Petrichor
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Petrichor (/ˈpɛtrɪkɔːr/ PET-rih-kor)[1] is the earthy scent from an array, in particular, of plant-derived chemicals, produced when rain falls on dry soil.[citation needed] The word was coined in 1964 by Australian scientist Richard Thomas,[2] in a paper co-authored with Isabel Bear which described the phenomenon.[3] The term was derived from from Ancient Greek πέτρα (pétra) 'rock'; or πέτρος (pétros) 'stone' and ἰχώρ (ikhṓr) 'ichor',[not verified in body] the ethereal fluid that is the blood of the gods in Greek mythology.[not verified in body]
History
[edit]![[icon]](/newspapers?url=https://en.wikipedia.org/wiki/File:Wiki_letter_w_cropped.svg){kind=small} | This section needs expansion with: a shorter, secondary source-derived summary of the reports from the 1890s, and a more thorough summary of the phenomenon's later study, explicitly filling gaps (1891-1964, >70 years; 1960s-2010s (~50 years); and since and before these periods), incl. secondary source descriptions after the 2010s, and any relevant scholarship on mention by ancient philosophers and later natural philosophers. You can help by adding missing information. (May 2026) |
An early primary report on the phenomenon by Thomas Lambe Phipson (1833–1908) appeared in The Chemical News on 17 April 1891,[4][non-primary source needed] which was re-published in its entirety, a month later, in The Scientific American.[5][non-primary source needed] In the American presentation, he wrote, "This subject, with which I was occupied more than twenty-five years ago, appears... in... the Chemical News to have recently attracted the attention of Professor Berthelot and [Monsieur G.] Andre."[5][non-primary source needed] Phipson refers to the short presentation of the two to a meeting of the French Académie des Sciences on 23 April 1891 (later printed in a French journal, as "Sur l'odeur propre de la terre" ("On the Earth's Own Smell").[6][non-primary source needed] Phipson continues, "I find... [from] my old notes... [of] 1865, that it is doubtful whether I ever published... these observations", going on to say, as the problem was not yet solved, he again offered his observations, theorizing that the odour "was due to the presence of organic substances closely related to the essential oils of plants", and that the substances consisted of "the fragrance emitted by thousands of flowers" that had been absorbed into the pores of the soil, only to be released by rain; based on his attempts at isolation, he proposed it as a singular substance, "very similar to, if not identical with, bromo-cedren derived from essence of cedar."[5][non-primary source needed]
A popular science summary of the phenomonen from this century states, rather, that the "[t]he smell is... a concoction of some 50 chemicals", plant-derived, and "trapped in the earth", awaiting release by rain, a perspective based on the mid-to-late 20th century research that would follow.[7] In particular, the phenomenon was further scientifically described in a March 1964 paper by Australian researchers Isabel Bear and Dick Thomas, published in the journal Nature.[8][9][3][7] Thomas coined the term "petrichor" to refer to what had previously been known as "argillaceous odour".[10] The authors describe how the scent derives from chemical compounds exuded by plants during dry periods, whereupon these are absorbed by clay-based soils and rocks.[according to whom?] In a follow-up paper, Bear and Thomas suggested in 1965 that the chemical components giving rise to the "argillaceous odour of petrichor" also slow seed germination and early plant growth.[11][non-primary source needed]
Research in 2015 suggested that as the falling droplets of rain impact the surface of various wettable types of soil that are porous, aerosols are generated that "deliver elements of the porous medium to the environment", and suggest that this is the mechanism by which the petrichor scent is generated.[12]
Research in the 2020s has indicated that the volatile array of bacterial compounds, which include "the well-known... soil-smelling terpenoids geosmin and 2-methylisoborneol—compounds which animals, including humans, can "sense at extremely low concentrations" arise from evolutionarily conserved genes common to most all species of genus Streptomyces, and that these specific compounds mediate attraction of springtails (genus Collembola), an attraction that is conjectured to be mutually beneficial.[13][non-primary source needed] Adding to contemporary studies of the decades-old subject of petrichor aerosols, further research suggests that detection of ozone by humans preceding rain—that chemical the product of various soil components and the action of lightning (when relevant)—adds to the phenomena of perichor sensing.[14][better source needed]
Mechanism
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Preliminary research in 2015 suggests that when a raindrop lands on a porous surface, air from the pores forms small bubbles, which float to the surface and release aerosols.[12][15] Such aerosols might carry the petrichor scent, as well as bacteria and viruses from the soil.[12] This primary research report conjectured that raindrops that move slower might produce more aerosols, offering this as an explanation as to why petrichor is more commonly detected after light rains.[12] Alongside plants, the Streptomyces genus of gram-positive bacteria, have, in part, been implicated in producing the chemicals that are found in these aerosols.[13][non-primary source needed] With regard to specific chemicals, the human nose is sensitive, for instance, to geosmin, and can detect it at concentrations as low as 0.4 parts per billion.[16][non-primary source needed]
In popular reporting, speculation has been offered that camels in the desert may rely on the petrichor scent to locate sources of water such as in oases.[17] Popular reporting has also suggested that some scientists believe humans might appreciate the scent of rain because ancestors relied on rainy weather for survival.[18][better source needed]
See also
[edit]- Geosmin – a compound contributing to the petrichor scent
- Dimethyl sulfide – A molecule contributing to the odour of the sea
- Mitti attar – a perfume recreating the loamy smell of rain
Citations
[edit]- ^ "petrichor". Dictionary.com Unabridged (Online). n.d.[better source needed]
- ^ Ward, Colin (11 April 2014). "Isabel 'Joy' Bear". CSIROpedia. CSIRO. Retrieved 9 May 2020.
Thomas gave the name 'petrichor' to this odour.
- ^ a b Bear, Isabel Joy; Thomas, Richard G. (March 1964). "Nature of Argillaceous Odour". Nature. 201 (4923): 993–995. Bibcode:1964Natur.201..993B. doi:10.1038/201993a0. S2CID 4189441.
The diverse nature of the host materials has led us to propose the name 'petrichor' for this apparently unique odour which can be regarded as an 'ichor' or 'tenuous essence' derived from rock or stone […] it does not imply that petrichor is necessarily a fixed chemical entity but rather it denotes an integral odour, variable within a certain easily recognizable osmic latitude.
[non-primary source needed] - ^ Phipson, T.L. (17 April 1891). "Cause of the Odour Emitted by the Soil of a Garden after a Summer Shower" (PDF). The Chemical News. 63 (1638): 179. Retrieved 2026-05-10.[non-primary source needed]
- ^ a b c Phipson, T. L. (May 16, 1891). "The Odor of the Soil after a Shower". Scientific American. 64 (20): 308. ISSN 0036-8733. JSTOR 26100386.[non-primary source needed]
- ^ Berthelot, M. & Andre, G. (January 1891). "Sur l'odeur propre de la terre" [On the Earth's Own Smell]. Comptes rendus de l'Académie des Sciences (Comptes Rendus). 112 (01): 598f.
{{cite journal}}: CS1 maint: multiple names: authors list (link)[non-primary source needed] - ^ a b Garg, Anu (2007). "There is Even a Word for That". The Dord, the Diglot, and an Avocado Or Two: The Hidden Lives and Strange Origins of Words. Penguin. p. 399. ISBN 9780452288614.
The smell is said to be a concoction of some 50 chemicals from dry plants that are trapped in the earth. With the rains, they are released in the atmosphere.
. - ^ Poynton, Howard (March 31, 2015). "The Smell of Rain: How CSIRO [scientists] Invented a New Word". The Conversation. Retrieved 2026-05-10.
- ^ Logan, Tim (August 27, 2018). "Why You Can Smell Rain". The Conversation. Retrieved July 14, 2020. Note, Professor Logan makes no mention of research prior to that of the 1960s, and so this citation was moved from its appearance in the opening paragraph about work in the 1890s.
- ^ Cite error: The named reference
wardwas invoked but never defined (see the help page). - ^ Bear, Isabel Joy; Thomas, Richard G. (September 1965). "Petrichor and plant growth". Nature. 207 (5005): 1415–1416. Bibcode:1965Natur.207.1415B. doi:10.1038/2071415a0. S2CID 4174301.[non-primary source needed]
- ^ a b c d Chu, Jennifer (14 January 2015). "Rainfall Can Release Aerosols, Study Finds". MIT News. Retrieved 17 January 2015.
- ^ a b Becher, Paul G.; Verschut, Vasiliki; Bibb, Maureen J.; Bush, Matthew J.; Molnár, Béla P.; Barane, Elisabeth; Al-Bassam, Mahmoud M.; Chandra, Govind; Song, Lijiang; Challis, Gregory L.; Buttner, Mark J.; Flärdh, Klas (2020-06-01). "Developmentally Regulated Volatiles Geosmin and 2-Methylisoborneol Attract a Soil Arthropod to Streptomyces Bacteria Promoting Spore Dispersal". Nature Microbiology. 5 (6): 821–829. doi:10.1038/s41564-020-0697-x. ISSN 2058-5276. PMID 32251369. S2CID 214808046. Retrieved 2022-01-01.[non-primary source needed]
- ^ Yuhas, Daisy (July 18, 2012). "Storm Scents: It's True, You Can Smell Oncoming Summer Rain". Scientific American. Retrieved July 20, 2012.
- ^ Joung, Y. & Buie, C. (14 January 2015). "Aerosol Generation by Raindrop Impact on Soil". Nature Communications. 6 (6083). doi:10.1038/ncomms7083. Retrieved 2025-05-10.
{{cite journal}}: CS1 maint: multiple names: authors list (link)[non-primary source needed] - ^ Polak, E. H.; Provasi, J. (1992). "Odor Sensitivity to Geosmin Enantiomers". Chemical Senses. 17 (1): 23–26. doi:10.1093/chemse/17.1.23. ISSN 0379-864X.[non-primary source needed]
- ^ Jordán , Antonio (2015-02-24). "Sure Can Smell the Rain". European Geosciences Union (EGU) SSS Division blog. Munich, Germany: EGU Soil System Science (SSS) Division. Retrieved 2023-08-24.
- ^ Palermo, Elizabeth (21 June 2013). "Why Does Rain Smell Good?". Live Science. LiveScience.com. Retrieved 17 January 2015.
Further reading
[edit]- Bear, I. J.; Thomas, R. G. (September 1966). "Genesis of petrichor". Geochimica et Cosmochimica Acta. 30 (9): 869–879. doi:10.1016/0016-7037(66)90025-1.
External links
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- "Petrichor" at A Word a Day
- From the Oxford English Dictionary
- Hansen, Joe (2014-08-18), Where does the smell of rain come from? (3-min YouTube video), It's Okay To Be Smart, PBS Digital Studios, archived from the original on 2021-12-12, retrieved 2018-01-04
- Adams, Cecil (2011-11-18), "What's that smell right before it rains?", The Straight Dope, Sun-Times Media Group, retrieved 2018-01-04
- Petrichor, U.K. Met office.
- Why Is the Smell After It Rains So Appealing? The Petrichor phenomenon
- Petrichor – Why we Love the Smell of Rain