Scientists say Earth’s core has stopped spinning, but it’s too soon to panic – it’s changing direction

A new theory explains 70-year cycles that affect the length of days and the planet’s magnetic field. Analysis initially showed that the spin of the inner core relative to the surface was accelerating, but it almost stopped around 2009. Now it’s slowly starting to move in the opposite direction, says Song Xiaodong, a geophysicist at Peking University.

what is known

Beneath our planet’s crust are masses of molten rock that are in constant motion, and beneath it is a liquid outer core. Metals responsible for the magnetic field circulate here. At its very center, a solid metal ball nearly the size of the Moon—the inner core—spins.

Early investigations showed that the rotation of the inner core is due to the moment of magnetic force (rotational moment or torque) originating from the outer core. There is also evidence that the strong gravitational force of the mantle could act as a kind of brake on the rotation of the inner core, causing it to oscillate.

The first hints of such fluctuations appeared as early as 1996. A study of seismic waves at the time showed that it takes varying amounts of time to travel through the Earth’s core over a 30-year period.

• Geophysicists concluded that the rotational speed of the inner core differs from the rotational speed of the mantle and crust – higher.
• However, some scientists doubted that they had their own calculations. They stated that the nucleus rotates more slowly on the reverse.
• Still others said there was generally no difference in the rotational speed of the core and the rest of the planet.

Song Xiaodong and colleagues made a new discovery by analyzing data from the past 30 years. Until 2009, seismic waves produced sequences and repeating pairs of earthquakes moving at different speeds through the inner core. This means that, according to past findings, waves passed through different parts of this core and rotated at a different speed than Earth’s. In 2009 these differences disappeared – the inner core stopped moving relative to the mantle and crust. And then the movement started again, but already in the opposite direction.