Several times since the age of the dinosaurs, the planet’s solid portion has tipped as a whole, submerging some continents and lifting others above water. This is the conclusion of a study published in Science on October 1, 2026, as reported by Scientific American. The phenomenon is not finished.
It continues today, at about 10 centimeters per year.
- Quatre épisodes de basculement complet de la croûte terrestre se sont produits vers 200, 150, 100, et entre 30 et 20 millions d’années.
- Ce mécanisme de « true polar wander » déplace les continents comme une orange qui roule, contrairement à la dérive continentale qui fragmente la croûte.
- Le déplacement actuel atteint environ 10 centimètres par an, principalement causé par la fonte des calottes glaciaires qui déséquilibre la planète.
An overall rotation, not a drift
Continental drift, popularized by Alfred Wegener in 1912, describes rigid plates sliding on the upper mantle, driven by convection currents. Their speed ranges from about 1.3 to 10 centimeters per year. What the new study describes corresponds to another mechanism: the entire solid Earth—crust and mantle—rotates relative to the Earth’s axis. This phenomenon is called “true polar wander,” which shifts the real geographic poles rather than the magnetic poles.
The most accurate image is that of a whole orange rolling, not a skin cracking into pieces. In this way, continents can traverse quickly across climatic belts while their positions relative to one another change far less, notes geologist Giovanni Muttoni (University of Milan).
The four-leaf clover of the seas
Until now, the strongest evidence for these spins came from magnetic signals recorded in ancient rocks, data that were sparse and not very conclusive. Mathew Domeier, a geoscientist at the University of Oslo and the lead author, thus chose another path. His team sifted through maps showing, in 10-million-year slices, which lands stood above water and which lay beneath.
The rotation of the Earth bulges rock as water bulges at the equator. When the solid block tips, it moves through this liquid bulge: pieces of continents rise out of the water, others sink back in.
This resembles a rise or fall in sea level, but Domeier emphasizes: the water stays in place; it is the continents that move. On the maps, this motion leaves a four-leaf-clover-shaped signature. It appears around 200, 150, and 100 million years ago, and again between 30 and 20 million years ago, i.e., at least four episodes. The clearest signal, between 150 and 140 million years ago, coincides with a period when magnetic data already suggested rapid displacement, which leads Muttoni to say the study offers an independent test. Domeier admits the results took him by surprise.
The melting of the ice sheets, a quiet engine of the current movement
What triggers these episodes remains unknown.
No one knows either how far the poles moved each time, and the amplitude is not quantified in the articles consulted. Understanding why these reversals occurred at these precise dates constitutes the next logical step for researchers.
For the present, satellite measurements are more precise. According to Domeier, the current movement is about 10 centimeters per year and is mainly explained by the melting of the ice sheets. The shifting of these water masses makes some areas denser than others, which upends the planet, and the solid layers re-adjust to rebalance the mass. The sources consulted do not say whether this movement signals a new episode of large-scale upheaval.
To compare: tectonic plates advance by 1.3 to 10 centimeters per year, roughly the same order of magnitude, but by a different mechanism.
