Rocks that Eat Carbon


As a political science student I’m a junkie for all the latest global happenings. I spend much of my free time scouring through news outlets such as the Economist and BBC. On a recent binge I stumbled across an article from the Economist that discusses a recent discovery that may be a key to solving the problem of carbon sequestration.



The capturing and storing of vast quantities of CO2 emitted from sources such as power plants and heavy industry has been attempted by scientists for several years now. However current approaches focus largely on simply taking the gas and forcing it into old oil fields or abandoned coal mines. Not only does this method fail to store large amounts of the stuff, but it also fails to chemically alter the CO2 which tends to then find its way back to the surface through minute cracks in the rocks.



Two scientists from Columbia University think they may have finally solved the problem. By mixing the carbon emissions with a rock called peridotite, which makes up much of the earth’s upper mantle and breaks through the surface in numerous locations around the world, the greenhouse gas is turned into harmless carbonate rocks such as limestone or marble. This unassuming rock has been shown to be absorbing thousands of tons more of CO2 then previously thought, and with a little help from science that number can be increased 100,000 times.



The particular outcropping that the scientists were studying in the deserts of Oman could hold up to 4 billion tons a year of the roughly 30 billion tons that humans produce annually. The main problem remaining lies in the construction of the infrastructure required for such an undertaking. Like any infrastructure project this will initially be expensive but payoff in the long term. While trapping the carbon is only a stopgap measure, it would greatly help the world in its transition to a green economy.



Eating carbon



Nov 13th 2008

From The Economist print edition



There is a type of rock with a voracious appetite for carbon dioxide





ONE way of helping to reduce emissions of carbon dioxide into the atmosphere is to pump the gas into underground caverns or old oil fields. But there is also a rock that is happy to gobble it up, and according to the latest research its appetite for the greenhouse gas is not only massive but could also be increased by a little human intervention.



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. 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. This happens in part of the Omani desert which Peter Kelemen and Juerg Matter, both from Columbia University, New York, have studied for years.





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. 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. The transportation would also create emissions. 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.



The team has shown that the Omani peridotite absorbs tens of thousands of tonnes of carbon dioxide a year, far more than anyone had thought. By drilling and fracturing the rock they believe they can start a process to increase the absorption rate by 100,000 times or more. They estimate this would allow the Omani outcrop, which extends down some 5km, alone to absorb some 4 billion tonnes of carbon dioxide a year, which is a substantial part of the annual 30 billion or so tonnes of the gas that humans send into the atmosphere, mostly by burning fossil fuels.



With such rocks situated in an area of the world where an increasing amount of energy is produced and consumed, it potentially provides a convenient carbon sink for the region’s energy industry, say the researchers. Peridotite can also be found at the surface in other parts of the world, including some Pacific islands, along the coasts of Greece and Croatia, and in smaller deposits in America. Nor is it the only rock with carbon-eating potential. The researchers are now looking at volcanic basalt in a new project in Iceland.




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