Radiocarbon or Carbon-14 dating is a technique used by scientist to date bones, wood, paper and cloth. It is produced in the Earth’s upper atmosphere when Nitrogen-14 is broken down to form the unstable Carbon-14 by the action of cosmic rays.The unstable Carbon-14 is transported down to the lower atmosphere by atmospheric activity such as storms.The Carbon-14 within a living organism is continually decaying, but as the organism is continuously absorbing Carbon-14 throughout its life the ratio of Carbon-14 to Carbon-12 atoms in the organism is the same as the ratio in the atmosphere.Once an organism dies it stops taking in Carbon in any form.This technique has become more widely used since the late 1950s.Its great advantage is that most rocks contain potassium, usually locked up in feldspars, clays and amphiboles.Radiocarbon dating is normally suitable for organic materials less than 50 000 years old because beyond that time the amount of 14C becomes too small to be accurately measured.
The half-life is the time it takes for half of the parent atoms to decay.
The relationship between the two is: T = 0.693 / λ Many different radioactive isotopes and techniques are used for dating.
All rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age.
Half of the remaining Carbon-14 then decays over the next 5730 years leaving one fourth of the original amount.
By measuring the ratio of Carbon-14 in a sample and comparing it to the amount in a recently deceased sample its date can be determined.