The Mysterious Slowdown & Reversal of Earth’s Inner Core: New Research Unveils 70-Year Rotational Cycle

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Recent scientific discoveries have unveiled that Earth’s inner core, a solid metal ball spinning independently within our planet, has significantly slowed down and is now moving in reverse. This groundbreaking revelation, published in the prestigious journal Nature, highlights a 70-year cycle in the core’s rotational speed.
The Mysterious Slowdown and Reversal of Earth's inner core: New Research Unveils 70-Year Rotational Cycle

The Earth’s inner core was first discovered by Danish seismologist Inge Lehmann in 1936. This solid metal ball, composed primarily of iron and nickel, lies about 3,220 miles (5,180 kilometers) beneath the Earth’s surface. Its temperature rivals that of the sun, reaching approximately 9,800 degrees Fahrenheit (5,400 degrees Celsius). The core is surrounded by a liquid metal outer core, and the dynamics between these layers have long intrigued scientists.

Since its discovery, the movement of the inner core, including its rotation speed and direction, has fascinated researchers. Seismic data have been crucial in studying this phenomenon, as direct observation or sampling of Earth’s deep interior is impossible. Scientists have used seismic waves generated by large earthquakes to gather information about the inner core’s motion.

The 70-Year Rotational Cycle

Recent research has confirmed a 70-year cycle in the rotational speed of the Earth’s inner core. This discovery is significant because it provides a clearer understanding of the complex interplay of forces influencing the core’s motion. According to the study, the core’s rotation has changed significantly in recent years, with evidence suggesting that it previously spun faster than Earth itself but has now slowed down and is rotating in the opposite direction.

Dr. John Vidale, a co-author of the study and Dean’s Professor of Earth Sciences at the University of Southern California, explains, “We’ve been arguing about this for 20 years, and I think this nails it. I think we’ve ended the debate on whether the inner core moves and what’s been its pattern for the last couple of decades.”

Seismic Data and Observations

To arrive at these conclusions, researchers examined seismic waves produced by earthquakes in the same locations at different times. The South Sandwich Islands are an archipelago of volcanic islands in the Atlantic Ocean, and they discovered 121 instances of these earthquakes taking place there between 1991 and 2023. Additionally, they analyzed core-penetrating shock waves from Soviet nuclear tests conducted between 1971 and 1974.

The seismic data revealed changes in the core’s rotation over time, confirming the 70-year rotation cycle. Dr. Vidale notes that the core is now spinning much slower and accelerates at different rates, suggesting that the metal inner core might not be as solid as previously thought. This deformation could affect the symmetry of its rotational speed.

Implications for Earth’s Magnetic Field

One of the significant questions arising from the core’s slowdown and reversal is its impact on Earth’s magnetic field. The movement of metal-rich fluid in the outer core generates electrical currents that power the magnetic field, which protects our planet from harmful solar radiation. While the inner core’s direct influence on the magnetic field is not fully understood, scientists have reported that a slower-spinning core could potentially affect it and also slightly shorten the length of a day.

Earth’s magnetic field yanks at the solid ball of hot metal, causing it to spin. The core is also dragged at the same time by gravity and the movement of the fluid outer core and mantle. These forces exert pressure on one another, causing fluctuations in the spinning speed of the core over many decades.

Day lengthening occurs when the Earth rotates faster due to increased mantle speed caused by the slower core rotation. However, these rotational shifts translate to mere thousandths of a second in day length, making them imperceptible to people on Earth’s surface.

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Earth's inner core

The Challenges of Studying the Inner Core

Studying Earth’s inner core presents numerous challenges due to its depth and inaccessibility. By analyzing the behavior of seismic waves from massive earthquakes that reach the inner core, seismologists are able to obtain information. Scientists have measured variations in the inner core’s position and calculated its spin by comparing waves of similar intensity that travelled through the core at different times.

The scientific community remains divided on the implications of the inner core’s slowdown. While Dr. Vidale believes the new research ends the debate on the core’s movement and its 70-year cycle, other experts call for more data to confirm these findings. The primary challenge lies in the core’s inaccessibility and the limited available data.

Dr. Lauren Waszek, senior lecturer in physical sciences at James Cook University in Australia, points out that the inner core’s remote location makes it challenging to understand its behavior. The inner core’s rotation has been debated for decades, with some analyses suggesting it doesn’t rotate at all.

Future Research and Implications

The recent findings have provided valuable insights into the behavior of Earth’s inner core, but many questions remain unanswered. Researchers are particularly interested in understanding how the core’s rotation influences other subsurface layers and the overall structure of the planet. The boundary where the liquid outer core envelops the solid inner core is of particular interest, as it is a region filled with potential for activity.

“We might have volcanoes on the inner core boundary, for example, where solid and fluid are meeting and moving,” Dr. Vidale suggests. Although further investigation is needed to determine its exact function, inner core rotation is believed to contribute to Earth’s magnetic field because it influences movement in the outer core.

Conclusion

The discovery of the 70-year cycle in Earth’s inner core rotation marks a significant advancement in our understanding of the planet’s deep interior. While the implications for Earth’s magnetic field and day length are still under investigation, this research highlights the complex interplay of forces influencing the core’s motion.

As scientists gather more data and refine their models, they hope to unravel the mysteries of the inner core and its impact on our planet.

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