Meteorite phosphates show constant 176Lu decay rate since 4557 million years ago.

The use of radioactive decay of 176Lu to 176Hf to study the evolution of the Earth requires a precise and accurate value for the 176Lu decay constant. Recent determinations of this decay constant by age comparison to the more precisely calibrated U-Pb isotopic system produced internally consistent but discrepant values between terrestrial minerals and meteorites. New highly radiogenic Lu-Hf data for phosphate minerals from Richardton (ordinary chondrite) and Acapulco (primitive achondrite) yield decay constant values of 1.864 x 10(-11) +/- 0.016 x 10(-11) and 1.832 x 10(-11) +/- 0.029 x 10(-11) year(-1), respectively, identical to the value determined from terrestrial minerals.