This is the clock that permits levels of c14 in organic archaeological, geological, and paleontological samples to be converted into an estimate of time.
The measurement of the rate of radioactive decay is known as its half-life, the time it takes for half of a sample to decay.
For example, it was once standard practice to simply burn whole bones, but the results were eventually seen to be unreliable.
Chemical methods for separating the organic (collagen) from the inorganic (apatite) components of bone created the opportunity to date both components and compare the results.
Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.