Between 2009 and 2024, the Anthropocene Working Group (AWG), an interdisciplinary team of geologists, archaeologists, Earth systems scientists, historians of science, and one lawyer, sought to formalise the Anthropocene as a formal unit of the Geologic Time Scale. Science, Politics, and the Anthropocene Working Group: What Was the Anthropocene? presents the first comprehensive, ethnographic and history of science study of the AWG's formalisation effort. Drawing on original archival research, this book provides a history of the formalisation procedure, as well as the practices of measurement and correlation, particularly to the amendment of the Geologic Time Scale. Through participant observation, this book explains how the AWG applied geological methods and practices to situate contemporary society within the context of 4.5 billion years of Earth's history. Positioning contemporary debates concerning the Anthropocene within a historical appraisal of geoscience, Science, Politics, and the Anthropocene Working Group: What Was the Anthropocene? offers a unique, multidisciplinary perspective on how scientific knowledge is shaped and legitimised under conditions of the climate crisis. Science, Politics, and the Anthropocene Working Group: What Was the Anthropocene? provides an invaluable resource for scholars of all levels studying geosciences, the history of science, social studies of science, and the Anthropocene.