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Petrichor ( ) is the earthy olfaction produced when rain falls on dry soil. The word was coined by Isabel Joy Bear and Richard Grenfell Thomas Nature of Argillaceous Odour. Nature 201, 993–995 (1964) , the ichor that is the blood of the gods in Greek mythology.
Phipson was referring to a short paper read by Berthelot and André at the meeting of the French Académie des Sciences on 23 April 1891, and printed in Volume 112 (1891) of Comptes Rendus, entitled "Sur l'odeur propre de la terre" ("On the earth's own smell").
Phipson continues, "I find, on referring to my old notes, which are dated 1865, that it is doubtful whether I ever published the results of these observations; and as the distinguished chemists I have just named have not quite solved the problem, I hasten to give the results I obtained so long ago." He then theorizes that the odour "... was due to the presence of organic substances closely related to the essential oils of plants ..." and that these substances consist of "... the fragrance emitted by thousands of flowers ..." absorbed into the pores of the soil, and only released when displaced by rain. After attempts to isolate it, he found that it "... appeared to be very similar to, if not identical with, Cedrene derived from Cedar oil."
The phenomenon was first scientifically described in a March 1964 paper by Australian researchers Isabel Bear and Dick Thomas, published in the journal Nature.
Apparently, the printed text is a copy from CSIRO journal ''Ecos'', issue February 1976, p. 32.
. Thomas coined the term "petrichor" to refer to what had previously been known as "argillaceous odour". The authors describe how the smell derives from an oil exuded by certain [[plant]]s 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|Actinomycetota]], such as ''[[Streptomyces]]'', 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 slows seed germination and early plant growth.
The human nose is sensitive to geosmin and can detect it at concentrations as low as 0.4 parts per billion. Some scientists believe that humans may appreciate the rain scent because ancestors relied on rainy weather for survival. in the desert also rely on petrichor to locate sources of water such as oasis.
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