Earth’s Outer Core Deep Beneath The Pacific Ocean Has Reversed Direction, And On Timescales Scientists Were Not Expecting

For all the ways we’ve explored and modeled our planet, the Earth’s inner core still holds a lot of mysteries and secrets we don't quite understand yet. That’s not especially shocking when you consider that it sits more than 5,100 kilometers (3,170 miles) beneath our feet, while the deepest humans have ever physically drilled into the planet is a comparatively tiny 12,263 meters (40,230 feet). Instead, scientists have to study the center indirectly, using seismic waves traveling through Earth and the planet’s magnetic field lines, both shaped by the extreme conditions deep within the core.

Over time, researchers have become remarkably good at wrangling useful information out of those signals, uncovering some unexpected findings about our planet along the way. In 2022, for example, a team analyzed data gathered during nuclear tests carried out in the 1960s and '70s. Their study suggested that the inner core had reversed direction relative to the Earth’s surface, sub-rotating (meaning moving more slowly than the surface) by around a tenth of a degree at least once per year. Rather than remaining relatively fixed, the core seemed to oscillate.

"Events triggered in the deeper core in 2010" 

“The inner core is not fixed – it’s moving under our feet, and it seems to [be] going back and forth a couple of kilometers every six years,” study author John E. Vidale, Professor of Earth Sciences at USC, explained in a statement at the time. “One of the questions we tried to answer is, does the inner core progressively move or is it mostly locked compared to everything else in the long term? We're trying to understand how the inner core formed and how it moves over time – this is an important step in better understanding this process.”

Subsequent studies showed further evidence that the rotation of the core has been acting in unexpected ways since around 2010. Monitoring the flow of the liquid iron alloy in the Earth’s outer core, the new study has found that it too is not behaving itself (as we had previously expected).

"Historically, the core-surface flow has been predominantly westward, as required to maintain a westward-drifting magnetic field," the authors of the new study write in their paper. "This westward flow is a component of an eccentric planetary gyre, offset from the Earth’s rotation axis. The flow in the equatorial Pacific is not part of this gyre, and we find that it changed in 2010 from weakly westward to strongly eastward. Our model suggests that the Pacific eastward flow has been weakening since 2020."

According to the team, who used data from the European Space Agency's Swarm and Cryosat missions, among others, this change in flow is likely related to "events triggered in the deeper core in 2010".

“The rise of the strong eastward flow in the Pacific is contemporary with a change in behaviour in the inner core, as inferred from geodesy and seismology, and we hypothesise that these changes in the deep interior are associated with the changes in flow beneath the Pacific," Frederik Dahl Madsen, from the University of Edinburgh's School of Geosciences, explained in a statement.

Raising new questions on the outer core's stability

“The large-scale flow reversal beneath the Pacific raises new questions about the behaviour of Earth’s deep interior. Scientists now want to understand whether the reversal represents a short-lived fluctuation, part of a repeating oscillation, or a new stable equilibrium for core circulation. Continued monitoring will be essential to determine how the flow evolves over the coming years," Madsen added.

While things like this can sound quite dramatic (and they are pretty dramatic, geologically speaking), it is not yet time to crack each other's heads open and feast on the gooey bits inside. We know that over long timescales, the Earth's magnetic fields – strongly tied to activities deep within our planet – can change and even flip, sometimes without anybody noticing. As far as scientists can tell, these changes pose no danger to the climate, nor the creatures dwelling on the Earth's surface. Nevertheless, it does challenge our previous assumptions about how stable the westward flow of the outer core really is.

“This study shows that regional changes can emerge rapidly within just a decade. The findings may also help scientists investigate possible interactions between Earth’s outer core, inner core, lower mantle and, therefore, give more insights into core-mantle boundary, which is a critical region for the deep Earth dynamics," Elisabetta Iorfida, ESA’s Swarm Mission Scientist, added.

“This research raises intriguing questions about how Earth’s deepest layers are dynamically connected. As the magnetic field continues to evolve, satellite missions are providing an increasingly detailed view of the dynamic processes unfolding deep inside our planet, revealing that Earth’s core may be far more variable and complex than once believed.”

The study is published in the Journal of Studies of Earth’s Deep Interior.