A knife (plural knives) is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knife-like tools were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools.
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 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. According to the age and location of the current evidence, the cradle of the genus is the East African Rift S
stem, especially toward the north in Ethiopia, where it is bordered by grasslands. The closest relative among the other living Primates, the genus Pan, represents a branch that continued on in the deep forest, where the primates evolved. The rift served as a conduit for movement into southern Africa and also north down the Nile into North Africa and through the continuation of the rift in the Levant to the vast grasslands of Asia.
Starting from about 3 mya a single biome established itself from South Africa through the rift, North Africa, and across Asia to modern China, which has been called "transcontinental 'savannahstan'" recently. Starting in the grasslands of the rift, Homo erectus, the predecessor of modern humans, found an ecological niche as a tool-maker and developed a dependence on it, becoming a "tool equipped savanna dweller. The handle, used to grip and manipulate the blade safely, may include the tang, a portion of the blade that extends into the handle. Knives are made with partial tangs (extending part way into the handle, known as a "Stick Tang") or full tangs (extending the full length of the handle, often visible on top and bottom).