Earth’s deep interior is cooling over geologic time, but not evenly. According to new research from the University of Oslo, one side of our planet has been losing heat dramatically faster than the other for hundreds of millions of years, and the reason traces back to ancient continent positions.
A study published in Geophysical Research Letters used large-scale computer models to reconstruct the distribution of continents and oceans over the last 400 million years. The researchers divided the world into two hemispheres: one broadly aligned with today’s Pacific region, and the other centered on Africa. Then, they calculated how much heat each side lost across time based on how insulated each region was by land.
The key insight: continents act somewhat like thermal lids. Thick continental crust traps heat beneath it. In contrast, oceanic crust is thinner, more porous, and continually replaced through seafloor spreading. Since the Pacific hemisphere has historically had far more ocean area, it has offered little insulation to underlying mantle heat. The African hemisphere, by contrast, has long been covered by large landmasses, slowing heat loss.
Earth’s interior constantly radiates heat outward, much of it through the oceanic lithosphere. New ocean floor forms at mid-ocean ridges, cools, then dives downward at subduction zones, carrying energy with it. The Pacific basin contains the largest and oldest seafloor on the planet, so its ability to drain heat is significantly higher.
The models suggest the Pacific hemisphere has cooled around 50 Kelvin more than the African side over 400 million years. That difference is far greater than scientists previously estimated and nearly doubles earlier studies that only examined the last 230 million years.
Yet the findings contain an intriguing contradiction. Faster plate movement generally corresponds with hotter mantle beneath. The Pacific has had higher tectonic speeds for hundreds of millions of years, implying it may have been hotter in the distant past before cooling rapidly. Researchers speculate that the region could have once hosted thick continental crust, lost over time to subduction.
This heat imbalance still affects modern geological behavior. More mantle melt allows plates to slide more easily, which may help explain why the Pacific region remains the most tectonically active on Earth, producing intense volcanism, earthquakes, and subduction activity today.
The study reinforces that Earth remains a dynamic, internally driven system, shaped not only by surface climate but by slow forces deep beneath our feet.
