Petrichor (//) is the scent of rain on dry earth, or the scent of dust after rain. The word is constructed from Greek, petros, 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, I. J. Bear and R. G. 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 certain Actinobacteria, 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.
- 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.
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