The Zircon's Tale

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Science  23 Dec 2005:
Vol. 310, Issue 5756, pp. 1865
DOI: 10.1126/science.310.5756.1865b

Earth's oldest preserved continental crust dates to about 4 billion years ago, much after Earth's formation (4.55 billion years ago); a major question has been how much continental crust had formed previously and been recycled back into the mantle. Some early rocks in Australia contain relic crystals of zircon, recycled from earlier rocks. Zircon harbors uranium, and these have been dated to up to 4.4 billion years ago. Harrison et al. (p. 1947, see Perspective by Amelin) have analyzed lutetium and hafnium isotopes in a large number of these early zircons. This isotopic system provides information on the differentiation of major silicate reservoirs on the Earth. The data imply that significant continental crust must have formed on Earth early on, perhaps by nearly 4.5 billion years ago.

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