Earth's inner core is a strange superionic iron alloy, study suggests
Researchers from the Chinese Academy of Sciences have found that Earth’s inner core may be stranger than we thought. Rather than a plain solid, new simulations suggest it exists as a superionic state of matter, partway between a liquid and a solid.
Since we can’t exactly drill down and visit, scientists study the Earth’s core primarily through seismic waves from earthquakes. As these vibrations ripple through the planet, they move at different speeds through different materials, and analyzing these changes can reveal the composition of the various layers.
Over the decades, these studies have consistently shown that the inner core can propagate a type of seismic ripple called shear waves, which indicates that it’s solid. However, these waves move through the core more slowly than would be expected for a ball of solid iron, suggesting it’s a bit softer.
For the new study, the researchers simulated temperature and pressure conditions at the center of the Earth to investigate what other types of matter might be possible down there. They found that some iron alloys could form a superionic state, which would explain the observations.
In a superionic iron alloy, the iron atoms form a solid lattice that holds the material in shape, while lighter elements diffuse through the lattice in an almost liquid state. Under the conditions at the Earth’s core, the simulations showed that these lighter elements could include hydrogen, oxygen or carbon.
Importantly, the team calculated how fast shear waves would move through these superionic alloys, and found that it fit well with observations. Other established properties of the inner core could also be accounted for with different distributions and convections of these liquid-like elements.
It’s an interesting idea, but it’s not the only possible explanation. Previous studies have hypothesized that the slower shear wave propagation could be due to “iron snow” falling on the inner core from the outer core.
The new research was published in the journal Nature.
Source: Chinese Academy of Sciences
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