Scientists from the University of Southern California (USC) have made a groundbreaking discovery – the Earth's inner core has been slowing down in relation to the planet's surface since around 2010.
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.
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.
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 kilometers beneath our feet. While it cannot be directly observed, researchers can study its behavior 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.
They analysed data from 121 repeating earthquakes around the South Sandwich Islands between 1991 and 2023, as well as data from Soviet, French, and American nuclear tests.
"When I first saw the seismograms that hinted at this change, I was stumped," Vidale said. "But when we found two dozen more observations signaling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades."
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.
While the impact on Earth's surface is expected to be minimal, altering the length of a day by fractions of a second, 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 and unravel the reasons behind its shifting behavior. 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.
