Inscriptions, distinctive markings, and historical documents can all offer clues to an artifact's age.
And if the artifact is organic—like wood or bone—researchers can turn to a method called radiocarbon dating.
The rate of cosmic rays which hit the Earth depends on two very slowly changing factors: the solar activity and the Earth's magnetic field.
This latter serves as a shield against all cosmic radiation - when its strength goes down, the bombardment increases, as does the number of carbon 14 atoms.
The carbon 14 present in the atmosphere is constantly renewed.
The cosmic rays originating from the Sun collide with nuclei in the upper atmosphere and are capable of breaking off individual neutrons.
One naturally assumes that the cosmic bombardment responsible for this transmutation remains constant over the millennia.
Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.
Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating.
In this interactive, learn how radiocarbon dating works, what it takes to determine a date in the lab, and why it's challenging to pinpoint a date precisely.
You probably have seen or read news stories about fascinating ancient artifacts.