Researchers report isotopic evidence of the differentiation of Earth's interior and the onset of plate tectonics and calculate the rate of stirring in the mantle. Isotopes of samarium and neodymium (Nd) are present in varying ratios throughout the history of planetary bodies, with some isotopes recording early differentiation and others persisting as records of ongoing crustal formation. Eugenia Hyung and Stein B. Jacobsen measured 142Nd/144Nd ratios with high precision in samples of rocks younger than the Archean eon, which ended around 2.5 billion years ago. Isotope ratios in the Archean vary widely, whereas post-Archean samples contain relatively homogenous ratios. The variability of the isotope ratios over time provide evidence for the rate of stirring in the mantle, which is calculated at around 400 million years. The authors report that some young rocks contain variability in 142Nd/144Nd ratios lower than expected, suggesting that some isotopic signatures of early Earth persist in the modern mantle. According to the authors, the results are consistent with an Earth on which plate tectonics have been in operation for most of its history, regulating the chemical evolution of the planet.
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Article #20-06950: "The 142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present," by Eugenia Hyung and Stein B. Jacobsen.
MEDIA CONTACT: Eugenia Hyung, California Institute of Technology, Pasadena, CA; e-mail: ehyung@caltech.edu
Proceedings of the National Academy of Sciences