Problems with radiogenic dating consolidating stafford and perkins loans
Others measure the subatomic particles that are emitted as an isotope decays.
Some measure the decay of isotopes more indirectly.
To calculate the age of a rock it is necessary to know the half-life of the radioactive decay series, the amount of the parent and daughter isotopes present in the rock when it formed, and the present proportions of these isotopes.
It must also be assumed that all the daughter isotope measured in the rock today formed as a result of decay of the parent.
For example, fission track dating measures the microscopic marks left in crystals by subatomic particles from decaying isotopes.
Another example is luminescence dating, which measures the energy from radioactive decay that is trapped inside nearby crystals.
Geologists often need to know the age of material that they find.
If the proportions of parent and daughter isotopes of these decay series can be measured, periods of geological time in millions to thousands of millions of years can be calculated.
A number of elements have isotopes (forms of the element that have different atomic masses) that are unstable and change by radioactive decay to the isotope of a different element.
Each radioactive decay series takes a characteristic length of time known as the radioactive half-life, which is the time taken for half of the original (parent) isotope to decay to the new (daughter) isotope.
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.
This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.