Examples of the earliest tools used by humans include the stone tools known as the Oldowan toolkit and include hammerstones, stones with chipped flakes, and stone flakes with sharp edges used for cutting. These tools date back at least 2.6 million years to the period known as the Stone Age.
The first tools had simple function such as grinding seeds and plant material for food, assembling wood for shelters and processing animal hides. A subsequent generation of tools known as the Acheulean toolkit involved sharpening the stones used for cutting into primitive axes. By 1.7 million years ago, these stones underwent further refinements to become spears used for hunting and as weapons. The materials used for tools also expanded into the use of ivory, bone and antlers.