On Sunday evening a few sprinkles moved through the area. Shortly after raindrops were spotted on the window, a distinctive odor gently wafted through the open windows. How very pleasant. Petrichor.

Petrichor?  Yes, that’s what that lovely smell when it rains is called.

In a paper called “Nature of Agrillaceous Odour” published in Nature in March, 1964 (Nature 201 (4923): 993–995), I. J. Bear and R. G. Thomas had described isolating and analyzing many of the chemical substances responsible for the smell, which are readily released when moistened. In case you’re wondering, the distillate they isolated is yellow. They suggested the name petrichor from “petra” for rock and “ichor,” the blood of the gods. The smell may also include geosmin, which is a substance that has the “smell of earth” and which we can detect in truly minute amounts (apparently as low as 0.1 nanograms/kilogram, or at a concentration of 0.1 parts per trillion).