Prehistory is the time period before people began keeping written records.  The two major time periods in prehistory are the Paleolithic and Neolithic Ages.  The Paleolithic Age lasted from about 2.5 million B.C. to 10,000 B.C.  It is considered the earliest period of human history.  Around 10,000 B.C. the ice from the Ice Age began to thaw leading to the Neolithic Revolution.  This was when people moved from being hunters/gatherers to farmers.  They learned to farm and domesticate animals which led to the development of permanent villages.