ask-a-scientist created by Dr. John Campbell
The 5000 year-old-man, the `ice mummy’ was dated
by carbon-14 dating. What is this and how does it
work?
Edward Winter, Heaton Normal Intermediate School.
Scientist Tom Higham, a radiochemist then with the
Radiocarbon Dating Laboratory at Waikato University,
responded:
A living organism is constantly incorporating carbon into
its body through food uptake, which builds bones, skin
and hair. A small part of the carbon we consume is called
`radioactive’ carbon or simply radiocarbon. Radioactive
means that it has an unstable atomic structure. This
means that after a certain period of time, carbon-14
decays or disappears. As long as a living organism is
taking up carbon, it is keeping the carbon-14 in its body
at a constant level, but when death occurs, the carbon14 begins to disappear and is not replaced. In the 1950s,
scientists discovered that carbon-14 disappears at a
known rate. They found that every 5568 years, half the
carbon-14 left in the remains of an organism has gone
(the radiocarbon `half-life’), so by measuring the carbon14 remaining, they were able to calculate independent
ages for carbon samples from archaeological sites. We
can date carbon samples from today, back to about 60
000 years ago using this method. Tiny fragments of the
Iceman’s bone, skin and grass from his boots have been
dated in two radiocarbon laboratories, in Oxford and
Zurich. (A piece of grass or skin about the size of one
grain of rice is needed for a date). The dates placed the
age of the Iceman between 3400-3100 B.C., or about
5500 years ago, the oldest example of a well-preserved
human body ever found.
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