Read the following passage
and mark the letter A, B, C, or D on your answer sheet to indicate the correct
answer to each of the questions from 43 to 50.
Carbon dating can
be used to estimate the age of any organic natural material; it has been
used successfully in archeology to determine the age of ancient artifacts or
fossils as well as in a variety of other fields. The principle underlying
the use of carbon dating is that carbon is a part of all living things on
Earth. Since a radioactive substance such as carbon-14 has a known half-life,
the amount of carbon-14 remaining in an object can be used to date that object.
Carbon-14 has a
half-life of 5,570 years, which means that after that number of years, half of
the carbon-14 atoms have decayed into nitrogen-14. It is the ratio of carbon-14
in that substance that indicates the age of the substance. If, for example, in
a particular sample the amount of carbon-14 is roughly equivalent to the
amount of nitrogen-14, this indicates that around half of the carbon-14 has
decayed into nitrogen-14, and the sample is approximately 5,570 years old.
Carbon dating
cannot be used effectively in dating objects that are older than 80,000 years.
When objects are that old, much of the carbon-14 has already decayed into
nitrogen-14, and the miniscule amount that is left doesn’t provide a reliable
measurement of age. In the case of older objects, other age-dating methods are available, methods which use
radioactive atoms with longer half-lives than carbon has.
This passage is mainly about _______.
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