In this article and slideshow from NOVA scienceNOW, learn how the Big Bang and the life cycles of stars created every single atom in your body. The lightest chemical elements (such as hydrogen and helium) originated with the Big Bang about 13.7 billion years ago. All other elements (including carbon, oxygen, and nitrogen) were made by stars. The text describes how stars are born, how thermonuclear reactions inside stars produce elements up to iron, how red giants and supernovas produce elements heavier than iron, and how the elements are dispersed from stars into space and incorporated into you.