Animations of how the radiocarbon curve has obtained the shape it has over time. Blue are initial C-14 concentrations (estimated from measuring the C-14 ages of known calendar age, such as tree rings), grey are remaining C-14 concentrations at time t (red), green is the calibration curve at time t. From top to bottom, panels show i the most recent 100 years which includes major changes in atmospheric C-14 concentrations owing to nuclear bombs, ii the most recent millennium, iii back to 15 kcal BP, andiv all the way back to 50 kcal BP.