How Does Carbon Dating Determine Age?

All living organisms absorb carbon from the environment, including a small proportion of radioactive carbon-14 (¹⁴C), which is continuously produced in the atmosphere by cosmic-ray interactions with nitrogen. While alive, an organism maintains a constant ratio of ¹⁴C to stable ¹²C. After death, ¹⁴C decays with a half-life of 5,730 years and is no longer replenished. By measuring the remaining ¹⁴C — typically using accelerator mass spectrometry (AMS), which can date samples as small as a few milligrams — scientists calculate the elapsed time since death. The method is reliable for organic materials up to about 50,000 years old. Calibration curves account for historical variations in atmospheric ¹⁴C levels caused by solar activity and ocean circulation.