Oct 3, 2012
More than ninety per cent of the universe is composed of hydrogen and helium. Both elements have been around since shortly after the beginning of the universe. Yet, hydrogen and helium together won't make anything as complex and as interesting as the earth, or a bacterium, or a refrigerator, or you and I. To do that we need carbon and oxygen and nitrogen and silicon and chlorine and every other naturally occurring element. Almost all the hydrogen and helium present in the universe today (and some of the lithium) were created in the first three minutes after the big bang. All of the other naturally occurring elements were created in stars.