![]() ![]() ![]() Dimethyl sulfide – One of the molecules responsible for the odour of the sea.Camels in the desert also rely on petrichor to locate sources of water such as oases. Some scientists believe that humans appreciate the rain scent because ancestors may have relied on rainy weather for survival. The human nose is sensitive to geosmin and is able to detect it at concentrations as low as 0.4 parts per billion. Members of the Actinomycetes, gram-positive bacteria, are responsible for producing these aerosols. Raindrops that move at a slower rate tend to produce more aerosols this serves as an explanation for why petrichor is more common after light rains. Such aerosols carry the scent, as well as bacteria and viruses from the soil. When a raindrop lands on a porous surface, air from the pores forms small bubbles, which float to the surface and release aerosols. In a follow-up paper, Bear and Thomas (1965) showed that the oil slows seed germination and early plant growth. During rain, the oil is released into the air along with another compound, geosmin, a metabolic by-product of certain actinobacteria, such as Streptomyces, which is emitted by wet soil, producing the distinctive scent ozone may also be present if there is lightning. 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. Thomas coined the term "petrichor" to refer to what had previously been known as "argillaceous odour". The phenomenon was first scientifically described in a March 1964 paper by Australian researchers Isabel Bear and Dick Thomas, published in the journal Nature. appeared to be very similar to, if not identical with, bromo-cedren derived from essence of cedar." After attempts to isolate it, he found that it ". " absorbed into the pores of the soil, and only released when displaced by rain. the fragrance emitted by thousands of flowers. " and that these substances consist of ". was due to the presence of organic substances closely related to the essential oils of plants. 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 ". 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"). ![]() On 17 April 1891, a brief note on the phenomenon, by Thomas Lambe Phipson (1833–1908), appeared in The Chemical News -it was re-published in its entirety, a month later, in The Scientific American -in which he wrote, "This subject, with which I was occupied more than twenty-five years ago, appears from a paragraph in a late number of the Chemical News to have recently attracted the attention of Professor Berthelot and Andre." Long before this phenomenon received its name in 1964, it had been noticed and discussed in scientific circles. The word is constructed from Ancient Greek πέτρα ( pétra) 'rock', or πέτρος ( pétros) 'stone', and ἰχώρ ( ikhṓr), the ethereal fluid that is the blood of the gods in Greek mythology. Petrichor ( / ˈ p ɛ t r ɪ ˌ k ɔːr/) is the earthy scent produced when rain falls on dry soil. Soil and water being splashed by a raindrop ![]()
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