Rock varnish itself contains some organic matter. Rock varnish forms very slowly, if at all, on trimmed stones that are stored in a dry, sheltered place. The Andean monument bears a striking resemblance to monuments found in ancient sites in western Asia. The reuse of ancient trimmed stones was common in the Andes both before and after 1492.
When a stone is trimmed by a mason and exposed to the elements, a coating of clay and other minerals, called rock varnish, gradually accumulates on the freshly trimmed surface. Organic matter trapped beneath the varnish on stones of an Andean monument was found to be over 1, 000 years old. Since the organic matter must have grown on the stone shortly after it was trimmed, it follows that the monument was built long before the arrival of Europeans in the Americas in 1492.
Which one of the following, if true, most seriously weakens the argument?