



 
Hi Christine. The general formula for exponential decay given a halflife is
where N(t) is the amount at time t, N_{0 } is the initial amount (at time t=0), and t_{1/2 } is the half life of the substance. Carbon14 (^{14}C) is a radioactive substance that has a halflife of about 5730 years. While a biological organism is alive and respiring, it absorbs ^{14}C from the air and has a constant percentage in its tissues. When the organism dies, the amount of ^{14}C gradually diminishes in accordance with the formula above. This makes it possible to measure the percentage of remaining ^{14}C in dead organic matter and determine the approximate time of death. You can read more about the science of radiocarbon dating here. Stephen La Rocque.>  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 