For some reason, waves travel through the Earth's core much faster when traveling between the North and South Poles than when they pass across the equator.
Scientists have discovered this mystery by analyzing seismic waves, but they cannot determine the reason.
They have known about this anomaly for decades, but could not explain the cause.
According to the latest research, during which scientists used a simulation of the growth of the Earth's core over the last billion years, they concluded that the cause could be an asymmetric growth of the inner core.
“The flow of liquid iron in the outer core dissipates heat from the inner core, which causes it to cool. So this means that the outer core was carrying more heat from the east (below Indonesia) than from the west (below Brazil)," explains seismologist Daniel Frost at the University of Berkeley for Live Science magazine.
Experts say that this asymmetric growth does not mean that the inner core is deformed or that some kind of imbalance will occur.
The radius of the inner core grows evenly on average by about one millimeter each year.
The force of gravity corrects the asymmetric growth of crystals on the east side of the core, pushing the new crystals to the west. These crystal structures, arranged parallel to the Earth's poles, are seismic "highways" that allow seismic waves to travel faster in that direction.
It's hard to say what's causing this imbalance if all the other layers inside the Earth aren't considered, Frost says.
"The inner core slowly cools and expands from the liquid outer core, like a spinning snowball growing. The outer core then cools the mantle above it. "If we want to ask why the inner core grows faster on one side, we also have to ask ourselves why one side is cooler than the other," adds Frost.
Plate tectonics may be responsible for this, Frost believes. When cold tectonic plates sink deep below the Earth's surface during the process of subduction (the subduction of one plate under another), they cool what is beneath them. But scientists still don't know for sure whether this cooling of the crust also affects the inner core.
It is also debatable whether this unilateral cooling of the core affects the Earth's magnetic field, which is created precisely because of the flow of iron in the outer core.
If the inner core loses more heat on the eastern side, then the outer core will also move to the east, and the question is whether this affects the strength of the magnetic field, the seismologist adds./ KosovaPress/
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