The oldest rock
The Acasta gneiss in Canada — anything older has been recycled
See it on the timeline →In depth
The Acasta gneiss near Great Slave Lake is dated to around 4.03 billion years. Older still are individual crystals: zircons from Jack Hills in Australia reach 4.4 billion years, but they sit inside far younger rock — they are heirlooms, not intact crust. Zircon survives precisely because the mineral is extremely durable, and because it traps uranium, which makes precise dating possible. That so little ancient crust exists is itself information: it tells us plate tectonics has been running for a long time.
For children
Earth is 4.5 billion years old, but the oldest rock we can actually touch is "only" 4 billion. The reason is that the crust is constantly dragged down into the depths and melted again. Earth keeps erasing its own childhood.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org