A Library of fallen worlds
The Atacama Desert is the oldest and driest non-polar desert on Earth. Some areas have been hyper-arid for at least 7 million years, creating a uniquely stable environment. While meteorites fall everywhere, they typically degrade and disappear within thousands of years due to weathering. Here, the lack of moisture and vegetation preserves them on the surface for immense timescales. This makes the Atacama a dense collection area, with some surveys finding up to 170 meteorites over 10 grams per square kilometer.
Scientific analysis of meteorites from the Atacama shows a continuous record of impacts stretching back over 2 million years. Cosmogenic age dating, using isotopes like chlorine-36, measures how long a meteorite has been on Earth's surface. Studies of specimens collected in the desert show that about 30% are over a million years old, with some having rested in the desert for more than two million years, making this the oldest known surface collection of meteorites on the planet. This long-term record allows scientists to study the meteorite flux, the rate and type of material falling to Earth, and has shown it remained relatively constant at about 222 meteorites (larger than 10 grams) per square kilometer every million years.
The Vaca Muerta and other treasures
One of the most significant finds from the region is the Vaca Muerta meteorite. First discovered by prospectors in 1861, it is a mesosiderite, a rare type of stony-iron meteorite composed of roughly equal parts nickel-iron metal and silicate rock. Mesosiderites are thought to originate from the boundary between the core and mantle of a large asteroid that was shattered by an impact. The total known weight of the Vaca Muerta strewn field exceeds 3,800 kilograms, spread across an area 11.5 kilometers long. The metallic portions of Vaca Muerta specimens display a fine Widmanstätten pattern, a crystalline structure unique to meteorites that cooled slowly over millions of years inside their parent body.
The majority of meteorites found in the Atacama are ordinary chondrites, stony meteorites that are remnants from the formation of the solar system. These are broadly classified into H (high-iron), L (low-iron), and LL (low-iron, low-metal) types. Analysis of the Atacama collection revealed a curious spike in the proportion of H chondrites that fell between one million and 500,000 years ago, suggesting a large asteroid disruption event in the solar system during that period.