This book is about nothing. Or at least 99.999999999999% bits of nothingness. And yet it is about everything – all that you can touch, see, taste, smell, and feel, and you, and the room in which you are sitting, and this planet, our solar system, the Milky Way, and the entire visible Universe. All of it is composed of the bits of nearly completely empty space we call atoms.You’ve never seen an atom because, besides being mostly empty space, they are very, very small: it takes 15 million trillion of them to make one poppy seed. If the atom were the size of a small marble, it would take a warehouse covering a full city block, twenty stories tall, to contain 1 trillion. Fifteen million trillion would be a warehouse covering all of New York State and extending upward to thirty stories. A lot of marbles. Despite their infinitesimal size and ephemeral nature, we have developed an intimate relationship with atoms. We can count them individually. We can distinguish the 118 different types and the dozen or two flavors in which each type exists. We can transform them from one type to another and can query their interior states. Most importantly, we can take advantage of their imperturbable internal clocks to reconstruct the history of the Universe. This book provides an accessible introduction to atoms and describes how we can use them as unbiased historians. From the detection of art forgeries to the dating of archeological artifacts, from the history of agriculture and human diet to the complex story of Earth’s constantly changing climate, the little atomic historians are faithful guides. From the death of the dinosaurs 66 million years ago to the origin of life more than 3.5 billion years ago, atoms recount the story. The solar system’s birthday is determined precisely; the history of the Universe and all it contains, back to the first fraction of a second of its existence 13.8 billion years ago -- all is revealed in striking detail by atoms, the universal timekeepers.