Rock layer dating
Argon then starts to re-accumulate at a constant rate in the newly formed rock that is created after the eruption.
This technique is, however, useful for providing relative dates for objects found at the same site.Radioactive elements decay at a certain constant rate and this is the basis of radiometric dating.But, the decay elements need to be set, much like you would re-set a stop watch for a runner, to ensure an accurate measurement.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.It is possible to calculate the age of a sample by measuring the uranium content and the density of the fission tracks.
The age of volcanic rocks and ash can be determined by measuring the proportions of argon (in the form of argon-40) and radioactive potassium within them.
An object can be given an approximate date by dating the volcanic layers occurring above and below the object.
Argon is gas that gradually builds up within rocks from the decay of radioactive potassium.
The older method required two samples for dating and could produce imprecise dates if the argon was not fully extracted.
This newer method converts a stable form of potassium (potassium-39) into argon-39.
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.