The Earth’s core may have stopped spinning, or may even now be spinning backwards, according to a new study.
The core of our planet is made up of an outer layer of liquid metal, and an inner core of solid metal that is about 70 per cent the size of the Moon.
It is generally believed that the core rotates counter-clockwise when viewed from the North Pole, like the rest of planet Earth.
But a study analysing seismic wave data over the past 60 years by researchers at Peking University in China has concluded that the core’s rotation stopped around the year 2009, and then restarted in the opposite direction.
“We think that the core is, relative to the surface of the Earth, rotating in one direction and then the other, like a swing,” Xiaodong Song and Yi Yang, the study authors, told AFP.
A complete cycle (in one direction and then the other) of this swing is about 70 years, they added.
According to the researchers, the last rotation change before 2009 would have occurred in the early 1970s, and the next one will take place in the mid-2040s.
There is still much debate about the nature of the Earth’s core, because gathering information on it is extremely difficult.
The edge of the outer core meets the Earth’s mantle at a depth of around 2,890 km, and this outer core is believed to be made of liquid iron and nickel.
The inner core starts around 5,000 km below the surface of the planet, and is thought to be made of solid iron and nickel, due to the extreme pressure forcing the atoms of the metal to pack together.
It sits within the liquid outer core, and is believed to have been rotating in the same direction as the rest of Earth, based on analysis of seismic waves caused by earthquakes.
Xiaodong Song and Yi Yang studied these seismic waves, finding an associated “gradual turning-back of the inner core as part of an approximately seven-decade oscillation”.