COLLEGE STATION --
By analyzing and dating rock paintings, two Texas A&M University chemists hope to develop better ways to preserve history while offering a glimpse into what life was like for ancient Native Americans.
Marian Hyman, a senior lecturer in chemistry, and chemistry professor Marvin Rowe and their colleagues and graduate students are using radiocarbon dating, x-ray diffraction and DNA analysis to study rock paintings in the lower Pecos River region of Texas. This area has the largest concentration of rock paintings in North America.
Archaeologists believe the region has been home to a series of Native American cultures for 11,000 years, Hyman said. By determining the approximate age of rock paintings, she said, they can help anthropologists assign the artworks to specific cultures.
Hyman said studying rock paintings reveals a different aspect of cultures from other artifacts that are left behind.
"The paintings are in a different realm from other artifacts because they tell what people were thinking about," Hyman said. "They're what was important to people in their thoughts."
Dating rock paintings presents special challenges, Rowe said. Radiocarbon dating requires the presence of dead animal or plant material to measure the rate of carbon decay.
"The paints are generally inorganic and can't be dated directly," he said. "For us to use radiocarbon dating, they had to have added something organic to the paint."
Collecting samples also presents a unique problem, Hyman said. Many of the paintings are located on the sides of cliffs, in rock overhangs or along river banks and are difficult to reach.
Once they collect samples and purify the organic components in the lab, they are often left with a sample weighing only 100 one-millionths of a gram to radiocarbon date, about the weight of a grain of salt.
They also face a lack of rock painting standards with which to compare their results, Rowe said. Because no other chemists have attempted to date rock paintings that utilize inorganic pigments such as iron oxides, Rowe and Hyman must find other ways to check their results.
"We don't have any paintings where we know exactly when they were painted," he said. "We have to rely on archaeological inference to determine how old they are.
"We have dated materials such as archaeological charcoal, 4,500-year-old wood, used worldwide as a radiocarbon standard, and an African ostrich eggshell of known age to verify our technique for dating rock paintings."
By studying the chemicals in the paints, the rocks they are painted on and the chemical deposits covering rock paintings, Rowe and Hyman also hope to devise better ways to protect and preserve them.
"One of the goals in the back of our minds is conservation," Rowe said. "Many of these paintings are on the verge of coming off the wall."
Rowe said that when a foreign surface is put on rock, such as water or a preservative coating, it may look stable, but over time, it may not be. If it comes off, he said, it may pull the paint off with it.
"People do things they think are totally innocuous, like spraying water on a painting to make a better photograph, and that can cause the surface to become more unstable," Hyman said.
Archaeologists from around the world have contacted Rowe and Hyman about dating paintings in other countries such as Angola, Australia, Mexico, France, Spain and Sri Lanka.
Meanwhile, work continues on the Pecos River paintings. Graduate students working under Rowe and Hyman have used DNA analysis to analyze blood used in the paints. They have identified the blood as having come from a hoofed mammal. Further tests should identify the exact species.
Rowe and Hyman's work is supported by the National Center for Preservation Technology and Training, which is connected with the U.S. National Park Service.
CONTACT: Mark Evans at (409) 845-4382 or firstname.lastname@example.org. Dr. Marvin Rowe may be reached at (409) 845-1929 and Dr. Marian Hyman at (409) 845-4084.
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