radioactive atoms and 96.875% daughter atoms, you can assume that the substance is 5
years old. The decay of radioactive materials can be shown with a graph (Figure11.25). If
you find a rock with 75% of the radioactive atoms remaining, about how old is it?
Figure 11.25: Decay of an imaginary radioactive substance with a half-life of one year. ( 10 )
Radiometric Dating of Rocks
In the process ofradiometric dating, several isotopes are used to date rocks and other
materials. Using several different isotopes helps scientists to check the accuracy of the ages
that they calculate.
Carbon Dating
Earth’s atmosphere contains three isotopes of carbon. Carbon-12 is stable and accounts for
98.9% of atmospheric carbon. Carbon-13 is also stable and accounts for 1.1% of atmospheric
carbon. Carbon-14 is radioactive and is found in tiny amounts. Carbon-14 is produced
naturally in the atmosphere when cosmic rays interact with nitrogen atoms. The amount
of carbon-14 produced in the atmosphere at any particular time has been relatively stable
through time.
Radioactivecarbon-14decaystostable nitrogen-14byreleasingabeta particle. The nitrogen
atoms are lost to the atmosphere, but the amount of carbon-14 decay can be estimated by