How is absolute dating done
Each volcanic eruption produces a new deposit of ash and rock.
Fossils and other objects that accumulate between these eruptions lie between two different layers of volcanic ash and rock.
Another useful chemical analysis technique involves calculating the amount of nitrogen within a bone.
The level of nitrogen gradually reduces as the bone decays.
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 problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
In special cases, bones can be compared by measuring chemicals within them.
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 number of tracks increases over time at a rate that depends on the uranium content.
These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.
Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
During this process the pieces of the atom move apart at high speed, causing damage to the rock or mineral.
This damage is in the form of tiny marks called fission tracks.