There is no definite date for the discovery of the first fossil fuel. According to the Kentucky Foundation, many ancient peoples used fossil fuels before they became popular as commercial sources of energy.
Decayed plant material that has not yet become coal is called peat. Cavemen burned both peat and coal for warmth. Greek historian Plutarch of the 1st century mentions "external fires," possibly referring to the ground fires lit when natural gas escapes from the ground and is ignited by lightning. In battle, Alexander the Great burned petroleum to fend off enemy war elephants. Asphalt, a derivative of petroleum, was used by the Egyptians to mummify corpses.
In the United States, the Hopi Indians burned coal for cooking and heating during the 1300s. Virginia settlers discovered coal in 1673, but did not use it commercially until the 1740s. Fossil fuels became the primary source of energy for the Industrial Revolution.