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I've heard that the wonderful smell of a fresh rain is actually chemicals released from the trees and grass and other plants.

  • What is the process that allows these chemicals to be released?
  • What are the chemicals that create that smell?
  • How is it advantageous for the plant to release the chemicals rather than hold onto them?
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    $\begingroup$ The fancy word for it seems to be petrichor. It has a nice wikipedia article which might lead you to some of the relevant publications. en.wikipedia.org/wiki/Petrichor $\endgroup$ – skymningen Jun 30 '15 at 7:19
  • $\begingroup$ Yeah, +1 and you go 2000+ :D Petrichor ;) $\endgroup$ – ABcDexter Jul 8 '16 at 20:50
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That molecule is called Geosmin. It is mainly produced 1 by Actinomycetes such as Streptomyces which are filamentous bacteria that live in soil. Other organisms also produce geosmin:

It is an intracellular metabolite and cell damage is the primary reason attributed to its release. However oxidant exposure and transmembrane pressure also causes geosmin release in cyanobacteria. It seems that the release is triggered by some kind of stress.

I am not quite sure about their advantage to the host species.


1 or perhaps the most well-studied in

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    $\begingroup$ Interesting answer! $\endgroup$ – AliceD Jun 30 '15 at 8:59
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    $\begingroup$ What about Petrichor that @skymningen suggested in the comments? $\endgroup$ – SolarLunix Jun 30 '15 at 9:01
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    $\begingroup$ @SolarLunix I guess that is the name of the smell, not the molecule itself $\endgroup$ – WYSIWYG Jun 30 '15 at 9:32
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    $\begingroup$ The Wikipedia article on Petrichor mentions geosmin, and indicates it is a compound different than petrichor. $\endgroup$ – mgkrebbs Jun 30 '15 at 16:17
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    $\begingroup$ The aerosol generation by the rain droplet impact on wettable surface being the mechanism releasing geosmin from the soil into the air completes the story. The paper is at nature.com/articles/ncomms7083, together with a PDF version of the paper. $\endgroup$ – Hans Apr 26 '17 at 7:33

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