A chemical signature found in 1000-year-old corn cobs may help solve the mystery of where the ancient denizens of New Mexico's Chaco Canyon got their dinner. Despite the canyon's barren and arid landscape, the Chaco people flourished from the 9th to 12th centuries A.D. in the mesa lands of northwest New Mexico, constructing many "great houses," some of which contained more than 500 rooms.
The origin of the food that supported the Chaco building spree and fed the presumably large population of residents and laborers has bedeviled archaeologists. Scant rainfall and early winter frosts make agriculture in the canyon unreliable. To take another stab at this mystery, a multidisciplinary team of scientists led by geochemist Larry Benson of the U.S. Geological Survey in Boulder, Colorado, and archaeologist Linda Cordell of the University of Colorado, Boulder, checked to see if maize takes on the isotope ratios for strontium and other trace elements of the soil that it grows in. When they established that it did, they compared corn found at the site with soil samples from potential agricultural sites outside of Chaco Canyon.
The team collected seven ancient corn cobs from the largest great house in Chaco and 10 cobs from a newer great house 100 kilometers to the northwest. Their isotope signatures suggest that the oldest corn from the Chaco site probably originated 80 kilometers away at the base of the Chuska Mountains, while later corn from Chaco and the outlying great house most likely came from the floodplains 90 kilometers to the north, the researchers report online this week in the Proceedings of the National Academy of Sciences.
The paper is "tremendous," says Mollie Toll, a paleoethnobotanist at the Office of Archaeological Studies at the Museum of New Mexico in Santa Fe. Toll and others suggested a similar pattern of corn trade 20 years ago, based on the large size and excellent quality of corn cobs found in the most central Chaco great houses--they didn't match the "runty" water-starved cobs found in smaller, less central Chaco Canyon communities. However, "there'd been no way to test the ideas before," she says. John Kantner, an archaeologist at Georgia State University in Atlanta, adds that the findings are consistent with a much-cited hypothesis, that Chaco was a ritualistic gathering spot that may not have had a permanent population--a center that exported some unknown ideology in return for life-supporting commodities such as maize.