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Carbon rocks

Professor Robert Hilton from our Department of Geography has found a missing link in the natural carbon cycle through the study of rocks.

What was the study about?

Robert, and postdoctoral researcher Guillaume Soulet, conducted a study which discovered that sedimentary rocks, which cover 60 per cent of the earth, release carbon dioxide into the atmosphere.

The study, which took place over a period of two-and-a-half years, researched the fluctuations of the release of carbon dioxide through different weather seasons, something which has rarely been researched or documented before.

How to measure carbon dioxide in rocks

The research was conducted at the Draix-Bléone Critical Zone Observatory in France and Prof. Hilton worked closely with the onsite experts to ensure the wildlife and natural environment would be preserved when selecting the sample areas.

Small holes were drilled into each of the rock samples before inserting a cylinder with a tube on the end, which allowed the gas to be extracted – a process which took several hours per rock.

The gas samples were then studied at the lab to determine if the carbon dioxide had come from the rock or from the atmosphere.

Findings of the study

The study discovered that that during the summer months, the rocks gave off five times as much carbon dioxide as in the winter months. This is known as positive feedback to warming, whereby the hotter weather will mean more CO2 being released into the atmosphere, which will in turn increased the temperature even more.

With these findings, Robert predicts that around 100 megaton of carbon dioxide is released into the atmosphere by sedimentary rocks every year but that is 100 times less than the carbon being released by the burning of fossil fuels.

Postdoctoral researcher Guillaume Soulet studying the rocksImage credit: Robert Hilton.

Find out more:

• The research paper can be read in full in the Nature Geoscience journal.

• Interested in studying Geography?