Seismic data revealed that the Earth’s inner core began to rotate more and more slowly, even slower than the surface layer.
Compared to the Earth’s surface speed, the inner core was previously thought to rotate faster. However, since 2010, it began to rotate slowly, according to research published in the journal Nature, Newsweek reported on June 14. The inner core now rotates more slowly than the surface layer for the first time in decades, and this could lead to changes in the length of the day.
“When I first saw the seismogram revealing this change, I was amazed,” said John Vidale, professor of Earth Sciences in the USC Dornsife College of Letters, Arts and Sciences. “But when we found dozens of other observations signaling the same pattern, the results were robust.”
The Earth consists of several layers: the crust, mantle, outer core and inner core, each layer has its own characteristics and structure. The crust is the outermost layer of the Earth and has a thickness between 4.8 – 70.8 km. Below the crust is the mantle, reaching a depth of about 2,896 km, composed mainly of silicate minerals rich in iron and magnesium. The outer core lies beneath the mantle, at depths from 2,896 km to 5,149 km, and is composed largely of liquid iron and nickel. The movement of the outer core creates the Earth’s magnetic field.
The inner core is the innermost layer of the Earth with a radius of about 1,223 km, equivalent to the size of the Moon, and is a solid sphere of iron and nickel in the center of the planet. Because it is located at extreme depths inside the Earth, scientists must rely on seismic waves from earthquakes to study the movement of the inner core. In the paper, the team describes how they analyzed seismic data from 121 earthquakes between 1991 and 2023 near the South Sandwich Islands in the South Atlantic, as well as data from multiple nuclear tests.
They found that the inner core is slowing down, resulting from the churning of liquid in the outer core, combined with gravitational pull from the mantle. This can lead to small changes in day length, as small as a few fractions of a second. The research team hopes that deeper drilling results will reveal exactly why the Earth’s core is slowing down and its effects on the planet.