Book excerpt: "Carbon in Earth is an outgrowth of the Deep Carbon Observatory (DCO), a 10-year international research effort dedicated to achieving transformational understanding of the chemical and biological roles of carbon in Earth (http://dco.ciw.edu). Hundreds of researchers from 6 continents, including all 51 coauthors of this volume, are now engaged in the DCO effort. This volume serves as a benchmark for our present understanding of Earth's carbon - both what we know and what we have yet to learn. Ultimately, the goal is to produce a second, companion volume to mark the progress of this decadal initiative.