Written in Starlight

Carl Sagan was fond of saying, "We are made of star stuff" — and he was not being poetic. He was being precise. Every carbon atom in your body, every oxygen molecule in your lungs, every iron atom in your blood was forged inside a dying star. Hydrogen, the simplest element, is abundant from the beginning of the universe. But heavier elements — the ones life requires — can only be produced through nuclear fusion inside massive stars.…