LAUSR

Significance The modern Earth is geologically dynamic. Convection in its rocky mantle drives plate tectonics that reshapes its surface, and currents inside its metallic core generate a strong planetary magnetic field. However, it is uncertain whether these processes had begun to shape Earth in its deep past. Our measurements of magnetic signals preserved in 3.25-billion-year-old rocks provide the earliest quantitative evidence of both rapidly moving crust—a hallmark of plate tectonics—and a stable ancient magnetic field that episodically alternated polarity. These observations suggest that the early Earth was remarkably geologically mature from its surface to its deep interior, potentially contributing to stable surface conditions for the evolution of early life.