Figure 1.

¹⁴C bomb-pulse curve. Concentration of ¹⁴C in atmospheric CO₂ (black line), shown as pMC (26). Testing of nuclear bombs from 1955 to 1963 nearly doubled the atmospheric levels of ¹⁴C, which was followed by an exponential decrease after the Test Ban Treaty in 1963. Measured levels of ¹⁴C are shown in relation to birth year for samples of human Achilles tendon (gray squares) and skeletal muscle (open circles) taken in year 2000. The levels of ¹⁴C found in the tendon tissue generally correspond to the atmospheric levels many years before sampling, thus indicating a very slow rate of tissue replacement. Skeletal muscle levels of ¹⁴C correspond to atmospheric levels ∼2 yr before the time of sampling (dashed arrow), thus indicating continuous tissue turnover, as essentially no memory of lifetime exposure to the bomb pulse remains in the muscle tissue.