Eating carbon - Greenhouse gases
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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