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 r adiation. This result strongly suggests that the He-4 was produced by hydro gen 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 c onclude that all of the chemical elements were synthesized from hydrogen in stars over a time of about 10(11) yr.