Natural gas, touted for its environmental, economic, and national security benefits, is often thought of as the fuel that will "bridge" our transition from oil and coal to renewables. The ability to extract natural gas from shale formations through a method called hydraulic fracturing has unleashed vast, untapped sources - by some estimates, the U.S. now sits on a 100-year supply. But contamination from toxic chemicals used in the fracking process has been the source of increasing health and environmental concerns. Can natural gas be part of a clean energy solution?