Archaeologists have discovered what may be the oldest remains of African slaves in the Americas.

They were found in a graveyard dating between the late-16th century and mid-17th century in Mexico. This was shortly after Columbus first landed in the Americas, reports LiveScience.com.

Researchers examined the remains of four people and determined they were of African origin by studying a chemical in their tooth enamel. It showed which plant and rock types were in their native land.

The chemical can be directly linked to the bedrock of certain places. Nutrients go from the bedrock through soil and water to plants and animals, according to LiveScience.com.

The remains were found in a multiethnic burial ground in the ruins of a colonial church in Campeche, Mexico.

"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."

Their findings are published in the American Journal of Physical Anthropology.