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- "Scent of rain" redirects here. For the play by Mark Dunn, see Scent of Rain. For other uses, see Scent of Rain (disambiguation)
- "Smell of rain" redirects here. For the Mortiis album, see The Smell of Rain.
Petrichor (pron.: // or //) is the scent of rain on dry earth. The word is constructed from Greek, petra, meaning stone + ichor, the fluid that flows in the veins of the gods in Greek mythology. It is defined as "the distinctive scent which accompanies the first rain after a long warm dry spell".
The term was coined in 1964 by two Australian researchers, Bear and Thomas, for an article in the journal Nature. 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, a metabolic by-product of bacteria, which is emitted by wet soil, producing the distinctive scent; ozone may also be present if there is lightning. In a follow-up paper, Bear and Thomas (1965) showed that the oil retards seed germination and early plant growth. This would indicate that the plants exude the oil in order to safeguard the seeds from germination under duress.
In popular culture 
- In the Discworld novel The Last Continent, there are frequent references to the Ecksian people (analogous to Australian Aborigines) being the only culture on the Disc to have a word meaning "that smell you get after rain".
- The word was featured in the Doctor Who episode "The Doctor's Wife" (written by Neil Gaiman), as part of a telepathic password to enter one of the TARDIS' old control rooms. To use it, Amy Pond had to imagine the smell of dust after rain. In "Closing Time" (written by Gareth Roberts), Amy is seen on an advertisement for a perfume with the same name; it shows a picture of her face and features a bottle of perfume and the phrase "Petrichor - For the girl who's tired of waiting".
See also 
- Actinomycetes, some types of Actinobacteria are responsible for the peculiar odor emanating from the soil after rain
- Geosmin, the chemical that produces this odour
- Bear, I.J.; R.G. Thomas (March 1964). "Nature of argillaceous odour". Nature 201 (4923): 993–995. doi:10.1038/201993a0.
- Garg, Anu (2007), The Dord, the Diglot, and an Avocado Or Two: The Hidden Lives and Strange Origins of Words, Penguin, p. 399, ISBN 9780452288614.
- Daisy Yuhas (July 18, 2012). "Storm Scents: It's True, You Can Smell Oncoming Summer Rain: Researchers have teased out the aromas associated with a rainstorm and deciphered the olfactory messages they convey". Scientific American. Retrieved July 20, 2012.
- Bear, I.J.; R.G. Thomas (September 1965). "Petrichor and plant growth". Nature 207 (5005): 1415–1416. doi:10.1038/2071415a0.
- Cooper, Steven; Mahoney, Kevin (2012), Steven Moffat's Doctor Who 2011: The Critical Fan's Guide to Matt Smith's Second Series (Unauthorized), Punked Books, pp. 53, 172, 178, 181, ISBN 9781908375117.