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Science 3 July 2009:
Vol. 325. no. 5936, pp. 44 - 45
DOI: 10.1126/science.1172587
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Perspectives

Geochemistry:

How Did Earth Accrete?

Alex N. Halliday and Bernard J. Wood

How did Earth form, and what were the conditions on the early Earth? With the aid of mass spectrometry, high-pressure experiments, and computer modeling, researchers are beginning to decipher the signs left behind by our planet's early and violent beginning. Recent studies of the nature of core formation and the age of the Moon provide evidence that the first half of Earth's growth took less than 10 million years and was associated with reducing conditions. The final stages were more energetic and oxidizing and were probably not completed until ~100 million years, possibly after a substantial hiatus, in contrast to the continuous exponentially decreasing accretion that has long been assumed (see the figure).

Department of Earth Sciences, University of Oxford, Parks Road Oxford, OX1 3PR, UK.

E-mail: alex.halliday{at}earth.ox.ac.uk

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