Earth’s poles do not always stay in the same place. For example, a region once near the North Pole can end up near the equator, and an area near the equator can shift up toward the pole. This is known as true polar wander (TPW), and it’s when Earth’s crust and mantle shift together relative to its spin axis.

Some scientists believe it is negligible or persistently slow. But a new study suggests that rapid polar wander happened several times during the last 320 million years, especially between 150 and 140 million years ago and between 100 and 90 million years ago.