Carbon dating used to date Adena Mound culture

A decision a century ago to save strips of tree bark and a phone call from a researcher last year led archaeologists at the Ohio Historical Society to more accurately date the former Adena Mound near Chillicothe.

Carbon dating used to date Adena Mound culture
Dates were obtained on two samples of bark and one fragment of textile. The bark produced dates of around A.D. 40, whereas the textile gave a date of 140 B.C. The explanation for why the textile appears to be so much older may be that the Adena people used an heirloom garment or shroud in the burial [Credit: Ohio Historical Society]
“Serendipity” is how Bill Pickard, the society’s assistant curator, described the events.

It started when Richard Sisson, a former Ohio State University provost, called from his home in New Mexico because he was researching a book. He wanted the precise dates for the early Ohioans.

“We had to tell him we didn’t know,” Pickard said. “But people like to know specifics.”

Precision dating of Ohio’s antiquities is important, said Bradley T. Lepper, the society’s curator of archaeology. “It’s hugely important in history for a particular site to have meaning."

Radiocarbon dating can be expensive, however — more than $500 per sample. And dating means destroying part of a collection to obtain organic samples.

In this case, Sisson and a group of students at Columbus School for Girls helped finance the project. But it never would have happened if it hadn’t been for William C. Mills.

In 1901, Mills, then curator of archaeology, excavated the 26-foot-tall burial mound that stood on former Ohio Gov. Thomas Worthington’s property in Chillicothe. It was Mills who saved bark that had lined the walls and shrouded the ancient people buried there.

“Mills chose to curate pieces of bark that had not been fashioned into artifacts and so could have been regarded by him as having no research value,” Lepper wrote in a paper to be published soon in the Midcontinental Journal of Archaeology.

Two fragments of black locust tree bark and one fragment of a plant-woven textile were adequate to produce three test results that dated the materials to 100 B.C. to A.D. 40. Previously, estimates were 700 B.C. to A.D. 100.

Carbon dating used to date Adena Mound culture
The Ohio Historical Society led the excavation of the Adena Mound in
Chillicothe in 1901 [Credit: Ohio Historical Society]
That means the state’s official artifact — the Adena Pipe — has a new date, too. Mills found the pipe during the excavation.

“These dates allow us to place this key mound and artifact more precisely within the sequence of Ohio’s American Indian history,” Lepper said.

The Columbus School for Girls students lobbied Ohio lawmakers for the pipe’s official designation.

“The girls thought it was very important for (the Adena) to be honored. They are our foundation for being a state,” said Charlotte Stiverson, one of two teachers who coordinated the project.

“They might not understand the exact time — 100 years, 1,000 years — when they are 10. But they understand all the different forms of science needed to learn more about history and how all of the different disciplines weave together.”

Years ago, large volumes of material were necessary to break down a sample small enough to analyze for carbon dating. That meant sacrificing large pieces of antiquity. But advances in radiocarbon dating have allowed the use of smaller fragments.

“We turn the sample into graphite, which is as close to 100 percent carbon as you can get,” said Chris Patrick, the deputy director of Miami-based Beta Analytic, which dated the Adena samples last year.

Carbon occurs in almost every organic life form on Earth. Its radioactive isotope, carbon 14, is sought for testing because its radioactivity decays over time at a known rate. Dating is made by measuring the activity level of the carbon 14.

The Adena collection consists of wood, bark, bone, clothing and human remains.

One of the pitfalls of dating wood or other historical artifacts is that they might be much older than the people who made things with them. Bark is desirable because it is newer than the wood it covers.

Clothing fibers often are used because they likely were grown and processed into yarn and fabric in a single year. The fiber in this sample was dated to 140 B.C., which is much older than the bark. It might have been an heirloom garment or burial shroud.

“I’ve always said that carbon-dating is like free shoes,” Pickard said. “If (the dates) fit, you keep them. If they don’t, you get rid of them.”

The dating work might one day pay dividends if Adena mounds can attract more visitors to Ohio, Lepper said.

“We should take more pride in it than many of us do,” he said. “These sites, and the Newark Earthworks, are spectacular — if you understand them.”

Source: The Columbus Dispatch [January 12, 2014]

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