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Nature’s Perfume: Petrichor and Geosmin

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posted on Jan, 21 2012 @ 03:54 AM
A storm blew in this afternoon and as I love storms I walked outside to watch it. As always, just before the rain started coming down heavily that amazing ‘rain smell’ hit me and it got me wondering – what exactly is it? So I decided to do a bit of research.

The official name for rain smell is Petrichor

Petrichor is the scent of rain on dry earth. The word is constructed from Greek, petra, meaning stone + ichor, the fluid that flows in the veins of the gods in Greek mythology.
The term was coined in 1964 by two Australian researchers, Bear and Thomas, for an article in the journal Nature. Source

What you are actually smelling is a number of different things. Firstly the rain itself, which is slightly acidic containing carbonic acid caused by the rain absorbing carbon dioxide from the atmosphere. If you live in the sitting this will begin reacting with various oils the road, rubber from car tires and other pollutants which have settled on various surfaces which will also release various aromas. Due all the carbon dioxide being pumped out into the atmosphere within areas containing a higher concentration of people this carbonic acid will be slightly stronger as well.

If you live however in a natural area then this mildly acidic rainwater reacts with various oils from certain plant species and is then absorbed into the ground. It also breaks down various soil minerals which also release an aroma. Another constituent to this petrichor perfume is the spoors of filamentous bacteria Actinomycetes.

Actinomycetes, a type of filamentous bacteria, grow in soil when conditions are damp and warm. When the soil dries out, the bacteria produces spores in the soil. The wetness and force of rainfall kick these tiny spores up into the air where the moisture after a rain acts as an aerosol (just like an aerosol air freshener). The moist air easily carries the spores to us so we breathe them in. These spores have a distinctive, earthy smell we often associate with rainfall. The bacteria is extremely common and can be found in areas all over the world, which accounts for the universality of this sweet "after-the-rain" smell. Since the bacteria thrives in moist soil but releases the spores once the soil dries out, the smell is most acute after a rain that follows a dry spell, although you'll notice it to some degree after most rainstorms. Source

There are main other aromatics which are released via water or react with the weak carbonic acid but the last main constituent is what’s known as Geosmin

Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma.

Geosmin is produced by several classes of microbes, including cyanobacteria (blue-green algae) and actinobacteria (especially Streptomyces), and released when these microbes die. Communities whose water supplies depend on surface water can periodically experience episodes of unpleasant-tasting water when a sharp drop in the population of these bacteria releases geosmin into the local water supply. Source

Geosmin is responsible for the earthy taste of beets, some varieties of potatos other ground derived foods. It is a chief contributor to the taste of snails, and also to the muddy smell of bottom dwelling freshwater fish such as carp or catfish as well as many crayfish species. It is also what you smell in freshly disturbed earth, say if you’ve just dug a hole, and as mentioned above it is one of the main constituents of petrichor – that beautiful smell of rain.

posted on Jan, 21 2012 @ 04:05 AM
Very informative post.

I have a love/hate relationship with the knowledge you have provided. I have always loved the smell of rain, but now that you have broken it down to scientific facts...It is much less romantic.

posted on Jan, 22 2012 @ 12:19 AM
reply to post by mileysubet

I hear your, but then again I know stars are just burning balls of gas and I know rainbows are just diffracted light through water droplets, but it still makes them know less magical to me……

posted on Jan, 22 2012 @ 03:00 AM

Originally posted by mileysubet now that you have broken it down to scientific facts...It is much less romantic.

Romance is just a curious pattern of electrical signals in the brain
Sorry, can't help it!

posted on Dec, 23 2012 @ 12:22 AM
Just had a massive summer storm in the middle of the Pilbara and the smell of Petichor was everywhere. Reminded me of this thread so I'm here to give it a shameless bump cos I think the information is really interesting.

posted on Dec, 23 2012 @ 05:30 AM
This is a very eye opening article or a way of change of thinking. For me the smell of the air after a lightening strike is also very fresh smelling.
It makes me think of the odd things about this blue planet in space and how everything is inter-related.
It brings the saying "A million years on one planet - we are all brothers and sisters" into better focus.
We humans couldn't be what we are today if dinosaurs had not roamed the planet eating whatever and pooping out recycled plants products that make up the earth/dirt covering in which everything grows.
Little bacteria and amoebas cover our planet and create a symbiotic living within all of us. Its all just too small for the human eye to see until we use a microscope to bring the little buggers into focus.
Thank you for your post OP it created a moment where I could think differently about my planet!

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