Changes

The technique is based on comparing the levels of C-14 and C-12 isotopes in the sample.  When the sample was living, the ratio of C-14 to C-12 in the material is the same as in the atmosphere.  But after death the C-14 isotope decays into N-14, while C-12 does not.  The loss in C-14 is then used to estimate how long ago the sample died, which is typically the same as how long the sample existed.   

The technique is based on comparing the levels of C-14 and C-12 isotopes in the sample.  When the sample was living, the ratio of C-14 to C-12 in the material is the same as in the atmosphere.  But after death the C-14 isotope decays into N-14, while C-12 does not.  The loss in C-14 is then used to estimate how long ago the sample died, which is typically the same as how long the sample existed.   

The rate of decay of C-14 is such that, 50% of the C-14 in the sample will decay in 5730 years: 50% of the C-14 in the sample is left, after  11460 years 25% will be left, after 17190 years 12.5% will be left, after 50,000 years only about 1/500th of the C-14 remains - and since even initially it is only present as a minute proportion of the whole (0.0000000001% of all Carbon atoms), measuring the exact quantity present accurately enough to be of use for dating purposes is extremely difficult. For this reason, scientists do not generally attempt to carbon date material that is believed to be older than about 50,000-60,000 years old.

The rate of decay of C-14 is such that, 50% of the C-14 in the sample will decay in 5730 years: 50% of the C-14 in the sample is left, after  11460 years 25% will be left, after 17190 years 12.5% will be left, after 50,000 years only about 1/500th of the C-14 remains - and since even initially it is only present as a minute proportion of the whole (0.0000000001% of all Carbon atoms)<ref>http://www.enviroliteracy.org/article.php/1006.html</ref>, measuring the exact quantity present accurately enough to be of use for dating purposes is extremely difficult. For this reason, scientists do not generally attempt to carbon date material that is believed to be older than about 50,000-60,000 years old.

== Limits of Carbon Dating ==

== Limits of Carbon Dating ==