Have you ever been outside on a warm day after it rained and wondered what the lovely, earthy smell is? The smell is created by a compound called geosmin, a by-product of soil-dwelling actinobacteria. The smell was given the name petrichor in 1964. It’s not the smell of rain falling. It’s the smell of the earth coming back to life after a dry spell.
As the ground dries, actinobacteria produce spores, generating geosmin in the process. The human nose is extremely sensitive to geosmin and can detect it at concentrations as low as 5 parts per trillion!
When the weather is dry for a period of time, plants release oils into the soil around them. The oils stop roots from growing and prevent neighbouring seeds from germinating, reducing competition for nutrients in tough times.
When it rains on dry ground, tiny bubbles of air are trapped underneath the rain. They rise through the water droplets and burst at the surface, releasing a fine mist of plant oils and earthy scents into the air. We recognise these scents as Petrichor!
Rainfall and bubbles
You can see the release of tiny air bubbles after rain hits the ground in this video from MIT.
More about petrichor
Geosmin is a metabolic by-product produced by soil microorganisms such as Streptomyces.
Joy Bear and Richard Grenfell Thomas first used the term petrichor in the science journal Nature.
Humans can smell geosmin at extremely low levels.
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Last Updated on September 18, 2026 by Emma Vanstone
