Another limitation is that carbon-14 can only tell you when something was last alive, not when it was used.A limitation with all forms of radiometric dating is that they depend on the presence of certain elements in the substance to be dated.We can measure directly, for example by using a radiation detector, and obtain a good estimate of by analyzing the chemical composition of the sample.
To date older fossils, other methods are used, such as potassium-argon or argon-argon dating.
Other forms of dating based on reactive minerals like rubidium or potassium can date older finds including fossils, but have the limitation that it is easy for ions to move into rocks post-formation so that care must be taken to consider geology and other factors.
It suffers from the problem that rubidium and strontium are very mobile and may easily enter rocks at a much later date to that of formation.
This method for rock dating is based on the decay of potassium-40 into argon: until the rock solidifies, argon can escape, so it can in theory date the formation of rock.
The key is to measure an isotope that has had time to decay a measurable amount, but not so much as to only leave a trace remaining.
Given isotopes are useful for dating over a range from a fraction of their half life to about four or five times their half life.Radiometric dating — through processes similar to those outlined in the example problem above — frequently reveals that rocks, fossils, etc.are very much older than the approximately 6,000 to 10,000 years reckoned by young earth creationists.Although the time at which any individual atom will decay cannot be forecast, the time in which any given percentage of a sample will decay can be calculated to varying degrees of accuracy.The time that it takes for half of a sample to decay is known as the half life of the isotope.This leaves out important information which would tell you how precise is the dating result.