Did Earth’s inner core change its rotation?
Planet Earth is made up of several layers which are, from the most external to the most internal, the crust, the mantle, the outer core, and the inner core. The latter is located at about 5000 km below the surface, mainly made of iron, and measures about 2,400 km in diameter. The inner core can rotate in the outer core because the latter is composed of iron and nickel in a liquid state. The solid nature of the inner core is due to the increase in pressure with depth.
The inner core’s rotation is known to be created by the magnetic field of the outer core and the gravitational force of the mantle. This paper published a few days ago by a Chinese team concluded that the difference in rotation speed between the core and the mantle would have been almost zero around 2009 and would have increased in the opposite direction since then, based on very precise analyses of the speed of seismic waves passing through the core. Moreover, the rotation’s direction would change with respect to the surface every 35 years or so, as the last one would be in the early 1970s. However, a previous study had suggested a much shorter time between two oscillations.
This subject is still a great source of debate among experts, and the differences in results do not yet allow for clear conclusions. New research will undoubtedly be carried out in the coming years in order to be able to solve this mystery one day.