One of the main questions that has plagued Earth scientists over the past decade is “What’s going on down there?”
Beneath your feet, some 3,400 miles down, is 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 that protects us from cancer-causing, cell-wiping space radiation.
In the last decade, scientists have obtained some unusual data about the behavior of the inner core – data that suggest that its rotation is going slightly off course.
The data imply that in 2010, the inner core reversed its direction of rotation relative to the Earth’s surface – a phenomenon called retrograde. Now, the inner core is spinning more slowly than before the switch.
There is no risk of a cataclysmic catastrophe of dead birds falling from the sky or sunburns that cause skin in seconds, as in the 2003 film The Core. The most we can experience on the surface is an extension of small on our days as the rotation slows down, but the difference would be so small – we’re talking milliseconds – that we probably wouldn’t even notice.
The new study may settle the debate back
Scientists aren’t even sure what’s really going on down there. It’s not like we can open up the planet and examine it.
The retrograde also hasn’t happened in the last 40 years, so the possibility of such a massive object undergoing such an extreme change has been more a topic of debate than a scientific certainty.
But a recent study offers a new way of looking at the data that may help settle the debate. The research team behind the study even goes so far as to say they have the “most conclusive evidence” yet that the inner core is, indeed, receding and moving more slowly.
“We’re showing that it really does happen when about half the community didn’t believe any of these studies for a while,” John Vidale, a researcher involved in the study and the dean’s professor of Earth sciences at the University of Southern California. said Business Insider.
The verification of the inner core is being withdrawn
John Vidale is part of new research that provides more evidence for the notion that the inner core is moving back. USC Photo/Stephen Gee
The research team analyzed and compared seismograms from over 100 repeated earthquakes that occurred between 1991 and 2023 in the South Sandwich Islands in the South Atlantic Ocean.
Repeated earthquakes are seismic events of nearly identical magnitude that occur in nearly the same location, along the same fault. Seismic energy is one of the few ways we can study the inner core, because waves of energy can travel from the surface, through the mantle, into the core, and back again, where scientists can detect and measure it.
Vidale and team looked at how well seismograms from repeated 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 conclusive evidence yet” that the reversal is occurring, the team reported in a paper published June 12 in the peer-reviewed journal Nature.
Typically, scientists 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 assumptions about the structure of the inner core, “and we don’t really know the structure down there,” Vidale told BI.
The team’s new method doesn’t require that kind of guesswork because they were just looking at how well the seismograms matched.
However, even if we can say with more certainty that the inner core is spinning back and slowing down, it is difficult to calculate the exact rotation speed or what is causing the drift in the first place.
More likely than not, the behavior of the inner core has to do with some sort of pull or friction with the outer core or gravitational influence from the Earth’s mantle, the researchers reported in the paper.
Whatever the reason, there’s still a lot we need to learn about the massive object that wobbles beneath our feet.