The flux of meteorites to the Earth and weathering in hot desert ordinary chondrite finds

Abstract

The abundance of ferric iron, produced by weathering in ordinary chondrites collected from hot desert regions, is related to their terrestrial age, enabling a variety of processes involved in meteorite weathering to be deduced. Fe 0/Fe 2+/Fe 3+ content was measured quantitatively by 57Fe Mössbauer spectroscopy. It is observed that meteorites from different regions are oxidised at different rates. We also propose the tentative hypothesis that one source of scatter in total oxidation versus terrestrial age for a region is climatic change. A mechanism to explain the variable response to climatic conditions involves the high initial porosity of samples being reduced as ferric oxides and other alteration products are produced. Reliable recovery data from a meteorite accumulation site (Roosevelt County, New Mexico, USA) and a quantitative measure of weathering and terrestrial age permit an estimate of the flux of meteorites to the Earth's surface. Having established a decay constant for meteorites, and accounting for the area of searches and pairing, we estimate an accumulation rate of 159 falls of mass greater than 20 g per 10 6 km 2 per yr. This calculation is distinct from, but in broad agreement with, previous estimates from camera observations, suggesting that the accumulation rate of meteorite falls to the Earth's surface has remained essentially unchanged over the last 50,000 years at between 59 and 159 falls of mass exceeding 20 g per 10 6 km 2 per yr. The error for both methods is approximately a factor of 2.