The layer of material that forms on the surfaces of arrow points, spearheads, and certain other natural-glass objects, as they age can be used to estimate the temperatures that the artifacts have experienced, a new analysis suggests.
The researchers focused on ancient objects made of the volcanic glass called obsidian. As soon as such an object breaks, its freshly exposed surfaces begin to absorb water, or hydrate. The rates at which those surface layers thicken depend on the temperature and humidity of the object's surroundings, says Lawrence M. Anovitz, a geochemist at the University of Tennessee in Knoxville. Now, he and his colleagues at the Oak Ridge (Tenn.) National Laboratory have turned that trait into a climate-monitoring tool.