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What is Carbon Dating?
The age of archaeological specimens can be
by looking at the amount of carbon-14 in a sample.
The method is a form of radiodating called carbon dating.
Radiodating can also be used to date rocks.
How is Carbon-14 formed?
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 in
the atmosphere and the rate at which it decays back to nitrogen.
How does Carbon Dating work?
All living things take in carbon from the environment.
Plants take in carbon during photosynthesis.
Animals take in carbon when
they eat food because food contains carbon.
things therefore have carbon-14 in
at the same amount which is present in the environment.
This amount is small. Only one in 850 billion carbon atoms
are the isotope carbon-14. The others are not radioactive.
They are carbon-12 (about 99%) and carbon-13 (about 1%).
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 will be present in it today.
The half-life of carbon-14 is 5,730 years.
Measuring the amount of carbon-14 in a sample today can tell you
how long ago the thing died and therefore the age of the sample.
Carbon dating is very useful but also has its limitations.
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