How Does Carbon Dating Work?

All living organisms constantly exchange carbon with the environment, absorbing a small proportion of radioactive carbon-14 (¹⁴C), produced in the atmosphere by cosmic rays hitting nitrogen atoms. When an organism dies, it stops absorbing new carbon, and its ¹⁴C begins to decay into nitrogen-14 at a predictable rate: half of it decays every 5,730 years (the half-life). By measuring the ratio of ¹⁴C to stable ¹²C in a sample using accelerator mass spectrometry (AMS), scientists can calculate how many half-lives have elapsed since death — and thus the age. The technique is reliable for organic materials up to about 50,000 years old.