Earth’s true North and South Poles have shifted four times over the past 320 million years, according to a study in the journal Science.
What Is True Polar Wander?
The Earth’s crust floats on a thick, fluid-like layer called the mantle. This mantle surrounds the planet’s core. When mass moves within Earth—like melting ice or shifting tectonic plates—the planet’s balance shifts. To restore balance, the crust and mantle reorient around the core. This realignment moves the geographic poles, a process called true polar wander.
True polar wander differs from magnetic pole drift. Magnetic poles shift due to changes in Earth’s magnetic field. True polar wander moves the actual axis of rotation. It can happen in sudden bursts, not just slowly.
Key Episodes of Movement
Scientists identified four major episodes of true polar wander:
- Early Jurassic: 190 to 200 million years ago
- Late Jurassic to Early Cretaceous: 140 to 150 million years ago
- Mid-Cretaceous: 90 to 100 million years ago
- Oligocene to Miocene: 20 to 30 million years ago
Each event left a unique signature in ancient sea-level records. Earth bulges at the equator. When poles shift, the equatorial bulge stays fixed. Landmasses move relative to the ocean. Some areas sink into water. Others emerge from it. This creates a four-quadrant pattern—like a four-leaf clover.
How Did Scientists Detect These Shifts?
Older studies confused tectonic plate movement with true polar wander. This led to inconsistent results. To fix this, researchers led by Mathew Domeier at the University of Oslo used ancient sea-level data from sediment layers.
They ran computer simulations of sea-level changes over 320 million years. The simulations showed a four-leaf clover pattern at exactly the four time points above. This match confirms the presence of true polar wander in the geological record.
Why Does This Matter?
These shifts aren’t minor. They can dramatically alter ocean currents. Changes in currents affect heat distribution. This may have triggered global cooling or ice ages.
One theory suggests the ice age starting 3.2 million years ago began during a true polar wander event. While not proven, the study shows deep Earth processes strongly influence long-term climate and sea level.
Geoscientist Sabin Zahirovic of the University of Sydney says the findings are a ‘very exciting development.’ He notes that true polar wander is not slow or background. It is episodic and has real effects on Earth’s climate and ecosystems.
What’s Still Uncertain?
Scientists don’t yet know what triggers these shifts. Possible causes include massive volcanic eruptions, ice sheet changes, or mantle convection. They also don’t know how far the poles moved during each event—only when they moved.
Mathew Domeier says understanding the triggers is the next step. ‘Trying to understand why these events happened at these times would be the next logical step,’ he told Scientific American. More data from the deep past is needed to fill this gap.
True polar wander is happening today. Satellite data shows the poles shift about ten centimeters per year. This movement is driven mainly by melting Arctic ice caps. While slow, it proves the phenomenon is active now.
The study refutes earlier views that true polar wander is negligible or slow. It shows these events are episodic and have real impacts on Earth’s environment. More research is needed to fully understand their causes and effects.
Learn more about Earth’s deep processes in our article on how the planet’s core is leaking ancient materials from its birth.
Sources & further reading
Featured image: NOAA-20 Shares New View of the North Pole for Earth… by NOAA, Public domain, via Wikimedia Commons. Image source
