The Earth's core is the very center of our planet and is composed mainly of iron and nickel. It is divided into two layers: the inner core, which is solid, and the outer core, which is liquid. The inner core is about the size of the Moon and has a temperature of around 5700 degrees Celsius (10,000 degrees Fahrenheit), while the outer core is about 2200 kilometers (1367 miles) thick and has a temperature of around 4400 degrees Celsius (7912 degrees Fahrenheit).

The core plays a crucial role in maintaining the Earth's magnetic field, which protects us from harmful solar radiation. This magnetic field is generated by the motion of the liquid outer core, which creates a dynamo effect. The outer core also plays a role in the Earth's tectonic activity, as it is the source of the heat that drives plate tectonics.

The Earth's core also plays a role in the planet's rotation. The inner core spins at a slightly faster rate than the rest of the planet, which helps to balance the Earth's rotation and maintain its stability. The exact speed at which the inner core spins is not known, but estimates suggest it is around 0.5 to 1 degree per year faster than the rest of the planet.

A 1996 study in Nature revealed that the travel times of seismic waves that traverse the Earth's inner core show a small but systematic variation over the past three decades. This variation is best explained by a rotation of the inner core and the rotation rate is on the order of 1° per year faster than the daily rotation of the mantle and crust.

The team from Peaking University analyzed earthquakes mostly from between 1995 and 2021 and the analysis revealed that sometime around 2009 the core stopped spinning and might be in the process of changing the spinning direction.

The study of the Earth's core is important for understanding how our planet formed and evolved. It also has practical applications, such as in the field of geophysics, where knowledge of the core's properties can be used to study earthquakes and volcanic activity. Additionally, understanding the dynamics of the core can help scientists predict changes in the Earth's magnetic field, which can have significant impacts on technology such as GPS and communication systems.

Scientists have revealed that the inner core of our planet has slowed down simply because it's tired of circling in the same direction for decades. And now, it's time for a change.

The study by scientists from Beijing's Peking University has revealed that sometime in the past decade, Earth's inner core (which usually spins faster in relation to the mantle) stopped doing so! Instead, it appears to be reversing the direction of its spin.

It was less than a decade ago when Xiaodong Song and fellow seismologist Paul Richards at Columbia University confirmed that the Earth's inner core, roughly 5,000 kilometers (3,100 miles) below the surface, can spin independently.

The researchers learned about the inner core's rotation by tracking seismic wave readings from repeated earthquakes that traveled through the inner core — from the South Atlantic to Alaska between 1967 and 1995.

Subsequently, they found that the quakes all originated in the same region, but the travel time of seismic waves stemming from those earthquakes had changed. This indicated that the inner core's rotation was faster compared to the planet's mantle.

Now, in this new study, geophysicists have revisited the data from the 1960s to 1990s and compared it with more recent seismic patterns. Their observations show that Earth’s inner core has paused its movements and may even be reversing the direction of its spin.

The patterns suggest that inner core rotation paused sometime around 2009. Interestingly enough, this isn’t the first time such an event has been recorded!

It turns out that Earth's inner core behaves like a swing, moving back and forth. One cycle of this swing lasts for almost seven decades, implying that every 35 years, the inner core undergoes rotation reversal. Such a phenomenon previously transpired around the 1970s, and the next change in direction may occur around the 2040s.

In fact, this seven-decade oscillation also seems to coincide with changes in the Earth's magnetic and gravitational fields, along with broader geophysical phenomena that impact the length of the day.

"These observations provide evidence for dynamic interactions between the Earth's layers, from the deepest interior to the surface," conclude Yang and Song, the co-authors of the study.

They have also hinted at "a resonance system across different Earth layers" – as if the planet's heart is thrumming to the same beat despite complex interactions and networks controlling a range of phenomena in this complex world.

This study was published in the journal Nature Geoscience and can be accessed "here"

Last June, Vidale and Wei Wang, an Earth scientist also at the University of Southern California, threw another spanner into the works. Using data on seismic waves generated by US nuclear test blasts in 1969 and 1971, they reported that between those years, Earth’s inner core had ‘subrogated’, or rotated more slowly than the mantle5. Only after 1971, they say, did it speed up and begin to super-rotate.

Hrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the inner core's cycle is every 20 to 30 years, rather than the 70 proposed in the latest study.

"These mathematical models are most likely all incorrect because they explain the observed data but are not required by the data," Tkalcic said.

"Therefore, the geophysical community will be divided about this finding and the topic will remain controversial."

He compared seismologists to doctors "who study the internal organs of patients' bodies using imperfect or limited equipment".

Lacking something like a CT scan, "our image of the inner Earth is still blurry", he said, predicting more surprises ahead.

That could include more about a theory that the inner core might have yet another iron ball inside it -- like a Russian doll.

"Something's happening and I think we're gonna figure it out," Vidale said.