Figure 1 (IMAGE) Kobe University Caption Figure 1: Graph showing the atmospheric levels of Δ14C values. The concentration was elevated by the nuclear bomb tests of the 1950s and 1960s. Credit Kobe University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.