The early history of the human race is mostclearly and readily studied by observing thestages of human technological progress. Thatis why it was a long-standing convention todivide early history into broad periodsaccording to the hard materials — stone,copper, bronze, and iron, in that order -—from which cutting tools and weapons weremade. Then, as knowledge of the pastincreased, the broad periods were furthersubdivided. The Stone Age was divided intothe Old (Paleolithic) period and the New(Neolithic) period when it was noticed thatthe technique of sharpening flint and otherstones changed from flaking to grinding.