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Science 26 May 2006:
Vol. 312. no. 5777, p. 1139
DOI: 10.1126/science.1125301
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Technical Comments

Comment on "Heterogeneous Hadean Hafnium: Evidence of Continental Crust at 4.4 to 4.5 Ga"

John W. Valley,1* Aaron J. Cavosie,1{dagger} Bin Fu,1 William H. Peck,2 Simon A. Wilde3

Harrison et al. (Reports, 23 December 2005, p. 1947) proposed that plate tectonics and granites existed 4.5 billion years ago (Ga), within 70 million years of Earth's formation, based on geochemistry of >4.0 Ga detrital zircons from Australia. We highlight the large uncertainties of this claim and make the more moderate proposal that some crust formed by 4.4 Ga and oceans formed by 4.2 Ga.

1 Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA.
2 Department of Geology, Colgate University, Hamilton, NY 13346, USA.
3 Department of Applied Geology, Curtin University, Perth, WA, Australia.

{dagger} Present address: Department of Geology, University of Puerto Rico, Mayaguez, PR 00681–9017, USA.

* To whom correspondence should be addressed. E-mail: valley{at}geology.wisc.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Temperature spectra of zircon crystallization in plutonic rocks.
T. M. Harrison, E. B. Watson, and A. B. Aikman (2007)
Geology 35, 635-638
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Magmatic and Crustal Differentiation History of Granitic Rocks from Hf-O Isotopes in Zircon.
A. I. S. Kemp, C. J. Hawkesworth, G. L. Foster, B. A. Paterson, J. D. Woodhead, J. M. Hergt, C. M. Gray, and M. J. Whitehouse (2007)
Science 315, 980-983
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