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Like many other fields, science has its own style of communication full of specific jargon and guided by unwritten rules.  Most of the posts on this blog focus on breaching this barrier to the public’s understanding and appreciation of science.  In this series, I’d like to take another approach by highlighting scientific words which have escaped the confines of jargon to reach a broader appeal because of their sound or their evocative power as metaphors.  Today’s word is petrichor.

Petrichor is the smell of rain falling on dry ground.  It’s a unique scent, somehow refreshing and dusty at the same time.  The word was coined from Greek (petros=”stone”; ichor=”the fluid that flows in the veins of the gods”) in a 1964 Nature paper where it was used to describe an earth-scented oil released by some plants.  The following year, scientists studying soil bacteria identified a chemical that was a major component of this scent and named it geosmin (from the Greek ge=”earth” and osmin=”odor”).  Geosmin is produced by several groups of bacteria, including actinobacteria and cyanobacteria, and released when they die; cultures of some of these bacteria, particularly the genus Streptomyces, have a strong earthy smell.  Since our sense of taste and smell are tightly linked, geosmin gives a strong earthy taste to water.  It can be taken up by other organisms and is responsible for the muddy taste of some fish, such as Tilapia.  This taste can be removed by adding vinegar to the fish before cooking; the acid in the vinegar converts geosmin into a very similar but odorless chemical called argosmin (from argos=”inactive” and osme=”odor”).

Petrichor is one of my favourite words.  The full, rich sounds of the word reflect the powerfully evocative scent — a reminder of the first rains of autumn and the lingering heat of summer — while the intertwined associations and precision of meaning make it a potent and expressive metaphor.

“But, even in the other pieces, her prose breaks into passages of lyrical beauty that come as a sorely needed revivifying petrichor amid the pitiless glare of callousness and cruelty.”

Pradip Bhattacharya
Forest Interludes; Indianest.com; Jul 29, 2001
(via A Word A Day)

Gerber NN, & Lechevalier HA (1965). Geosmin, an earthly-smelling substance isolated from actinomycetes. Applied microbiology, 13 (6), 935-8 PMID: 5866039