Archaeologists have found what they think are the oldest remains of slaves brought from Africa to the New World.

The remains, in a colonial era graveyard in one of the oldest European cities in Mexico, date between the late-16th century and the mid-17th century, not long after Columbus first set foot in the Americas.

The African origin of the slaves was determined by studying a chemical in their tooth enamel that reveals plant and rock types of their native land. The chemical enters the body through the food chain as nutrients pass from bedrock through soil and water to plants and animals. It is an indelible signature of birthplace, the researchers said, because it can be directly linked to the bedrock of specific locales.

Researchers examined remains of four individuals from among 180 burials found in a multiethnic burial ground associated with the ruins of a colonial church in Campeche, Mexico, a port city on the Yucatan Peninsula.

"This is the earliest documentation of the African Diaspora in the New World," said study co-leader T. Douglas Price of University of Wisconsin-Madison. "It does mean that slaves were brought here almost as soon as Europeans arrived."

The discovery will be detailed in the American Journal of Physical Anthropology.