A nucleosynthetic origin for the Earth's anomalous (142)Nd composition
C Burkhardt1,2, L E Borg3, G A Brennecka2,3
1Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA.
Nature
|September 16, 2016
Summary
Earth's accessible silicate has a higher neodymium-142 to neodymium-144 ratio than chondrites. This difference is due to an excess of slow neutron capture process neodymium, not early Earth differentiation, suggesting a chondritic Sm/Nd ratio for bulk Earth.
Area of Science:
- Geochemistry
- Cosmochemistry
- Planetary Science
Background:
- The bulk silicate Earth's chemical and isotopic compositions are often assumed to mirror chondrites.
- However, accessible Earth exhibits a higher (142)Nd/(144)Nd ratio compared to chondrites.
- This isotopic offset has been attributed to early Earth differentiation, implying a hidden or lost complementary reservoir.
Discussion:
- This study investigates the origin of the (142)Nd excess in the accessible silicate Earth.
- The research analyzes the role of nucleosynthetic processes, specifically the slow neutron capture process (s-process), in neodymium isotopic composition.
- The findings challenge the necessity of early differentiation models and hidden reservoirs.
Key Insights:
- Earth's precursor bodies were enriched in s-process neodymium, leading to higher (142)Nd/(144)Nd ratios.
- After correcting for the s-process effect, the (142)Nd/(144)Nd ratios of accessible Earth and chondrites are indistinguishable.
- The (142)Nd offset is explained by variations in s-process neodymium abundance, not early differentiation.
Outlook:
- These results suggest that the bulk Earth has a chondritic Sm/Nd ratio, simplifying models of planetary composition.
- The study implies that chondrites remain suitable proxies for Earth's bulk chemical composition.
- This research has implications for understanding Earth's bulk composition, heat content, structure, and geodynamical evolution.
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