Sunday, February 22, 2009

Technical Interlude - Arguing from Ignorance

Recently I had a discussion with a Chabadnik who parroted the Lubavitcher "young earth creationist" viewpoint (a literal 6000-year-old age of the universe). This concept is almost universally held by Chabad because it was the viewpoint of the last rebbe, M.M. Schneerson, and God forbid (or "Rebbe Forbid" for some of their more extreme adherents) that he was wrong in his views! This individual raised issues concerning the validity of Carbon-14 (aka C-14 or radiocarbon) dating, reflecting basic misunderstandings that are quite common among folks that have not only a meager scientific background but a propagandized one at that. A somewhat recent post on Lubabnomore featuring a video by Ronen Segal made similar claims. As I mentioned in my comment there, the video contains nothing new in the meager arsenal that OrthoFundies wield when they argue against scientific theories such as evolution or the age of the universe.

Although I find it quite irksome when assertions are made that reflect a gross misunderstanding of scientific principles, this post should be considered more of a public service announcement for those who are guilty of one of the more egregious errors, so that they won't embarrass themselves in the future. After all, in Jewish thought embarrassing someone is a very serious matter and is often said to be equivalent to murder. Therefore saving someone from embarrassing oneself is analogous to preventing someone from committing suicide!

I want to make a few points concerning the C-14 radiometric dating technique. The technical nitty-gritty is beyond the scope of this post, so refer to the Wiki article if you are so inclined.

Radiocarbon dating is only one of a number of dating techniques, each of which is useful for specific materials and/or environments. Most importantly, C-14 can only be used on organic materials (only living organisms take up C-14) which are younger than approximately 10 half-lives. Since the half-life of C-14 is about 5700 years (coincidentally very close to the age of the universe, heh heh), it can be used to date objects - at most - up to approximately 60,000 years old. The upper-age limits usually require special enrichment techniques and are therefore less accurate because problems such as sample contamination (always a concern) become increasingly problematic at such low levels of remaining C-14.

Somewhat unintuitively, very young samples are also not usually suitable for dating simply because so much fossil fuel carbon has been released into the atmosphere by humans over the last couple hundred years. Such carbon is very old and thus has negligible C-14, so the initial C-14/C-12 ratio (the critical factor in dating) taken up by organisms is too low to provide meaningful decay data.

Finally, note that radiometric dates are always given as "plus or minus" dates, reflecting the level of certainty of the measurement (unless otherwise stated, usually a 68% confidence level is given, i.e., one standard deviation.)

So, Chabadniks, Dovid Gottlieb-ists, and other young earth creationists, to avoid peoples' BS meters from going off the scale, please do not:
  • use the terms "age-of-the-earth" and C-14 in the same sentence or talk about using C-14 to date "rocks"
  • assert that C-14 dating of dinosaur bones proves that dinosaurs and man were contemporaneous (refer to The Great Dinosaur Mystery) - scientists simply do not use C-14 for determining the age of dinosaurs.
  • point out anomalous dating determinations for very young specimens in an attempt to discredit the validity of C-14 dating
  • suggest that dating uncertainties demonstrates a flaw in the technique itself
Somewhat more sophisticated fundies (that is, they have memorized more sophisticated sounding talking points) may point to other types of anomalous readings or discarded data, or claim circular reasoning in the dating of samples, or assert that C-14 calibrations (adjusting the original C14/C12 ratio) are nothing more than "fudge factors" to arrive at a desired date. Suffice it to say that scientists are well aware of when it is appropriate to use radiocarbon dating and the statistical models are well-established. Nor are calibrations "fudge factors"; on the contrary, they strengthen the model by using independent dating methods "such as examination of tree growth rings (dendrochronology), deep ocean sediment cores, lake sediment varves, coral samples, and speleothems (cave deposits)."

Yes, that last sentence was a direct wiki quote, and no, that is not the limit of my knowledge in the area. Although it has admittedly been many years, I have grad-school level experience in the field.

1 comment:

Joshua said...

Minor issue: Even if the ratio of C-14/C-12 were not changing you still wouldn't be able to use C-14 dating on objects less than a few hundred years old. The younger an object the less decay that has gone on and so the more of an issue with accurately measuring the remaining C-14 level enough for it to matter. Moreover, for sufficiently young, small, samples the simple probability issue could possibly come up: decay is a random process. It is only on the average that the decay rate is predictable. However, the vast majority of objects are old enough and have enough C-14 that this isn't an issue. For small younger objects that might not be the case. However my impression is that the technique is nowhere near refined enough for this to be anything other than a theoretical problem.