Deep within Earth lies a solid metal ball that rotates independently of our spinning planet. This inner core, discovered by Danish seismologist Inge Lehmann in 1936, has fascinated researchers for decades due to its mysterious behavior and elusive nature.
Unveiling the Core’s Motion
Earth’s deep interior remains inaccessible for direct observation, but seismologists study the inner core’s motion by examining earthquake waves as they pass through this area. Differences between waves of similar strengths that passed through the core at different times have helped scientists measure changes in the core’s position and calculate its spin.
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Dr. Lauren Waszek, a senior lecturer of physical sciences at James Cook University in Australia, noted that the idea of the core’s differential rotation was proposed in the 1970s and ’80s, but it wasn’t until the ‘90s that seismological evidence was published. However, researchers have since disagreed on the rate and direction of the core’s rotation.
New Insights into Core Dynamics
A promising model proposed in 2023 described the inner core as having spun faster than Earth in the past but now spinning slower. For a period, the core’s rotation matched Earth’s spin, then slowed even more, eventually moving backward relative to the fluid layers around it.
Recent research published on June 12 in the journal Nature supports this 2023 model. It confirms the core’s slowdown and suggests that this deceleration is part of a 70-year cycle of speeding up and slowing down. Dr. John Vidale, a co-author of the study and a professor at the University of Southern California, believes this new evidence ends the debate over the inner core’s movement patterns.
Inner Core’s Characteristics
The inner core, about 3,220 miles deep, is a solid ball of iron and nickel as hot as the sun’s surface. Earth’s magnetic field and the flow of the outer core and mantle influence its spin. However, changes in the core’s rotation speed might affect Earth’s magnetic field and slightly shorten the length of a day.
To track the inner core’s spin, scientists compared seismic waves from earthquakes occurring in the same locations at different times. They found 121 such examples between 1991 and 2023 in the South Sandwich Islands. These observations confirmed the 70-year rotation cycle, indicating that the core is about to start speeding up again.
Future Directions and Implications
Despite these findings, uncertainties remain. The core’s rotational speed varies in forward and backward motion, suggesting it might not be as solid as previously thought. More data and improved tools are needed to further investigate the core’s behavior and its impact on Earth’s magnetic field and day length.
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Scientists study the inner core to learn how Earth’s deep interior formed and how activity connects across all the planet’s subsurface layers. The mysterious region where the liquid outer core envelops the solid inner core is especially interesting, filled with potential for activity.