Geothermal energy uses the Earth’s internal heat and is a renewable energy source; fossil fuels such as coal and petroleum are nonrenewable energy sources.
Hot water contained in the ground near a volcano, geyser or thermal source is piped to the surface by drilling to extract steam and produce electricity.
Flammable, relatively viscous oily liquid that is used as an energy source; it is made up of various hydrocarbons resulting from the decomposition of plant life over millions of year.