There’s some fascinating science behind the aroma some of us call the smell of rain—part of an earthy process called “petrichor”—a term derived from the ancient Greek, Petrichor (“petra”/rock and “ichor”/tenuous essence).

One contributing source is a yellowish oil trapped within most rocks. Significant amounts of silica tend to yield a higher or stronger “rain smell.” Another source is the mix of chemicals produced and then released by soil-dwelling bacteria when raindrops pelt the ground.

The other smell associated with rain is, of course, ozone. Created when lightning blasts apart oxygen and hydrogen molecules during a thunderstorm, those molecules reform and are joined by others to produce a smell mildly like chlorine.