Secular Cooling of the Earth Inferred from Hemispheric Mantle Dichotomy

Secular mantle cooling is the most fundamental boundary condition for understanding Earth's dynamics and history. Despite the importance of Earth's thermal history, both radically different forms of thermal models and data constraints render its interpretation ambiguous. Compositions of primitive basalts reflect mantle temperatures in Earth's past, but questions remain over which data are reliable and representative of ambient mantle cooling. We report that seismically inferred temperatures of volcanic hotspots reveal a hemispheric dichotomy between the Pacific and African mantle domains, providing a guide to tracking secular mantle cooling. Whereas hot hotspots like in the Pacific and Archean komatiites should be excluded, cold and warm hotspots in the continental domain can be used to exponentially increase the number of data used to estimate Earth's cooling history.