Swift Group Movement of Iron Atoms Observed in Earth’s Solid Inner Core

Interactions between charged ions and Earth’s magnetic field frequently produce phenomena like auroras near the planet’s polar regions. The “southern lights,” or aurora australis, have been documented by NASA’s IMAGE satellite. Image credit: NASA

A recent study has unveiled the fast-paced group movement of iron atoms within the Earth’s inner core. This newfound behavior could provide insights into the unanticipated softness of the core revealed by seismic data and may also offer a better understanding of the generation of Earth’s magnetic field.

The iron atoms constituting Earth’s inner core are densely packed due to extreme pressures—some of the highest pressures present anywhere on the planet.

Nevertheless, researchers have discovered that there is still room for some level of atomic movement within this densely packed environment.

The research, led by The University of Texas at Austin and involving collaborators from China, revealed that specific clusters of iron atoms in the Earth’s solid inner core can undergo swift movements. These atoms can switch positions within fractions of a second while preserving the basic metallic framework, a behavior classified as “collective motion,” analogous to guests rearranging seats at a dinner table.

A computational model illustrating the motion of iron atoms within the Earth’s inner core shows how they are anticipated to shift over a span of 10 picoseconds, with one picosecond equating to one trillionth of a second. Image credit: Zhang et al.

Implications for Understanding Earth’s Magnetic Field

The study’s outcomes, derived from both lab experiments and theoretical models, suggest that there is greater atomic mobility within the inner core than was previously considered.

These results may clarify multiple puzzling aspects of the inner core that have confounded scientists for years. The findings could also illuminate the role that the inner core plays in fueling Earth’s geodynamo—the complex process responsible for generating the planet’s magnetic field.

“As a result of this study, we are now better equipped to comprehend the dynamic processes and evolutionary development of Earth’s inner core,” remarked Jung-Fu Lin, a professor at the UT Jackson School of Geosciences and one of the principal authors of the study.

The research was published on October 2 in the journal Proceedings of the National Academy of Sciences.

Investigative Methods and Key Findings

Directly sampling Earth’s inner core is impractical due to its exceedingly high temperature and pressure conditions. Therefore, Lin and his colleagues simulated these conditions in a lab by shooting a fast-moving projectile at a small iron plate. Data on temperature, pressure, and velocity were collected and incorporated into a machine-learning model depicting atomic activity in the inner core.

Historically, it is believed that iron atoms in the inner core form a recurring hexagonal pattern. Most computer models depicting this atomic lattice have featured a small number of atoms—generally fewer than one hundred. However, by utilizing an AI algorithm, the team could develop a more comprehensive “supercell” model with approximately 30,000 atoms to more accurately predict iron’s properties.

Within this expansive atomic environment, the team noticed sets of atoms rearranging themselves but maintaining the overall hexagonal architecture.

Explanation for Seismic Data Anomalies

Youjun Zhang, a co-lead author and professor at Sichuan University, stated that the observed atomic activity could account for the softer and more pliable characteristics of the inner core, as indicated by seismic measurements.

“Seismic data has shown that Earth’s inner core exhibits unexpected softness, resembling the soft texture of butter at room temperature,” Zhang said. “Our significant discovery is that solid iron turns out to be unexpectedly malleable deep within the Earth due to the higher-than-anticipated atomic mobility. This heightened movement results in a core that is less rigid and less resistant to shear forces.”

The quest to explain the unexpected softness, as indicated by seismic data, served as the impetus for this research.

Contribution to Earth’s Magnetic Field Generation

According to the study, nearly half of the geodynamo energy responsible for Earth’s magnetic field is derived from the inner core, with the outer core contributing the remainder. The new revelations regarding atomic behavior in the inner core could significantly inform future studies investigating how energy and heat are produced there, and how this relates to the dynamics of the outer core and their collective role in generating Earth’s magnetic field crucial for planetary habitability.

Reference: “Collective motion in hcp-Fe at Earth’s inner core conditions” by Youjun Zhang, Yong Wang, Yuqian Huang, Junjie Wang, Zhixin Liang, Long Hao, Zhipeng Gao, Jun Li, Qiang Wu, Hong Zhang, Yun Liu, Jian Sun and Jung-Fu Lin, published on 2 October 2023 in Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2309952120

The research was financially supported by the National Natural Science Foundation of China and the Geophysics Program of the National Science Foundation.

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More about Earth’s Inner Core Atomic Movement

• Proceedings of the National Academy of Sciences: Original Study
• The University of Texas at Austin: Geosciences Department
• National Natural Science Foundation of China
• Geophysics Program of the National Science Foundation
• NASA IMAGE Satellite Information
• Earth’s Magnetic Field and Geodynamo
• Introduction to Seismic Data
• Atomic Movement in Materials
• Laboratory Simulation Techniques
• Machine Learning in Geophysics