The Two Faces of Earth — How One Hemisphere Lost Its Heat

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Scientists report that Earth’s interior is cooling unevenly: the hemisphere that contains the Pacific Ocean has lost heat much faster over the past hundreds of millions of years than the hemisphere containing Africa, Europe, and Asia.

The key physical reason is the distribution of land and sea. Continental crust is a far better thermal insulator than oceanic crust, so hemispheres with more land trap interior heat while ocean-dominated hemispheres let more heat escape through the seafloor.

Researchers modeled Earth’s thermal history by reconstructing continental positions and seafloor ages across roughly 400 million years and then calculating how much mantle heat each grid cell would have lost. Their results show sustained, cumulative cooling concentrated beneath the Pacific hemisphere, producing a long-term temperature difference between the two sides of the planet.

This asymmetry helps explain geological and geodynamic contrasts such as differences in mantle convection patterns, hotspot distributions, and the thermal evolution of large low-shear-velocity provinces beneath Africa and the Pacific, and it implies that plate tectonics and surface geography feed back on Earth’s internal temperature over geologic time.

Uneven mantle cooling is not a short-term climate issue for humans, but it reshapes our understanding of deep Earth processes and their long-term influence on volcanism, continental breakup, and the planet’s thermal future. The observation that one hemisphere can act like a partial thermal blanket while the other acts like a cooling vent reframes how scientists think about Earth’s interior over hundreds of millions of years.