IMERETI, GEORGIA -- Ca' Foscari University of Venice announced that when an international team of researchers first began to analyze 34,000-year-old stone tools found in the Dzudzuana Cave in the foothills of Georgia's Caucasus, they were just hoping to learn something about how they were used. However, as they peered closer, they uncovered incredible evidence of human behavior and complexity dating back tens of thousands of years. The pebble grinding tools contained traces of plant matter and indigotin, the deep blue compound also known as indigo. The results were stunning -- not only was this the first time that indigo has been found on ancient tools, but the substance does not naturally occur in its blue form. It is born from a reaction when the leaves of the woad plant are crushed and exposed to oxygen. What surprised researchers even more is that woad is not edible, so hunter-gatherers would have had no immediate need to harvest it. Although experts still do not know why indigo was being processed, whether for dying or medicinal purposes, the discovery shows that Upper Paleolithic peoples were able to identify secondary uses for plants beyond their nutritional value. "Rather than viewing plants solely as food resources, as is often the case," said archaeologist Laura Longo of Ca' Foscari University of Venice, "this study highlights their role in complex operations, likely involving the transformation of perishable materials for use in different phases of daily life." Read the original scholarly article about this research in PLOS One. To read about the use of indigo to dye textiles some 5,800 years ago, go to "Blue Collar in Ancient Peru."