Readers ask about Earth’s inner core, plant movement and more

Earth’s uneven layers

The rotation of Earth’s solid inner core may have recently paused relative to the mantle and crust and now appears to be reversing direction, Nikk Ogasa reported in “Earth’s inner core may ‘reverse’ its spin” (SN: 2/25/23, p. 7).

The inner core’s rotation is thought to be partly influenced by the mantle’s gravitational pull, Ogasa reported. Reader Robert G. Chester wondered how that could be true given the shell theorem, which states that a body inside a spherically symmetrical shell should experience a net-zero gravitational force.

The mantle indeed serves as a shell around the core.