• Dhruvi Gohil

The Earthy Smell-Petrichor

The earthy smell of soil as raindrops touch the soil particles has mesmerized us all. Have you ever wondered from where did it come?


Petrichor is the scent that is released from the soil as it rains. A stream that runs through the veins of a Greek deity is referred to as 'petrichor. You'll be surprised to learn that it's all thanks to actinobacteria, a marvelous microscopic organism. Actinobacteria are gram-positive filamentous bacteria that produce a substance called geosmin, which is a form of rubbing alcohol. These bacteria grow where the soil is damp and warm. Geosmin is also produced by blue-green algae(cyanobacteria) such as Phormidium, Dolichospermum. Geosmin is made from farnesyl pyrophosphate, which belongs to the Sesquiterpenes terpene family.


Photo credit-wikiwand.com


When the soil is dry, these bacteria produce spores in the soil. As the rain falls on soil the spores are released up in the air and the spore-bearing moisture in the air works as an aerosol. The spores carry the earthy smell. In fact, the human nose is able to detect a concentration of geosmin as low as 5 parts per trillion. The slower the raindrops fall, the more concentration of geosmin and aerosols are released. Hence, petrichor is maximum on light rain days.


Petrichor aids camels in finding their way to an oasis and disperses bacteria on soil in deserts, acting as a signal not only to camels but also to fish. This fragrance has captivated humans to the point that it can be used in a variety of items such as perfumes, scented candles, and essential oils. In India, this earthly smell has been bottled for years and it is called 'Mitti Attar'


How is Mitti Attar made?

The clay from the topsoil is extracted from the ground, baked in a kiln, and soaked in water in enormous circular pots that are then filled with the earth's soil. A fire is ignited underneath it, and vapors pass through the tubing, condensing on the oil base to form perfume.

Until next time, stop and breathe in the earthly aroma.

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