Produced by: BT Desk Designed by: Manoj Kumar
While we understand Earth’s surface, the deeper layers remain mysterious. One key question involves the movement of the inner core—forward, backward, or even side to side? A new study may have the answer.
A study published in Nature suggests Earth’s inner core is backtracking relative to the surface, supporting a controversial finding from last year by Peking University researchers.
The Earth’s inner core is a solid, crystallized iron sphere about the size of the Moon, floating in a sea of molten iron and nickel, known as the outer core. The core’s movement has long been debated.
"Nothing holds the core in place," says Prof. John Vidale of USC. He explains that scientists have argued over the core’s movement since the 1990s, but this new study may settle the debate.
The study provides strong evidence that the core slowed around 2010, creating the illusion that it’s moving backward relative to the surface, much like how a slower car appears to reverse from a fast-moving driver’s perspective.
If the findings are correct, this marks the first observed slowdown in 40 years and supports the theory that the core’s movement follows a 70-year cycle of speeding up and slowing down.
Researchers studied 121 earthquakes from 1991 to 2023, along with Soviet-era nuclear test data, to track the core's motion. Seismic waveforms revealed patterns indicating the core’s changing rotation.
The study found that if the core had reversed rotation, seismic waves would match earlier patterns, confirming the core realigned with its past movement path—a crucial discovery.
While the core’s movement is dramatic deep below, its surface effects are minimal. Vidale notes it might change the length of a day by a thousandth of a second, almost unnoticeable amidst oceanic and atmospheric noise.
The team plans to measure more seismic waveforms and continue monitoring the core's motion. As Vidale says, “The core is moving back through some positions where it did weird things, and we aim to uncover more.”