July 28, 2022 | David F. Coppedge

Carbon Dating Is Becoming Useless

Due to atmospheric trends, the
usefulness of carbon dating may die.

 

“It’s kind of depressing,” remarked a forensic scientist at Columbia University in a surprising article by Nature News yesterday. It may be even more depressing than scientists realize.

Carbon dating hampered by rising fossil-fuel emissions (Nicola Jones, Nature News, 27 July 2022).

Archaeologists will increasingly have to rely on other techniques as emissions continue to alter the composition of carbon isotopes in air.

While many have heard of carbon dating, they may not realize that it relies on a radiocarbon curve that is calibrated by atomic bomb tests in the 1960s. Those tests produced anomalously high levels of radioactive carbon-14. That spike has been a “silver lining of bomb testing” because it provided a recognizable “wiggle” in the calibration curve that enabled precise forensic dating of modern objects younger than the 1960s. Two factors have removed that benefit: the decay of bomb carbon-14, and the rise of fossil fuel burning that has put more CO2 into the air that is free of carbon-14.

When there are wiggles and spikes in the proportion of carbon-14 in the air over time, radiocarbon dating can’t always distinguish one date from another. This is true for the period of 800 bc to 400 bc, for example: “You literally can’t date anything [precisely] within that 400 years,” says Higham. The phenomenon of fossil fuels cancelling out bomb carbon provides yet another opportunity for radiocarbon confusion.

The decreasing accuracy of radiocarbon due to rising fossil fuel emissions was known years ago (6 Aug 2015). The two factors have now canceled each other out. What are the implications for dating objects?

This could cause problems for valuable carbon-dating techniques. Modern items now look like objects from the early twentieth century in terms of radiocarbon dating, says Heather Graven, a chemical physicist at Imperial College London who has been charting this effect for years. The trend “could soon make it difficult to tell if something is 1,000 years old or modern”, says Paula Reimer, a radiocarbon-dating specialist at Queen’s University Belfast, UK.

The half-life of carbon-14 is 5,730 years. Typically, the older the object, the less carbon-14 it contains as the radioactive isotope decays. The short half-life means that not enough carbon-14 is detectable after 55,000 years, and there should be none at all for 100,000 years or more. For these reasons, radiocarbon dating can never give dates of millions of years. And the further back in time, the more unverifiable assumptions must be made about the state of the atmosphere to use the method.

Carbon-14 is not used to date rocks. It only works for biological material from plants or animals that incorporated carbon into their tissues while alive. When an organism dies, the C14 starts decaying at a known rate, but a lab needs to know (or assume) the ratio of carbon-14 to carbon-12 that existed in the atmosphere at the time of death.

Willard Libby had invented radiocarbon dating in 1946, before the bomb test spike from 1952 to 1962 that doubled the amount of atmospheric carbon-14. Many refinements have been made to the technique over the decades, especially the ability to detect very minute amounts of C14 in a sample (19 April 2016). Still, the calibration curve has undergone numerous updates over the years (25 May 2020). The most recent one raised eyebrows (20 Aug 2020).

Researchers have long known that the end of this technique was coming, but increasing CO2 emissions have accelerated the process. In the coming decades, as fossil-fuel use wanes and the bomb curve flattens, the carbon-14 value will no longer be diagnostic of a date. “It’s such a shame,” says Higham.

Already the loss of the bomb-carbon signal means that “By 2050 … the carbon-14 ratio will be similar to what it was in the Middle Ages (between the fifth and fifteenth century).”

Biblical creationists do not accept radiocarbon dates beyond a few thousand years, but find them useful for cross-checking some archaeological remains from known historical episodes, like the date of Hezekiah’s Tunnel in Jerusalem (3 May 2007). Older events like the Genesis Flood would have dramatically altered the atmosphere, rendering antediluvian radiocarbon dates unreliable because materials would appear older than they really are. And no radiocarbon could have existed before the creation of the Earth.

Scientists will continue to use radiocarbon on very old materials. What this news item reveals is the problem of unknowns and assumptions. Without observable corroborating evidence, like the historically known bomb tests, assumptions must be made. And without information on the provenance (location and date) of an artifact, it may become impossible to tell if a recent object is 10 years old or 1000 years old.

You can’t just take a fossil to a radiocarbon lab and get an accurate date without giving the technician some clue as to where it was found, and what the range of expected dates might be. The answers could vary by orders of magnitude. This is why old-earth scientists reject evidence of carbon-14 in diamonds and in coal, because their worldview assumptions prevent them from believing it is possible any C14 remains after millions of years. It shouldn’t be present, but it is. They will dismiss it as contamination even when contamination has been ruled out: e.g., how could you get a carbon-14 molecule inside a diamond? Read about C14 in coal and diamonds by Andrew Snelling, PhD geologist for Answers in Genesis.

If the uncertainties reported here create new problems for objects in the last millennium, how much more uncertain will dates be that are claimed to be older? What other unknowns have not been added to the calibration curve? And are there any “unknown unknowns”? (Example: 31 May 2018, 6 Aug 2015).

Methods that give older dates into the millions or billions of years are even more unreliable. This news story reminds us to apply critical thinking when hearing date claims, and to evaluate the assumptions involved. The refusal of old-earthers to acknowledge objective evidence of anomalous C14 in coal, diamonds and dinosaur bones shows that there is more than science at work in their thinking. They know it would falsify their worldview and overturn all that they have worked for. It’s too big a price to pay.

 

 

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Categories: Dating Methods, Physics

Comments

  • I can sure agree with the information, having first-hand experience with the problem. When working on the CalTech carbon-14 dating project in the early 1950’s to get baseline data for reference, I carbon dated some dried persimmon leaves from the backyard of my professor, Don Yost. I got an age of -2300 years (minus!). We determined the problem was fallout in the Los Angeles area from Nevada nuclear tests. A good early lesson about the method. And, then later I was on the staff of Dr. Willard Libby at UCLA and we discussed the problem then.
    Dr. Henry Richter

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