A 4,500-year-old rain of iron
Between 4,200 and 4,700 years ago, a meteoroid with an estimated mass of 800 tons tore through Earth's atmosphere over northern Argentina. The parent body, originating from the asteroid belt between Mars and Jupiter, broke apart during its fiery descent. This atmospheric fragmentation created a meteor shower that scattered thousands of iron-fragments over a long, narrow area measuring approximately 18.5 by 3 kilometers. The event changed the area, forming a field of at least 26 impact craters. The largest of these craters measures 115 by 91 meters.
The meteorites belong to the IAB-MG classification, a type of iron meteorite. Their composition is roughly 92% iron and 6.7% nickel, with trace amounts of cobalt, phosphorus, and other elements like gallium, germanium, and iridium. The total weight of all recovered pieces exceeds 100 tons, making Campo del Cielo the heaviest set of meteorites ever found on Earth. Two fragments in particular are among the largest single-piece meteorites in the world: the Gancedo meteorite, weighing 30.8 tons, and the El Chaco meteorite, at 28.8 tons. For comparison, the world's largest, the Hoba meteorite in Namibia, weighs about 60 tons.
From sky-metal to earthly tools
Long before Spanish explorers arrived in the 16th century, the region's indigenous peoples knew of the iron masses. The Moqoit people called the site Pigüem N'onaxá and considered the metal to be gifts from the sky, incorporating the event into their oral histories. They treated the area as a sacred place of pilgrimage and used the extraterrestrial iron to forge weapons and tools. This is one of the earliest examples of humanity using iron from space, predating the Iron Age in the Americas.
In 1576, a Spanish governor, hearing tales of iron falling from the sky, sent an expedition to investigate. The expedition found a large metal mass protruding from the ground, which the indigenous people called Piguem Nonralta. The Spanish translated this as Campo del Cielo, or "Field of the Sky." Early European explorers mistakenly believed the iron to be the outcrop of a vein, with one expedition in 1783 even using explosives to try and assess the mass before abandoning it. It was not until later analysis of samples sent to the Royal Society of London, which were found to contain 90% iron and 10% nickel, that the meteoritic origin was confirmed.