Age of Allan Hills 82102, a meteorite found inside the ice

THE recovery of thousands of meteorites in the Antarctic since 1969 has not only greatly increased knowledge of the meteorites themselves but has also provided a new tool for glaciology. Most Antarctic meteorites are found on blue ice areas where old ice is continuously ablated. A measurement of the age of this ice helps us understand meteorite accumulation mechanisms and the dynamics of ice movement. The terrestrial age of a meteorite, the time period since the date of meteorite fall, can be determined from the reduction in concentration of cosmogenic radionuclides during the time the meteorite has been shielded by the Earth's atmosphere. Here we report the terrestrial age of a meteorite that was recovered from below the surface of the ice and argue that this represents a measurement of the age of the ice itself. We measured the cosmogenic radionuclides ¹⁰Be (half-life = 1.5 Myr), ¹⁴C (5,730 yr), ²⁶A1 (0.71 Myr), ³⁶C1 (0.30 Myr) and ⁵³Mn (3.7 Myr) in the meteorite and ¹⁰Be and ³⁶C1 in the ice. We obtained a terrestrial age of 11,000 years for the meteorite which suggests that the snow accumulation area where it fell was only a few tens of kilometres away.