A crew works on a drilling rig at a well site for shale-based natural gas in Zelienople, Pa. Though hydraulic fracturing is thought of as a relatively new technique, the federal government began funding research into it and horizontal drilling in the 1970s. (Associated Press)

A crew works on a drilling rig at a well site for shale-based natural gas in Zelienople, Pa. Though hydraulic fracturing is thought of as a relatively new technique, the federal government began funding research into it and horizontal drilling in the 1970s. (Associated Press)