Relative dating methods in archaeology
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.
Stratigraphy is the oldest of the relative dating methods that archaeologists use to date things.
Stratigraphy is based on the law of superposition--like a layer cake, the lowest layers must have been formed first.
Limits to relative dating are that it cannot provide an accurate year or a specific date of use.
Today, many different radioactive elements have been used, but the most famous absolute dating method is radiocarbon dating, which uses the isotope C.
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.
For example, JJA Worsaae used this law to prove the Three Age System.
For more information on stratigraphy and how it is used in archaeology, see the Stratigraphy glossary entry.