What is the purpose of the half-life method?

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The purpose of using the half-life concept is to be able to date things that reach back into the geological time scale.  A half-life is the amount of time it takes for a sample of a radioactive element within an organism to have it's nuclei decay to a more stable form by one-half.  A good example would be the use of carbon-14, which is unstable, and takes 5000 years for half it's nuclei to deteriorate to a more stable nitrogen-14.  Therefore, if a scientist knew the starting amount of carbon-14 in a sample, and measured what was left, the scientist could get a pretty accurate idea of the age of the sample.  It should be noted that carbon-14 dating measures decay in an exponential rate.

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