The inner core of the Earth is located deep inside and extends for about 746 miles, according to NASA. It is primarily made of pure, solid iron. The inner core is thought to rotate, as evidenced by research, but a recent study contends that it may have "paused" or even reversed its spin.

Earth's outer core

Earth's magnetic field is produced by the liquid outer core that encircles the inner core. NASA claims that as the outer core's molten iron and nickel move, electrical currents are produced that result in a magnetic field. Nature explains that the outer core also enables the inner core to spin independently.

How is the core tracked?

Even though scientists cannot directly track the core, they can analyze seismic waves caused by earthquakes and Cold War-era nuclear weapon tests as they approach the core. That's what study co-authors Yi Yang and Xiaodong Song, both seismologists at Peking University in Beijing, did for their new study, which was published on Monday in the journal Nature Geoscience.

Yang and Song discovered that the inner core's rotation "paused" between 2009 and 2020, and may even be reversing "by a small amount," based on their analysis of seismic waves caused by similar earthquakes dating back to the 1960s.

Scientists warn against panic because this isn't the first time our inner core has stopped working. Instead, they believe the change is “associated with a gradual turning-back of the inner core as part of an approximately seven-decade oscillation.”

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What triggers such a rotation? 

Changes in the speed at which seismic waves travel through the inner core, according to seismologists, coincide "with changes in several other geophysical observations, especially the length of day and magnetic field," both of which are influenced by the inner core's movement, according to research.

While the changes are “valid,” what Yang and Song found may not be exactly what’s happening in the depths of our planet. A professor of earth sciences at the University of Southern California, John Vidale, that wasn’t involved in the study, noted “several competing ideas” about the Earth’s core in The Wall Street Journal.

This includes theories regarding the inner core reversing its rotation more frequently than the 70 years Yang and Song determined and that it stopped rotating in the early 2000s.  “No matter which model you like, there are some data that disagrees with it,” Vidale told The New York Times.

Vidale recently co-authored a study that showed the inner core changed its spin between 1969 and 1974, and that it seems to oscillate “a couple of kilometers every six years.”

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