Earth spins about an axis, and its crust and mantle — not perfectly balanced — can shift relative to that axis. Geologists call the phenomenon "true polar wander" (TPW). The question has always been how fast and how often that happens.
Paleomagnetic evidence had hinted at rapid episodes, but the record is noisy enough that ordinary plate motion can masquerade as TPW, so the results stayed contested. Some researchers treated true polar wander as negligible or persistently slow.
A team at the University of Oslo's Centre for Planetary Habitability tried a different test. Rapid TPW should redistribute mass and change the centrifugal potential, leaving a fingerprint in ancient sea levels: predictable, globe-spanning patterns of continental flooding and exposure. The researchers analysed continental flooding reconstructions mapped at 10-million-year intervals and combined them with statistical modelling.
They identified multiple robust quadrupolar patterns over the past 320 million years, consistent with episodes of rapid true polar wander — including distinct events in the mid-Cretaceous (about 100–90 million years ago) and the Late Jurassic to Early Cretaceous (about 150–140 million years ago).
The findings, published in Science, refute the view that TPW was negligible or persistently slow and challenge researchers to treat it as "an episodic control on sea level change and likely other global environmental and biological dynamics." The team also found little evidence of rapid TPW during most of the Cenozoic, and no strong support for the idea that the northward drift of the supercontinent Pangaea was driven primarily by TPW during the late Carboniferous and Permian.
True polar wander is not a thing of the distant past. The authors note it is presently occurring at roughly 10 centimetres per year — faster than the mean rate of differential plate motion. If rapid episodes recur, they would reshape climate belts, stress the biosphere and influence the planet's magnetic field, since the core and climate system stay tied to the rotation axis while the crust slides across it.
