Radioisotopes used for dating
All rocks and minerals contain long-lived radioactive elements that were incorporated into Earth when the Solar System formed.
These radioactive elements constitute independent clocks that allow geologists to determine the age of the rocks in which they occur.
Eggs and some meat, such as beef, pork, and poultry, can also be irradiated.
As radioactive Parent atoms decay to stable daughter atoms (as uranium decays to lead) each disintegration results in one more atom of the daughter than was initially present and one less atom of the parent.
The probability of a parent atom decaying in a fixed period of time is always the same for all atoms of that type regardless of temperature, pressure, or chemical conditions. The time required for one-half of any original number of parent atoms to decay is the half-life, which is related to the decay constant by a simple mathematical formula.
(Recall that tritium, H, is a radioactive isotope of hydrogen.) Tracers can also be used to follow the steps of a complex chemical reaction.
After incorporating radioactive atoms into reactant molecules, scientists can track where the atoms go by following their radioactivity.