Yang, Y. and Song, X. 2023. Multidecadal variation of the Earth’s inner-core rotation: Nature Geoscience, v.16. https://doi.org/10.1038/s41561-022-01112-z
What’s it about?
The Earth’s core is composed of two parts, the liquid (molten) outer core and the solid inner core. The inner core spins while floating in the outer core in the same direction, but not necessarily at the same speed, as the rest of the Earth.
Why does it matter?
The liquid outer core is the part of the Earth that generates the magnetic field. How the molten core flows is affected by interactions with its external contact with the solid mantle and the internal contact with the solid inner core. Changes in the flow of the outer core may result in subtle changes in the Earth’s magnetic field, which in turn affects life on Earth.
Why did I read this?
The Earth’s magnetic field serves as a shield against cosmic radiation. Periods of weakened magnetic field and increasing radiation could relate to burst of genetic mutation in Earth’s life forms. This would be evidenced by increases in species origination or extinction. How to correlate these things together may not be feasible, but it’s interesting to me, so this paper drew my eye.
What did I learn?
The headlines about this have been deceptive. Many have said things that make it sound like the inner core has stopped spinning or is spinning in reverse. The confusion is that all this is relative to the rest of the planet. That is to say that when it’s suggested the inner core has stopped spinning, that means it is spinning at the same pace as the rest of the Earth. When the inner core has ‘reversed’ its spin, this is a state called subrotation. The core is spinning in the same direction as the rest of the planet, but slower. Super-rotation is the case where the inner core is spinning faster than the rest of the planet.
The authors think they have discovered an oscillating pattern of super-rotation and subrotation. This pattern may also be related to periodic climate changes, including global mean temperature and global mean sea level. That is pretty darn interesting!