Nd isotope variation between the Earth-Moon system and enstatite chondrites.

Area of Science:

• Planetary Science
• Geochemistry
• Cosmochemistry

Background:

• Understanding Earth and Moon's formation requires reconstructing their primordial building blocks.
• Neodymium (Nd) isotopes and samarium (Sm)/Nd ratios serve as crucial tracers for these early materials.
• Previous studies interpreted Earth's ¹⁴²Nd/¹⁴⁴Nd ratio differences from chondrites as nucleosynthetic variations, implying similar Sm/Nd ratios in their precursors.

Purpose of the Study:

• To precisely determine the Sm/Nd ratio of Earth and Moon's precursor materials.
• To re-evaluate the initial ¹⁴²Nd/¹⁴⁴Nd ratio of Earth's building blocks.
• To clarify the implications for Earth-Moon system formation and lunar differentiation.

Main Methods:

• Analysis of neodymium (Nd) and samarium (Sm) isotope systems, specifically the ¹⁴⁶Sm-¹⁴²Nd and ¹⁴⁷Sm-¹⁴³Nd decay chains.
• Comparison of isotopic ratios between Earth, Moon, and various chondrite groups.
• Modeling of isotopic evolution to constrain initial Sm/Nd ratios and ¹⁴²Nd/¹⁴⁴Nd.

Main Results:

• Earth and the Moon possess a samarium (Sm)/neodymium (Nd) ratio approximately 2.4% higher than the average for chondrites.
• The initial ¹⁴²Nd/¹⁴⁴Nd ratio of Earth's precursor materials is more akin to enstatite chondrites than previously suggested.
• These findings challenge the notion of significant nucleosynthetic isotope variation as the sole explanation for Earth's ¹⁴²Nd anomaly.

Conclusions:

• The observed Sm/Nd ratio difference between Earth and chondrites likely stems from mineralogical partitioning during inner protoplanetary disk mixing.
• Lunar differentiation can be explained by a single-stage process from magma ocean formation to solidification.
• No significant Sm/Nd fractionation occurred between the proto-Earth and the Moon during the giant impact event.