Relative dating includes methods that rely on the analysis of comparative data or the context (eg, geological, regional, cultural) in which the object one wishes to date is found.
This approach helps to order events chronologically but it does not provide the absolute age of an object expressed in years.
In other words, Chronology is the arrangement of events, or the materials which represent them, in the order of their occurrence in time.
For those researchers working in the field of human history, the chronology of events remains a major element of reflection.
Archaeologists use several methods to assign ages to events of the past.
They are engaged in defining the stages of hominid evolution and their artifactual record, and the assignment of a chronology to these stages.
The absolute dating method first appeared in 1907 with Lord Rutherford and Professor Boltwood at Yale University, but wasn’t accepted until the 1950s.
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.
This isotope, which can be found in organic materials and can be used only to date organic materials, has been incorrectly used by many to make dating assumptions for non-organic material such as stone buildings.
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.
Though still heavily used, relative dating is now augmented by several modern dating techniques.
The half-life of C is approximately 5730 years, which is too short for this method to be used to date material millions of years old.
The isotope of Potassium-40, which has a half-life of 1.25 Billion years, can be used for such long measurements.