General principles
Radiometric dating methods

With the exception of a few methods based on the counting of annual cyclicity events (dendrochronology, chronology based on lake deposits called varves), most absolute dating methods are based on the natural radioactivity of certain elements. Here, we briefly review the laws of radioactivity used for radiometric dating.

For a large number of radioactive atoms, we can write the following law describing the decay of atoms over time (expressed in number of years, a). $\frac{\text{d}N}{\text{d}t}=-\lambda N$