Geothermal energy is one of the oldest renewable resources used by humans. It has been used since the ancient Roman times as a heat source. Recently, it has been harnessed and used as a source of power. Explains a few different ways that geothermal power plants operate. Discusses how experts are working to fine-tune the process and make the power plants more affordable and useful across the country. Accessibility options on the DVD are: (1) expanded description, (2) English subtitles in a black box, (3) subtitled description.