This technique is, however, useful for providing relative dates for objects found at the same site.Another useful chemical analysis technique involves calculating the amount of nitrogen within a bone.This form of uranium usually decays into a stable lead isotope but the uranium atoms can also split – a process known as fission.During this process the pieces of the atom move apart at high speed, causing damage to the rock or mineral.Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.
The older method required two samples for dating and could produce imprecise dates if the argon was not fully extracted.
This damage is in the form of tiny marks called fission tracks.
When volcanic rocks and minerals are formed, they do not contain fission tracks.
Instead, other methods are used to work out a fossil’s age.
These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.