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