Brigham Young University scientists are part of a team that coaxed dirt into giving up chemical secrets, proving that an ancient Mayan city had a marketplace economy.

The discovery may overturn the prevailing theory about food distribution among the lowland Maya who lived in what became Mexico, Guatemala and Belize. The site is the ruined city of Chunchucmil in Mexico's Yucatan Peninsula, an important center during what's termed the Early Classic era, 450 A.D. to 700 A.D.

A report on the find is published in today's edition of Latin American Antiquity, a quarterly journal of the Society for American Archaeology. Authors are Bruce H. Dahlin, archaeologist at Shepherd University, Shepherdstown, W.V., the paper's lead; Christopher T. Jensen, Richard E. Terry and David Wright, BYU, Provo; and Timothy Beach, Georgetown University, Washington, D.C.

A humid tropical climate quickly destroys organic material, and experts calculate that 90 percent of the Mayas' belongings were made of perishables like wood, shell, fabric or other types of organic matter.

But architectural remains show that many of the ancient cities, including Chunchucmil, were so extensive that they could not have supported themselves through farming the nearby available agricultural land, so they needed to import food.

Dahlin said conventional wisdom was that the Maya didn't have a market economy, that "they depended on a redistribution economy." Under that theory, royal families would demand tax or tribute "and then redistribute them back down (to their subjects) as payment for loyalty and fealty."

When he began working at Chunchucmil, he said, it became clear that the city had a huge population. "We're talking maybe 40,000 people." Yet it was built in an area that was "horrible" for agriculture, unable to support the city. Food must have been imported.

Then Terry and some of his students from BYU visited. Talking with Dahlin, they became interested in a leveled central plaza, a place where streets converged in the center of the city. It seemed ideal for a marketplace, and Terry and the students went to work, searching for indications in the rich, black soil that could show its use.

Terry, environmental scientist and professor in the BYU Department of Plant and Wildlife Sciences, said his group is carrying out soil chemistry analysis of samples from the plaza. "Every few meters we take a soil sample," he said. They gather hundreds, noting where they were obtained. Then he and student researchers "take them to the laboratory for analysis."

At the Provo lab, some BYU students who are not able to travel to Mexico for on-site work are involved in the analysis.