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Evolution of the Continents and the Atmosphere Inferred from Th-U-Nb Systematics of the Depleted Mantle

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Science  05 Mar 1999:
Vol. 283, Issue 5407, pp. 1519-1522
DOI: 10.1126/science.283.5407.1519

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Abstract

Temporal evolution of depleted mantle thorium-uranium-niobium systematics constrain the amount of continental crust present through Earth's history (through the niobium/thorium ratio) and date formation of a globally oxidizing atmosphere and hydrosphere at approximately 2.0 billion years ago (through the niobium/uranium ratio). Increase in the niobium/thorium ratio shows involvement of hydrated lithosphere in differentiation of Earth since approximately 3.8 billion years ago. After approximately 2.0 billion years ago, the decreasing mantle thorium/uranium ratio portrays mainly preferential recycling of uranium in an oxidizing atmosphere and hydrosphere. Net growth rate of continental crust has varied over time, and continents are still growing today.

  • * To whom correspondence should be addressed. E-mail: k.collerson{at}mailbox.uq.edu.au

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