Recently, news articles have been suggesting that the earliest archeological finding of human inhabitants in all the Americas is at at Toca da Bastiana rockshelter at Serra da Capivara National Park, Piaui, Brazil. At this sandstone overhang shelter, rock paintings of red ochre symbolizing humans, animals, and designs were found.

These “cave-paintings” were found under a 2 mm thick layer of the mineral calcite, suggesting the antiquity of the paintings. Calcite is formed when water deposits calcium-rich minerals on a rock surface over time, which builds up gradually with successive wettings and dryings of the rock surface. Very similar to how stalactites and stalagmites form in caves. When the calcite crystals first form out of aqueous solution, their radioactive decay first begins, and so they keep the radio-carbon “signature” of the time of their formation.

Watanabe et al. (2003) decided to radio-carbon date the calcite layer, since they supposed…