In their lab they applied heat and pressure to water with a high carbon content - and diamonds emerged.

The liquid metal was fed into a steel furnace, where the iron's carbon content was reduced and impurities removed, producing raw steel.

But most of these are mineral-based, and will have a higher carbon content than wood and biomass fuels.

Furthermore, even if it were practicable, surely it would be better to preserve areas of forest with the highest biodiversity value, rather than on the basis of carbon content alone.

Steroids produced naturally in the body have a heavier carbon content than synthetic substances but, until now, it has been difficult to measure the different carbon ratios.