Rotation pause in the Earth’s interior: The Earth’s inner core rotates more slowly

Deep inside our planet, at a depth of about 2900 kilometers, the Earth’s liquid core begins. In it, from a depth of 5150 kilometers, the solid core of the earth, which probably consists of an alloy of iron and nickel, swims as in a metal bath. Uncomfortable conditions prevail here: the temperature is about 6000 degrees Celsius, and the pressure reaches 330 gigapascals. The interaction of the Earth’s outer and inner core creates the Earth’s magnetic field, which protects us from cosmic rays.

Like the other layers of the earth, the inner core of the earth also revolves around the earth’s axis. However, it can move independently of the outer layers in its iron bath. In fact, based on what we know so far, it appears to be rotating slightly faster than the rest of the planet, about a degree per year.

However, this so-called super rotation, i.e. the offset in , does not remain constant. A study from more than a decade ago showed that the core rotates at 0.1-1 degree per million years, much slower than previously thought. Now, a new study by geoscientists at Beijing University has found that the rotation slowed even more recently.

Yi Yang and Xiaodong Song, who published their findings in the journal Nature Geoscience, analyzed several dozen earthquake waves between 1995 and 2020 that spread across the entire planet and thus through the Earth’s inner core. For the period from 2009 onwards, they concluded that the Earth’s core no longer rotated faster than the rest of the planet and the superrotation is now paused. They take this as an indication that the inner core could slow even further in the future and then rotate even more slowly than the outer layers.

There were also indications of a change in rotational behavior as early as the early 1970s. The temporal reversal of relative rotation was demonstrated by seismic waves from atomic bomb tests.

Yang and Song therefore hypothesize that the relative rotation of Earth’s inner core follows a cycle that reverses approximately every seven decades. Geophysicists believe that changes observed at the Earth’s surface may also have something to do with this cycle, such as small fluctuations in the magnetic field or small changes in the length of the day. However, for this connection to go beyond the status of a hypothesis, further research is needed. (i.e)