Every period has its very typical range of objects like ceramics, tools, jewelry et cetera. Grouped by way of making or decoration an object can be assigned very precisely to a period of time (typology). Taking ceramics as example, on base of shape, way of making and decoration, a vessel can even be assigned to a specific culture. Certain materials were first used from a certain moment onwards, like ceramics again: we find this first from the Young Stone Age onwards. bronze, glass or gold again are first worked in the Bronze Age and the metal iron was first showing up frequently in the Iron Age. Other materials again, like flint, loose their meaning over time and are replaced by other materials. At an archaeological excavation, the layers with younger items are lying on top of the layers with older artifacts, it means the deeper you dig, the older the finds are you will encounter. Besides this, there are complicated nature scientific methods (f. ex. dating year rings of trees, radiocarbon dating et cetera) which allow archaeological material to be dated on 10 or 20 years exact.