After a creature's death the isotope would slowly decay away over millennia at a fixed rate.
Thus the less of it that remained in an object, in proportion to normal carbon, the older the object was.
CAMS is one of several dozen labs worldwide that conduct accelerator mass spectrometry, or AMS.
To understand this, you must first understand radioactivity and decay.The ratio of unstable carbon-14 to stable carbon-12 atoms reveals the age of the sample—be it an ancient manuscript or a Neanderthal skull.Likewise, other isotopes like beryllium-10 and aluminum-26 divulge how long a sample has been subjected to the constant barrage of cosmic rays that comes with sitting on the surface of Earth—telling geologists, for example, how quickly a region of rock is eroding or how long ago an earthquake brought sediment to the surface.I know can be hard to wrap your head around, so let's model it with a six-sided die. You can use Lego bricks, pennies, beans—anything you can easily count. Every time you roll a one, put that object into a separate pile.Count the remaining objects and repeat the process until half of them have decayed. It took a while, but we finally got pretty close to 40 tiles left.