Taken from the Book of Facts
written by Readers Digest
early archaeologists relied on two major techniques for calculating the age of what they found: the principle of stratigraphy - that the remains of earlier generations are covered over by those of their successors; and comparison of style of, say, pottery to determine whether one influenced and therefor preceded the other.
In the 1950s, however, a new technique know as radio-carbon- 14 dating came into use.
carbon -14 is a radioactive isotope of carbon present in tiny amounts in the atmosphere.
Living things such as wood and the bones of living animals absorb this carbon naturally.
But when the tree is cut down or the animal dies, the absorption stops and the level of carbon -14 begins to fall as the isotope decays.
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