Relative rock dating methods
When an unstable radioactive isotope, or parent, decays or loses radiation such as a beta particle, antineutrino or a gamma ray, a daughter product is left behind.The time it takes for an unstable nucleus to decay to the daughter product is called a half-life.These simple parameters provide the fundamental basis for relatively dating geologic strata.The weakness of relative dating is inherent to its very nature.Exposure to the elements can create an addition or loss of parent or daughter isotope, skewing the results.
The most reliable way to accomplish this is through radiometric dating.
As an example of how they are used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale.
To get to that point, there is also a historical discussion and description of non-radiometric dating methods.
The example used here contrasts sharply with the way conventional scientific dating methods are characterized by some critics (for example, refer to discussion in "Common Creationist Criticisms of Mainstream Dating Methods" in the Age of the Earth FAQ and Isochron Dating FAQ).
A common form of criticism is to cite geologically complicated situations where the application of radiometric dating is very challenging.