Earth’s inner core, a solid metal ball that is 75 percent the size of the Moon, may have recently stopped spinning and may now be reversing the direction of its rotation, according to a new study published in Nature Geoscience. The study, conducted by researchers at Peking University’s SinoProbe Lab at the School of Earth and Space Sciences, used seismic waves from earthquakes to probe the inner core and found that it may be experiencing a periodic cycle of rotation reversal lasting about 60 to 70 years.
This is a significant discovery as it might solve longstanding mysteries about climate and geological phenomena that occur on a similar timeframe and affect life on our planet. The inner core is located some 3,000 miles beneath the Earth’s surface and experiences intense heat on par with the surface of the Sun. Because it is so remote and difficult to study, the inner core remains one of the least understood environments on our planet, despite playing a role in many processes that make our world habitable to life such as the generation of Earth’s protective magnetic field.
The study’s lead authors, Yi Yang and Xiaodong Song, explain that there are two major forces acting on the inner core: the electromagnetic force and the gravity force. The Earth’s magnetic field is generated by fluid motion in the outer core, and the magnetic field acting on the metallic inner core is expected to drive the inner core to rotate by electromagnetic coupling. On the other hand, the mantle and inner core are both highly heterogeneous, so the gravity between their structures tends to drag the inner core to the position of gravitational equilibrium, known as gravitational coupling.
If the two forces are not balanced out, the inner core will accelerate or decelerate. Both the magnetic field and the Earth’s rotation have a strong periodicity of 60-70 years. The authors believe that the proposed 70-year oscillation of the inner core is driven by the electromagnetic and gravitational forces. The study’s authors also added that this is not the first time that scientists have observed the inner core rotation, but the origin of the temporal changes has been a matter of debate within the geoscience community ever since, as some scientists think the wave patterns arise from phenomena at the boundary between the outer and inner core.
It’s important to note that while the inner core’s rotation influences Earth’s surface environment, scientists think this periodic spin switch is a normal part of the inner core’s behavior and does not pose risks for life on Earth. This study provides a new insight into the inner workings of our planet and further research is needed to understand the full implications of this discovery.
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