Geophysicist John Vidale noticed something striking while tracking the way seismic waves move from Earth’s crust through its core.

The very center of the planet, a solid ball of iron and nickel floating in a sea of molten rock, appears to be slowing down in relation to the movement of Earth itself. The inner core has slowed so much that it has essentially kicked into reverse.

The finding by Vidale and his counterpart Wei Wang of the Chinese Academy of Sciences, published recently in the journal Nature, offers the most convincing evidence yet that the core seems to operate with a mind of its own.

“It might be cycling back and forth but it might also be on a random walk,” Vidale said. “It went one way for a while, then it’s going back the other way. Who knows what it’s going to do next?”

The fluctuations happening 3,000 miles beneath us won’t affect life on the planet’s surface in any noticeable way — at least not for now, Vidale said.

“There’s essentially no effect on people, from what we’ve seen,” said Vidale, who is Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences. “It’s a part of basically understanding the evolution of the planet. What we’d also like to know in more detail is what are the forces that are moving the inner core.”

Scientists first had a hunch that the inner core was moving in the 1990s, he said. It has taken years to back up that theory with hard evidence, mainly because of the difficulty of studying a mass located so far out of reach — and suspended inside a hellish sea of liquid iron that’s between 8,000 and 10,000 degrees.

Instead, Vidale, who was director of the Southern California Earthquake Center at USC from 2017 to 2018, peered into the planet by tracking seismic waves from quakes occurring off the lower tip of South America. As the waves passed through the heart of the planet, they were recorded on 400 seismometers positioned at the other end of the globe in Alaska and Northern Canada. The sensors were the same kind used to measure ground vibrations during nuclear tests.

He compared those refined readings to quake signals recorded in past years to see where they matched. That’s how he determined that the rotation has been decreasing since 2010. Prior to that, the core’s spin had been accelerating.

The findings add to the mystique of the most inscrutable part of our world, Vidale said. Literature and lore involving Earth’s core have filled the knowledge void with all sorts of fanciful ideas.

“I’m not such a philosopher but we’ve all had nightmares of what’s going on down in the planet,” Vidale said. “Just a couple hundred years ago, people thought the planet was hollow and that there were people living down there. It’s pretty exotic — exotic like Jupiter, but it’s just right under our feet.”

In Jules Verne’s 1864 science-fiction classic “Journey to the Center of the Earth,” a German professor, his nephew and their guide descend into the planet through a volcano in Iceland — along the way encountering caverns, a subterranean ocean, living dinosaurs, strange sea creatures and even a prehistoric giant herding mastodons — and are finally spat out through a volcano off the coast of Sicily.

The 2003 disaster film “The Core” imagines that the rotation of Earth’s center has stalled, damaging the magnetic field that envelops the planet — and triggering a violent lightning storm that destroys Rome and “invisible microwaves” that melt the Golden Gate Bridge. A hotshot crew of scientists burrows down through Earth’s layers to jump-start the core with a nuclear bomb.

In the real world, no human could survive the unimaginable heat and bone-crushing pressure, even if there were a vehicle capable of tunneling to the core, Vidale said.

It is true that the outer core generates electrical currents that sustain the planet’s magnetic field, but Vidale says shifts in the Texas-size inner core are too minuscule to have an impact.

While the planet’s subterranean reality is less fantastical than novels and Hollywood movies make it out to be, it is still fascinating to those like Vidale whose job is to counter conjecture with facts.

What is increasingly clear is that the inner core is susceptible in different ways to activity in the layers of Earth that encircle it.

“The mechanics are that the outer core is circulating and making a magnetic field, and so it’s kind of pulling the inner core back and forth,” Vidale said.

The latest discoveries about the inner core have fueled vigorous disagreements among the world’s top Earth scientists, USC’s John Vidale says. Some don’t believe the core turns at all.

(Christina House/Los Angeles Times)

Another player in the endless tug-of-war taking place inside the planet is the lower level of the planet’s mantle, whose mix of hard and less-dense matter results in its own peculiar magnetic pull, Vidale said.

“We sort of think the outer core is stirring up the inner core, but the mantle’s trying to keep it aligned — maybe that’s why it’s oscillating,” he said.

The latest discoveries about the inner core have fueled vigorous disagreements among the world’s top Earth scientists and given rise to competing theories of varying credibility, Vidale says. Some don’t believe the core turns at all. Some insist that forces on the surface, such as quakes, briefly alter the rotation.

Over the phone, Vidale reads a review from a scientist in Australia who greeted Vidale’s recent findings with much skepticism. The Australian proclaims that the analysis will lead to “the erosion of seismology as a credible branch of science and the destruction of seismologists as credible researchers.”

“I think he’s just frustrated — he knows he’s lost,” Vidale said, gently ribbing his peer.

“It’s exciting because the core is pretty big, it’s moving by measurable amounts and it’s a mystery,” Vidale said. “We’re making progress and seeing more things, arguing with people around the world and trying to get more data … What our paper’s done is it’s convinced most of the community.”