The sequence of development of culture or the relationship between events that represent culture can be established only when events can be placed in proper time.
Chronology, the study of events in time frame, is hence the central theme of archaeologist, like the geologist who deals with the story of earth history.
Carbon-14, or radiocarbon, is a naturally occurring radioactive isotope that forms when cosmic rays in the upper atmosphere strike nitrogen molecules, which then oxidize to become carbon dioxide.
Green plants absorb the carbon dioxide, so the population of carbon-14 molecules is continually replenished until the plant dies.
Until this century, relative dating was the only technique for identifying the age of a truly ancient object.
By examining the object's relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site.
The scholar most associated with the rules of stratigraphy (or law of superposition) is probably the geologist Charles Lyell.
Archaeological scientists have two primary ways of telling the age of artefacts and the sites from which they came: relative dating and absolute dating.Carbon-14 is also passed onto the animals that eat those plants.After death the amount of carbon-14 in the organic specimen decreases very regularly as the molecules decay.Though still heavily used, relative dating is now augmented by several modern dating techniques.Radiocarbon dating involves determining the age of an ancient fossil or specimen by measuring its carbon-14 content.The style of the artefact and its archaeology location stratigraphically are required to arrive at a relative date.