At death, the amount of radioactive carbon begins to decay at a constant rate. These measurements can tell us how old the once-living material is, up to 100,000 years ago. The older the material, the less radiation there is left to release. Bone, wood, cloth, shell, and other materials can all be C-14 dated. Site A location, place.
Sites are places where humans did things and left their things behind.
Stratigraphy The science of studying layers of materials, as in rock layers in the Earth, or deposits in archaeological sites. Usually, the layer on the bottom is the oldest, the layer on the top is the youngest.