The natural product of combustion, seen in the form of flame and smoke. The use of fire was a major landmark in man's adaptation to the cooler environment of the earth; it is often considered the single most important discovery by early man. Man probably knew how to make fire between 500,000-800,000 years ago in Europe or Asia. The ability to make fire efficiently and at will rather than merely catching it from natural sources may date from less than 200,000 years ago. Fire is first found on occupation sites of the Lower Palaeolithic period, approximately half a million years ago, although true hearths do not become typical until the penultimate glacial period, perhaps 200,000 years ago. Hearths and thick deposits of burnt material are typical of the last glacial period, by which time it is likely that the two main methods of making fire (the friction method of rubbing or rotating sticks to generate heat and the percussion method of striking sparks with iron and flint) were both in use.