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Science 24 January 1997:
Vol. 275. no. 5299, pp. 498 - 499
DOI: 10.1126/science.275.5299.498
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Perspectives

A. W. Hofmann

How did the continents form, and how long ago? These questions have been the subject of debate for 30 years. As Hofmann discusses in his Perspective, results reported by Sylvester et al. (p. 521) reveal that measurements of niobium and uranium isotopes indicate that ancient rocks from Western Australia are indistinguishable from modern mantle rock. This finding suggests that the mass and extent of continents today is comparable to that 2.7 billion years ago.

The author is at the Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany, and is a visiting investigator at the Institut de Physique du Globe, 4 Place Jussieu, 75252 Paris, France. E-mail: hofmann{at}geobar.mpch-mainz.mpg.de

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