"This is a serious, excellent piece of science writing ... Bratman's prose captures the core idea and gives a faithful rendering for a non-specialist audience" - Eric Smith, PhD. Coauthor of The Origin and Nature of Life: The Emergence of the Fourth Geosphere. Metabolism-First is a theory that claims life arose out of energy-driven organic chemistry in ancient hydrothermal vents. From this perspective, life is not a lucky accident but a logical consequence of early Earth conditions. Like many other processes driven by a flow of energy, the origin of life exemplifies the phenomena of spontaneous order. Metabolism-First views the biosphere as a feature of Earth as a whole, a companion to the hydrosphere, lithosphere and atmosphere. Just as ordinary phase transitions change the properties of a liquid or gas, the biosphere can be viewed as emerging through a series of phase transitions operating on chemical reaction networks. A key concept of the theory is autocatalysis, the property of some chemicals to amplify their own rate of formation. Autocatalysis plays the same role in "chemical evolution" as Darwinian selection does in the standard theory of evolution. Additional key concepts include phase transformations, modularity and dissipative adaptation. The text includes a glossary and an annotated bibliography.