Geosmin, I learned, causes the funky-great smell of earth after a rain. Like many of the phytoncides, it is a turpene, a family of aromatic hydrocarbons and a major component of natural resin (incidentally, turpenes are also a big ingredient of hops, giving dark beer its rich flavor and aroma). Geosmin comes from soil organisms, particularly the streptomyces bacteria that are key to so many antibiotics. According to the Royal Society of Chemistry, we are alert to this rich smell in incredibly small quantities. We can detect the equivalent of seven drops of geosmin in a swimming pool. This
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