“The discovery of deuterium and the marked differences in the physical and chemical properties of hydrogen and deuterium, together with an efficient method for the separation of these isotopes, have opened an interesting field of research in several of the major branches of science.” -Harold Urey
By time the first few minutes of the Big Bang are over, the Universe has formed all the elements it’s ever going to form until the first stars are born. At that point, the Universe is made out of 75% hydrogen and 25% helium, with only tiny, trace amounts of other isotopes and elements like deuterium, helium-3, and lithium-7.
Yet if the Universe were truly hydrogen and helium only, you’d never be able to form a star more massive than about three times the Sun’s mass, preventing the creation of the heavy elements necessary for life! That tiny, trace amount of deuterium that the Big Bang creates, even though it’s just 0.0025% of the Universe, efficiently pushes back in the core of a young proto-star, delaying the amount of time it takes to ignite true fusion, and enabling stars to become tens or even hundreds of times as massive as our Sun. And yes, that’s more than enough for supernovae to occur.
Without this tiny inefficiency in the nuclear reactions taking place in the early Universe, the Earth and life on it could never have existed. Come get the scientific story of how this imperfection helped create you!