Half-life and initial Solar System abundance of ¹⁴⁶ Sm determined from the oldest andesitic meteorite

Significance 146 Sm- 142 Nd radioactive systematics can provide constraints on the timing of early differentiation processes on Earth, Moon, and Mars. The uncertainties related to the initial abundance and half-life of the extinct isotope 146 Sm impede the interpretation of the 146 Sm- 142 Nd systematics of planetary materials. The accurate determinations of Sm, Nd, and Mg isotopic compositions of the oldest “andesitic” achondrite Erg Chech 002 (EC 002) define a crystallization age of 1.8 Myr after the formation of the Solar System and provide the most accurate and reliable initial ratio of 146 Sm/ 144 Sm for the Solar System at 0.00840 ± 0.00032 using a 146 Sm half-life of 103 Ma, making EC 002 an anchor for 146 Sm- 142 Nd systematics for Earth and planetary materials.