Validating 70 Million Years of Convection Driven True Polar Wander and Dynamic Flattening with Paleomagnetic Data

Mantle convection drives changes in Earth's ellipsoidal figure and corresponding moment of inertia, causing shifts in the planet's rotation axis known as true polar wander (TPW). Using seismic tomography and the Back-and-Forth Nudging (BFN) method, we developed a time-dependent convection model that reconstructs the evolution of mantle density distribution and Earth’s moment of inertia over the past 70 million years. This modelling approach provides a close match with independent paleomagnetic constraints on the Cenozoic shifts of Earth’s rotation pole, specifically resolving the previously unexplained U-turn in TPW trajectory at approximately 50 million years ago. Our findings reveal TPW shifts exceeding 5 degrees, despite the temporal stability imposed by high lower-mantle viscosity and the stabilizing effect of Earth's remnant rotational bulge. Verification of our predicted changes in Earth’s ellipsoidal figure through independent paleomagnetic data provides a robust calibration for new predictions of convection-induced dynamic flattening variations. Over the past 70 million years, we find convection-induced changes of flattening that shift from -0.2% to +0.1 % during the Paleogene. Our predictions of Earth's axial precession frequency in the Paleogene align with recent independent cyclostratigraphic studies, thus validating our model's accuracy and supporting the hypothesis of reduced luni-solar tidal dissipation during this period.