What causes the smell after the first rain?

Do you remember the distinctive smell of the earth when it rains for the first time. (Marathi readers will be reminded of the song aala aala ga sugandh maaticha.) Ever wondered what causes it? Ever wondered what this smell is called? Obviously not.

But, by now you should know that if there is one thing I enjoy, it is to take a poetic concept and kill it by introducing the prosody of science.

Anyway, the smell is called geosmin. And, in the spirit of scientific enquiry, here are the gory details, from howstuffworks.com:

As it turns out, the smells people associate with rainstorms can be caused by a number of things. One of the more pleasant rain smells, the one we often notice in the woods, is actually caused by bacteria! Actinomycetes, a type of filamentous bacteria, grow in soil when conditions are damp and warm. When the soil dries out, the bacteria produces spores in the soil. The wetness and force of rainfall kick these tiny spores up into the air where the moisture after a rain acts as an aerosol (just like an aerosol air freshener). The moist air easily carries the spores to us so we breathe them in. These spores have a distinctive, earthy smell we often associate with rainfall. The bacteria is extremely common and can be found in areas all over the world, which accounts for the universality of this sweet “after-the-rain” smell. Since the bacteria thrives in moist soil but releases the spores once the soil dries out, the smell is most acute after a rain that follows a dry spell, although you’ll notice it to some degree after most rainstorms.