Rising Silicon-rich 'Snow' From the Outer Core Might Help Explain Inconsistencies in Seismic Waves

Scientists determine the components of Earth without splitting it up by listening to the echo of earthquakes bouncing inside it. Sadly, seismic waves frequently exhibit discrepancies that scientists have yet to completely comprehend. A source of variation is found in low-density pockets of material between the liquid iron alloy outer core and the mantle, around 3,000 kilometers (just under 1,900 miles) below the surface.

How Rising Silicon-rich Snow Occurs in Outer Core

Recent research suggests that a silicon-rich 'snow' rising from the outer core might help explain some of the observed abnormalities, Science Alert reported. Since silicon makes particles lighter than the surrounding liquid iron, the material might flow out into the mantle and settle in drifts, causing sound waves to distort in unanticipated ways.

Geoscientist Suyu Fu of Japan's University of Tokyo explained that rising silicon-rich snow can develop if silicon and hydrogen are the two primary light elements abundant in the outer core.

To put this theory to the test, the researchers simulated conditions inside Earth's outer core in a laboratory. Before being ultra-compressed within a diamond anvil cell, an iron-silicon alloy was put inside a hydrogen-argon gas.

Geologists frequently utilize these machines to create compression levels close to those found within planets like Earth. Samples are mechanically squeezed between two diamonds and examined for changes.

The sample was heated using lasers and monitored with X-rays in this example. Previous research had run into a difficulty where high temperatures caused the hydrogen with the iron alloy to seep into the diamond.

Geoscientist Sang-Heon Dan Shim from Arizona State University said that they developed a new method where hydrogen is combined with argon in diamond anvil cells. He explained that argon suppresses hydrogen diffusion into diamond anvils which allowed them to achieve extreme conditions in the lab.

The researchers discovered that silicon-rich crystallite 'snow' could form and rise through the denser liquid iron to accumulate at the mantle-outer core boundary, possibly causing some of the anomalies they observed while scanning the planet's deepest parts under similar pressure and temperature conditions to Earth's outer core.

Why the Movement of Silicon-rich Snow in Outer Core Matters

While it may appear that none of this matters to Earth's surface, it is important to note that the movement of the outer core drives the magnetic field, which protects the planet from the corrosive effects of space and solar weather.

Understanding the what is inside of the outer core, how it is moving, and how this movement can alter its interaction with the mantle is critical for projecting how the Earth's magnetic field will function in the future.

Shim said in the press release that the silicon-rich alloy crystallization was found during snowy winter days in Chicago during the period of pandemic. It is interesting that such behavior can lead to rising silicon-rich snow thousands of kilometers below the surface.

If the rising silicon-rich crystal snows are captured by the convecting mantle flow, they may emerge as a fine-scale structure with very low seismic velocities in the lowermost mantle, explaining the ultralow velocity zones observed in seismic research for decades in the region.

Fu noted that their analysis, titled "Core Origin of Seismic Velocity Anomalies at Earth's Core-Mantle Boundary" published in the journal Nature, suggests that the silicon-rich snow started at the outer core and can develop into larger depths with continued secular cooling of the planet.

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