ENERGY FOR PEOPLE: Fuels

For thousands of years, the work that humans needed to do was powered directly by plants and animals. People burned wood, peat, or cow dung for heat and light, and tilled their fields with a plow pulled by a horse or cow.

In some parts of the world, these fuels or sources of power are still used. It's pretty easy to trace their energy back to the sun. Wood and peat come directly from plants. Cow dung is left over after the cow has digested its meal of grass. Some of the sun's energy captured by the grass goes to the cow, but some of it passes right through and is still there in the dung, to be converted into light and heat energy when the dung is burned. The process of burning to release energy is called combustion.

NEXT: Fossil Fuels