A newly published finding connects ancient changes in sea level with movement of Earth's geographic poles. The process, called true polar wander, involves the crust and mantle changing their orientation relative to the spin axis. It brings the planet's deep interior into the history of coastlines, alongside the familiar movement of individual tectonic plates. Geographic poles and magnetic poles belong to different physical processes.
A finding published in Science on October 1 connects ancient sea-level changes with episodes when Earth's geographic poles moved. The team includes Mathew Domeier, a geoscientist at the University of Oslo in Norway. Its findings place true polar wander, the reorientation of the planet's solid outer layers, within the history of coastlines and seas.[1], [2]
Geographic poles mark where Earth's spin axis meets its surface. Magnetic poles arise from the magnetic field and can occupy different positions. During true polar wander, the crust and mantle change their orientation relative to the spin axis. Domeier describes those solid layers slipping over the core. This moves the geographic poles across the surface as the continents' positions relative to the axis change.[1]
Plate movements and circulation in the mantle gradually redistribute mass inside Earth. That distribution is tied to the planet's rotational balance, and the outer layers can reorient as the balance changes. Ocean water can adjust to rotation-related forces more quickly than the rocky sea floor. This physical difference underlies the connection to sea level. Domeier says true polar wander continues today, imperceptibly in everyday experience, while long geological periods encompass changes in the distribution of land and sea.[1]
