New research shows that the Pacific Hemisphere is losing heat faster than the African Hemisphere. Heat comes from the Earth’s molten interior, causing continents to drift. The land traps more heat than the seafloor surface, indicating a hotter Pacific Ocean in the past.
In a new study, scientists from the University of Oslo argue that one side of Earth’s interior is losing heat much faster than the other, and the culprit is almost as old as time.
The study, published in Geophysical Research Letters, uses computer models of the past 400 million years to calculate how “isolated” each hemisphere has been in terms of continental mass, which is a key quality that keeps heat in rather than releasing it. This pattern can be traced all the way back to Pangea.
The Earth has a red-hot liquid inside that warms the entire planet from the inside out. It also rotates, creating the Earth’s gravity and magnetic field. This keeps our protective atmosphere close to the Earth’s surface.
In the very long run, this interior will continue to cool until the Earth looks like Mars. What is surprising about the new study is how unevenly the heat dissipates, but the reason for this is intuitive: Parts of the Earth have been isolated by a lot of land, creating a sort of thermos layer that holds the heat in.
This contrasts with how the Earth loses most of its heat: “The Earth’s thermal evolution is largely controlled by the rate of heat loss through the oceanic lithosphere,” the study authors write. Why is this where most of the loss occurs? For that, we need a quick, detailed look at continental drift.
Earth’s mantle is like a convection furnace that feeds a treadmill. Every day the surface of the seafloor moves by a small amount; new seafloor is born from magma erupting on a continental rift, and the old seafloor breaks up and melts under the existing continental landmasses.
To study how the Earth’s internal heat behaves, scientists built a model that divides the Earth into the African and Pacific Hemispheres and then divides the entire surface of the Earth into a grid of half-degree latitudes and longitudes.
Scientists combined several previous models for such things as the age of the seafloor and the position of the continents over the past 400 million years. The team then calculated how much heat each grid cell contained over its long life. This allowed the total cooling rate to be calculated, and the researchers found that the Pacific side was cooling much faster.
Accumulated mantle heat loss (oceanic + continental) over the past 400 years. Regions over the Pacific and African major provinces with low shear rates are shown in blue and orange lines. Dotted meridians in light color indicate the separation of the Pacific and African hemispheres.
The seafloor is much thinner than the bulky landmass, and the temperature inside the Earth is “dampened” by the huge volume of cold water above it. Think of the giant Pacific Ocean compared to the opposite landmasses of Africa, Europe, and Asia-it makes sense that heat dissipates faster from the largest seafloor in the world.
Previous studies of this seafloor effect have only covered 230 million years, so the new model, which covers 400 million years, almost doubles the time frame being studied.
There is a surprising contradiction in the findings. The Pacific hemisphere cooled about 50 Kelvin more than the African hemisphere, but the “consistently higher rate of plate motion in the Pacific hemisphere during the last 400 [million years]” suggests that the Pacific was much hotter at some point in time.
Was it covered by the Earth’s surface at some point in the distant past, keeping more heat inside? There are other possible explanations, but either way, the high tectonic activity of the Pacific today points to a heat disparity. The smoother the mantle, the more the plates can slide and collide with each other.
