Scientists have uncovered 3.95-billion-year-old rocks in northern China that indicate plate tectonics may have been active nearly four billion years ago.
The rocks were found in the Shimen Complex in Hebei province and dated by analyzing tiny zircon crystals that record uranium decay.
Chemical analysis of oxygen and hafnium isotopes shows the rocks formed from material that interacted with water at Earth's surface and was later buried more than 50 kilometers deep.
Computer simulations suggest this burial could have occurred through a transient subduction event, implying that plate tectonics was already operating by 3.95 billion years ago.