The rock is peridotite, which is one of the main rocks in the upper mantle, an area that provides a girth below the Earth's crust.

ECONOMIST: Greenhouse gases

The rock occurs some 20km or more down, although in areas where plate tectonics have forced up some of the mantle, peridotite reaches the surface.

ECONOMIST: Greenhouse gases

Geologists have long known that when peridotite is exposed to the air it can react quickly with carbon dioxide to form carbonates like limestone or marble.

ECONOMIST: Greenhouse gases

In Proceedings of the National Academy of Sciences, Messrs Kelemen and Matter suggest an alternative: pumping the gas from places where it is produced and into underground strata of peridotite.

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Some people have looked at the idea of grinding up peridotite and using it to soak up emissions from power stations, but the process turns out to be expensive, partly because of the costs of transporting all the rock.

ECONOMIST: Greenhouse gases