2020/09/091020_CG_diamond_feat.jpg?fit=1028%2C579&ssl=1)
Superdeep diamonds, such as the Hope Diamond, are formed in an ancient reservoir of carbon in the lower mantle that is separate from the carbon cycle that operates at Earth’s surface.
Smithsonian National Museum of Natural History