Security concerns during the early Cold War prompted United States strategists to solicit worldwide assistance in studying Earth’s physical environment. Comprehensive geophysical knowledge required cooperation between researchers on every part of the planet, leading practitioners to tout transnational earth science – despite direct military applications in an age of submarines and ballistic missiles – as a non-political form of peaceful universalism. This article examines the 1957–58 International Geophysical Year as a powerful fulcrum in the transfer of ideas about Earth’s global environment from Western security establishments to conservationists worldwide. For eighteen months, tens of thousands of researchers across every continent pooled resources for data collection to create a scientific benchmark for future comparisons. Illuminating Earth as dynamic and interconnected, participants robustly conceptualized humanity’s emergence as a geophysical force, capable of ‘artificially’ modifying the natural world. Studies of anthropogenic geophysics, including satellites, nuclear fallout, and climate change, conditioned the global rise of environmentalism.