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Fossil Fuels Are Messing With Carbon Dating

Burning gasoline and coal is bad news for archaeologists and forensic scientists alike.
(Photo: Lindert/Wikimedia Commons)

(Photo: Lindert/Wikimedia Commons)

There are many consequences of burning fossil fuels, though usually the focus is on climate: oceans will rise; megadroughts will attack; growing seasons will shorten. Now, there's another negative side effect to add to the list. According to a new report, our continual burning of fossil fuels is likely to mess with a key tool in science, industry, and even law enforcement: carbon dating.

Radiocarbon dating—carbon dating for short—is probably best known for its role in paleontology and archaeology, where it's used to figure out how old things like dinosaur bones or the Dead Sea Scrolls are. But the method's uses extend well beyond that: Researchers are hoping carbon dating can help prosecute ivory poachers, and the FBI's utilized the technique to help investigate unidentified human remains.

We won't be able to tell the difference between recently deceased plants and 2,000-year-old papyrus—the Dead Sea Scrolls, for example—by the year 2100.

But climate change may set back scientific and practical applications of carbon dating, Heather Graven, a climate physicist at Imperial College London, writes today in Proceedings of the National Academy of Sciences. If emissions grow as they have been, the carbon difference between something that's brand new and something that's 2,000 years old will negligible by 2100, Graven explains.

To understand Graven's argument, you must first understand how carbon dating works. Like most elements, carbon comes in multiple forms, or isotopes. One form, carbon-14, is radioactive. Over time, carbon-14 decays into nitrogen, but cosmic rays convert nitrogen into carbon-14, keeping supply high. The result is that the carbon ratio in the atmosphere stays the same over the years.

Now, plants constantly breathe in fresh carbon (in the form of carbon dioxide) from the atmosphere, so the ratio of carbon-14 to carbon-13 in their cells matches the ratio in the atmosphere. The same goes for animals that eat plants, and animals that eat those animals, and on up the food chain. But once they die, they stop taking in new carbon. In particular, they stop taking in new carbon-14, and what's left over at the time of death is left to decay. With time, the carbon ratio falls; the lower the ratio, the older the remains.

Trouble is, humans have surprising power over the relative amount of carbon-14 and carbon-13 in the world. Nuclear tests between 1954 and 1963, for example, increased atmospheric carbon-14 significantly.

Now, Graven points out, we're exerting our influence in the opposite direction by burning fossil fuels, which are, after all, the very ancient remains of formerly living things. Because they're so old, they contain a low amount of radioactive carbon-14, and burning them pumps mostly carbon-13 into the atmosphere. In other words, burning fossil fuels is making our environment appear much older, in carbon-14 terms, than it actually is. Using standard models and assuming carbon emissions continue on pace, Graven calculates we won't be able to tell the difference between recently deceased plants and 2,000-year-old papyrus—the Dead Sea Scrolls, for example—by the year 2100.

With implications in everything from archaeology to detecting fake wine vintages, "changing atmospheric radiocarbon content will have far-reaching impacts," Graven writes.

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