The black square above symbolizes a piece of carbon, mostly consisting of C-12 and C-13, but containing some C-14 atoms (yellow dots; initial concentration 10 thousand atoms). Because C-14 is radioactive, as time goes on the C-14 atoms will desintegrate. When exactly an individual atom will disappear cannot be predicted; it could happen within a few seconds, but it could also survive several tens of thousands of years. The survival-time of the atoms is modelled through randomly selecting 10,000 values from an exponential distribution with a Libby half-life of 5568 yr (red line), and then plotting the remaining atoms for each 200-yr time slice of the animation. It is easy to see that dating of old samples is difficult, as only few C-14 atoms remain. Modern natural carbon contains many more C-14 atoms than the 10 thousand shown here (some 50 million per mg); this number was chosen for illustration purposes only.