Prehistoric people in Saharan Africa had dairy farming operations 7,000 years ago, a new study reports — an insight revealed by their pottery. Researchers performed isotope analysis on samples drawn from excavated pottery, and were able to identify organic residues that originated from dairy fat.

The findings appear in the current issue of the journal Nature. The researchers found that the pottery, from a site in Libya known as the Takarkori rock shelter, retained an abundance of carbon isotopes related to fats from ruminant animals, like dairy and adipose fats, said Julie Dunne, an archaeologist at the University of Bristol in England and the study’s first author.

The analysis also indicates that the prehistoric dairy farmers were processing milk.

“We know that they were heating it, to make butters and so on,” Ms. Dunne said. “We can’t tell whether it was butter, cheese or yogurt, but we can tell they were processing it in the pots.”