Very often we come across reports like, "Archeologists have found a 20,000-year-old wooden tool." If you've ever wondered how scientists predict the age of these substances, read on.
How was radiocarbon discovered?
The technique of radiocarbon dating was discovered by Willard Frank
Libby and his colleagues in 1949. He was at that time working as a
professor of chemistry at the University of Chicago.
Since then it has proved to be a useful tool, mainly for archeologists for dating ancient objects. Today we can find out the age of several substances using samples from biological remains found in excavations and other archeological findings.
Carbon dating can be used to find the age of matter as old as 60,000 years.
What is carbon dating?
Carbon dating or radiocarbon dating is a technique used in dating matter such as bone, cloth, wood and plant fibre - anything that was once alive.
All living things contain an element called carbon. This carbon is
present in different varieties, one of which is carbon-14. Out of the
different forms, carbon-14 is special because it is radioactive.
Being radioactive, in simple terms, means that the element
disintegrates over time. The time in which it decays to half the
original amount is called its half-life. The half-life of carbon-14 is
All living things maintain a specific content of carbon-14
right up to the moment of death. When an organism dies, the amount of
carbon-14 available within it begins to decay at a half-life rate i.e.,
it takes 5730 years for half of the carbon-14 available in the organism
to decay. After 11,000 years, one quarter of the original carbon-14
atoms will be left and after another 5,500 years (i.e. 16,500 years
later), one eighth of the original amount will be left, and so on.
How does it work?
Radio carbon dating determines the age
of ancient objects by measuring the amount of carbon-14 left in it.
When a particular fossil was alive, it had the same amount of carbon-14
as the same living organism today. Thus by counting how many carbon-14
atoms are there in an object and comparing it with a living sample, we
can work out how old the object is or how long ago it died.
Consider an example: Suppose a sample of wood is
taken from some ancient structure like a temple. This sample of wood is
heated and burned in the laboratory when it releases various gases,
including carbon dioxide. The gases include carbon-14 atoms. These
atoms of carbon-14 are continuously breaking down since they are
radioactive. With each breakdown a tiny particle is sent speeding out
of the atom.
These gases are collected and placed in an instrument called a Geiger counter,
which detects the particle given off by the atoms of carbon-14. By
counting the number of particles given off, scientists can determine
the amount of carbon-14 atoms left in the sample.
Scientists compare this finding with the amount of carbon-14
contained in an equal amount of wood from the same living tree. If the
ancient sample contains half the amount of that in the new sample, one
can calculate that the wood is 5,500 years old. Thus, we can say that
the temple is also as old.
In 1960, Libby was awarded the Nobel Prize in Chemistry for leading the team that developed Carbon-14 dating.