The easiest way to begin is to step back a few million light years, and take a more detached view of the material universe. Some of the complexities then smooth out and the scene becomes simpler.

What we see are many glowing bodies - stars - organized into star clusters, galaxies, and clusters of galaxies, extending to the outermost reaches of the universe. In our field of view, 999 out of 1000 atoms are either of the two lightest chemical elements - hydrogen or helium - with only a lone one-in-a-thousand being a heavier atom.

All of the elements, compounds, and substances that loom so large on our planet are nothing more than "minor impurities" in the universe as a whole. The dust clouds between stars are predominately hydrogen, although careful examination will show a few other simple molecules. The heavier elements are found scattered in these dust clouds, in the centers of stars, and in the cold satellites such as Earth, which travel virtually undetected around some of the stars.

On this scale, the material universe is mainly a world of hydrogen and helium. The illustration opposite gives some idea of the enormous number of hydrogen and helium atoms in the universe compared to those of the heavier elements.