Galactic origin of life. Artwork of the limb of a spiral galaxy turning into the double helix structure of a strand of DNA surrounded by green chemical structures and X-shaped chromosomes (genetic material). DNA (Deoxyribonucleic Acid) is a complex organic chemical which is the building block of life. The chemicals needed to make DNA (carbon, oxygen, nitrogen & others) were made by the fusion of hydrogen and helium nuclei in the hearts of stars. These were ejected into space when these stars exploded as supernovae. Ultra- violet light from other stars promoted the combin- ation of these elements into complex organic chem- icals which may have initiated life.