Courier-Journal: Drillers have bored nearly 4,000 feet below the green pastures of a Hancock County farm as part of a project that could hold a key to the future of coal in Kentucky. They’re about halfway to their goal of 8,300 feet, aiming for rock that’s 550 million years old. Next, researchers will inject small amounts of carbon dioxide to test the ability of underground layers to hold the greenhouse gas that many scientists say has become a serious global threat. “We don’t have a choice,” …