Using carbon-14 Carbon-14 or radiocarbon, a radioactive isotope produced in the upper atmosphere by cosmic rays, is rapidly incorporated into the terrestrial carbon cycle and provides a way to calculate the age of carbon-bearing materials as old as 55,000 years. Heaton et al . review recent progress that has allowed the construction of better radiocarbon age calibration curves and discuss the new insights into climate processes, the Sun, Earth’s geodynamo, and the carbon cycle that have emerged from these efforts. —HJS