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 isotope146 Sm impede the interpretation of the146 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 of146 Sm/144 Sm for the Solar System at 0.00840± 0.00032 using a146 Sm half-life of 103 Ma, making EC 002 an anchor for146 Sm-142 Nd systematics for Earth and planetary materials.