COLLEGE STATION --
Among the canyons of the Lower Pecos, Marvin Rowe climbed up a ladder to sample ancient cave paintings moldering on the ceiling of a bluff shelter. In Missouri, he descended 60 yards into a pitch-black cave to sample pictographs by the light of his miner's helmet. When he confronted a painting called "Red Diablo" on the face of a towering cliff in the wilds of Guatamala, Rowe balked: He sent a local fireman down the rope instead. But he got his sample.
Rowe, a chemistry professor at Texas A&M University, has been exploring caves and taking tiny samples of rock art for more than a decade. Dank limestone and fading pictographs are an odd milieu for a chemist, but this chemist can say something about cave art that anthropologists can only guess at: How old it is.
Rowe developed a technique for dating the figures and shapes that ancient people painted on cave walls. Though they expressed their humanity with art, it takes chemistry to put the bygone artists on a historical timeline, said Emile Schweikert, head of the Department of Chemistry. Schweikert presented Rowe a chronometer Tuesday to mark Tuesday as the occasion that Rowe gave the final lecture of the season in the university's Distinguished Lecture Series.
This "Snake Shaman" about 4 feet tall in the Lower Pecos
Karen Steelman, Dr. Rowe's current graduate student, standing by the plasma-chemical extraction apparatus they use iin dating cave art.
Before a large crowd in the auditorium of the Presidential Conference Center, Rowe said he started thinking about rock art when a friend in the Department of Anthropology asked him if he could try to determine the age of a chunk he had acquired from a rock painting.
"I said sure," Rowe said.
He researched the subject but, finding no clues about how to do it, he was left to come up with his own way. The existing radiocarbon dating process required carbon. But how to extract carbon from manganese and iron oxides on a cave wall?
"In principle it's very simple," Rowe said. "In reality, it's not so simple."
His solution involves a borrowed radio-frequency generator, a mass spectrometer and a reaction that oxidizes organic material in the ancient artwork while leaving it largely intact.
But would the process work? Rowe recalled an early test run on a sample that anthropologists had estimated as between 1,000 and 8,000 years old.
He ran it through his process and determined the age to be 4,000 years. "Right in the middle - so we knew it worked," Rowe said, deadpan.
He introduced his technique in 1990, and since then his expertise has borne him to caves around the world.
Though he has done much of his work among the deep canyons of the Lower Pecos, a Southwest Texas region thick with rock art, he has traveled to several continents. He flew to France, where the caves are famous for beautiful paintings done in charcoal. Although charcoal was easy to date by earlier techniques, Rowe did his own tests, using the established dates as a baseline to test the accuracy of his results. In Guatamala, Rowe sampled rock art as clear as subway graffiti (except where vandals had smeared it). And in Australia, he encountered the tattooed man of caves -- every surface was covered with rock art, including many pictures of naked women.
Rowe's dating process has placed some art within the expected timeframes, but it also has exposed some false assumptions.
It turns out, for instance, that he goggle-eyed figure with footprints on his face, adorning a cave wall in Hueco Tanks State Historical Park, was not an Aztec god after all. Rowe revealed the picture to be too old.
A crescent moon and a star-like figure were thought to represent a supernova explosion recorded nearly 1,000 years ago.
"Unfortunately we found that it's much too young," Rowe said.
In Russia, a local cave-art expert had convinced himself that the figure he was looking at on one cave wall was a wooly mammoth.
But Rowe dated it at only 7,000 years old - much too recent. The Russian was reluctant to abandon his mammoth theory in the face of Rowe's results. His stubbornness brought another timeline into play.
"It took two years for us to convince him," Rowe said.
Contact: Mark Minton, communications specialist, Texas A&M University College of Science; (979) 862-1237 or firstname.lastname@example.org