Last Updated on December 7, 2023
Petrichor is the smell of rain, the earthy, pungent smell that envelops the air just before a downpour.
It is created by bacteria in the soil that rise into the air along with their products when it rains, and is a phenomenon that has been known for a very long time, even before it was given a name.
Petrichor is a very distinct and pleasant olfactory sensation that is perceived when rain falls on land that has been dry for a long time, for example in the desert after a flash flood.
What does Petrichor mean?
The term Petrichor was coined by Isabel Bear and Dick Thomas, two Australian researchers who first studied the phenomenon in the 60s, and then published the results in the journal Nature.
The etymology comes from Greek, a blend of ‘petro‘, i.e. ‘which relates to rocks’ and ‘ichor‘, the mythical blood of the gods.
What causes rain to smell?
Each impact of a raindrop is, in its own small way, a violent collision with very particular effects.
According to MIT scientists, in fact, when the rain hits a porous surface, it traps very small air bubbles at the point of contact.
At that point the bubbles rise upwards at great speed, exploding in a sort of microscopic effervescence.
Now try to expand this effect for each drop and we will have a sort of giant aerosol that happens every microsecond.
However, even though we understand how it is formed, we don’t know what in the soil causes petrichor, whether the soil, organic matter or microorganisms, or all of these factors combined.
What does Petrichor smell like?
The components of petricore are ozone and geosmin: ozone has a smell like a fresh ‘clean’ smell that we feel after a thunderstorm when the air has finally cooled and all the dust has settled on the dry earth.
But ozone is also felt by those people who can smell a thunderstorm before it arrives. It is released into the air as a result of lightning.
Geosmin, on the other hand, characterizes the smell of petricore as ferrous and particularly pleasant, it is especially strong when it rains after a long drought.
Bacteria present in the soil produce spores, releasing geosmin. Finally there are all the oils of the plants that are spread into the atmosphere with the rain.
Why do we love Petrichor so much?
The human organism is very sensitive to this fragrance and is capable of detecting it even from far away.
In fact, many perfumes on sale are formulated with solutions containing geosmin because this substance is particularly pleasing to people.
It is difficult to find an explanation as to why we like the smell of rain on dry earth so much.
Some scientists believe that identifying rain could have been crucial to our ancestors’ survival.
It could be that the human brain evolved to respond positively to this smell because it meant that crops could thrive and there would be food for everyone, or to locate potential sources of water for hydration.
There is even a term for those who enjoy this smell so much.
A petrichor lover is called a “pluviophile”, literally a “friend of the rain”. Pluviophiles find joy and peace of mind during rainy days.
The smell of the desert
Normally, deserts have a dry, dusty, and earthy smell due to the lack of moisture in the air and the presence of sand and rock.
However, after a rain shower, the desert suddenly finds itself featuring a strong and distinctive smell of petrichor.
Even camels in the desert are able to perceive petrichor.
They are able to smell it even at a distance of 10-15 kilometers in order to chase it and reach the oasis which emanates it and where they can find water for survival.
As they are drinking, moreover, the spores of streptomycetes (the bacteria that produce geosmin) remain on the animals that carry them throughout the desert.
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