- Scientists have been debating what happens to the Earth’s inner core for years.
- A new study provides compelling evidence that the inner core has changed direction and is slowing down.
- The shift occurred in 2010, but it is unclear what caused it or when the core will change again.
One of the major questions that has occupied Earth scientists over the past decade is, “What’s going on down there?”
Beneath your feet, some 3,400 miles deep, lies the Earth’s inner core. It’s nearly the size of the moon, as hot as the surface of the sun, and helps maintain the planet’s magnetic field, which protects us from cell-destroying, cancer-causing space radiation.
Over the past decade, scientists have gathered some unusual data about the behavior of the inner core, data that suggests its rotation is not quite right.
The data suggest that the inner core reversed its rotation direction relative to Earth’s surface in 2010 — a phenomenon called backtracking. Now the inner core is rotating more slowly than before the shift.
There is no risk of a catastrophic disaster with dead birds falling from the sky or skin-burning sunburns within seconds, as in the 2003 blockbuster “The Core.” The best we might experience on the Earth’s surface is a minuscule lengthening of our days as the rotation slows, but the change would be so small — we’re talking milliseconds — that we probably wouldn’t even notice.
New research could settle debate over rollback
Scientists don’t even know what’s really going on down there. It’s not like we can crack open the planet and explore it.
Furthermore, there has been no talk of going back in time in the last 40 years, so the possibility of such a large object undergoing such an extreme change is more a matter of debate than a scientific certainty.
But a recent study offers a new way of looking at the data that could help settle the debate. The research team behind the study goes so far as to say that they have the “most definitive evidence” yet that the inner core is indeed receding and moving more slowly.
“We show that it’s really happening, whereas for a while about half the community didn’t believe any of these studies,” John Vidale, a researcher involved in the study and a professor of earth sciences at the University of Southern California, told Business Insider.
Evidence that the inner core is going back
The research team analyzed and compared seismograms from more than 100 repeating earthquakes that occurred between 1991 and 2023 in the South Sandwich Islands in the South Atlantic Ocean.
Repeating earthquakes are seismic events with nearly identical magnitudes that occur at nearly the exact same location, along the same fault line. Seismic energy is one of the few ways we can study the inner core, because the energy waves can travel from the surface, through the mantle, to the core and back again, where scientists can detect and measure it.
Vidale and the team looked at how well the seismograms from recurring earthquakes correlated with each other.
“We can see changes in the waveforms of the seismograms as the inner core moves,” Vidale told BI.
Their approach provides “the most definitive evidence yet” that backtracking occurs, the team reported in a paper published June 12 in the journal Nature.
Typically, scientists measure the time differences between seismic waves and how long it takes to travel to the core and back. This can help map the position of the core and how it changes over time. But it involves a lot of guesswork about the structure of the inner core, “and we don’t know the structure down there that well,” Vidale told BI.
The team’s new method doesn’t require that kind of guesswork, because they simply looked at how well the seismograms matched.
But even if we can say with more certainty that the inner core is receding and slowing down, it’s difficult to calculate the exact rotation rate or figure out what’s causing the shift in the first place.
The researchers write in the paper that the behavior of the inner core is most likely related to some kind of friction with the outer core or to the influence of the Earth’s mantle’s gravity.
Whatever the reason, we still have a lot to learn about the massive object moving beneath our feet.