for National Geographic News
Researchers studying prehistoric human migration patterns in northern Chile's Atacama Desert have concluded that a mysterious pattern of early occupation and abandonment of the region was related to climate change.
Humans first occupied the high-altitude desert, which extends from the Pacific Ocean to the base of the Andes, from around 13,000 to 9,500 years ago. The region was then more or less abandoned until around 4,500 years ago, when people began returning.
This occupation, abandonment, and recolonization pattern has long intrigued archaeologists. One possible explanation was that the region may have had an inhospitable environment. Or the pattern could simply reflect holes in the archaeological record or some cultural bias at the time.
By matching climate and archaeological records, the researchers concluded that environmental conditions—specifically, bouts of extreme drought—explain the unusual pattern.
An Archaeological Puzzle
The team of two archaeologists and a geoscientist reached their conclusion based on their survey of archaeological sites at three elevations: the shorelines of paleo-lakes above 3,600 meters (12,000 feet); caves at elevations between 3,000 to 3,600 meters (12,000 to 9,800 feet); and low-altitude paleo-wetlands at 2,400 meters (7,900 feet).
To fill in the archaeological record—there was only one high-altitude campsite known to have been occupied between 13,000 to 9,500 years ago—the scientists adopted a somewhat novel interdisciplinary approach: They recreated the landscape that existed around 15,000 years ago.
"We first tried to reconstruct the paleo-environmental conditions in great detail," said Martin Grosjean, a geoscientist at Switzerland's climate research center at the University of Bern.
After identifying lake levels, shorelines, springs, and other geological formations, the researchers drew a map of ancient paleo-shorelines. From this they selected the most promising places where people are likely to have lived, then dug thousands of test pits.
"The first people arrived in small groups of extremely mobile hunters. They did not build houses, had no architecture of any kind," said Grosjean.
Taking the geo-scientific approach enabled the team to find 38 previously unknown high-altitude campsites that were occupied between 13,000 and 9,500 years ago.
"The sites are really small, absolutely unspectacular," he said. "The most we might find would be some obsidian flakes, maybe some small fireplaces, usually buried 2 to 5 centimeters [0.8 to 2 inches] below the surface. This is the only way you could find archaeological sites in such a large area."
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