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| This flowering cholla, like all living organisms, continously "cycles" atmospheric carbon, including tiny fractions of radioactive carbon-14 (C14). Once an organism dies, the accumulated C14 slowly decays (breaks down) into the stable form, C12. Since the decay rate is known (C14 has a half-life of 5,730 years), the ratio of C14 to C12 in a sample of dead organic material, such as charred wood, allows the calculation of a statistical estimate of the elapsed time since death. Photo by Kris Erickson. |