Beware of Ancient Zircon Ages

Electron backscatter diffraction and cathodoluminescence images of the culprit zircon grain from the Jack Hills of Western Australia

Electron backscatter diffraction and cathodoluminescence images of the culprit zircon grain from the Jack Hills of Western Australia Credit: Lunar and Planetary Institute/T. Erickson

A study out this month in the journal Geology led by researchers from Curtin University in Western Australia cautions researchers to be wary of some ancient zircon ages. Age analyses of a zircon grain from the Jack Hills of Western Australia record a concordant apparent U-Pb age of 4463 ± 17 million years old, which would make this the oldest Earth material. However, careful ion imaging of the distribution of Pb in the crystal structure shows that this grain crystallized a ca. 4.3 Ma and subsequent heating mobilized some of the Pb causing a false age spectrum. These results highlight the caution that must be taken when assessing the isotopic systematics of the oldest material on Earth.

A 4463 Ma apparent zircon age from the Jack Hills (Western Australia) resulting from ancient Pb mobilization

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