Buried bones absorb chemicals, such as uranium and fluorine, from the surrounding ground and absorb more of these chemicals the longer they remain buried.
The rates of absorption depend on a number of factors which are too variable to provide absolute dates.
The heat from a volcanic eruption releases all the argon from the molten rock and disperses it into the atmosphere.
Argon is gas that gradually builds up within rocks from the decay of radioactive potassium.
It is initially formed in the molten rock that lies beneath the Earth’s crust.
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.
This technique is, however, useful for providing relative dates for objects found at the same site.