The Earth’s core is growing out of balance, scientists have found, but it’s unclear why.

The solid iron core in the middle of the planet has grown faster under Indonesia’s Banda Sea, seismologists at the University of California at Berkeley have found.

The growth on one side of the molten metal is the product of iron crystals that form when the molten iron cools, but something in the Earth’s core or outer mantle beneath the Southeast Asian country is bleeding out. heat at a faster rate than on the opposite side, under Brazil. The faster the cooling, the faster the crystallization of iron occurs – and the faster the growth increases.

Such a disparity has important implications for the Earth’s magnetic field, and the convection currents in the nucleus that generate the field are what protect us from dangerous solar particles.

While the core is solid iron, it is surrounded by a fluid outer core and then a mantle of hot rock. In the mantle and outer core, heat from the crystallizing iron and warmer rock in the mantle rises to the surface, pushing cooler materials down. This movement is what generates the magnetic field.

“We provide rather loose limits on the age of the inner core – between half a billion and 1.5 billion years – which may be useful in the debate on how the magnetic field was generated before existence. strong inner core, “said Barbara Romanowicz, professor at UC Berkeley in the Graduate School of the Department of Earth and Planetary Sciences and director emeritus of the Berkeley Seismic Laboratory (BSL).

“We know that the magnetic field already existed three billion years ago, so other processes must have caused convection in the outer core at that time.”

The relatively young age of the inner core suggests that, in the history of our planet, the heat that keeps iron liquid came from light elements separating from iron, and not from the crystallization of iron. But a complicated question remains: “If the inner core could only have existed for 1.5 billion years … then where did the old magnetic field come from?” BSL deputy scientist Daniel Frost posed. “This is where the idea of ​​dissolved light elements came from, which then freeze.”

One possible explanation could be tectonic plates, with cold plates cooling the mantle as they sink into zones of subduction, but it’s unclear whether mantle cooling could impact the inner core.

However, the asymmetric growth of the nucleus answers a mystery that scientists have been trying to solve for 30 years: why does the crystallized iron core appear to be aligned along the Earth’s axis of rotation farther west than ‘to the East ? Seismic waves travel faster in a north-south direction than along the equator, due to the asymmetry of iron crystals, and this difference in growth is one possible explanation.

“The simpler model seemed a bit unusual – that the inner core was asymmetric,” Frost said. “The west side is different from the east side all the way to the center, not just at the top of the inner core, as some have suggested. The only way to explain this is that one side is growing faster than the other. “

As the iron crystals grow, gravity redistributes the excess growth from east to west in the inner core. This movement in the soft solid of the inner core lines up along the crystal lattice, suggests the scientists’ computer model. In the east, the core grows 60% more than in the west, which explains the differences in the speed of seismic waves that can lead to earthquakes, volcanic eruptions and other phenomena.