Those of you who, like me, wish they understood chemistry should check out Derek Lowe's fascinating discussion of how anti-doping agencies can tell the difference between natural and artificial testosterone. I always assumed that for naturally-present performance enhancers, the amount present in the body was the only indicator of cheating — and presumably not a very accurate indicator, since different people naturally produce different levels of hormones/red blood cells/whatever.

But it turns out there are other ways to catch cheaters. For one thing, you can indentify an unnatural level of testosterone by examining the relative levels of its (inactive?) enantiomer. More interesting (and accurate) is the use of a technique (sort of) related to carbon dating. Lowe lays it out.

Speaking of carbon dating, I understood how it works, but never really got why it works — I get that carbon isotope levels have changed over time, but I always thought it was due to radioactive decay. But of course that doesn't make any sense, since an unstable isotope in a dinosaur bone should decay just as quickly as one in the atmosphere (assuming that cosmic rays aren't a big factor, which, as a non-Fantastic Four fan, I'm ready to do). Besides which, I guess C13 is a stable isotope, so the decay thing never made any sense anyway. Thankfully, Lowe fills in the gaps on all this, too. Good stuff.

UPDATE: Whoops! Forget what I said about carbon dating. Derek was kind enough to drop by in comments and lay out the actual reason that carbon dating works — it's unrelated to biological systems slowly filtering out C13, the phenomenon that's the basis for the artificial testosterone assay his post discusses.

The cosmic-rays-hitting-nitrogen business rings a bell, though, and I'm a little embarrassed to have forgotten it. Sorry for the confusion — I told you I was a dope when it comes to chemistry.