The pleasant smell after the rain is called “petrichor” (from the Greek word petra (stone) and ichor (blood of Greek gods)).
This term was coined in 1964 when two Australian scientists began studying the rain’s aroma and its leading causes.
In this study and several others that followed it, scientists found that during the dry seasons, some plants secrete oils that inhibit seed germination.
Stopping seed germination means preventing the birth of new plants, thereby reducing the competition for scarce water supplies.
These secretions accumulate on soil over time, and when the rain comes, these oils mix with each other and are released into the air.
These oils in the air mix with other airborne substances to produce petrichor.
One such substance is called geosmin, which is produced by bacteria living on the soil.
The highly common bacteria produce geosmin during reproduction,Reproduction is a misnomer here because bacteria produce spores, which is a reproductive cell and not an individual. However, this spore eventually develops into an individual through asexual reproduction. which mostly takes place during the dry seasons.
Another substance, nitric oxide, is contributed by lightning—when it strikes, lightning splits molecules of oxygen from ozone (O3) and nitrogen (N2) in the air, and they recombine to form nitric oxide (NO).
The reason we find this smell pleasant has been linked to our evolution.
For our ancestors, rain indicated abundance—plants grew and bore fruit; cattle feeding on these plants became healthy, and so did the animals that were hunted for food.
And this abundance is now hardwired into our brains, which is why rain and its associated smell feel pleasant.
