Dr Takashi is yer man
Observation of deuterium gives an additional support of the big bang nucleosynthesis. Deuterium, unlike helium, is not produced in stars at all. At temperatures above about one million degrees K, it dissociates into proton and neutron. Astronomers in the early 1970s realized that no known process in the present universe could have produced deuterium. This is because any deuterium created in stars will immediately dissociate or convert to helium due to the high temperatures in interiors of stars. However, in 1973, studies of absorption spectra of nearby stars showed that interstellar medium (material between stars) contains a trace of deuterium. Since stars could not have produced the deuterium, it must have been created either very early in the formation of the galaxy or even before. Despite the high temperature at the beginning, the big bang nucleosynthesis could create deuterium because the expansion of the universe lowered the density and temperature so quickly that there was hardly time for the deuterium to decay.
Thus, the abundance of helium and existence of deuterium provide strong evidence that the universe began with a hot, violent explosion consistent with the big bang model.