WADI ABDAH, OMAN — 

Deep in the jagged red mountains of Oman, geologists are searching for an efficient and cheap way to remove carbon dioxide from the air and oceans — and perhaps begin to reverse climate change.

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.