This article explores the temporalities of deep-sea core research in the 1970s and traces how this small scientific field became a site in which geological, environmental, and political times were negotiated in novel ways. Rather than conceiving of deep-sea cores as containers of data, which provide unmediated access to the planetary past, the article shows how the cores were temporally fluid objects which, in the 1970s, were picked up in settings well beyond the ocean sciences. By following the evolution of the deep-sea core project Climate: Long range Investigation, Mapping, and Prediction (CLIMAP), which brought together deep-sea core research with climate modeling and economic and agricultural forecasting, the article argues that the ways in which deep-sea core data entered the field of climate modeling mirrored contemporary fears of overpopulation as well as dreams of abundant energy reserves hidden in the seabed.Even though the deep-sea core scientists spoke of their work as “exploration” or “discovery,” the history of CLIMAP reveals a much more temporally complex enterprise and highlights the instability of planetary and historical times in the postwar era. Drawing on recent developments in time studies as well as the history of the geosciences, the article shows how present theoretical deliberations on the temporalities of the planetary scale can be understood in light of a longer historical process of negotiating multiple temporalities in the geosciences. By considering the history of deep-sea core research in the 1970s as a history of temporal negotiation, the article calls for increased collaboration and engagement between time studies and the history of science.