How sweet is the smell of fresh earth.

A lot of people love that fresh-dirt smell. The surprising thing, though, is that it isn't coming from the dirt itself. Microbiologists have traced the pleasant odor to an organic chemical called "geosmin."

Bacteria actually finds its way in through the geosmin. A microbial geneticist named Keith Chater at the John Innes Center in England has traced geosmin down to a common bacterium called Streptomyces coelicolor. He even found out exactly which gene in the little critters causes them to produce geosmin.

A bacterium is actually producing the chemical that smells so good.

Interestingly enough, there are unconfirmed reports that animals are attracted to fresh dirt in the desert, and go there looking for water. As they nose around the dirt, they pick up plenty of S. coelicolor, which then hitch a ride from one oasis to the next.

If it's true, then the bacteria in general may create the odor in order to attract animals. The animals find water, the bacteria are spread, and everyone is happy.