Evolution of the continents and the atmosphere inferred from Th-U-Nb systematics of the depleted mantle |
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Authors: | Collerson Kamber |
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Institution: | Department of Earth Sciences, The University of Queensland, Brisbane, QLD 4072, Australia. |
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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. |
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