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Line 2: − − The rate of decay of <SUP>14</SUP>C is such that 50% of the <SUP>14</SUP>C in the sample will decay in 5730 years: 50% of the <SUP>14</SUP>C 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 <SUP>14</SUP>C 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. Line 16:
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rm redundant section
The technique is based on comparing the levels of <SUP>14</SUP>C and <SUP>12</SUP>C isotopes in the sample. When the sample was living, the ratio of <SUP>14</SUP>C to <SUP>12</SUP>C in the material is the same as in the atmosphere. But after death the <SUP>14</SUP>C isotope decays into N-14, while <SUP>12</SUP>C does not. The loss in <SUP>14</SUP>C 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 <SUP>14</SUP>C and <SUP>12</SUP>C isotopes in the sample. When the sample was living, the ratio of <SUP>14</SUP>C to <SUP>12</SUP>C in the material is the same as in the atmosphere. But after death the <SUP>14</SUP>C isotope decays into N-14, while <SUP>12</SUP>C does not. The loss in <SUP>14</SUP>C is then used to estimate how long ago the sample died, which is typically the same as how long the sample existed.
[[Image:C-14decay.JPG|framed|The first-order decay curve of carbon-14 based on the half-life of 5730 years. Because of the small amount of <SUP>14</SUP>C remaining after 50,000 years, the rate of decay becomes small.]]
[[Image:C-14decay.JPG|framed|The first-order decay curve of carbon-14 based on the half-life of 5730 years. Because of the small amount of <SUP>14</SUP>C remaining after 50,000 years, the rate of decay becomes small.]]
Carbon dating cannot give accurate numbers if the sample is younger than 150 years or older than 50,000 years. The inaccuracy for material younger than 150 years is ascribed to changes in the ratio of <SUP>14</SUP>C to <SUP>12</SUP>C in the atmosphere.<ref>http://www.talkorigins.org/indexcc/CD/CD011.html</ref>
Carbon dating cannot give accurate numbers if the sample is younger than 150 years or older than 50,000 years. The inaccuracy for material younger than 150 years is ascribed to changes in the ratio of <SUP>14</SUP>C to <SUP>12</SUP>C in the atmosphere.<ref>http://www.talkorigins.org/indexcc/CD/CD011.html</ref>
Since the half-life of <SUP>14</SUP>C is only 5715 years, after 50,000 years only about 1/500th of the <SUP>14</SUP>C 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 with precision 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. However, isotopes with longer half-lives may be used.
Since the half-life of <SUP>14</SUP>C is only 5715 years, after 50,000 years only about 1/500th of the <SUP>14</SUP>C 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 with precision 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. However, isotopes with longer half-lives may be used.
==See also==
==See also==
*[[Martin Kamen]]
*[[Martin Kamen]]
*[[Reaction kinetics]]
== References ==
== References ==