Instead, other methods are used to work out a fossil’s age.
This newer method converts a stable form of potassium (potassium-39) into argon-39.
Measuring the proportions of argon-39 and argon-40 within a sample allows the age of the sample to be determined.
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.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.
Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
Accurate dates also allow us to create sequences of evolutionary change and work out when species appeared or became extinct. These are: Where possible, several different methods are used and each method is repeated to confirm the results obtained and improve accuracy.
The technique can, however, provide the relative ages of bones from the same site.