Science. A strange phenomenon that disturbs the balance of the Earth’s core

04-06-2021 A new model by seismologists at the University of California, Berkeley, suggests that the Earth’s inner core is growing faster on its east side (left) than on its west (MARINE LASBLEIS RESEARCH AND TECHNOLOGY POLICY)

Madrid, 4 (European Press)

Earth’s solid iron inner core is growing faster than the other side, and since it began solidifying from molten iron 500 million years ago.

The causes of this strange phenomenon are unknown, according to a new study published in Nature Geoscience by seismologists at the University of California, Berkeley.

This faster growth under the Banda Sea in Indonesia did not leave the core unbalanced. Gravity evenly distributes new growth (iron crystals that form when molten iron cools) to keep a spherical inner core growing at an average radius of one millimeter per year.

But the high growth on one side suggests that something in the Earth’s outer core or mantle below Indonesia is removing heat from the inner core at a faster rate than on the other side, below Brazil. Faster cooling on one side would speed up the crystallization of iron and the growth of the inner core on that side.

Esto tiene implicaciones para el campo magnético de la Tierra y su historia, porque la convección en el núcleo externo impulsada por la liberación de calor del núcleo interno es lo que hoy impulsa la dínamo que quetic genera el peculías no culas campo Sun.

“We put somewhat imprecise limits on the age of the inner core, between 500 and 1.5 billion years, which can be useful in the discussion of how the magnetic field was created before the solid inner core existed,” said Barbara Romanovich, a professor from Barbara Romanovich University. . University of Berkeley Graduate School of Earth and Planetary Sciences and Director Emeritus of the Berkeley Seismological Laboratory (BSL).

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“We know that the magnetic field was already around 3 billion years ago, so other processes must have driven convection in the outer core at that time.”

The younger age of the inner core may mean that early in Earth’s history, the heat that boiled the liquid core came from light elements separated from iron, not from crystallization of iron, which we see today.

“The debate about the age of the inner core has been going on for a long time,” Daniel Frost, assistant project scientist at BSL, said in a statement. “The complexity is this: If the inner core has only been able to exist for 1.5 billion years, based on what we know about how it loses heat and how hot it gets, then where did the oldest magnetic field come from? From thawed elements of light that later froze.

The asymmetric growth of the inner core explains a three-decade-old mystery: crystallized iron in the core appears preferentially aligned along the Earth’s spin axis, more in the west than in the east, while one would expect that the crystals would be randomly oriented.

Evidence for this alignment comes from measurements of the time of transmission of seismic waves from earthquakes through the inner core. Seismic waves travel faster in the direction of the north-south axis of rotation than along the equator, an asymmetry that geologists attribute to iron, asymmetric crystals, which have long axes and are preferably aligned along the Earth’s axis.

If the core is solid crystalline iron, how are the iron crystals preferentially oriented in one direction?

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In an attempt to explain the observations, Frost and colleagues Maren Lasplace of the University of Nantes in France and Brian Chandler and Romanovich of the University of California, Berkeley, created a computer model of crystal growth in the inner core that incorporates models of geodynamic growth and physics. Under high pressure and high temperature.

“The simplest model seemed a little unusual: that the inner core is asymmetric,” Frost said. “The west side looks different from the east side to the center, and not just at the top of the inner core, as some have suggested. The only way we can explain this is that one side is growing faster than the other.”

The model describes how asymmetric growth, about 60% higher in the east than in the west, can preferentially orient the iron crystals along the spin axis, with greater alignment in the west than in the east, and explains the difference in seismic wave velocity in the inner core.

“What we propose in this paper is a solid-asymmetric thermal model in the inner core that reconciles seismic observations with plausible geodynamic boundary conditions,” Romanovich said.

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