Carbon dating accuracy called into question after major flaw discovery
When news is announced on the discovery of an archaeological find, we often hear about how the age of the sample was determined using radiocarbon dating, otherwise simply known as carbon dating.
Deemed the gold standard of archaeology, the method was developed in the late 1940s and is based on the idea that radiocarbon (carbon 14) is being constantly created in the atmosphere by cosmic rays which then combine with atmospheric oxygen to form CO2, which is then incorporated into plants during photosynthesis.
When the plant or animal that consumed the foliage dies, it stops exchanging carbon with the environment and from there on in it is simply a case of measuring how much carbon 14 has been emitted, giving its age.
But new research conducted by Cornell University could be about to throw the field of archaeology on its head with the claim that there could be a number of inaccuracies in commonly accepted carbon dating standards.
If this is true, then many of our established historical timelines are thrown into question, potentially needing a re-write of the history books.
In a paper published to the Proceedings of the National Academy of Sciences, the team led by archaeologist Stuart Manning identified variations in the carbon 14 cycle at certain periods of time throwing off timelines by as much as 20 years.
The possible reason for this, the team believes, could be due to climatic conditions in our distant past.
…
This is because pre-modern carbon 14 chronologies rely on standardised northern and southern hemisphere calibration curves to determine specific dates and are based on the assumption that carbon 14 levels are similar and stable across both hemispheres.
However, atmospheric measurements from the last 50 years show varying carbon 14 levels throughout. Additionally, we know that plants typically grow at different times in different parts of the northern hemisphere.
The paper: (open access) http://www.pnas.org/content/early/2018/05/23/1719420115
Fluctuating radiocarbon offsets observed in the southern Levant and implications for archaeological chronology debates
Significance
We observe a substantive and fluctuating offset in measured radiocarbon ages between plant material growing in the southern Levant versus the standard Northern Hemisphere radiocarbon calibration dataset derived from trees growing in central and northern Europe and North America. This likely relates to differences in growing seasons with a climate imprint. This finding is significant for, and affects, any radiocarbon application in the southern Levant region and especially for high-resolution archaeological dating—the focus of much recent work and scholarly debate, especially surrounding the timeframe of the earlier Iron Age (earlier Biblical period). Our findings change the basis of this debate; our data point to lower (more recent) ages by variously a few years to several decades.
Abstract
Considerable work has gone into developing high-precision radiocarbon (14C) chronologies for the southern Levant region during the Late Bronze to Iron Age/early Biblical periods (∼1200–600 BC), but there has been little consideration whether the current standard Northern Hemisphere 14C calibration curve (IntCal13) is appropriate for this region. We measured 14C ages of calendar-dated tree rings from AD 1610 to 1940 from southern Jordan to investigate contemporary 14C levels and to compare these with IntCal13. Our data reveal an average offset of ∼19 14C years, but, more interestingly, this offset seems to vary in importance through time. While relatively small, such an offset has substantial relevance to high-resolution 14C chronologies for the southern Levant, both archaeological and paleoenvironmental. For example, reconsidering two published studies, we find differences, on average, of 60% between the 95.4% probability ranges determined from IntCal13 versus those approximately allowing for the observed offset pattern. Such differences affect, and even potentially undermine, several current archaeological and historical positions and controversies.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
“We observe…”
I already like it.
“throwing off timelines by as much as 20 years”
So x was made in 100 BC now becomes 120 BC. Hardly important is it.
The problem seems like it should be far worse than a 20-year issue.
I’m surprised “squiggle matching” is not discussed in the article nor has made it into any one’s comments. Maybe there is another word for the process that I don’t know?
My understanding of best practice prior to the article:
With a single carbon-14 measurement you can cost effectively date an object, but the accuracy is rather poor and that is where the +/- 250 years for a 2,000 year old test object comes from.
But, the most accurate method of carbon dating is to perform squiggle matching between the reference timeline and a wooden object being tested. Let’s say an object under evaluation has 50 wood grains in it, that means you have sample wood from 50 consecutive tree rings. Each tree ring would have accumulated carbon-14 originally based on the density of carbon-14 in the atmosphere the year the tree ring grew.
If all 50 wood grains have their carbon-14 content measured, you now have a 50-year squiggle. You take that 50-year squiggle and overlay it with the reference carbon-14 decay timeline and you should be able to get an exact match for the shape. In particular, any spikes or annual anomalies in the subject squiggle should be able to be aligned with corresponding spikes in the reference carbon-14 decay timeline.
The reference carbon-14 residual timeline was created by taking core samples of long lived trees such as some trees living in California (2,000 consecutive years of tree rings in some of those trees). Then do the same for a long lived tree that died say 1500 years ago. If it too lived 2,000 years you now have 2 2,000 year carbon-14 decay graphs with about a 500-year overlap. By matching the squiggles of those 2 graphs you can match up precisely how to use the second decay graph to extend the first graph. So now you have a very precise 3,500 year long reference carbon-14 decay graph.
Now, if you take your 50-year squiggle graph from your test object you can very precisely determine the age of the wooden test object to the individual year of each tree ring.
The biggest accuracy issue relates to when was the wood from the tree actually used to make something. That is, if I cut down a 100-year old oak today and use lumber from the center of the tree today to make something, then carbon date it immediately via squiggle matching, my brand new object would match the squiggles from 100-years ago.
Thus, the most accurate object to date is a wooden object with numerous rings and the bark still attached. That way the age of the tree ring next to the bark is the age of the tree when it was cut down and in theory you can know that to the precise year.
====
The problem identified by this article is that a reference carbon-14 decay timeline created by analysing long lived trees in California may not be usable at all for squiggle matching wooden objects from the middle east!
The good news is reference carbon-14 decay timelines can be built for each region of the globe. But until that happens, I don’t see how the authors of the article can say the newly identified error is only 20 years.
This is of very limited practical interest. Such wooden objects (numerous treerings + bark) are very rare, and can usually be directly dated by squiggle matching of the treerings in any case.
I’m surprised “squiggle matching” is not discussed in the article nor has made it into any one’s comments. Maybe there is another word for the process that I don’t know?
I believe the technical term is ‘wiggle matching’. 🙂
http://homepage.univie.ac.at/Peter.Stadler/Stadler/StadlerP_2002i.pdf
Squiggle matching sounds better! And none of the commenters here seem familiar with wiggle matching either.
High-precision carbon dating involves wiggle matching, so most of the comments here are uninformed from what I understand.
I note that in the link they dated graves from ~600AD +/-14 years via wiggle matching.
If this new paper changes that to +/- 34 years, that’s a big change.
So C14 dating is accurate to +/- 20 years for a living penguin carbon dated at 8,000 years old.
Certainly not. At such a time depth the uncertainty would be on the order of a century. Correction for marine reservoir effect would also be necessary.
Apparently you missed my sarcasm. LIVE penguins have been carbon dated to 8000 years old. It’s crappy science.
Even if it only works with wood, it works well with wood. The reason being each wood grain (tree ring) can be tested and the aggregate picture used to make an accurate assessment.
I too do not see where 20 years is anything to worry about. I get the impression that this quantity is within ordinary error estimates, and so I wonder how it is even possible to detect a difference that is within the error bars themselves.
Confused.
Oh, and I still cannot get an image to post and embed.
One should not overestimate the precision of radiocarbon dates. Modern radiocarbon measurement (AMS (mass spectrometry) + ultrafiltration) usually have measurement uncertainties on the order of a few decades, but the age uncertainty is larger. Multiple measurements that applies to what should be a single point in time (e. g. different parts of the same animal skeleton, pieces of charcoal from a single campfire) typically have a spread of 100-200 years.
Also there are “radiocarbon plateaus” where changes in the stratospheric production of C14 and/or abrupt changes in the carbon cycle means that a given level of activity can apply for several dates, sometimes several centuries apart. This is a big problem when studying the younger Dryas for example:
https://journals.uair.arizona.edu/index.php/radiocarbon/article/viewFile/3569/3082
Twenty years more or less is hardly significant.
The paper is talking about bronze age dating. That’s only 3500 years ago and wiggle matching is supposedly accurate enough that adding +/-20 years to the error is significant in many cases.
You keep harping on “wiggle matching” which is very rarely practicable, and when it is direct tree-ring dating is at least as reliable.
There were papers years ago that showed plants used various isotopes at different rates. C12 CO2 was more likely to be absorbed than C14. That meant C/O2 from fossil fuels were removed faster than CO2 from respiration or forest fires. The differences were small but measurable.
Generally speaking lighter molecules are “preferred” in biological processes, so the lightest CO2 molecule (C12+2O16) is favored. The (very rare) molecule with C14+2O18 is least desirable.
A critter dies and is buried by one inch of soil. His remaining C12 is subject to a certain amount of cosmic radiation. His buddy is buried by four feet of soil. The cosmic radiation reaching the second unfortunate would be less. Make a difference?
The neat part is when they find dinosaur bones with bone marrow in them, but are supposedly 65 million years old.
So where are the billions of bones anyway?
Long gone. Fossilization is rare.
“Make a difference?”
Not really. It’s not the cosmic radiation per se that creates C14. It is thermal neutrons. There are (fortunately) very few thermal neutrons at ground level.
This raises a question in my mind. (so many questions so little mind).
As I understand it the sun influences the number of cosmic rays striking the earth.
Wouldn’t this further complicate the issue of C14 dating?
Oh no does this mean I’m maybe not as old as my children think I am!
James Bull
This is why we ‘calibrate’ radiocarbon dates – it’s reallt quite simple and inconsistency with carbon in the atmosphere has been known about for a long time.
https://simplearchaeology.wordpress.com/2018/05/25/radiocarbon-dating-simplified/
Wait, What, This can’t be. This science is settled!
How DARE those anti-science DENIERS challenge the consensus that radiocarbon dating is infallible!!!!!
The science is settled…these deniers must have their careers destroyed immediately!!!
Any archaeologist you actually talk with will tell you that C-14 is a rubber ruler. There are far too many imponderables in the production and uptake to make it a really reliable date. The northern hemisphere standards are easy to undertsand and logically established, but assume a global uniformity in C-14 production that has been know not to be there for decades. Other glitches in C-14 dating include the marine off set. Shell from mariine and freshwater lake environments show consistent offsets from C-14 derived from trees and other organic terrestial matter. In fact, standard practice takes a ratio of stable carbon isotopes because the kind of plant the carbon derives from can make an inportant difference. CAMS cycle and C4 plants segregrate carbon isotopes differently from “normal” plants, so grains like maize for example will yield a different age than charcoal from the tree used as fuel the corn meal was cooked over. “Gold standard” is in the media’s – to be polite – minds. The advantage of C-14 dates is primarily that they can be handled repeatedly. The source and measurements do not change, only the estimated age based on them. So, unlike historic temerpature data where measurements are changed repeatedly to meet expectations, C-14 measures remain fixed. The data is never “adjusted” only the estimated age based on the data.