A joint research team led by Prof. He Yu of the Geochemistry Institute of the Chinese Academy of Sciences (IGCAS) has found that Earth's inner core is not a normal solid, but consists of a subcyclical of solid iron mixed with mild elements shaped like liquids otherwise known as superionic states.
A superionic state is a transitional state between liquid solids, which are found in many parts of the planet. It is known using computational simulations of high pressure and high temperatures based on the theory of quantum mechanics.
Researchers from IGCAS and the Center for High Pressure Science & Technology Advanced Research (HPSTAR) found that some fe-H (iron-hydrogen), Fe-C (iron-carbon) and Fe-O (iron-oxygen) alloys turn into superionic states under inner core conditions.
"We found that the hydrogen, oxygen, and carbon in tightly packed hexagonal iron turned into a superionic state under deep core conditions, demonstrating a high coefficient of diffusion like a liquid," the team wrote in their new paper. "This suggests that the inner core could be in a superionic state rather than a normal solid state."
Superionic is another state of matter — in addition to solid, liquid, and gas — but with clear differences. In superionic water — recently created in a laboratory — very high temperatures and pressures break down each water molecule, leaving oxygen ions to form solids, while hydrogen ions float more like liquids.
In Earth's hot core, the team used computer simulations of how seismic waves would travel through a combination of different elements, and found that iron alloys with carbon, hydrogen, and oxygen could work in the same way as superionic water.
Iron atoms are 'solid' in the crystal lattice structure, while carbon, hydrogen, and oxygen molecules will diffuse through the medium, creating a liquid-like element. "It's very abnormal," he said. "Iron compaction at the inner core boundary does not change the mobility of this light element, and light element convection continues in the inner core."
This work is unlikely to be the last word on the matter. The paper's conclusions provide a good model for this softer, less dense pure iron, but it doesn't answer another question about the inner core – why it doesn't seem to be entirely evenly distributed. Located deep beneath the Earth's crust, passing through a thick mantle and liquid outer core, there is a dense inner core sphere 1,220 kilometers (760 miles) long.