The Earth's Inner Core May Be A Winter Wonderland Of Iron "Snow"


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A new study asserts that the Earth's inner core is covered with a thick layer of iron "snow" (Credit: The University of Texas at Austin/Jackson School of Geosciences)

The Earth's inner core, which boasts temperatures exceeding 9,000 degrees Fahrenheit (5,000 degrees Celsius), may not evoke images of a winter wonderland. Yet, a new study by a team of scientists led by Youjun Zhang, an associate professor at Sichuan University in China, asserts that the deepest part of our planet may be covered with a 200-mile-thick layer of "snow." However, before you rush to pack your skis, be aware that the "snowflakes" are not composed of frozen water crystals, but of tiny particles of iron!

As you probably know, the Earth's structure comprises several layers. The crust is the outermost layer on which we live. Right beneath lies the mantle, a warm, semi-liquid layer of rock that is always in flux. This is followed by a thin shell of liquid iron that forms the outer core. Finally, there is a solid inner core, which mostly consists of iron and is responsible for our planet's magnetic field.

Since collecting samples from the core is impossible, scientists study the area by analyzing signals from seismic waves as they pass through the Earth's structure. The waves of energy, which are caused by earthquakes, travel at distinct speeds as they traverse through the different materials, allowing researchers to determine the density and the composition of the various layers.

A better understanding of the Earth's inner core will provide valuable insights into phenomena that affect the entire planet (Credit: Derivative work: SrimadhavEarth cutaway schematic-en.png: USGS /Public domain)

Zhang and his colleagues were monitoring recent seismic wave data when they noticed a series of anomalies. The energy waves were moving slower than expected through the bottom of the outer core and faster than expected through the eastern hemisphere of the top inner core. This information, along with other experiments conducted to mimic the Earth's core, led the team to propose that the irregular speeds could be the result of a snowbank located in the inner core.

According to the scientists, the "snow" is caused by the crystallization of the molten iron at the base of the outer core. As the "snowflakes" sink, they settle atop the solid inner core, creating a layer thick enough to slow down the seismic waves at the base of the outer core. Similarly, the variation in snow pile size — lighter in the eastern hemisphere and more substantial in the western hemisphere — explains the more rapid pace of the seismic waves through the top inner core.

"It's sort of a bizarre thing to think about," study co-author Nick Dygert of the University of Tennessee said. "You have crystals within the outer core snowing down onto the inner core over a distance of several hundred kilometers."

Minerals from the melting magma rise and crystallize before cooling inside the magma chamber to become cumulate rocks (Credit: Woudloper /CC BY-SA -3.0 /

The researchers, who published their study in the journal JGR Solid Earth on December 23, 2019, compare the process to what happens inside magma chambers closer to the Earth’s surface. In this case, the minerals that solidify from the melting magma accumulate inside the magma chambers and compact, creating what are known as "cumulate rocks."

From forming a protective magnetic field around Earth that deflects solar winds to driving tectonic activity, the inner core plays a significant role in phenomena that affect the entire planet. Hence, understanding more about its composition and behavior is crucial for scientists to better understand how these larger processes work.



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