The Stone Age is a broad prehistoric period during which stone was widely used to make implements with a sharp edge, a point, or a percussion surface. The period lasted roughly 3.4 million years, and ended between 4500 BC and 2000 BC with the advent of metalworking. Stone Age artifacts include tools used by humans and by their predecessor species in the genus Homo, as well as the earlier partly contemporaneous genera Australopithecus and Paranthropus. Bone tools were used during this period as well, but are more rarely preserved in the archaeological record. The Stone Age is further subdivided by the types of stone tools in use. The Stone Age is the first of the three-age system of archaeology, which divides human technological prehistory into three periods: The Stone Age is nearly contemporaneous with the evolution of the genus Homo, the only exception possibly being at the very beginning, when species prior to Homo may have manufactured tools.