In the desolate landscape of western Australia, a rocky outcrop that formed more than three billion years ago is giving geologists an unprecedented look at the early churnings of our planet. These rocks—among the most ancient in the world—contain what may be the oldest direct evidence of the movement of tectonic plates.

The rocks formed when magma oozed up from beneath Earth’s surface into a now-vanished ocean, cooling and hardening into a bulbous mass. As detailed in a new study in Science Advances, magnetic signatures preserved in the rock suggest the region was inching across the planet 3.2 billion years ago at similar speeds to tectonic plates today—nearly half a billion years earlier than previous evidence of such movement.

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