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== Principles ==
== Principles ==
[[Image:C-14decay.JPG|framed|The first-order decay curve of carbon-14 based on the half-life of 5730 years.]]
The technique is based on comparing the levels of <SUP>14</SUP>C and <SUP>12</SUP>C [[isotope]]s in the sample.
The technique is based on comparing the levels of <SUP>14</SUP>C and <SUP>12</SUP>C [[isotope]]s in the sample.
<sup>14</sup>C is produced in the atmosphere by cosmic ray [[neutron]]s replacing a [[proton]] in [[nitrogen]] (<sup>14</sup>N), producing <sup>14</sup>C.<ref name="TH">Higham, Thomas, [http://www.c14dating.com/int.html Introduction], Radiocarbon web-info.</ref>
<sup>14</sup>C is produced in the atmosphere by cosmic ray [[neutron]]s replacing a [[proton]] in [[nitrogen]] (<sup>14</sup>N), producing <sup>14</sup>C.<ref name="TH">Higham, Thomas, [http://www.c14dating.com/int.html Introduction], Radiocarbon web-info.</ref>
In the meantime, however, the <sup>14</sup>C will combine with [[oxygen]] in the atmosphere to form [[carbon dioxide]], which enters the food chain via [[photosynthesis]] in plants.<ref name="TH" />
In the meantime, however, the <sup>14</sup>C will combine with [[oxygen]] in the atmosphere to form [[carbon dioxide]], which enters the food chain via [[photosynthesis]] in plants.<ref name="TH" />
By this means, most living things also have <sup>14</sup>C and <sup>12</sup>C in the same ratio as in the atmosphere.
By this means, most living things also have <sup>14</sup>C and <sup>12</sup>C in the same ratio as in the atmosphere.
This ratio is about one <sup>14</sup>C atom for every 1,000,000,000,000 currently but this is a decelerating rate of change. <sup>12</sup>C atoms.<ref name="TH" />
This ratio is about one <sup>14</sup>C atom for every 1,000,000,000,000 <sup>12</sup>C atoms.<ref name="TH" />
However, when the sample dies, it stops ingesting <sup>14</sup>C, so as the <sup>14</sup>C decays to <sup>14</sup>N, the ratio of <sup>14</sup>C and <sup>12</sup>C changes.
However, when the sample dies, it stops ingesting <sup>14</sup>C, so as the <sup>14</sup>C decays to <sup>14</sup>N, the ratio of <sup>14</sup>C and <sup>12</sup>C changes.
This ratio of <sup>14</sup>C to <sup>12</sup>C is measured and a calculation turns the measurement into a figure representing how long ago the sample died.
This ratio of <sup>14</sup>C to <sup>12</sup>C is measured and a calculation turns the measurement into a figure representing how long ago the sample died.
Depending on the method used to measure the <sup>14</sup>C, after about 50,000 years or so there is not enough left to measure, although advanced techniques can possibly stretch that to 100,000 years.<ref>Nave, R., [http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html Carbon Dating], Georgia State University.</ref>
This then becomes the maximum age that can theoretically be derived by this method.
Therefore, any sample with too little <sup>14</sup>C to measure must, in theory, be older than 50,000 to 100,000 years, and it is not possible to determine how much older.
Similarly, any sample with measurable <sup>14</sup>C must be younger than 50,000 to 100,000 years, assuming that adequate precautions have been taken to eliminate contamination.
== Limits of Carbon Dating ==
== Limits of Carbon Dating ==
It was later measured more accurately to be 5730±40 years, now known as the ''Cambridge half-life''.<ref name="TH" />
It was later measured more accurately to be 5730±40 years, now known as the ''Cambridge half-life''.<ref name="TH" />
== Widespread misunderstandings ==
Many people believe that carbon dating has proved that the Earth is millions or billions of years old, much older than the biblically-derived date of around 6,000 years.
However, as explained above, carbon dating is incapable of providing dates in the range of millions or billions of years.
Some also argue that carbon dating should only be used on samples that fall within the range over which it can measure.
However, this begs the question of how one might determine this prior to using carbon dating to determine the age.
They further argue that dating much older items will result in anomalous dates, which might fall within the range that carbon dating can measure.
This is incorrect. Any sample that is older than the range that carbon dating will measure will record zero <sup>14</sup>C, and can therefore not be confused with younger samples.
==See also==
==See also==