One of the key questions that has plagued Earth scientists for the past decade is “What’s going on down there?”
Below your feet, some 3,400 miles down, is the Earth’s inner core. It’s almost as big as the Moon, as hot as the Sun’s surface, and it helps maintain the planet’s magnetic field, which protects us from cancer-causing, cell-destroying cosmic radiation.
In the past decade, scientists have obtained some unusual data about the behavior of the inner core—data that suggests its rotation is going a bit out of whack.
The data suggest that in 2010 the inner core reversed its direction of rotation relative to Earth’s surface – a phenomenon called backtracking. Now the inner core rotates more slowly than before the shift.
There’s no risk of the catastrophic disaster of dead birds falling from the sky or sunburned skin in seconds, like in the 2003 blockbuster “The Core.” The most we might experience on the surface is a tiny lengthening of our days as rotation slows, but the change would be so small—we’re talking milliseconds—that we probably wouldn’t even notice.
A new study may settle the retreat debate
Scientists aren’t even sure what’s really going on down there. It’s not like we can open up a planet and explore it.
Backtracking has also not occurred in the last 40 years, so the possibility of such a massive object undergoing such an extreme change has been more of 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 even goes so far as to say they have the “most definitive evidence yet” that the inner core is indeed receding and moving more slowly.
“We’re showing that this is really happening when about half of the community didn’t believe any of these studies for a while,” John Vidale, a researcher involved in the study and dean’s professor of earth sciences at the University of Southern California. he told Business Insider.
Proving the inner core is coming back
John Vidale is part of new research that offers further evidence that the inner core is retreating. USC Photo/Stephen Gee
The research team analyzed and compared seismograms from more than 100 recurring earthquakes that occurred between 1991 and 2023 in the South Sandwich Islands in the South Atlantic Ocean.
Recurring earthquakes are seismic events with nearly identical magnitudes that occur at nearly the same location along the same fault. Seismic energy is one of the few ways we can study the inner core, because energy waves can travel from the surface, through the mantle, into the core, and back again, where scientists can detect and measure them.
Vidale and team looked at how well seismograms from repeated earthquakes correlated with each other.
“We can see changes in the seismogram curves as the inner core moves,” Vidale told BI.
Their approach offers “the most definitive evidence yet” that backtracking occurs, the team said in a paper published June 12 in the peer-reviewed journal Nature.
Scientists usually measure the time differences between seismic waves and how long it takes them to travel to the core and back. This can help map the core’s position and how it changes over time. But it comes with a lot of conjecture surrounding the structure of the inner core, “and we don’t really 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.
However, while we can say with more certainty that the inner core is receding and slowing down, it is difficult to calculate the exact rate of rotation or what is causing the shift in the first place.
More likely than not, the behavior of the inner core has to do with some kind of resistance or friction with the outer core or the gravitational influence of the Earth’s mantle, the researchers said in the paper.
Whatever the reason, there’s still a lot to learn about the massive object swirling beneath our feet.