There are two techniques for dating in archaeological sites: relative and absolute dating.Relative dating stems from the idea that something is younger or older relative to something else.In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.
More recently is the radiocarbon date of 1950 AD or before present, BP.
Geologists often need to know the age of material that they find.
They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.
The atoms of some chemical elements have different forms, called isotopes.
These break down over time in a process scientists call radioactive decay.