A new study finds evidence that Earth may have undergone several episodes of rapid true polar wander during the past 320 million years, with the strongest signals in the Jurassic and Cretaceous. Instead of relying primarily on ancient magnetic fields, researchers tracked patterns of continental flooding and retreat caused when the solid Earth shifted relative to its spin axis. The results support rapid events between about 150 and 140 million years ago and 100 and 90 million years ago, while challenging the idea that true polar wander has always been negligible or persistently slow. Earth’s geographic poles can appear permanent on human time scales, but the planet’s solid exterior has not always remained fixed relative to its rotation axis. A new study suggests that the crust and mantle underwent several episodes of relatively rapid reorientation during the past 320 million years. Instead of relying mainly on magnetic signatures preserved in rocks, researchers found evidence in an unexpected archive: ancient changes in where oceans flooded the continents. The study, led by Mathew Domeier at the University …