Argon is gas that gradually builds up within rocks from the decay of radioactive potassium.

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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.

Another useful chemical analysis technique involves calculating the amount of nitrogen within a bone.

The technique can, however, provide the relative ages of bones from the same site.

Most fossils are found in sedimentary rocks deposited in layers.Different methods have their own limitations, especially with regard to the age range they can measure and the substances they can date.A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.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 level of nitrogen gradually reduces as the bone decays.