Measurement of N, the number of 14 C atoms currently in the sample, allows the calculation of t, the age of the sample, using the equation above. How old is the sample? When an organism dies the carbon slowly decays, so the proportion of C is reduced over time. To measure the age of something, then, you measure the activity of carbon, and compare it to the activity you'd expect it to have if it was brand new. Radiocarbon dating can be used on samples of bone, cloth, wood and plant fibers. The trick is to use a half-life which is of the order of, or somewhat smaller than, the age of the object.