Radioactive carbon dating fossils
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.Where t is the age of the fossil (or the date of death) and ln() is the natural logarithm function.If the fossil has 35% of its carbon 14 still, then we can substitute values into our equation.In the case of radiocarbon dating, the half-life of carbon 14 is 5,730 years.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.After 5,730 years, the amount of carbon 14 left in the body is half of the original amount.
The stable form of carbon is carbon 12 and the radioactive isotope carbon 14 decays over time into nitrogen 14 and other particles.So, the fossil is 8,680 years old, meaning the living organism died 8,680 years ago. As soon as a living organism dies, it stops taking in new carbon.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.