The accuracy of carbon dating may soon be a thing of the past.
Carbon emissions from burning fossil fuels threaten the method’s ability to definitively pinpoint the age of organic materials, new research suggests. The extra carbon flooding the atmosphere dilutes the relative number of radioactive carbon atoms that are vital to the dating method. By 2050, the age of fresh organic matter will appear indistinguishable from material created in A.D. 1050, predicts Heather Graven, an atmospheric scientist at Imperial College London. Her work appears online July 20 in the Proceedings of the National Academy of Sciences.
“It’s quite rapid,” Graven says. “By the end of the century, the atmosphere will look a couple thousand years [older than it really is]. Some of the ways that we use radiocarbon now will be less effective.”
Carbon dating can identify how long ago a living thing died going back around 50,000 years. The method can detect newer objects passed off as old, such as counterfeit relics or ivory poached after a 1989 international trade ban (SN Online: 5/6/15).
Following a spike in radioactive carbon-14 atoms from Cold War–era nuclear testing, carbon emissions from fossil fuel burning could reduce the ratio of stable and radioactive carbon below preindustrial levels by 2030. The rate of future emissions (colored lines represent different scenarios) will largely determine how much the atmosphere will appear to age by the end of the century, affecting the apparent age of organic materials.
Credit: H.D. Graven/PNAS 2015
In the atmosphere, cosmic rays convert stable nitrogen-14 atoms into radioactive carbon-14 atoms. Plants and animals absorb this radioactive carbon alongside stable carbon. When something living dies, its radioactive carbon-14 decays, leaving behind the stable carbon atoms. Comparing the number of stable and radioactive carbon atoms can determine an object’s age.
The method assumes, however, that atmospheric carbon-14 concentrations remain relatively steady. That assumption has already been muddled by a temporary carbon-14 spike following Cold War–era nuclear testing (SN: 2/21/15, p. 4). Now, an increase in fossil fuel emissions threatens to muddy the picture even more. Carbon atoms inside fossil fuels are so old that all the radioactive carbon has decayed and only stable atoms remain. As these ancient atoms saturate the atmosphere, they thin the concentration of carbon-14 atoms. Graven calculates that carbon emissions currently “age” the atmosphere by 30 years annually. Objects without sufficient clues to rule out modern origins will soon give ambiguous results, she says.
Researchers should now investigate alternative dating techniques, says Kevin Uno, a geochemist at Columbia University. “This work lays out when we’ll start having problems and [will] need to start going down these other paths,” he says. “It’s going to be a game of creativity.”