This is well-established for most isotopic systems. The emissions are measured to compute the age. The study of strata and their relationships thermoluminescence: Others measure the subatomic particles that are emitted as an isotope decays. A Review". Carbon is continually being created in the atmosphere due to the action of cosmic rays on nitrogen in the air.
The students find it quite engaging.
Relative Vs. Absolute Dating: The Ultimate Face-off
Techniques include tree rings in timbers, radiocarbon dating of wood or bones, and trapped-charge dating methods such as thermoluminescence dating of glazed ceramics. Determining the number of years that have elapsed since an event occurred or the specific time when that event occurred. What is the Age of the Solar System?