Rotation of Earth's inner core has slowed down

   Study confirms the rotation of Earth's inner core is slowing down : Process started in 2010     

Movement of the inner core has been debated by the scientific community for two decades, with some research indicating that the inner core rotates faster than the planet's surface. The new USC study provides unambiguous evidence that the inner core began to decrease its speed, moving slower than the Earth's surface. This finding, published in the journal Nature, resolves a long-standing debate within the scientific community regarding the movement of our planet's innermost layer. Following are the some of the important points:-

This layer has a rich inner structure

The inner core is a solid iron-nickel sphere 

It influences the pattern of outer core convection

It also has a big role in maintaining Earth’s magnetic field

Scientists from the University of Southern California (USC) have made a ground breaking discovery that the Earth's inner core has been slowing down in relation to the planet's surface. The inner core began to decrease its speed around 2010, moving slower than the Earth’s surface. University of Southern California scientists have proven that the Earth's inner core is backtracking, slowing down, in relation to the planet's surface, as per the new research. This finding resolves a long-standing debate within the scientific community regarding the movement of our planet's innermost layer. This layer has a rich inner structure and influences the pattern of outer core convection and therefore Earth’s magnetic field. Earth has four main layers: the solid inner core, composed of iron and nickel; the liquid outer core, which generates the magnetic field; the viscous mantle, with convection currents driving plate tectonics; and the thin, solid crust, where life exists and geological activity occurs. 

"When I first saw the seismograms that hinted at this change, I was stumped," said John Vidale, Dean's Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences. "But when we found two dozen more observations signalling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades. Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution." The inner core, a solid iron-nickel sphere surrounded by the liquid outer core, is roughly the size of the moon and lies over 4,500 km's beneath our feet. It can't be visited or viewed. Scientists must use the seismic waves of earthquakes to create renderings of the inner core's movement. While it cannot be directly observed, researchers can study its behaviour by analysing seismic waves generated by earthquakes and nuclear tests. John Vidale, Dean's Professor of Earth Sciences at USC, and his team employed a unique approach, utilising waveforms and repeating earthquakes instead of relying on individual seismic events. 

The inner core is considered to be reversing and backtracking relative to the planet's surface due to moving slightly slower instead of faster than the Earth's mantle for the first time in approximately 40 years. Relative to its speed in previous decades, the inner core is slowing down. Seismic ray paths and event locations. a, Ray paths of PKIKP and PKP from the SSI source region to the two arrays (ILAR and YKA). The sampled IC region with a representative 1.5 Hz Fresnel zone is marked with dashed circles centered at the PKIKP pierce points at the ICB. Inset, the ray paths of PKP (PKP(AB) and PKP(BC)), PKiKP(CD) and PKIKP(DF). b, Map of the SSI region with the source locations coloured by focal depth. 

Vidale and Wei Wang of the Chinese Academy of Sciences utilized waveforms and repeating earthquakes in contrast to other research. Repeating earthquakes are seismic events which occur at the same location to produce identical seismograms. In this study, the researchers compiled and analysed seismic data recorded around the South Sandwich Islands from 121 repeating earthquakes that occurred between 1991 and 2023. They have also utilized data from twin Soviet nuclear tests between 1971 and 1974, as well as repeated French and American nuclear tests from other studies of the inner core.

Vidale said the inner core's slowing speed was caused by the churning of the liquid iron outer core which surrounds it, which generates Earth's magnetic field, as well as gravitational tugs from the dense regions of the overlying rocky mantle. The implications of this change in the inner core's movement for Earth's surface can only be speculated. Vidale said the backtracking of the inner core may alter the length of a day by fractions of a second: "It's very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere."

The inner core began to decrease its speed around 2010, moving slower than the Earth’s surface. According to Vidale, the inner core's deceleration is caused by the churning of the liquid outer core, which generates Earth's magnetic field, and gravitational tugs from the dense regions of the overlying rocky mantle. The implications for the planet's interior processes are yet to be fully understood. The USC scientists plan to continue their research, aiming to chart the inner core's trajectory in greater detail. As Vidale aptly stated, "The dance of the inner core might be even more lively than we know so far." The study not only resolves a long-standing scientific debate but also opens up new avenues for understanding the intricate dynamics of our planet's interior, with potential implications for Earth's magnetic field and rotational patterns. The USC scientists' future research aspires to chart the trajectory of the inner core in even greater detail to reveal exactly why it is shifting.