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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.
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.
But knowledge that its surface hardened so early raises the tantalising prospect that our world became ready to host life very early in its history.
"This confirms our view of how the Earth cooled and became habitable," said lead author Prof John Valley, from the University of Wisconsin-Madison, US.
"We have no evidence that life existed then. We have no evidence that it didn't. But there is no reason why life could not have existed on Earth 4.3 billion years ago," he told the Reuters news agency.