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Half-Life - Measuring the Age of Rocks and Archaeological Specimens.
The age of archaeological specimens can be
calculated
by looking at the amount of carbon-14 in a
sample.
The method is called carbon dating or radiodating.
Carbon-14 is
created at a constant rate in the
upper atmosphere
by cosmic rays acting on nitrogen.
The carbon-14 which is formed is radioactive
and decays to produce nitrogen
again.
There is therefore a fixed amount of
carbon-14
in the environment
which is a balance between the
rate at which it is formed
and the rate at which it decays.
All
living things take carbon into themselves.
Plants take in carbon during photosynthesis.
Animals take in carbon when they eat
their food.
All living
things therefore have carbon-14 in
them
at the same amount which is
present in the environment.
The amount is small,
only one in 850
billion carbon atoms are carbon-14,
the rest are mainly carbon-12 which are
not radioactive.
When a living thing dies, it
stops taking in carbon from its environment.
The amount of carbon-14 in it will
start to decrease
as the carbon-14 slowly
decays.
The further back in time that something died, the less
carbon-14
it will have.
Measuring the amount of carbon-14 can tell
you how long ago the thing
died
and therefore the "age" of the
sample (continued on the next
page).
Headings Radioactivity Search
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