The Paleolithic Period is often divided into three parts: Lower, Middle, and Upper. However, anthropologists resist placing hard time boundaries on each subdivision and the stages within them, because technologies characteristic of different industries emerged at different times in different regions. In addition, there is some level of overlap between stages and subdivisions because it took time for new technologies to spread, which created the circumstance in which some groups of people had access to higher levels of technology earlier than their contemporaries. The Lower Paleolithic is traditionally divided into the Oldowan Stage (about 2.6 million to 1 million years ago), which saw the development of pebble (chopping) tools, and the Acheulean Stage (1.7–1.5 million years ago to about 250,000–200,000 years ago), in which more sophisticated hand axes and cleaving tools emerged. With the discovery of the tools excavated at Lake Turkana, some anthropologists have suggested adding a third stage, the Lomekwian Stage, to account for 700,000 years of early hammering and other rock-chipping tools that predated the Oldowan Stage. The Middle Paleolithic, which was characterized by flake tools and the widespread use of fire, lasted from about 250,000 to 30,000 years ago. The Upper Paleolithic, which saw the emergence of more sophisticated tools, lasted from about 50,000–40,000 years ago until about 10,000 years ago.
The Neolithic stage of development was attained during the Holocene Epoch (the last 11,700 years of Earth history). The starting point of the Neolithic is much debated, as different parts of the world achieved the Neolithic stage at different times, but it is generally thought to have occurred about 10,000 BCE. During that time, humans learned to raise crops and keep domestic livestock and were thus less dependent on hunting, fishing, and gathering wild plants. Neolithic culturesmade more-useful stone tools than those of earlier cultures, by grinding and polishing relatively hard rocks rather than merely chipping softer ones down to the desired shape. The cultivation of cereal grains enabled Neolithic peoples to build permanent dwellings and congregate in villages, and the release from nomadism and a hunting-gatheringeconomy gave them the time to pursue specialized crafts.