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View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
No, the inner core has definitely not reversed direction. Most of those headlines were extremely misleading, if not outright nonsense. The dynamo is also not generated by the inner core spinning within the outer core.
The inner core had generally been thought to be rotating *very slightly* faster than the overlying liquid outer core and solid mantle/crust, caused to do so by forces in the outer core (roughly analogous to a type of electric motor). This difference in rotational would amount to a few degrees per year at most--possibly much less. What the new paper argues, instead, is that the core oscillates between rotating slightly faster than and slightly slower than the outer core on a ~70 year cycle, and is currently on the slower part of that cycle. The inner core always rotates eastwards, completing a rotation roughly every 23 hours and 56 minutes[1]. Just according to this paper it is now doing so slightly slower than the rest of Earth--for example every 23 hours and 57 minutes. (Rotation involves acceleration, and so unlike linear velocity, is absolute. This cycle would be completely different from any geomagnetic reversals ("pole flip"), and is really only of academic interest.
Earth's magnetic field is generated within the liquid outer core. Convection currents in the liquid iron-rich metal are twisted into columns as a result of Earth's rotation, and this motion of the electrically conductive fluid sustains the dynamo. (See dynamo theory[2].) Over the past ~500-1500 million years since the inner core first formed, the gradual freezing of the outer core to grow the inner core has powered Earth's dynamo.* However, the inner core itself doesn't play an active role.
2: https://en.wikipedia.org/wiki/Dynamo_theory
Earth had a dynamo for most or all of its history, In general, a solid inner core isn't necessary for a rocky planet to have a dynamo. Dynamos of non-terrestrial bodies work via different mechanisms and in different materials, but in general there is some kind of motion (usually, but not necessarily, convection) of an electrically conductive fluid, which requires a source of energy (and entropy). For example, Jupiter's dynamo is generated by convection of the liquid metallic hydrogen that makes up the vast majority of its interior. (Whether Jupiter even has a solid(-ish), rock/metal core isn't clear, and if it does, there certainly isn't a clear transition point from liquid to solid.) Stellar magnetic fields are generated by convection in their hydrogen-helium plasma interiors.
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