Why the Pacific Hemisphere Is Cooling Faster Than the African Side — New 400‑Million‑Year Model Explains Why

Scientists at the University of Oslo report that Earth’s interior is cooling unevenly: the hemisphere beneath the Pacific Ocean has lost internal heat far more rapidly than the hemisphere beneath Africa. The finding — based on numerical reconstructions of the past 400 million years — highlights how the long-term arrangement of continents and oceans controls the planet’s thermal evolution.

How The Study Was Done

In a paper published in Geophysical Research Letters, researchers combined published reconstructions of seafloor age and continental positions with a grid-based numerical model that covers the planet at half‑degree latitude–longitude resolution. For each grid cell they estimated the cumulative heat stored and released over geological time, then compared the integrated cooling of two hemispheres they define as the Pacific and the African hemispheres.

Why The Pacific Has Cooled Faster

Continental crust acts like insulation: thick, buoyant landmasses slow the escape of internal heat. By contrast, oceanic lithosphere is thin and overlain by deep, cold seawater that efficiently extracts heat from the mantle below. Because the Pacific side contains the largest continuous swath of seafloor, the model finds that it has dissipated interior heat more efficiently — cooling roughly 50 Kelvin more than the African hemisphere over the modeled 400‑million‑year interval.

A Deeper Puzzle: Faster Plates, Cooler Mantle?

There is a surprising tension in the results. The Pacific hemisphere has exhibited consistently higher plate velocities during the past 400 million years, and faster plate motions are usually associated with a hotter, more molten mantle. That raises the question: how could the Pacific be cooler now while showing signs of greater thermal vigor in plate tectonics?

Possible resolutions include a dynamic history in which the Pacific region was once more extensively insulated by continental fragments (trapping heat) before opening into the large ocean basin we see today. Alternatively, variations in mantle composition, localized upwellings, or changes in plate configuration could produce transient periods of high plate speed even as the long-term average heat content declined.

Why This Matters

Extending previous analyses from about 230 million years to 400 million years, this study shows that hemispheric differences in heat loss are an ancient and persistent feature of Earth’s thermal history. The result has implications for understanding mantle convection, the driving forces of plate tectonics, and how the distribution of continents and oceans shapes planetary cooling over geologic time.

Bottom line: The balance between insulating continents and heat-leaky oceans determines how interior heat escapes, and the Pacific hemisphere’s extensive seafloor has been the planet’s most effective thermal valve — cooling substantially more than the African side across hundreds of millions of years.