That wonderful smell that frequently accompanies the first rain after a long period of warm, dry weather is called Petrichor – a heady mixture of plant oils, bacterial spores and ozone.
In 1964, two Australian scientists, Isabel Joy Bear and R. G. Thomas, determined that one of the main causes of this distinctive smell is a blend of oils secreted by some plants during arid periods. When a rainstorm comes after a drought, compounds from the oils—which accumulate over time in dry rocks and soil—are mixed and released into the air.
In moist, forested areas in particular, a common substance is geosmin, a chemical produced by a soil-dwelling bacteria known as actinomycetes. The bacteria secrete the compound when they produce spores, then the force of rain landing on the ground sends these spores up into the air and the moist air conveys the chemical into our noses.
Who knew that something so complex lay behind our enjoyment of a freshly cut lawn after a downpour ? There is a deeper question of why we enjoy it so much and scientists have speculated that it’s a product of our evolution.
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