We report 36Cl (301-kyr half-life) data obtained by accelerator mass spectrometry allowing nominal terrestiral ages to be determined for 39 Antarctic H4-6 chondrites for which contents of volatile trace elements are known. the compositional difference between these Antarctic meteorites and 58 non-Antarctic falls increases with terrestrial age and, using multivariate statistical techniques, becomes highly significant for Antarctic samples with ages >50 kyr. The compositional difference is inconsistent with trivial causes such as weathering and seems to reflect differences in thermal histories of parent sources. Temporal source variations for the H chondrite flux on Earth thus exist not only on a short-term, 40 years, basis (Dodd et al., 1993) but also on a long-term, >50 kyr, basis. ¿ American Geophysical Union 1995