After 5,730 years, the amount of carbon 14 left in the body is half of the original amount.

If the amount of carbon 14 is halved every 5,730 years, it will not take very long to reach an amount that is too small to analyze.

Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years.

Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).

By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: t = [ ln (0.10) / (-0.693) ] x 5,700 years t = [ (-2.303) / (-0.693) ] x 5,700 years t = [ 3.323 ] x 5,700 years Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old.

However, the principle of carbon-14 dating applies to other isotopes as well.

After death the amount of carbon-14 in the organic specimen decreases very regularly as the molecules decay.

Carbon-14 has a half-life of 5,730 ± 40 years, meaning that every 5,700 years or so the object loses half its carbon-14.

This half life is a relatively small number, which means that carbon 14 dating is not particularly helpful for very recent deaths and deaths more than 50,000 years ago.But while the difficulties of single life may be intractable, the challenge of determining the age of prehistoric artifacts and fossils is greatly aided by measuring certain radioactive isotopes.Until this century, relative dating was the only technique for identifying the age of a truly ancient object.By examining the object's relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site.Though still heavily used, relative dating is now augmented by several modern dating techniques.Archaeologists use the exponential, radioactive decay of carbon 14 to estimate the death dates of organic material.

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