This project is a historical study that asks: how have naturalists and scientists since the nineteenth century used ice to understand geologic timescales? And how, in broader cultural representations of the past and future of the planet, has ice been deployed as a register, index, and interlocutor of geologic time? By tracing the ways ice has been an important means of understanding deep time for geologists and climatologists and highlighting how advances in “cryosphere science” informed various presentations of planetary futures, this project shows that ice has been instrumental in articulating human-geologic relationships since the nineteenth century. Ice, then, has been an essential material and agent—sticky yet slippery, deceptively transparent, solid yet fragile— in conceptualizing, defining, and imagining the Anthropocene.