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.
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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 number of tracks increases over time at a rate that depends on the uranium content.
Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.
Uranium is present in many different rocks and minerals, usually in the form of uranium-238.
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.
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.