Archaeologists use many different techniques to determine the age of a particular artifact, site, or part of a site.
Two broad categories of dating or chronometric techniques that archaeologists use are called relative and absolute dating.
Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.
A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.
These techniques can be grouped as numerical, relative dating, and correlation.
Numerical techniques are best, but datable materials are often lacking, and in these cases age estimation must be made using relative-dating or correlation techniques.
The scholar most associated with the rules of stratigraphy (or law of superposition) is probably the geologist Charles Lyell.
The basis for stratigraphy seems quite intuitive today, but its applications were no less than earth-shattering to archaeological theory.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.