A tiny 4.4-billion-year-old crystal has been confirmed as the oldest fragment of Earth's crust.
The zircon was found in sandstone in the Jack Hills region of Western Australia.
Scientists dated the crystal by studying its uranium and lead atoms. The former decays into the latter very slowly over time and can be used like a clock.
The finding has been reported in the journal Nature Geoscience.
Its implication is that Earth had formed a solid crust much sooner after its formation 4.6 billion years ago than was previously thought, and very quickly following the great collision with a Mars-sized body that is thought to have produced the Moon just a few tens of millions of years after that. Before this time, Earth would have been a seething ball of molten magma.
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