DDURING THE NINETEENTH CENTURY, archaeologists coined labels for eras of the human past according to the primary material out of which surviving tools had been made. Thus the earliest human era became the Stone Age, the next era the Bronze Age, and the next the Iron Age. They further divided the Stone Age into the Paleolithic era, during which people used stone and other natural products to make tools and gained food largely by foraging. This was followed by the Neolithic era, which started around 9000 B.C.E.and saw the beginning of agricultural and animal domestication.