The meteorite flux of the past 2 m.y. recorded in the Atacama Desert

The evolution of the meteorite flux to Earth can be studied by determining the terrestrial ages of meteorites collected in hot deserts. We measured the terrestrial ages of 54 stony meteorites from the El Mdano area, in the Atacama Desert, Chile, using the cosmogenic nuclide 36 Cl. With an average age of 710 ka, this collection is the oldest collection of nonfossil meteorites at Earth's surface. This allows both determination of the average meteorite flux intensity over the past 2 m.y. (222 meteorites larger than 10 g per km 2 per m.y.) and discussion of its possible compositional variability over the Quaternary Period. A change in the flux composition, with more abundant H chondrites, occurred between 1 and 0.5 Ma, possibly due to the direct delivery to Earth of a meteoroid swarm from the asteroid belt.