Beginning with a mind-boggling stunt that only science or spirituality can justify—a veritable walk through fire—this program examines humankind’s long, complicated relationship with the ravenous power of combustion. Fire was, for millennia, humanity’s principal source of heat and energy, and viewers learn the implications of that fact in scenes of Britain’s industrial revolution as well as China’s past development challenges. Along the way, the film dives into a mysterious lake in Oregon, ventures through an extraordinary cave in Iran, climbs a glacier of salt, and presents the therapeutic potential of a bath in crude oil. A BBC/National Geographic-U.S. Co-production in Association with ZDF. Part of the series How Earth Made Us: The Untold Story of History. (50 minutes)