NATURAL GAS: The hard facts about fracking. “There’s a wealth of natural gas trapped underground—but what depths do we have to plumb to extract it? More and more, oil and gas companies are opting for fracking, or hydraulic fracturing: injecting a mixture of sand, water and chemicals into dense rock layers and shale, creating cracks that allow natural gas trapped inside to flow to the earth’s surface. Once an also-ran in fossil-fuel prospecting, fracking now figures heavily into the future of U.S. energy production.”