A new study published in Science reveals that Earth may have undergone several episodes of rapid true polar wander over the past 320 million years, with the strongest signals occurring during the Jurassic and Cretaceous periods.
Tracking Axis Shifts Through Continental Flooding
For decades, researchers relied primarily on paleomagnetism to chart how Earth’s solid exterior shifted relative to its rotation axis. Magnetic minerals trapped in ancient rocks preserve historical field directions, helping scientists estimate where continents once sat. However, separating whole-Earth reorientation from ordinary plate tectonics remains difficult.
To bypass these uncertainties, a team led by Mathew Domeier at the University of Oslo turned to a different archive: the geological record of continental flooding and retreat. When true polar wander occurs, the solid Earth moves relative to its transient equatorial bulge. Oceans respond almost immediately, while the mantle and lithosphere take longer to reshape themselves.
This dynamic creates a distinct global pattern of sea-level changes. Some continental regions experience rising waters, while others face falling seas and land exposure. Domeier and his colleagues analyzed global maps tracking submerged and exposed areas at 10-million-year intervals, using logistic regression to test whether these historical flooding geometries matched the expected signatures of rapid polar reorientation.
Statistically Significant Intervals in Deep Time
The analysis identified four intervals featuring statistically significant signals consistent with rapid true polar wander. The strongest evidence emerged between approximately 150 and 140 million years ago, as well as between 100 and 90 million years ago.
These findings challenge the idea that true polar wander has always been negligible or persistently slow. The new sea-level data instead point to evidence of rapid events.
Earth is not a perfect sphere, possessing an equatorial bulge driven by its rotation. The planet naturally arranges its internal mass so that its largest moment of inertia stays aligned with the spin axis. When mantle convection, sinking tectonic slabs, and other internal forces redistribute mass, the solid crust and mantle rotate together relative to the rotational axis.
Implications for Deep-Time Reconstructions
The core of the planet and its broad climate belts remain tied to that rotational axis while the solid exterior shifts beneath them. Pinpointing these movements has historically relied on hotspot reference frames, but hotspots move, and reliable tracks grow scarce further back in geological history.
By mapping flooding patterns rather than absolute sea-level changes, the University of Oslo research team established an independent line of evidence for how the planet periodically rebalances its mass distribution. The findings offer a fresh framework for interpreting how Earth’s geography shifted.
