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MistWeaver80 t1_j5na6ov wrote

Earthquake data hint that the inner core stopped rotating faster than the rest of the planet in 2009, but not all researchers agree.

>In 1996, Song and another researcher reported studying earthquakes that originated in the same region over three decades, and whose energy was detected by the same monitoring station thousands of kilometres away. Since the 1960s, the scientists said, the travel time of seismic waves emanating from those earthquakes had changed, indicating that the inner core rotates faster than the planet’s mantle, the layer just beyond the outer core.

>Later studies refined estimates of the rate of that ‘super-rotation’, to conclude that the inner core rotates faster than the mantle by about one-tenth of a degree per year. But not everyone agrees. Other work has suggested that super-rotation happens mostly in distinct periods, such as in the early 2000s, rather than being a continuous, steady phenomenon. Some scientists even argue that super-rotation does not exist, and that the differences in earthquake travel times are instead caused by physical changes on the surface of the inner core.

>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 ‘subrotated’, or rotated more slowly than the mantle5. Only after 1971, they say, did it speed up and begin to super-rotate.

>Now, Yang and Song say that the inner core has halted its spin relative to the mantle. They studied earthquakes mostly from between 1995 and 2021, and found that the inner core’s super-rotation had stopped around 2009. They observed the change at various points around the globe, which the researchers say confirms it is a true planet-wide phenomenon related to core rotation, and not just a local change on the inner core’s surface. The data hint that the inner core might even be in the process of shifting back towards subrotation. If so, something is probably happening to the magnetic and gravitational forces that drive the inner core’s rotation. Such changes might link the inner core to broader geophysical phenomena such as increases or decreases in the length of a day on Earth.


thulesgold t1_j5plwmb wrote

It doesn't make sense. First of all, there is considerable friction between the core and mantle so having a spin rate difference between them for billions of years is improbable. Second of all, the theory the core spins faster then slows down also makes no sense. It would imply there is an elastic oscillation between the core and mantle as they trade off angular momentum, but this is something we can measure... If the core slowed, then the mantle would speed up making the day shorter. Since I haven't heard news reports of drastic time changes every 70 years Imma gonna call BS on all this recent news on core spin.


GeoGeoGeoGeo t1_j5suvl3 wrote

There is a suggested different spin rate between the inner solid core and liquid outer core. The difference, however, is exceptionally small, and they both rotate at the same speed to within 0.001%.

The difference in speed is believed to be a result of two competing forces: The gravitational tug of the surrounding mantle, and the torque induced by the electromagnetic field from the outer core.

So when they report that its stopped spinning they mean relative to the mantle, same as when they say its reversed, and sped up.


thulesgold t1_j5sw160 wrote

Sure but slowing down the angular momentum of such a large mass would have noticable effects. For example, since the core is spinning at different velocities relative to the outer core then oscillates back to the original velocity then that energy would need to be banked in a magnetic field or some other means so that the energy is regained. We would see strong changes in Earth's magnetic field. Either way, billions of years of this happening would reduce this oscillation to nothing and affect the rate of the spin of the earth as a whole (beyond slowing due to tidal forces).

It might be interesting to think about the moon forming collision and there was an oscillation billions of years ago but much worse than it is today.


LordZon t1_j5t1d60 wrote

What if it isn't a cycle? Then the findings make more sense. Ie the core really is stopping.