What is
carbon14 dating?
Scientists use radioactivity to determine the age of many ancient
objects. The technique they use is called carbon14 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 halflife of carbon14
is 5,730 years, it is only reliable for dating objects up to about
50,000 years old.
How is carbon14 formed? Proton


Neutron 

Carbon14

When a neutron collides with and is captured by a nucleus of nitrogen, a proton is ejected and radioactive carbon14 is formed.
How does
carbon14 get to so many places?
The carbon14 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 carbon14 as well. The ratio of normal
carbon (carbon12) to carbon14 in the air and in all living things at
any given time is nearly constant. The carbon14 atoms are always
decaying, but they are being replaced by new carbon14 atoms at a
constant rate. Today, your body has a certain percentage of carbon14
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 halflife of Carbon14