4.4 Billion-Year-Old Zircon Crystal is Oldest Known Piece of the Earth's Crust
Posted on February 25, 2014
This 4.4 billion-year-old microscopic zircon crystal is the oldest known piece of the Earth's crust. A magnified image of the crystal is pictured above. The crystal fragment was extracted from a remote rock outcrop in the Jack Hills region of Western Australia. Researchers led by University of Wisconsin-Madison geoscience Professor John Valley say data indicates the Earth's crust first formed at least 4.4 billion years ago, which is just 160 million years after the formation of our solar system.
Valley says in a release, "This confirms our view of how the Earth cooled and became habitable. This may also help us understand how other habitable planets would form."
The researchers used atom-probe tomography in conjunction with secondary ion mass spectrometry to establish the age and thermal history of the zircon by determining the mass of individual atoms of lead in the sample. The scientists say the lead was not randomly distributed in the zircon sample as expected. Instead the researchers found the lead atoms were clumped together in the zircon sample like "raisins in a pudding." The scientists say the clusters of lead atoms formed 1 billion years after crystallization of the zircon.
Valley says, "The zircon formed 4.4 billion years ago, and at 3.4 billion years, all the lead that existed at that time was concentrated in these hotspots. This allows us to read a new page of the thermal history recorded by these tiny zircon time capsules."
Valley told CNN that the Earth's surface formed a crust much more quickly than previously thought. He also says that steam from the atmosphere condensed to form oceans after the planet cooled enough to form a crust. He says there could have been life on Earth even when our planet was just 200 million years old.
The research paper, "Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography," was published here in Nature Geoscience.
Photo: John Valley