The flux of meteorites to the Earth over the last 50 000 years

Abstract

98 ordinary chondrite finds, terrestrial age-dated using 14C analyses by Jull et al., from three arid/semi-arid meteorite accumulation sites (New Mexico, the Sahara, and the Nullarbor Region, Australia) have been examined by Mössbauer spectroscopy to determine quantitatively the terrestrial oxidation for each sample. A comparison of weathering over time, and its effect in ‘eroding’ meteorites, allows a calculation of a decay constant for meteorites from each hot desert site. This, together with the number and mass distribution of paired meteorites in each region, enables us to derive estimates of the number of meteorite falls over a given mass per year: we calculate between 36 and 116 falls over 10 g per 106 km2 yr−1. In addition, we constrain the total mass flux to the Earth's surface over the 10 g to 1 kg interval to between 2900 and 7300 kg yr−1. We find remarkable agreement in our estimates from each accumulation site, and also with the estimate of the present flux made from MORP camera network data presented by Halliday, Blackwell & Griffin, suggesting that the flux of meteorites to the Earth has remained essentially constant over the last 50 000 yr. This work is the first independent confirmation of the MORP estimate, and indicates that meteorite accumulation sites provide an alternative method of calculating flux. We suggest that the application of a similar methodology to the Antarctic meteorite population may be used to explore the possibility that the flux of meteorites to the Earth has varied over the 1-Ma time-scale sampled by these meteorites.