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

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.
The nature and time scales of differentiation of Earth's silicate portion into depleted mantle and continental crust, as well as the effects of a changing atmosphere on this process, remain [...]