Plate tectonics may be unique to Earth and may be an essential characteristic of habitable planets. Estimates for its onset range from over 4 billion years ago to just 800 million years ago. A new study reports evidence of a transition in multiple locations around the world, 3.8-3.6 billion years ago, from stable 'protocrust' to pressures and processes that look a lot like modern subduction, suggesting a time when plates first got moving.