Element Abundances

The chemical composition of the universe is rather simple. About 75% (by mass) of atomic matter is in the form of hydrogenHydrogen, and almost all the rest is in the form of heliumHelium. All other chemical elementsElements contribute less than 2% of the atomic mass. Why is it that some elements are more abundant than others? And where did the elements come from in the first place? These questions cannot be avoided, since atoms, and even atomic nucleiAtomic nuclei, could not exist in the early moments after the big bangBig bang. The challenge, then, is to understand how the elements were created by physical processes during the course of cosmic evolution.