A common rock can be harnessed to soak up the main greenhouse gas carbon dioxide at a rate that could help slow global warming, scientists reported in a new study.
When carbon dioxide comes in contact with the rock, known as peridotite, the gas is converted into a solid carbonate like limestone or marble.
Geologist Peter Kelemen and geochemist Juerg Matter said the naturally occurring process can be supercharged 1 million times to grow underground minerals that can permanently store 4 billion or more of the 30 billion tons of carbon dioxide emitted by human activity every year.
Peridotite is the most common rock found in the Earth's mantle, or the layer directly below the crust. In some places it also appears on the surface — particularly in the Middle Eastern nation of Oman, which is conveniently close to a region that emits substantial amounts of carbon dioxide in the production of fossil fuels.
"To be near all that oil and gas infrastructure is not a bad thing," Matter said in an interview.
Supercharge via drilling, hot water
The scientists, who are both at Columbia University's Lamont-Doherty Earth Observatory in New York, say they could kick-start peridotite's carbon storage process by boring down and injecting it with heated water containing pressurized carbon dioxide.
"Once jump-started in this way, the reaction would naturally generate heat — and that heat would in turn hasten the reaction, fracturing large volumes of rock, exposing it to reaction with still more CO2-rich solution," the university said in a statement. "Heat generated by the Earth itself also would help, since the further down you go, the higher the temperature. The scientists say that such a chain reaction would need little energy input after it was started."
The peridotite field in Oman is already naturally absorbing 10,000 to 100,000 tons of carbon a year, the researchers found, far more than anyone had thought.
The two made the discovery during field work in Oman's desert. "Their study area, a Massachusetts-size expanse of largely bare, exposed peridotite, is crisscrossed on the surface with terraces, veins and other formations of whitish carbonate minerals, formed rapidly in recent times when minerals in the rock reacted with CO2-laden air or water," the university stated.
Peridotite also occurs in the Pacific islands of Papua New Guinea and Caledonia, and along the coast of the Adriatic Sea and in smaller amounts in California.
The study by Kelemen and Matter will appear in the Nov. 11 edition of the Proceedings of the National Academy of Sciences.
Not a silver bullet
Many companies are hoping to cut their greenhouse gas emissions by siphoning off large amounts of carbon dioxide from coal-fired power plants and storing it underground.
But big greenhouse gas emitters like the United States, China and India — where abundant surface supplies of the rock are not found — would have to come up with other ways of storing or cutting emissions.
Using underground caverns could require thousands of miles of pipelines and nobody is sure whether the potentially dangerous gas would leak back out into the atmosphere in the future.
Kelemen cautioned that this discovery alone would not solve the carbon problem.
"We see this as just one of a whole suite of methods to trap carbon," Kelemen said. "It’s a big mistake to think that we should be searching for one thing that will take care of it all."
To that end, Matter has also been working on a project in Iceland where a different rock, volcanic basalt, might be able to absorb CO2. Tests are set for next spring, the university said.