In the Anthropocene, International Relations must confront the possibility of anthropogenic extinction. Recent, insightful attempts to advance new vocabularies of planet politics tend to demote the profound historical and intellectual links between our current predicament and the nuclear age. In contrast, we argue that it is vital to revisit the nuclear-environment nexus of the Cold War to trace genealogies of today's intricate constellation of security problems. We do so by reappraising the work of Jonathan Schell (1943-2014), author of The Fate of the Earth (1982), who came to regard extinction as a defining feature of the nuclear age. We show how a deep engagement with nuclear weapons led Schell to an understanding of the Earth as a complex, delicate ecology and fed into a sophisticated, Arendtian theory of extinction. Despite its limitations and tensions, we argue that Schell's work remains deeply relevant for rethinking human-Earth relations and confronting the Anthropocene.