Study Finds Earth's Geographic Poles Shifted Four Times in 320 Million Years

Earth’s geographic North and South poles have shifted dramatically four times over the past 320 million years, according to a study published on October 1 in the journal Science. The research identifies these events as episodes of "true polar wander," a phenomenon where the planet's solid crust and mantle reorient themselves around the core to restore balance after mass distribution changes.

Distinguishing Geographic from Magnetic Poles

The study focuses on the movement of the geographic poles, which is distinct from the wandering of Earth's magnetic poles. While magnetic poles can move away from the planet's true North and South Poles, the geographic poles themselves are also mobile. The crust floats atop a viscous rock layer called the mantle, which surrounds the core. When movements in the crust and mantle disrupt Earth's balance around its rotational axis, the crust and mantle reorient themselves, causing the geographic poles to slide.

Evidence from Ancient Sea Levels

Lead study author Mathew Domeier, a geophysicist at the University of Oslo in Norway, explained that investigating past episodes is difficult because tectonic plate movement can be mistaken for true polar wander. To overcome this, Domeier and colleagues used a new strategy: tracking ancient sea-level changes. Because Earth is not a perfect sphere and has a bulging belt of water around the equator, true polar wander causes landmasses to move while the water bulge stays still. This results in some dry regions plunging underwater and previously submerged regions becoming exposed.

The affected areas form a specific pattern with four quadrants, resembling a four-leaf clover. "This is a very strange pattern that is not caused by other Earth processes," Domeier tells New Scientist’s James Woodford. Computer simulations of flooding dynamics over the past 320 million years highlighted four specific time points where this signature appeared:

• The Oligocene to Miocene, about 20 million to 30 million years ago
• The mid-Cretaceous, about 90 million to 100 million years ago
• The Late Jurassic to Early Cretaceous, about 140 million to 150 million years ago
• The Early Jurassic, about 190 million to 200 million years ago

Current and Future Implications

True polar wander is occurring today at a rate of about ten centimeters a year, mainly due to melting ice caps, according to satellite measurements cited by Domeier in Scientific American. The study authors write that their findings "refute the view of [true polar wander] as negligible or persistently slow" and highlight the need to consider it as an episodic control on sea level change and other global environmental dynamics.

These shifts can disrupt ocean currents, climate systems, and ecosystems. Sabin Zahirovic, a geoscientist at the University of Sydney in Australia who was not involved in the study, told New Scientist that the findings help link deep Earth processes to changes in long-term climate and sea level. However, the triggers for these events remain unknown. "Trying to understand why these events happened at these times would be the next logical step," Domeier tells Scientific American.

Why it matters

Understanding true polar wander provides critical context for how Earth's climate and sea levels have changed over geological time. By identifying that these shifts occur in rapid bursts rather than just slow, steady drifts, scientists can better model past environmental changes and potentially improve predictions for how current ice melt might influence the planet's rotation and climate stability.

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Sources

• newser.com: Earth's Poles Have Dramatically Shifted 4 Times
• smithsonianmag.com: Earth's True North and South Poles Have Wandered Four Times Over the Past 320 Million Years, Study Suggests

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.