Climate Change in Human Teeth
Here’s a bit of quirky research (link for any of you with subscriptions to Climatic Change):
In order to study climate variations during the last 1700 years in eastern France, fifty-eight oxygen isotope compositions of phosphate were measured in human tooth enamel. […] We propose that these relatively high delta(18)O values of human tooth enamel reflect higher mean delta(18)O values of meteoric water which can be attributed to an increased proportion of summer rainfall during the “Little Ice Age” time frame in Lorraine.
Oxygen has three stable isotopes, with atomic weights of 16, 18, and 17 (in order of abundance). Most chemical processes don’t distinguish between isotopes, but a few do, notably evaporation, condensation, and a few biochemical processes. Evaporation favors light isotopes, and even more usefully, this favoritism is temperature-dependent: the water going in to clouds near you is heavy when it’s warm, and light when it’s cold. So if you’re clever about complicating factors like clouds moving around or water hiding in the ground, you can use a series of oxygen isotope ratios to recover temperature changes through time.
Apparently, the oxygen in your teeth comes mostly from the water you drink. Therefore, if you’re interested in the isotopic composition of water in an inhabited place and time, you just dig up some dead people and throw their teeth in a mass spectrometer.