The solid swirling ball at the center of Earth’s inner core appears to have recently broken off and may now be spinning in the opposite direction from previous decades, according to a new study.
A pair of scientists from Peking University in China looked into the motions of Earth’s mysterious interior by studying seismic wave data from earthquakes that occurred in Earth’s inner core.
By watching the changes in these waves, they can get an idea of what is happening in the inner layers of the Earth, much deeper than any drill and tool can reach. Their data details the change in seismic waves over several decades, starting with records in Alaska from the early 1960s to records collected in 2021.
The data showed that parts of the core that previously showed clear signs of variation suddenly showed very little change around 2009, which they say suggests that the rotation of the inner core stopped.
They also noted notable changes in the tides that began in the early 1970s, suggesting that this pause was part of an oscillation that occurs every seven decades or so, when the inner core gradually returns to the opposite direction.
The inner workings of the Earth are a mysterious business
Its structure can be cut into four major layers: the outer crust, then the mostly solid mantle, followed by the liquid metal outer core and the final iron and nickel inner core.
Because the inner core is separated from the rest of the solid Earth by the liquid outer core, it can start a different rotation than the Earth’s surface. The direction of the inner core is governed by the magnetic field generated in the liquid metal outer core as well as by the gravitational effects of the mantle.
Many researchers previously argued that the planet’s inner geological layer rotates along with the rest of the planet at a slightly faster rate than the surface, but it is now believed to be less straightforward.
Last year, research suggested that Earth’s inner core oscillates, gently rocking and spinning from one direction to another in a cycle. Interestingly, they found some unusual data from the early 1970s, as did this new study.
The results suggested that the inner core slowly moved in a different direction between 1969 and 1971, under-rotating by at least a tenth of a degree per year compared to the direction it moved between 1971 and 1974.
“From our findings, we can see displacements of the Earth’s surface compared to its inner core, as people have claimed for 20 years,” said John E. Vidale, co-author of the study. “However, our latest observations show that the inner core rotated slightly more slowly between 1969-71 and then moved in the other direction from 1971-74.”
The strange movements of the Earth’s core might seem very distant to us, but its behavior actually has an influence on life above the surface.
The Earth’s core, especially its outer core, influences the planet’s magnetic field. Since the Magnetic North Pole was first scientifically documented in the early 19th century, it has wandered approximately 2,250 kilometers across the upper reaches of the Northern Hemisphere from Canada to Siberia.
Between 1990 and 2005, the rate of this movement accelerated from less than 15 kilometers per year to about 50 to 60 kilometers per year. This flow is likely to be the effect of two magnetic “blobs” of molten material inside the planet, causing a titanic change in its magnetic field.