Earth Tipped on Its Side During the Age of Dinosaurs–and Not Just Once

Researchers analyzed 320 million years of continental flooding maps at 10-million-year intervals to detect episodes of true polar wander - solid-Earth reorientation relative to the spin axis that occurs when mass redistribution upsets rotational balance. Instead of relying on paleomagnetic records alone, the team used changes in exposed versus inundated land (hydrospheric response) to amplify signals that lithospheric motion (damped by mantle viscosity) would mute. The approach highlights how Earth's non-spherical, rotating shape drives pole wander when surface or mantle mass shifts, and it isolates sea-level redistribution patterns as a fingerprint of such events.

The analysis identifies four intervals of rapid true polar wander: Early Jurassic (200-190 Ma), Late Jurassic-Early Cretaceous (150-140 Ma), mid-Cretaceous (100-90 Ma), and Oligocene-Miocene (30-20 Ma). These episodes produced major regional sea-level shifts, especially far from the rotational equator and its perpendicular axis, and align with independent paleomagnetic estimates for some intervals. Findings imply that episodic, multi-million-year-scale polar reorientations played a larger role than previously appreciated in reshaping coastlines and likely influenced global climate, biospheric distributions, and the geodynamo, warranting inclusion of true polar wander as a driver in deep-time environmental reconstructions.