Easy dating method
For example, the decay of potassium-40 to argon-40 is used to date rocks older than 20,000 years, and the decay of uranium-238 to lead-206 is used for rocks older than 1 million years.Radiocarbon dating measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14.
Another example is luminescence dating, which measures the energy from radioactive decay that is trapped inside nearby crystals.
The table below shows characteristics of some common radiometric dating methods.
Geologists choose a dating method that suits the materials available in their rocks. Measuring isotopes is particularly useful for dating igneous and some metamorphic rock, but not sedimentary rock.
These rates of decay are known, so if you can measure the proportion of parent and daughter isotopes in rocks now, you can calculate when the rocks were formed.
Because of their unique decay rates, different elements are used for dating different age ranges.
The New Zealand physicist Ernest Rutherford, suggested in 1905 that the exact age of a rock could be measured by means of radioactivity.