Terrestrial ages of meteorites from the Atacama Desert (Chile) and insights into the past meteorite flux to Earth

Abstract The Atacama Desert in Chile is characterized by its high meteorite density and old meteorite terrestrial ages. In this work, we present new terrestrial ages derived from measurements of the concentration of cosmogenic 36 Cl in the metal fraction of 51 ordinary chondrites collected over a 6.8 km 2 area located in the Catalina Dense Collection Area (Atacama Desert). Cosmic‐ray exposure ages were also measured on a subset of the oldest meteorites to confirm that all but one had reached 36 Cl saturation before atmospheric entry. These meteorites have exceptionally old terrestrial ages, with an average of 937 ka (median 701 ka), making this collection the oldest known meteorite collection among hot deserts. This confirms that the Atacama Desert can preserve meteorites for long periods due to the prevailing stable hyper‐arid climatic conditions. By combining terrestrial ages with pairing‐corrected meteorite density estimates, we estimate the long‐term meteorite flux to Earth over the past 2 Myr to be 74 ± 9 meteorites >20 g per km 2 per Myr. This is consistent with estimates of (i) the modern flux, (ii) the integrated flux over the last ~100 kyr determined from Antarctic meteorites, and (iii) the average flux during the last ~50 kyr inferred from other hot desert collections. This suggests that the bulk meteorite flux to Earth has remained roughly stable over the past 2 Myr. We also investigate the compositional evolution of the flux by normalizing the H chondrite abundance to the total abundance of ordinary chondrites. Our results show a higher H chondrite abundance between 1200 and 400 ka, followed by a decline to present‐day values. This temporal variation is not captured by the current dynamical models for meteoroid transfer to Earth, suggesting that short‐term changes in the meteorite flux may be influenced by additional processes operating at a scale not considered by these models.