Through radiocarbon dating and by comparing collections from hundreds of sites, archaeologists have gradually classified a large number of regional prehistoric artifact types. Styles of pottery and stone tools especially varied through time and across regions. This variation allows these artifacts to be identified and dated based on their appearance and manufacturing technique. The artifacts above were identified using this type system. Based on the net-impressed surface treatment and the grit used as temper, the pottery sherd above is probably a Popes Creek type (about 2000 years old). The shape of this quartzite spear point identifies it as a Bare Island type (5000 years old).