Many ifferent techniques for making fire exist. Smoldering plants and trees, or any source of hot coals from natural fires is the oldest way to make a fire. Other ancient techniques involve a fire drill or fire stick that is rotated or rubbed on a base. For thousands of years humans would strike a stone containing iron to produce sparks and then tinder was used to make a fire from the sparks. A flint alone doesn't produce incandescent sparks; it is the flint's ability to violently release small particles of iron, exposing them to oxygen that actually starts the burning. These methods are known since the Paleolithic ages, and still commonly in use with certain 'primitive' tribes but difficult to use in a damp atmosphere. (The control of fire by early humans is said to date back to either Homo erectus or very early Homo sapiens, that is, hundreds of thousands of years ago, based on archaeological evidence of hearths. )