The origin of helium and the other light elements

The energy released in the synthesis of cosmic He-4 from hydrogen is almost exactly equal to the energy contained in the cosmic microwave background radiation. This result strongly suggests that the He-4 was produced by hydrogen burning in stars and not in the early stages of a big bang. In addition, we show that there are good arguments for believing that the other light isotopes, D, He-3, Li-6, Li-7, Be-9, B-10, and B-11, were also synthesized in processes involving stars. By combining these results with the earlier, much more detailed work of Burbidge et al. and of Cameron, we can finally conclude that all of the chemical elements were synthesized from hydrogen in stars over a time of about 10(11) yr.