Rising silicon-rich snow in the Earth's outer core

February 15, 2023

Deep below the Earth’s surface lies the outer core, which is made up a 2,000-km-thick liquid iron alloy layer. Despite being located 3,000 km deep from the surface, the outer core affects our surface habitability as it is the region where Earth’s magnetic field is generated. 

In a study recently published in the journal Nature, a team of scientists, including Sang-Heon Dan Shim and Suyu Fu of Arizona State University, have completed an experimental observation of silicon-rich crystal formation in iron-hydrogen alloy liquid at high pressure and high temperature conditions expected for the Earth’s outer core.  Illustration of Earth interior core Top right corner figure is a modification from a figure included in the Nature paper. Image courtesy Wired UK Download Full Image

Crystals predict snow 

The crystals contain enough silicon to be lighter than the liquid, and therefore the crystals will rise in liquid iron metal.

For this experiment, lead author Fu, former ASU postdoc now at University of Tokyo as a postdoctoral fellow for the Japan Society for the Promotion of Science, and Shim, a professor at ASU's School of Earth and Space Exploration and Navrotsky Professor, along with Stella Chariton and Vitali Prakapenka, both of University of Chicago, focused their laboratory observation to predict that silicon-rich crystals may snow in the outer core, but instead of sinking they will rise. 

“The silicon-rich alloy crystallization was found during our experiments in snowy winter days at Chicago during the pandemic,” Shim said. “It is interesting that such crystallization behavior can lead to rising silicon-rich snow in the outer core.”

For this experiment, iron-silicon alloy is loaded in a hydrogen-argon gas mixture at ASU. Then the samples were compressed to the pressures expected for the core in a diamond-anvil cell. While being held at high pressure, the sample is heated by laser beams to temperatures expected for the core at the Advanced Photon Source, a U.S. Department of Energy user facility at DOE’s Argonne National Laboratory, where the researchers can monitor crystallization in a diamond-anvil cell using extremely bright X-ray beams. 

“Creating high enough temperatures for melting of iron alloys in hydrogen at high pressure has been very difficult,” Shim said. “The reason is that hydrogen can diffuse into diamond anvils and breaks them and fail the experiments.”  

For this experiment, “Our team developed a new method where hydrogen is mixed with argon in diamond-anvil cells. Argon does not react with the sample but suppresses hydrogen diffusion into diamond anvils, enabling us to achieve the extreme conditions in laboratory,” Shim said.

This phenomenon can make silicon-rich snow piles at the boundary between the metallic core and the rocky mantle where many enigmatic fine-scale structures have been found in seismic imaging studies for decades. 

“If silicon and hydrogen are the two main light elements in the outermost core with appropriate abundances, such a rising silicon-rich snow can occur,” Fu said. 

Indeed, among those structures, the core-rigidity zones (a few hundred meters thick with solid-like properties in the liquid iron metal outer core) found at the core side of the core-mantle boundary may be the silicon-rich snow piles. 

If the convecting mantle flow can capture some of these rising silicon-rich crystal snows, they may appear as a fine-scale structure with very low seismic velocities at the lowermost mantle, which can explain the ultralow velocity zones documented in seismic studies for decades in the region. 

“Our study also predicts that the silicon-rich snow starts at the outermost-core region and can develop into greater depths with further secular cooling of Earth,” Fu said.

Media Relations and Marketing Manager, School of Earth and Space Exploration


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Black Women in Engineering panel provides perspective for students pursuing careers in STEM

February 15, 2023

Multicultural Communities of Excellence spaces provide students safe place to congregate, learn

This month, the Tempe campus Multicultural Communities of Excellence space kicked of its spring faculty series with a Black Women in Engineering/STEM Faculty panel where students could hear from faculty members and gain more insight into fields where women and minorities are underrepresented.

“Remain authentic and look for mentors,” advised Brooke Coley, assistant professor of engineering in the Ira A. Fulton Schools of Engineering.

Coley told the audience that she didn’t quite know what her life journey would look like, but she knew her core values and was committed to justice, and remained true to that guiding principle.

Coley was joined by four other professors — Kimberly Scott, founding executive director and professor at the Center for Gender Equity in Science and Technology; Vernon Morris, from the New College of Interdisciplinary Arts and Sciences; and Meseret Hailu, assistant professor of higher and postsecondary education in the Mary Lou Fulton Teachers College; and Marielle Iroko Abalo, an interdisciplinary scientist who works at ASU's Education Outreach and Student Services.

“Events like the 'Black Women in Engineering/STEM Faculty Panel' create an opportunity to expand the perspectives in these fields. It promotes an expanded narrative of who represents the driving force within these fields," said Kira Gatewood, assistant dean for Educational Outreach and Student Services. "Often these voices are not at the forefront because they do not represent the majority of those in the field. Events like this provide a platform for these women to be recognized for their contribution and provide them a platform to share about their excellence.” 

The members of the panel each spoke about the individual experiences that shaped their lives and helped them become who they are today.

Scott talked about the exact moment that made her realize she wanted to pursue a career in STEM; she had been working as a special-needs teacher when she saw another teacher yelling at a student and she secretly hoped she would not have that student, only to find out that the next year she did. After speaking to the child’s mother, she realized that the student needed different interventions to be successful. That was the moment that made her go on to Rutgers University to address the myth that some kids cannot be successful.

Understanding that the learning process is not the same for everyone, she says, is so important.

According the Pew Research Center analysis, Black and Hispanic workers are highly underrepresented in science, technology, engineering and math professions. 

“For me, personally, events that shine a spotlight on those history likes to forget, or overlook, is a win. These women work hard at what they do and should be applauded for their contributions,” Gatewood said.

Caroline Pete, a junior earning a degree from the Ira A. Fulton Schools of Engineering, who helped facilitate the event along with her STEM classmates, said, “Being able to talk to faculty doesn’t always come that often, and being in the same room with them and having them accessible was great.”

Pete, a Tempe, Arizona, native who went to McClintock High School, has always had an interest in math and science and plans to become a neuroscience professor.

“More research needs to be done and it comes naturally for me,” Pete said

Video by Ken Fagan/ASU News

The Multicultural Communities of Excellence spaces on each campus bring diverse student groups together in a welcoming environment. There are currently eight student coalitions utilizing the Multicultural Communities of Excellence, but everyone is welcome. Find each campus location: Downtown Phoenix, Tempe, West and Polytechnic.

The spring faculty series offers an array of diverse programming meant to inspire collaborative conversation and open dialogue between students, faculty and peers. View the schedule of upcoming Multicultural Communities of Excellence events.

Top photo: The Black Women in Engineering/Faculty STEM panel held at the Multicultural Communities of Excellence space on the Tempe campus on Feb. 8. Photo by Christopher Goulet/Arizona State University

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