They are coring samples from one of the world's only exposed sections of the Earth's mantle to uncover how a spontaneous natural process millions of years ago transformed carbon dioxide into limestone and marble. As the world mobilizes to confront climate change, the main focus has been on reducing emissions through fuel efficient cars and cleaner power plants. But some researchers are also testing ways to remove or recycle carbon already in the seas and sky.
The Hellisheidi geothermal plant in Iceland injects carbon into volcanic rock. At the massive Sinopec fertilizer plant in China, carbon is filtered and reused as fuel. In all, 16 industrial projects currently capture and store around 27 million tons of carbon, according to the International Energy Agency. That's less than 0.1 percent of global emissions — human activity is estimated to pump about 40 billion tons a year into the atmosphere — but the technology has shown promise. "Any one technique is not guaranteed to succeed," said Stuart Haszeldine, a geology professor at the University of Edinburgh who serves on a U.N. climate body studying how to reduce atmospheric carbon. "If we're interested as a species, we've got to try a lot harder and do a lot more and a lot of different actions," he said.
Travertine pools with white films of carbon fused with calcium
One such action is underway in the al-Hajjar Mountains of Oman, in a quiet corner of the Arabian Peninsula, where a unique rock formation pulls carbon out of thin air. Peter Kelemen, a 61-year-old geochemist at Columbia University's Lamont-Doherty Earth Observatory, has been exploring Oman's hills for nearly three decades. "You can walk down these beautiful canyons and basically descend 20 kilometers (12 miles) into the earth's interior," he said. The sultanate boasts the largest exposed sections of the Earth's mantle, thrust up by plate tectonics millions of years ago. The mantle contains peridotite, a rock that reacts with the carbon in air and water to form marble and limestone. "Every single magnesium atom in these rocks has made friends with the carbon dioxide to form solid limestone, magnesium carbonate, plus quartz," he said as he patted a rust-colored boulder in the Wadi Mansah valley. "There's about a billion tons of CO2 in this mountain," he said, pointing off to the east.
Rain and springs pull carbon from the exposed mantle to form stalactites and stalagmites in mountain caves. Natural pools develop surface scum of white carbonate. Scratch off this thin white film, Kelemen said, and it'll grow back in a day. "For a geologist this is supersonic," he said. He and a team of 40 scientists have formed the Oman Drilling Project in order to better understand how that process works and whether it could be used to scrub the earth's carbon-laden atmosphere. The $3.5 million project has support from across the globe, including NASA. Carbon dioxide is the primary greenhouse gas driving climate change, which threatens political instability, severe weather and food insecurity worldwide, according to the United Nations climate body.
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