Evidence for widespread Al-26 in the solar nebula and constraints for nebula time scales

qA search was made for Mg-26 (Mg-26*) from the decay of Al-26 (half-life = 0.73 million years) in Al-rich objects from unequilibrated ordinary chondrites. Two Ca-Al-rich inclusions (CAls) and two Al-rich chondrules (not CAls) were found that contained Al-26 when they formed. Internal isochrons for the CAls yielded an initial Al-26/Al-27 ratio [(Al-26/Al-27)(0)] of 5 x 10(-5), indistinguishable from most CAls in carbonaceous chondrites. This result shows that CAls with this level of Al-26 are present throughout the classes of chondrites and strengthens the notion that Al-26 was widespread in the early solar system. The two Al-rich chondrules have lower Mg-26*, corresponding to a (Al-26/Al-27)(0) ratio of similar to 9 x 10(-6). Five other Al-rich chondrules contain no resolvable Mg-26*. If chondrules and CAls formed from an isotopically homogeneous reservoir, then the chondrules with Al-26 must have formed or been last altered similar to 2 million years after CAls formed; the Mg-26*-free chondrules formed > 1 to 3 million years later still, Because Mg-26*-containing and Mg-26*-free chondrules are both found in Chainpur, which was not heated to more than similar to 400 degrees C, it follows that parent body metamorphism cannot explain the absence of Mg-26* in some of these chondrules. Rather, its absence indicates that the lifetime of the solar nebula over which CAls and chondrules formed extended over similar to 5 million years.