What is
carbon-14 dating?
Scientists use radioactivity to determine the age of many ancient
objects. The technique they use is called carbon-14 dating. It is used
in dating things such as bone, cloth and wood or in fact anything that
was made of matter that once lived. Because the half-life of carbon-14
is 5,730 years, it is only reliable for dating objects up to about
50,000 years old.
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How is carbon-14 formed? Proton
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Neutron |
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Carbon-14
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When a neutron collides with and is captured by a nucleus of nitrogen, a proton is ejected and radioactive carbon-14 is formed.
How does
carbon-14 get to so many places?
The carbon-14 atoms created by cosmic rays combine with oxygen to form
carbon dioxide, which plants absorb naturally by photosynthesis. Animals
and people eat plants and take in carbon-14 as well. The ratio of normal
carbon (carbon-12) to carbon-14 in the air and in all living things at
any given time is nearly constant. The carbon-14 atoms are always
decaying, but they are being replaced by new carbon-14 atoms at a
constant rate. Today, your body has a certain percentage of carbon-14
atoms in it, and all living plants and animals have the same percentage.
How is the dating done?
As soon as a living organism dies, it stops taking in new carbon. The
ratio of carbon -12 to carbon -14 at the time of death is the same as
every other living thing, but the carbon -14 decays and is not replaced.
Since carbon -14 decays, while the amount of carbon -12 remains constant
in the sample, then the ratio of carbon -12 to carbon -14 in the sample
diminishes as time passes. By comparing the ratio for the sample under
investigation to the ratio in a living organism, it is possible to
determine the age of the sample.
How is the date calculated?
When the measurements have been taken, the results are substituted into
the formula
t = [ ln (N/No) / (-0.693) ] x T
where t is the age of the sample and T is the half-life of Carbon-14