Beryllium-10 and Aluminum-26 in Individual Cosmic Spherules from Antarctica

We present data for the cosmogenic nuclides Be-10 and A-26 in a suite of 24 extraterrestrial spherules, collected from Antarctic moraines and deep sea sediments. All of the 10 large spherules collected in glacial till at Lewis Cliff are extraterrestrial. As in earlier work, the great majority of particles show prominent solar cosmic-ray (SCR) production of Al-26, indicating bombardment ages on the order of 106 years or even longer. These long ages are in direct contradiction to model ages for small particles in the inner Solar System and may require reconsideration of models of small particle lifetimes. A small fraction of the particles so far measured (6/42) possess cosmogenic radionuclide patterns consistent with predictions for meteoroid spall droplets. We believe that most of the spherules were bombarded in space primarily as bodies not much larger than their present size. The content of in situ produced Be-10 and Al-26 in quartz pebbles in the same moraine suggests that these spherules may have on average a significant terrestrial age.