Earth’s Inner Core Slows Down Its Spin; How Can It Affect Length of a Day?

Scientists have confirmed that the rotation of the Earth's inner core has slowed down, or perhaps even lagging. This raises the question as to what is happening in the center of the Earth and how humans might be affected.

Layers of the Earth

The Earth is made up of several layers, namely, crust, mantle, outer core, and inner core. Each of them has distinct characteristics and compositions.

The crust is the outermost layer of our planet, and it varies in thickness from 3 to 44 miles (4.8 to 70.8 kilometers). Beneath this layer is the mantle which extends up to 1,800 miles (2,896.8 kilometers) deep. The mantle is composed of liquid iron and nickel whose movement generates the magnetic field of the Earth.

Meanwhile, the inner core of the Earth is the innermost layer, which measures 760 miles (1,223 kilometers) wide. It is the same size as the moon and is made of a solid sphere of iron and nickel located at the center of the Earth.

Slowing Rotation

The inner core was previously thought to be rotating faster compared to the speed of the Earth's surface. However, it has begun to slow down since 2010, according to the study "Inner core backtracking by seismic waveform change reversals."

For a time in decades, our planet's inner core was found to be spinning slower than the surface. Scientists assume that this might lead to possible changes in the length of our days.

John Vidale, professor of Earth Sciences at the University of Southern California (USC) Dornsife College of Letters, Arts and Sciences, was one of the first to see the seismograms that hinted at this change. According to him, the result was inescapable when they discovered two dozen more observations that signal the same pattern.

While other experts argue for similar and different models, Vidale believes that the latest study offers the most convincing resolution. Because of the immense depth of the inner within the Earth, experts must depend on the seismic waves of earthquakes to investigate its motion.

In this study, the research team described the analysis they made on the seismic data from 121 repeating earthquakes from 1991 and 2023 near the South Sandwich Islands in the South Atlantic Ocean. They also studied data from different nuclear tests.

The team discovered that the inner core was slowing down its movement due to the churning of the liquid in the outer core, in addition to the gravitational pulling from the mantle. It could result in slight changes to the length of a day, but only fractions of a second.

As noted by the authors, this change is very hard to notice, on the order of a thousandth of a second. As a matter of fact, it may get lost in the noise of the churning oceans and atmosphere.

In the future, the research team plans to investigate further why the Earth's inner core is slowing down. They also aim to study the effects that this may have on the planet and humans.