This book project unearths the labour regimes that wrought combined sciences of earth and atmosphere around 1800. It is an archaeology of what humanists and scientists alike have called the Critical Zone, the complex and fragile film of earth and air, several kilometres deep, that spans the globe. This book studies the global sciences that first constructed the Critical Zone as an object of inquiry, engaging physique du monde, physical geography, and Klimatologie as a coherent set of interrelated practices (or geo-atmospherics). At its core is a critical revision of the Prussian savant Alexander von Humboldt (1769–1859). I locate Humboldt at the helm of a frontier science based—and employed—in far-flung systems of metallurgic industry and military surveillance, what I call mineral empire. Humboldt’s science was co-extensive with infrastructures of extraction and governance, from Prussian Franconia, where he served as a mining officer in the 1790s, through his travels to New Spain in 1803 and Russian Siberia in 1829. There, his program of inquiry expropriated workmen’s ways of knowing and enacted settler colonial enterprises. Science from Below therefore reimagines Humboldt’s life and travels as a new social history of the marginal actors—miners, surveyors, calculators, serfs, and convicts—who made his global science possible.