Radiometric age dating
When a life form is alive and undergoing some sort of respiration, it will be gaining C-14 at a relatively high rate (it will equilibrate with the C-14 in the atmosphere) and losing it to decay at a different rate.
However, when the life form dies and is buried or otherwise stops interacting with atmospheric gases there will be no further increase in the amount of radioactive carbon in the system.
Radiocarbon dating is so well-known because it can be applied to nearly any organism that was living at some time.
 While radiocarbon dating is very useful in cases where organic matter is being analyzed, in many cases the samples that are being dated were never alive.
Like K/Ar dating, U/Pb dating is more suited to determining the age of matter that was not ever alive.
In this case determining the age of the surrounding earth or rock materials can be very helpful in determining the age of the sample.
Potassium-Argon (K/Ar) dating is a method that applies directly the dating of rocks.
While the overall method of Radiometric Dating is the same through each type, the specific isotopes that are used changes.
With these changes in materials, different types of dating apply to different situations.