Australian scientist seeks to update carbon-14 dating techniques

Carbon-14 dating of fossil bones is an important tool for a variety of scientific disciplines, yet its inaccuracy is called "the elephant in the room" by an ecologist at the University of Adelaide in Australia. 

The case for dating reform appears in the Jan. 13 issue of the Royal Society Open Science journal. Author Salvador Hernando-Pérez, a quantitative ecologist, reviews the problem, using results from a questionnaire survey he conducted involving 132 researchers in 25 countries. Hernando-Pérez also makes recommendations for correcting the problem.

Carbon-14 (C-14) dating, the author states, "has meritoriously established itself as one of the most powerful tools for dating cultural and paleontological deposits from the late Quarternary" period, approximately the past 55,000 years. C-14 dating determines a sample's geological age by counting the C-14 atoms remaining in the sample using accelerator mass spectrometry, or by measuring radioactive beta decay of carbon-14 into nitrogen-14.

The problem is that the contamination of the fossil samples, even with small amounts of modern C-14 and other substances, significantly distorts the results. Also the different methods used to prepare and decontaminate the samples contribute to unreliable dating, the author says. 

The inaccuracy is not trivial.

"Suffice it to say," Hernando-Pérez writes, "a 55,000-year-old sample contaminated with only 1% modern [C-14] will result in a 40,000-year [age] measurement." 

He elaborates on what this means for scientists seeking to determine the date of major extinctions. Contamination can cause age discrepancies ranging from hundreds to thousands of years, he writes. 

"If we were characterizing the environment experienced by the animal or human individual being dated, this 15,000-year error would place the fossil in any of three different transitions from cold (stadial) to warm (interstadial) palaeoclimates over the Last Glacial Period," he said.

Fossil bone contamination, the author says, is caused by the collagen protein in the bone and the bone's mineral content both reacting with their environments such as soils, sediments rain and groundwater. 

Four standard pretreatment methods currently are used to remove contamination before the sample is sent to a facility for accelerator mass spectrometry, he writes, including gelatinization, ultrafiltration, XAD-2 resin (chemical) purification, and hydroxyproline isolation. He notes that there's also a possibility that the equipment used in the procedures could contaminate the sample. 

Researchers rarely talk about or report which methods they use in preparing their fossil sample when writing about their results, Hernando-Pérez says.

Hernando-Pérez's survey involved a wide range of Quarternary scientists in archaeology, geochronology and paleontology. He found that most researchers were aware of the contamination problem (86%). But more than half the researchers surveyed (52%) left the pretreatment choice up to the accelerator mass spectrometry facility. Procedures at these accelerator facilities vary, he writes, and make it difficult to compare results.

Hernando-Pérez has specific recommendations to fix the problem. First, he says, new, affordable methods of analytic chemistry should be developed specifically for measurement of low-mass samples of collagen amino acids, and funding agencies should finance this research.

Second, a certification agency needs to be established to "oversee quality control, training and certification" in the field of C-14 dating. Third, there should be encouragement of cross-disciplinary relationships to create awareness of the best pretreatment methods and standardization of those methods for dating bone using carbon-14.

Hernando-Pérez concludes that scientists using C-14 data "should be conceptually more involved in the chemical processes of data generation--without such involvement, bone pretreatment might yet remain for many years as an elephant in the room of [C-14 dating]." 

A short video on carbon-14 dating appears here.