How Does Earth’s Inner Core Remain Solid Despite Extreme Heat?

Posted: Feb 14 2017, 6:25am CST | by , Updated: Feb 14 2017, 8:29am CST, in News | Latest Science News

 
How Does Earth’s Mantle Remain Solid Despite Extreme Heat
Credit: NASA

New study may settle a longstanding debate over the structure of iron crystals within Earth's core

Earth’s inner core is a solid ball of iron surrounded by a layer of liquid iron alloy. At the temperature higher than 5,000 Celsius, the inner core is as hot as the Sun’s surface, but it still remains solid.

Researchers have long wanted to know how the Earth’s inner core maintains its solid state despite such an extreme heat. The answer lies in knowing the atomic structure of this almost pure crystallized iron - something never before achieved.

Atoms are found in the variations of cubic and hexagonal formations and like all metals, the change in the atomic structure of iron depends on the temperature and pressure the metal is exposed to. Iron is known to have body centered cubic (BCC) structure at room temperature, which is crystal architecture with eight corner points and a center point. But at extremely high pressure the crystalline structures transform into 12-point hexagonal forms, or a close packed (HCP) phase.

At Earth's core, where pressure is 3.5 million times higher than surface pressure – and temperatures are some 6,000 degrees higher, scientists suggest that the atomic architecture of iron must be hexagonal. But they were surprised to find that iron at Earth's core is indeed in the BCC phase.

Their conclusion is drawn from computer simulations performed using Triolith, one of the largest Swedish supercomputers.

"Under conditions in Earth's core, BCC iron exhibits a pattern of atomic diffusion never before observed," said Anatoly Belonoshko, a researcher in the Department of Physics at KTH Royal Institute of Technology, Sweden.

“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.”

Researchers explain that this is a bit like shuffling a deck of cards. No matter how you change position of the cards, the deck is still a deck. The same goes for the iron crystals within the Earth’s core. Even though the temperature is high in Earth’s interior, the BCC iron does not turn into liquid and retains its cubic structure.

Normally, shuffling leads to distribution of molecules which destroys crystal structures. But in this case, it allowed iron to preserve its structure and made it even more stable.

“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,” said Belonoshko.

“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.”

As the researchers note, understanding the true makeup of Earth’s interior may help better understand its history and more accurately predict its future.

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Hira Bashir covers daily affairs around the world.

 

 

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