UNIVERSITY PARK, Pa. — Mysteries of the ancient world, buried deep in the earth or hidden in a silent tomb, can provide clues and context to history. However, for those mysteries to be fully understood, radiocarbon dating is often an essential step in the process. The researchers in Penn State’s Radiocarbon Laboratory, Brendan Culleton and Maggie Davis, provide those services to Penn State researchers. They also collaborate with researchers from around the world. Through these collaborations, they share best practices, their expertise and training to improve what can be a delicate science with no room for error. 

Radiocarbon dating is the process of determining the age of things that once lived. The process is possible because during any living thing’s existence, it absorbs carbon. That includes a portion of carbon that is radioactive, called carbon-14. When the plant or animal dies, carbon is no longer absorbed. However, the carbon-14 inside the now-deceased fauna or flora continues its radioactive decay. Radiocarbon dating measures the amount of radioactive carbon remaining in the subject and provides an estimated date of when something died.

Since Penn State's Radiocarbon Laboratory started in 2016, Culleton and Davis have produced nearly 11,000 radiocarbon measurements. Last year, they provided more than 2,200 measurements. However, for a sample to be measured, it must be prepared for the accelerator mass spectrometer (AMS). 

“We can do a lot of chemical processing to purify the sample and get it into a form that we can put on the AMS, which is graphite,” said Culleton, a research professor in the Institutes of Energy and the Environment (IEE) and principal operator of the AMS. “For samples that require that level of preparation, it is a time-consuming process.” 

Davis, a research technologist in IEE, works in the Radiocarbon Prep Lab, where samples are transformed into graphite.  

“I preclean, chemically purify, combust to carbon dioxide and graphitize the carbon dioxide to turn the samples into graphite whose radiocarbon ratio can be measured by the AMS,” Davis said. 

The AMS will precisely measure the amount of carbon-14 in a sample, but in the case of contamination, it cannot distinguish between the carbon from the sample and carbon from contaminants, so proper sample preparation is a crucial step. 

“For example, a piece of charcoal buried in soil for 1,000 years may contain carbon from the organic material in soil, or soil humates, that have soaked into the charcoal, and the charcoal may be covered in sediment,” Davis said. “These soil humates and the sediment are probably a very different radiocarbon age from the charcoal. Careful sample prep removes the contaminating material that is a different radiocarbon age, so that the AMS measurement of the radiocarbon ratio accurately reflects the age of the charcoal rather than the age of a mixture of charcoal, soil humates and sediment.”

Currently, Penn State’s Radiocarbon Laboratory has strong collaborative relationships with multiple institutions around the world, including numerous U.S. schools, such as Baylor University; Harvard University; Texas A&M University; University of Nevada, Reno; University of New Mexico; University of Oregon; and the University of Pittsburgh. 

“Expanding access to our radiocarbon facilities, knowledge and expertise is a key part of Penn State’s Radiocarbon Lab's mission and a critical aspect of developing the lab as a vital enterprise,” Culleton said. “Ongoing efforts to help colleagues equip their own labs for sample preparation reduces sample costs for them, reduces labor demands on our staff, and gives researchers, graduate and undergraduate students hands-on experience with radiocarbon science.” 

One of the individuals who works with Culleton and Davis is Heather Thakar. She is an assistant professor at Texas A&M who operates a radiocarbon and stable isotope sample preparation lab. One of her focus areas is archaeobotany, the study of ancient plant remains. 

“The sample preparation lab that I run at Texas A&M is modeled after the sample preparation lab at Penn State,” Thakar said. “It was built in collaboration with and under the advisement of Brendan. Additionally, we run all our standards with the Penn State Radiocarbon Lab to verify that our protocols are giving us a good date.” 

Claire Ebert, a Penn State alumna who graduated with her doctoral degree in anthropology in 2017, is an assistant professor of anthropology at the University of Pittsburgh. Her research focuses on relationships between humans, their environments and sustainability among the ancient Maya. 

“I like to collaborate with Penn State’s Radiocarbon Lab because of the expansive knowledge that Brendan has on the topic and his willingness to teach students about these important archaeological dating methods,” Ebert said. “For example, when I was a postdoc at the University of Pittsburgh, I taught a course called ‘Radiocarbon Chronology Building in Comparative Archaeology.’ The goal of the course was to expose students to the broad array of research questions that can be addressed with radiocarbon dating, in addition to providing hands-on experience in analyses.” 

Ebert made a field trip to Penn State’s Radiocarbon Laboratory as a part of the course.  

“Serving as our guide, Brendan walked students through the process of collecting samples in the field, chemically treating them in the lab, and running them on the AMS,” Ebert said. “This was a truly unique learning experience to see every step in the process.”  

Christopher Jazwa, who received his doctoral degree from Penn State in 2015, is an associate professor of anthropology at the University of Nevada, Reno. Jazwa uses radiocarbon dating to build and refine chronologies of past human settlements.  

“Brendan and Maggie have supported our research through collaboration, advice and generating data from samples,” Jazwa said. “This includes discussing best strategies for sample selection and processing, particularly for sensitive samples.” 

Jazwa’s long-standing connection to Penn State’s Radiocarbon Laboratory has had many benefits. 

“In addition to trusting the reliability of the data they provide, I know that they provide well-informed and academically rigorous responses to any questions that I have,” Jazwa said. “They have also shared international sample standards and have assisted with processing challenging samples. It is also enjoyable to work together on research projects in which we each contribute different expertise.”