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Science 21 December 2007:
Vol. 318. no. 5858, pp. 1907 - 1910
DOI: 10.1126/science.1145928
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Reports

Coupled 142Nd-143Nd Isotopic Evidence for Hadean Mantle Dynamics

Vickie C. Bennett,1,2* Alan D. Brandon,3 Allen P. Nutman4

The oldest rocks—3.85 billion years old—from southwest Greenland have coupled neodymium-142 excesses (from decay of now-extinct samarium-146; half-life, 103 million years) and neodymium-143 excesses (from decay of samarium-147; half-life, 106 billion years), relative to chondritic meteorites, that directly date the formation of chemically distinct silicate reservoirs in the first 30 million to 75 million years of Earth history. The differences in 142Nd signatures of coeval rocks from the two most extensive crustal relicts more than 3.6 billion years old, in Western Australia and southwest Greenland, reveal early-formed large-scale chemical heterogeneities in Earth's mantle that persisted for at least the first billion years of Earth history. Temporal variations in 142Nd signatures track the subsequent incomplete remixing of very-early-formed mantle chemical domains.

1 Research School of Earth Sciences, The Australian National University, Canberra ACT, 0200 Australia.
2 Lunar and Planetary Institute, Houston, TX 77058, USA.
3 NASA Johnson Space Center, Mail Code KR, Houston, TX 77058, USA.
4 Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing, 100037, China.

* To whom correspondence should be addressed. E-mail: vickie.bennett{at}anu.edu.au

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