| Summary: | The cosmogenic radionuclides $\sp{26}$Al (t$\sb{{1\over 2}}$ = 0.71 Myr), $\sp{10}$Be (t$\sb{{1\over 2}}$ = 1.5 Myr), and $\sp{36}$Cl (t$\sb{{1\over 2}}$ = 0.30 Myr) have been measured in 12 fragments of the Canyon Diablo meteorite and in 39 Antarctic meteorites. Canyon Diablo results have experimentally confirmed theoretical calculations that there is a very significant matrix-dependent component to the build-up and development of the secondary flux of cosmic rays in meteorites. Cosmic-ray exposure ages calculated using these results are about 540 Myr in most cases. Terrestrial ages calculated for Antarctic meteorites from $\sp{36}$Cl data are generally $<$100 kyr. Multivariate statistical analyses of the labile trace elements in 38 Antarctic finds and 58 non-Antarctic falls, all H chondrites, indicates that meteorites of long ($>$50 kyr) terrestrial age are the most compositionally distinct from falls. Meanwhile, the Antarctic meteorites most recently captured by the Earth are not distinguishable from the (also recently captured) falls. This is strong evidence that the differences seen between Antarctic and non-Antarctic meteorites are the result of temporal variations in the H chondrite flux to Earth.
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