The isotopic composition of strontium and the age of stone meteorites - I

New measurements of the Rb and Sr content and Sr isotope composition are reported for four Ca-rich achondrites and five bronzite or hypersthene chondrites. All the achondrites have identical ⁸⁷Sr /⁸⁶Sr ratios; one chondrite, Beardsley, is very much enriched in Rb relative to the other chondrites. Several alternative interpretations of the data are discussed; all agree on a period of chemical differentiation 4.3 to 4.7 Aeons ago (Aeon = 10 ⁹ yrs.) in the parent body of the meteorites.