Generally regarded as one of the worst ‘science’ movies ever made, The Core is so bad that it caused a government response. The Science & Entertainment Exchange, a National Academy of Sciences programme that connects entertainment industry workers with scientists and engineers to promote better science in movies and television, was the direct result of The Core’s un-scientific awfulness.
The basic plot is: the Earth’s core stops rotating, and the planet’s ‘electromagnetic’ field collapses. People with pacemakers suddenly drop dead, lightning strikes cause Rome’s Colosseum to explode and the Pacific Ocean begins to boil. If they don’t restart the core, all life on Earth will end.
To which end, the movie’s intrepid scientists build a burrowing ship out of ‘unobtanium’ and tunnel to the core to restart it… with nuclear bombs.
As it happens, The Core got one thing right: the Earth’s core can – and has – slowed down and even stopped moving in relation to the Earth’s crust. In fact, it may have reversed spin completely.
What’s going on?
Deep inside Earth is a solid metal ball that rotates independently of our spinning planet, like a top whirling around inside a bigger top, shrouded in mystery.
Of course the Earth’s core is impossible for us to observe or sample directly. Like a gigantic submarine active sonar ping, seismologists examine how waves from large earthquakes travel through the Earth.
Variations between waves of similar strengths that passed through the core at different times enabled scientists to measure changes in the inner core’s position and calculate its spin.
“Differential rotation of the inner core was proposed as a phenomenon in the 1970s and ’80s, but it wasn’t until the ’90s that seismological evidence was published,” said Dr Lauren Waszek, a senior lecturer of physical sciences at James Cook University in Australia.
But researchers argued over how to interpret these findings, “primarily due to the challenge of making detailed observations of the inner core, due to its remoteness and limited available data,” Waszek said. As a result, “studies which followed over the next years and decades disagree on the rate of rotation, and also its direction with respect to the mantle,” she added. Some analyses even proposed that the core didn’t rotate at all.
Recent research has supported the hypothesis that the core spins – and at different speeds to the rest of the Earth.
Research published June 12 in the journal Nature not only confirms the core slowdown, it supports the 2023 proposal that this core deceleration is part of a decades-long pattern of slowing down and speeding up.
The new findings also confirm that the changes in rotational speed follow a 70-year cycle, said study coauthor Dr John Vidale, Dean’s Professor of Earth Sciences at the University of Southern California’s Dornsife College of Letters, Arts and Sciences.
“We’ve been arguing about this for 20 years, and I think this nails it,” Vidale said. “I think we’ve ended the debate on whether the inner core moves, and what’s been its pattern for the last couple of decades.”
The new study suggests that the core rotation follows a 70-year cycle.
According to the researchers’ calculations, the core is just about ready to start speeding up again […]
The seismographs also revealed that, during its 70-year cycle, the core’s spin slows and accelerates at different rates, “which is going to need an explanation,” Vidale said. One possibility is that the metal inner core isn’t as solid as expected. If it deforms as it rotates, that could affect the symmetry of its rotational speed, he said.
Well, that’s all well and good, doc, but what does it means for us shmoes crawling around on the surface?
Not a hell of a lot, really. No exploding Colosseum or boiling Pacific. At most, a tiny adjustment to the Earth’s rotation.
If the inner core’s rotation continues to decelerate, its gravitational pull could eventually cause the outer layers of our planet to spin a little more slowly, altering the length of our days the researchers wrote.
However, any potential change would be on the order of thousandths of a second, which would be “very hard to notice,” Vidale said. As a result, we would likely not have to change our clocks or calendars to adjust for this difference, especially if it were only a temporary change.
The only places the effect would be noticed at all would be in GPS satellites, which already have to be continually adjusted due to the effects of relativity. Due to both their speed and the weaker gravity in orbit, time moves slightly relatively slower for these satellites, around 38 milliseconds per day. But even that is enough to potentially throw their measurements out by kilometres per day.
To counter this, GPS satellites’ clocks are continually corrected by an in-built ‘factory reset’. Should the need arise, the reset could be further adjusted to account for any effects from the Earth’s core changing rotation.
