Fossil record radiometric dating
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.
The heat from a volcanic eruption releases all the argon from the molten rock and disperses it into the atmosphere.
Argon then starts to re-accumulate at a constant rate in the newly formed rock that is created after the eruption.
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.
Uranium is present in many different rocks and minerals, usually in the form of uranium-238.
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.
The level of nitrogen gradually reduces as the bone decays.
Absolute dating is not possible with this method because the rate at which the nitrogen content declines depends on the surrounding temperature, moisture, soil chemicals and bacteria.
Buried bones absorb chemicals, such as uranium and fluorine, from the surrounding ground and absorb more of these chemicals the longer they remain buried.