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Science 17 July 2009:
Vol. 325. no. 5938, p. 267
DOI: 10.1126/science.1169695
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Technical Comments

Response to Comment on "Neodymium-142 Evidence for Hadean Mafic Crust"

Jonathan O’Neil,1,* Richard W. Carlson,2 Don Francis,1 Ross K. Stevenson3

Andreasen and Sharma raise concerns about the neodymium-142 data and age that we reported for rocks from the Nuvvuagittuq greenstone belt in Quebec, Canada. We agree that the issue of accurate mass fractionation correction is important, but stand by our discussion of this issue in our original report and our conclusion that the variation in 142Nd/144Nd ratios reflects the decay of 146Sm caused by Sm-Nd fractionation within 300 million years of Earth’s formation.

1 Earth and Planetary Sciences Department, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada.
2 Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA.
3 GEOTOP (Centre de recherche en géochemie et géodynamique), Université du Québec à Montréal, Post Office Box 8888, Succursale Centre-ville, 210, Président-Kennedy Avenue, Montreal, Quebec H3C 3P8, Canada.

* To whom correspondence should be addressed. E-mail: oneil_jo{at}eps.mcgill.ca

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Science. ISSN 0036-8075 (print), 1095-9203 (online)