Carbon 14 dating works
The total mass of the isotope is indicated by the numerical superscript.
While the lighter isotopes C has decayed that what remains can no longer be measured. In 5,730 years half of the C in the atmosphere, and therefore in plants and animals, has not always been constant.
From these records a “calibration curve” can be built (see figure 2, below).
A huge amount of work is currently underway to extend and improve the calibration curve.
This method requires less than 1g of bone, but few countries can afford more than one or two AMSs, which cost more than A$500,000.