Petrichor
- The smell of rain on dry ground
Petrichor (pronounced /ˈpɛtrɨkər/; from Greek petros "stone" + ichor the fluid that flows in the veins of the gods in Greek mythology) is the name of the scent of rain on dry earth.
The term was coined in 1964 by two Australian researchers, Bear and Thomas, for an article in the journal Nature.[1] In the article, the authors describe how the smell derives from an oil exuded by certain plants during dry periods, whereupon it is absorbed by clay-based soils and rocks. During rain, the oil is released into the air along with another compound, geosmin, producing the distinctive scent. In a follow-up paper, Bear and Thomas (1965) showed that the oil retards seed germination and early plant growth.[
Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather (petrichor) or when soil is disturbed.[1] The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion[citation needed].
Geosmin is produced by several classes of microbes, including cyanobacteria (blue-green algae) and actinobacteria (especiallystreptomyces), and released when these microbes die. Communities whose water supply depends on surface water can periodically experience episodes of unpleasant-tasting water when a sharp drop in the population of these bacteria releases geosmin into the local water supply. Under acidic conditions, geosmin decomposes into odorless substances.[2]
Geosmin is also responsible for the muddy smell in bottom-dwelling freshwater fish such as carp and catfish. Cyanobacteria produce geosmin and 2-methylisoborneol, which concentrate in the skin and dark muscle tissue. Geosmin breaks down in acid conditions; hence vinegar and other acidic ingredients in fish recipes help reduce the muddy flavor.
http://encyclopedia.thefreedictionary.com/Geosmin July 6,2011
http://encyclopedia.thefreedictionary.com/petrichor July 6,2011
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