Researchers at the University of Bristol have discovered new insights into previously hidden parts of the soil's carbon cycle. The team found that carbon recycling extends into the deep mantle by plate subduction,but is still primarily constrained to upper mantle depths, above 700km. The researchers made the discovery that certain scarce diamonds are formed when carbon that was sequestered from seawater into the soil's shifting tectonic plates reacts with the mantle after the plate is subducted – a process by which it moves under another tectonic plate and sinks into the mantle as the plates converge.
Source: phys.org