Privileged Planet: solving Earth's core mystery (Introduction)

by David Turell , Wednesday, February 09, 2022, 19:29 (1019 days ago) @ David Turell

We know there is lots of iron, but seismic activity is still not fully explained:

https://www.sciencenews.org/article/earth-inner-core-superionic-matter-weird-solid-liquid

"Computer simulations described in two studies suggest that the material in Earth’s inner core, which includes iron and other, lighter elements, may be in a “superionic” state. That means that while the iron stays put, as in a solid, the lighter elements flow like a liquid.

"The research gives a potential peek at the inner workings of an enigmatic, inaccessible realm of the planet. According to conventional scientific wisdom, Earth’s core consists of a liquid outer core surrounding a solid inner core. But beyond knowing that the inner core is rich in iron, scientists don’t know exactly which other elements are present, and in what quantities.

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"Seismic waves stirred up by earthquakes can plow through the inner core, providing clues to what’s inside. But measurements of these waves have left researchers puzzled. The velocity of one type of wave, called a shear wave, is lower than expected for solid iron or for many types of iron alloys — mixtures of iron with other materials. “That is a mystery about the inner core,” says geophysicist Yu He of the Chinese Academy of Sciences in Guiyang.

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"In a superionic material, some of the atoms arrange neatly, as in a solid, while others are liquid-like free spirits that slip right through the solid lattice. In the simulation, the researchers found, the lighter elements moved about while the iron stayed in place.

"That superionic status slowed shear waves, the researchers report February 9 in Nature, suggesting the weird phase of matter could explain the unexpected shear wave velocity measured in the inner core.

"Shear waves, also known as secondary or S waves, jiggle the Earth perpendicular to their direction of travel, like the undulations that move along a jump rope that’s wiggled up and down. Other waves, called primary or P waves, compress and expand the Earth in a direction parallel to their travel, like an accordion being squeezed.

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"In a study published in August 2021 in Earth and Planetary Science Letters, a simulation of iron, silicon and hydrogen atoms reproduced the inner core’s known characteristics. In the simulation, the material was also superionic: the iron and silicon stayed in position while the hydrogen flowed like a liquid.

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"Another puzzle of Earth’s heart is the fact that the inner core’s structure seems to change over time. This has previously been interpreted as evidence that the inner core rotates at a different rate than the rest of the Earth. But He and colleagues suggest that it could instead result from the motions of liquid-like light elements swirling inside the inner core and changing the distribution of elements over time. “This paper sort of offers an explanation for both of these phenomena” — the slow shear wave velocity and the shifting structure — says Tkalčić, who was not involved with either new study.

"One thing missing is laboratory experiments showing how these combinations of elements behave under inner core conditions, says geophysicist Daniele Antonangeli of Sorbonne University in Paris, who was not involved with the new research. Such tests could help confirm whether the simulations are correct."

Comment: So our Earth is still mysterious, but it works and life here is richly provided for.