After a prolonged spell of dry weather the sound of thunder can uplift us, with the smell of rain-soaked pavements soothing and comforting our frayed nerves, and, as it turns out, there is a science behind the delicious scent of rain.
Back in in the 1960s, a couple of Australian researchers introduced the term petrichor into the English lexicon, which is the name given to describe the pleasant smell of wet earth after a long stretch of intensely dry weather, according to the BBC. The word is derived from the Greek word petros, which can be roughly translated to the word “stone,” with ichor describing “the fluid that flows in the veins of the gods.” An apt name for the freedom that comes from falling rain.
As it turns out, that earthy, nostalgic scent that revives our senses after it rains and produces a sense of euphoria is actually created by bacteria, as molecular biologist Professor Mark Buttner explains.
“These critters are abundant in soil. So when you’re saying you smell damp soil, actually what you’re smelling is a molecule being made by a certain type of bacteria.”
Geosmin just happens to be that molecule and Streptomyces is the bacteria. This bacteria can normally be found living in soils that are healthy, while the bacteria known as Streptomyces is commonly used in many different antibiotics.
When rain plummets to the ground, geosmin is magically cast forth into the air, which is the reason why it is so noticeable after a torrential downpour. And in fact, humans aren’t the only ones whose senses are heightened by the scent of rain, according to Professor Buttner, who noted that “lots of animals are sensitive but human beings are extremely sensitive to it.”
Isabel Bear and RG Thomas, the Australian researchers who have gifted us with the term petrichor, discovered that, in India, the scent was so beloved by its people that it was swiftly bottled up into a scent there called “matti ka attar.”
Interestingly, according to perfumer Marina Barcenilla, geosmin is today fast becoming a popular ingredient that is used in perfumes all over the world, and this really should not surprise people.
“It’s a really potent material and it smells just like the concrete when the rain hits it. There’s something very primitive and very primal about the smell. Even when you dilute it down to the parts per billion range, humans can still detect it.”
Professor Jeppe Lund Nielsen, from Aalborg University in Denmark, believes it is highly probable that geosmin could stem from terpenes, which is how many plants obtain their scent.
Professor Philip Stevenson, who conducts research at the Royal Botanic Gardens, Kew, notes that rain may help to bring out this strongly pleasurable scent that is inherent in plants.
“Often the plant chemicals that smell pleasant are produced in leaf hairs and the rain may damage these, releasing the compounds. Rain may also break dry plant material releasing chemicals in a similar way to when you crush dried herbs — the smell becomes stronger.”
So the next time you find yourself in stifling heat, longing for the pleasant scent of rain to transport you to happier places, consider the science of petrichor and how bacteria is the substance that is responsible for that warm feeling you get after heavy rains have finally cleared the air.