The first method was based on radioactive elements whose property of decay occurs at a constant rate, known as the half-life of the isotope.
Today, many different radioactive elements have been used, but the most famous absolute dating method is radiocarbon dating, which uses the isotope C.
Dating methods in historical archaeology differ little from the methods of archaeology in general.
Both absolute and relative dating approaches are employed.
For more information on stratigraphy and how it is used in archaeology, see the Stratigraphy glossary entry.
For those researchers working in the field of human history, the chronology of events remains a major element of reflection.
The contrast might also be drawn between two 'dimensions', the historical, and the archaeological, corresponding roughly to the short-term and long-term history envisaged by Fernand Braudel.
On the one level, events and individuals are placed in an absolute chronology: the exact years and sometimes even months and days of the events and biographies are known.
On the other level, the exact years may not be known, but it is known that one feature is earlier or later in relation to another; this is typically the case on an excavation, where the different archaeological strata allow objects found to be placed in a relative historical framework.
For a long period in the 20th century Egyptian and Near Eastern chronology seemed to be the earliest of absolute chronologies, and imports from these areas were used to reconstruct the chronology of European prehistory.