Uses radioisotopes carbon 14 dating
Human remains, fossils and organic materials from archaeological sites are all dated using carbon-14.
Generally, that means that 37 billion atoms in the sample are decaying and emitting a particle of nuclear radiation (such as an alpha particle) per second.
One gram of of the element radium generates approximately 1 curie of activity (Marie Curie, the woman after whom the curie is named, did much of her research using radium).
After death, the carbon-14 to carbon-12 ratio begins to decrease because carbon-14 is decaying away at a constant and predictable rate.
Remembering that the half-life of carbon-14 is 5700 years, then after 5700 years half as much carbon-14 remains within the organism.
The age of glaciers, snow fields, and even wines can be estimated by radioisotopic dating.