Science

New theory explains why the Earth's core doesn't melt

New theory explains why the Ea...
A new theory may explain why the inner core of the Earth remains solid iron, despite the extreme temperatures
A new theory may explain why the inner core of the Earth remains solid iron, despite the extreme temperatures
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A new theory may explain why the inner core of the Earth remains solid iron, despite the extreme temperatures
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A new theory may explain why the inner core of the Earth remains solid iron, despite the extreme temperatures

Geologists estimate that the Earth's core is a sweltering 5,700 K (5,427° C, 9,800° F), putting it about on par with the surface of the Sun – and yet the inner core is a solid ball of iron. Why it doesn't liquify is a bit of a mystery, but now a study from KTH Royal Institute of Technology puts forward a new theory, simulating how solid iron can remain atomically stable under such extreme conditions.

Here on the surface of the Earth, iron atoms arrange themselves into cubes, in what's known as a body-centered cubic (BCC) phase. Since this state is a product of room temperature and normal pressure, scientists have long believed that iron couldn't exist in this form in the broiling temperatures and intense pressure at the planet's center. Under those conditions, the crystal architecture of iron was expected to take on the shape of a hexagon, in a state called the hexagonal close-packed (HCP) phase.

Using the Swedish supercomputer Triolith, the new study from KTH crunched larger volumes of data than had previously been analyzed. The data indicated that the core was likely composed of 96 percent pure iron, with the remaining four percent made up of nickel and some light elements. But most importantly, the study found that BCC iron can indeed exist in the core, with its crystal structure remaining stable thanks to the very characteristics that were previously assumed to destabilize it.

"Under conditions in Earth's core, BCC iron exhibits a pattern of atomic diffusion never before observed," says Anatoly Belonoshko, one of the study's authors. "It appears that the experimental data confirming the stability of BCC iron in the core were in front of us – we just did not know what that really meant."

The crystal structures can be thought of as being divided into "planes" of atoms – that is, two-dimensional layers of atoms. So, iron atoms in a cubic phase are arranged in two planes of four atoms, making up the eight corners of a cube. These structures are normally fairly unstable, with planes sliding out of shape, but at extreme temperatures, the layers that slide off are reinserted into the mix, occurring reliably enough that it stabilizes the structure.

This diffusion normally destroys the crystal structure by liquifying it, but in this case, the iron manages to preserve its BCC structure. The researchers liken the planes to cards in a deck.

"The sliding of these planes is a bit like shuffling a deck of cards," says Belonoshko. "Even though the cards are put in different positions, the deck is still a deck. Likewise, the BCC iron retains its cubic structure. The BCC phase goes by the motto: 'What does not kill me makes me stronger.' The instability kills the BCC phase at low temperature, but makes the BCC phase stable at high temperature."

This finding also helps explain another inner-Earth mystery: why do seismic waves travel faster pole-to-pole than east-to-west, through the core? This phenomenon has been explained by the core being anisotropic, meaning it has a directional texture like the grain of wood. If that texture runs north-south, that difference would be expected, and the stable BCC phase iron could create this texture.

"The unique features of the Fe BCC phase, such as high-temperature self-diffusion even in a pure solid iron, might be responsible for the formation of large-scale anisotropic structures needed to explain the Earth inner core anisotropy," says Belonoshko. "The diffusion allows easy texturing of iron in response to any stress."

The research was published in the journal Nature Geosciences and the team explains the finding in the video below.

Source: KTH Royal Institute of Technology

How Earth's inner core remains solid despite heat

7 comments
Thinker
I often wonder: if the core of the earth is so hot, does it not make sense that over time it cools? If it is cooling, wouldn't that cause shrinkage? If shrinkage occurs, wouldn't that account for our mountains and oceans? If shrinkage is occurring would that suggest that the earth was much larger in circumference effecting gravitational intensity? Just wondering.
Lardo
"...and yet the inner core is a solid ball of iron" How do they know that? I mean, to speculate that the core COULD be a solid ball of iron, is one thing. But, seems to me, saying that it IS a solid ball of iron is a wee bit arrogant. 'cause the truth is, they don't really know for certain. As a matter of fact they don't really know the temperature, for certain, either.
BobLoblaw
It might also help understand the planet's magnetic field. @Tina The rotation of the earth + friction between the mantle and core and crust ensures it doesn't cool off much so long as the planet keeps spinning. Mountains come from tectonic plates being forced together especially when new crust is formed (volcanoes). Students, crack open your 5th grade science books to the section on plate tectonics. @Lardo They have this thing called math. They know all the measurements of the earth like the magnetic field, seismic readings etc. that can be used to determine the mass and density of the core.
Robert in Vancouver
I thought the science was settled about this issue because it's been discussed, studied, and that's all that's required. Al Gore said "science is settled" right after his theory of global warming came out and he won a Nobel prize for that, and made a billion $ from his carbon credit scams. Since Al Gore is the guru of science, that means all science is settled and we don't have anything new to learn about anything.
MK23666
They "know" that the core is solid because it behaves seismically like a "solid" metallic object. Seismic waves travel differently in liquids than they do in solids. Seismic waves also travel differently through various solids or liquids, that is how they can determine how large the core is and how large the molten outer core is and to a great degree of certainty what it is made of.
Agamemnon
What comes immediately to my mind, is the deck of cards, skewered like a corkscrew, which is brought about by opposing grip shifts of both hands. This would mean that the tectonic shift interacts with Fe BCC phase cube in this highly empirical model of the earths core. Hmm interesting 😇
That1Guy
Wouldn't this explain the phenomena of gravity perfectly, Take this dense object that generates an electromagnetic field and throw less dense matter near it until buoyancy comes into play, then it would be just density - Buoyancy = gravitational force? This would explain collisions with solid objects, against a dense object creating rock type planets. I believe gas giants hold similar solids inside, just less collisions and more gas dubris with buoyancy at play with electromagnetism.