Life Science Teachers: Take special note!

This is not yet an error in the mainstream press, but there is an error afoot, currently represented in the widely read slashdot, which I imagine will propagate. The purpose of this post is to alert you to this problem and prepare you for the occasion when you run into a wackaloon creationist waving their arms around and screaming “Carbon dating does not work! It’s been proven.” This story also has a Global Warming Denialism component.

What I’m going to do here is give you the basic facts, then the misinterpreted text.

We start with the basic facts.

The paper of interest is by Peter Swart and it is published in PNAS.

Carbon is one of the ‘building blocks’ of life, and thus, carbon atoms are incorporated into living tissues. But there are several isotopes of carbon, including Carbon 12 and Carbon 13. These two isotopes are stable … they do not decay radioactively like Carbon 14 does.

The differences between these different number’d carbons is the exact molecular weight. This is a difference that for many purposes probably does not matter. But in biological systems, there is a small bias in the use of each isotope (called “fractionation”) which results in biological tissues having a different ratio of 12C to 13C than the ‘wild’ carbon floating around, say, in the atmosphere.

The ratio also tells us, in turn, about organic activity. Carbon can be trapped in sediments available to geologists in a number of ways, and when you look at these sediments, you can tell how much of the Earth’s carbon is likely trapped in organic tissue (dead or alive). Inorganic carbon would mirror the organic trap, and organic carbon ratios would also be affected by what is already trapped, as new tissue uses the extant atmospheric carbon. For this reason, 12C/13C ratios have been used to infer important aspects of the global organic carbon cycle over time ranges of hundreds of millions of years.

The carbon used in such studies may come from deep sea sediment, and this is the best place to get the carbon in many ways: There is some chronological control, it is the output of a large, buffered, reasonably well understood system, other data comes out of the same sediments, and so on. But going back before something like 150 million years, there are no known/sampled sea floor sediments for this purpose. For this, geologists look to other sediments called platforms, which are also sea-features but formed under different conditions (I’m oversimplifying this part a lot), or other sediments.

It turns out that a study of these different depositional environments, in the paper by Swart, indicates that the two data sources behave differently and the non-ocean bottom deposits cannot be used as they previously were. As a result of this, our understanding of the history of the Earth’s carbon cycle has gone all topsy-turvy and now needs to be re-examined.

Science marches on. This assertion by Swart will be tested, challenged, and if he is wrong, tossed out or modified. At the same time, people will be working on reassessing the pre 150 mya record. There is a lot of work to do an if it is really true that the pre 150 mya record is borked, this means that we will soon be exposed to a new and different (presumably) understanding of early life on earth! Cool!

Now, look at the following statement from a report in Science Daily News:

…the history of organic material has been interpreted by geologists using the 13C/12C ratio of carbonates and organics, wherever these materials can be sampled and dated.

That statement is embedded in a description pretty similar to what I give you above. Note that the statement explicitly states that the carbon samples can be used where they can be dated. Not that the carbon samples are used to date anything. This is an important difference.

The following is the offending statement from today’s Slashdot News:

“New research funded by the National Science Foundation at the University of Miami is showing that carbon dating (the 13C/12C ratio used to infer age) in the ocean can only be trusted up to 150 million years ago. From the primary researcher, ‘This study is a major step in terms of rethinking how geologists interpret variations in the 13C/12C ratio throughout Earth’s history. If the approach does not work over the past 10 million years, then why would it work during older time periods? As a consequence of our findings, changes in 13C/12C records need to be reevaluated, conclusions regarding changes in the reservoirs of carbon will have to be reassessed, and some of the widely-held ideas regarding the elevation of CO2 during specific periods of the Earth’s geological history will have to be adjusted.’ While this research doesn’t necessarily throw carbon dating out the window, it should cause people to rethink so many theories about early life that revolved around ages of sediment in the oceans.”

Obviously, this writer gets it totally wrong. But more importantly, if you look at this text, it is clear that this is the writing of someone steeped in the creationist literature. This tells me that we are seeing the beginning of a disinformation campaign regarding this research. There are several clues in here that link this paragraph to the Creationist Conspiracy. For example, the mention of NSF funding in the first paragraph, followed by the phrase “carbon dating can ony be trusted up to 150 mya” is a clue.

Carbon dating is NOT what his research about. Carbon dating is different. Here is carbon dating in a nutshell: Organic tissue incorporate 12C, 13C and 14C. The 14C is radioactive and decays over time (into something that is not carbon) so tissue older than several tens of thousands of years has virtually none. If the sample is suitable for analysis, and has above a certain ratio of 14C to the other C’s, the ratio can indicate the time since death of the tissue-forming organism. There are caveats: Marine life and terrestrial life are different, for example. Carbon dating (aka radiocarbon dating) is pretty reliable, when the samples are good, up to 30 or 40 thousand years ago, and in some cases the method can be extended to just over 100 thousand years ago. Not even one million years, though. This is not a technique that is used, or could be used, in relation to the origin of life.

The middle of the Slashdot quote is mostly quotes of the Science Daly piece. The end, however, brings us back into creationist think. Here we learn that while this new research (remember, this was funded by the NSF!) does not totally throw carbon dating out the window (true, because it has absolutely nothing to do with carbon dating) it should cause people to rethink … as in understand that there is a controversy … so many theories about early life etc. etc. must be questioned. You get the idea.

Since this research calls into question currently used data on early periods of earth’s carbon cycle, there will also be those who claim that this means that the jury is still out on Global Warming. However, this is absurd. We could understand current climate and climate change with far less than the last 100 million years of a climate record. Regarding the relationship of this research and the origin of life: Again, most of the early evidence for the origin of life is based on fossil material dated in a way that has nothing to do with this. The overall pattern of life and the carbon cycle prior to 150 million years ago may be reassessed in relation to this research, but not the existence of life during this period.
P. K. Swart (2008). Global synchronous changes in the carbon isotopic composition of carbonate sediments unrelated to changes in the global carbon cycle Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0802841105


  1. #1 Mimi
    September 12, 2008

    Oh no! I just had my Debate! on creationism this week too… This is gonna be fun. At least it will get my readers talking about it. *sheesh*

  2. #2 Henry Harpending
    September 12, 2008

    Nice job Greg, thanks.

  3. #3 Greg Laden
    September 12, 2008

    Henry! Nice to ‘see’ you. I hope you’ve been well.

  4. #4 Justin M
    September 12, 2008

    Greg, I heard you talk at the Evolution Conference this summer and was wondering if you are still polling incoming freshmen on their views on creationism and evolution?

    I’m teaching an AP bio course in rural MN and curious to see what type of reaction I get from my seniors. Have you had any run in this year with students? On yeah, one more thing, did you ever find out from the legal people at the U. if you could tell students who use creationism in the classroom that they are wrong or making claims that are supernatural?

  5. #5 Dan S.
    September 13, 2008

    “carbon dating can ony be trusted up to 150 mya”

    Oh, good lord.

  6. #6 Inquisitive Raven
    September 14, 2008

    Well, it’s nice to see that some of the commenters at Slashdot got it right, but geeze, the stupid of some of the others.

  7. #7 greg laden
    September 14, 2008

    Justin: You should contact Mark Decker at UMN for the most updated information. None of my students this year are incoming frosh, but nedxt year I believe I will have a small group.

  8. #8 dave UH
    September 14, 2008

    Thank you for writing about this, I was throughly disappointed by the misleading description given to this by science daily:

    “Scientist Uncovers Miscalculation In Geological Undersea Record

    ScienceDaily (Sep. 13, 2008) — The precise timing of the origin of life on Earth and the changes in life during the past 4.5 billion years has been a subject of great controversy for the past century.”

    I am just waiting in dismay for the creationists to jump all over this.

  9. #9 Mike Haubrich, FCD
    September 16, 2008

    How hard is it to fact check before writing an article on science. I learned way back in the 1970s that carbon-dating is only useful up to a range of 100,000 years. I mean I know what a half-life is.

    It bugs the crap out of me that there are people earning a living on “science journalism” when they don’t even care.

    As for creationists picking up on it, I say let ’em run with it for a while. Let’s see how long it takes for this to become a new “Icon of Creationism.”

  10. #10 Robert Estrada
    September 16, 2008

    Science does not fail by making mistakes. It thrives on them by learning from them. By discovering it’s own mistakes and owning them it can self correct. Not my wisdom, but the wisdom of giants I wil never equal but admire.

  11. #11 Eric Blievernicht
    September 29, 2008

    Given that C-14 dating has fallen into the young-earth model for some time (given the ubiquity of measurable C-14 in coal, diamonds and other samples that should have none if they were under 1 mya, and the ease of explaining C-12/13/14 profiles in a diluvial model), I don’t think your grasp of this topic is very good. It is the old-earth model that no longer has a good explanation for radiocarbon profiles, except to castigate dating labs for supposedly omnipresent ‘contamination’ – which is just not reasonable and certainly not accepting of the facts of science.