A Fuel is a substance used to release energy. Archeologic evidence indicates pre-humans learned to release energy, from wood, for cooking, in the distant past.
As human technology developed, fats and oils from plants and animals, were added as fuels. Fuels started to be used for industrial purposes - not just for food preparation. Humans learned to process wood into charcoal, and fats and oils into waxes, which had advantages over purely natural fuels, in portability, safety, and maximum heat production.
- Joe Schwarcz (2017-03-20). Charcoal is one of the most important substances ever discovered. McGill Office for Science and Society. “The fact that charcoal burns better than wood was probably noted soon after man learned to control fire over a million years ago. The first use of charcoal for purposes other than providing heat was around 30,000 BC when cavemen used it as a pigment for drawing on the walls of caves.”
- Nonrenewable Energy Resources. “The first use of coal may have occurred in China at about 1000 BC when it was used to smelt copper.”