GeoGeoGeoGeo t1_j5suvl3 wrote
Reply to comment by thulesgold in Earth's inner core seems to be slowing its spin according to new research published in Nature Geoscience. The study authors suggest this might be part of an approximately 70-year cycle where the core speeds up and slows down relative to the rest of the planet. by shiruken
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.
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