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Primitive Solar System materials and Earth share a common initial (142)Nd abundance
1University of Western Ontario, Department of Earth Sciences, Centre for Planetary Science and Exploration, London, Ontario N6A 3K7, Canada.
Nature
|September 16, 2016
Summary
Early Earth's composition aligns with calcium-aluminium-rich refractory inclusions (CAIs), suggesting a chondritic Sm/Nd ratio. This resolves the neodymium-142 (142Nd) offset without needing hidden reservoirs.
Area of Science:
- Cosmochemistry: Investigating the isotopic evolution of the early Solar System using samarium-neodymium (Sm-Nd) systematics.
- Planetary Science: Constraining the early evolution of planetesimals and planets through isotopic analysis.
- Geochemistry: Analyzing neodymium-142 (142Nd) variations to understand planetary formation and differentiation.
Background:
- Neodymium-142 (142Nd) variations offer insights into early planetary evolution, stemming from initial disk distribution and short-lived samarium-146 (146Sm) decay.
- Previous studies noted an offset in 142Nd abundance between chondritic meteorites and Earth, with interpretations including nucleosynthetic variations or early Earth differentiation.
- Calcium-aluminium-rich refractory inclusions (CAIs) and enstatite chondrites are key materials for reconstructing the early Solar System's isotopic composition.
Discussion:
- High-precision Sm and Nd isotopic analyses were performed on CAIs from carbonaceous chondrites and whole-rock samples of enstatite chondrites.
- Mineral isochron dating of CAIs revealed that those without Nd isotopic anomalies share an isotopic evolution with Earth.
- The calculated 142Nd/144Nd composition of pristine enstatite chondrites matches that of Earth's accessible silicate layers.
Key Insights:
- Earth inherited the same initial 142Nd abundance and chondritic proportions of Sm and Nd as observed in certain CAIs and enstatite chondrites.
- The study supports a chondritic samarium-neodymium (Sm/Nd) ratio for the bulk silicate Earth, implying chondritic abundances for other refractory elements.
- The findings eliminate the need for a hidden reservoir or collisional erosion to explain Earth's 142Nd/144Nd composition.
Outlook:
- Further investigation into 142Nd isotopic heterogeneities in other CAIs and chondrite groups may reveal the role of extrasolar grains.
- This research provides a robust framework for understanding the initial isotopic composition of terrestrial planets.
- Continued high-precision isotopic analysis will refine models of protoplanetary disk evolution and early Solar System processes.
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