Mysterious Life of Caves (2002, PBS Nova)

 While exploring world-famous Carlsbad Caverns in New Mexico, geologists Carol Hill and Dave Jagnow stumbled across a startling find—giant blocks of a mineral that conventional theories said shouldn't be there. This discovery set them on the trail of a radically new explanation of how certain caves form, involving extremophile microbes that live off toxic hydrogen sulfide gas and literally eat away the rock (since one of their byproducts is sulfuric acid). At the time of Hill and Jagnow's first investigations, the idea that microbes could flourish in total darkness and help etch out huge underground caverns was revolutionary. https://www.pbs.org/wgbh/nova/caves 52 minutes | 1120x630 | 30fps | 1022kbps | Subtitles: English (embedded)