Mochi IsleWhy does it smell earthy after rain?
In short: That fresh smell after rain comes mainly from geosmin, made by tiny bacteria in the soil, and from oils plants leave on soil and rocks in dry weather. Raindrops hitting dry ground trap tiny air bubbles that rise and burst, flinging scented specks into the air.
How it works
Soil is home to huge numbers of bacteria, and one group, the actinomycetes, makes a substance called geosmin. Our noses are extremely sensitive to it, so even a tiny amount is easy to smell.
In dry weather, some plants give off oils that settle on soil and rocks. When raindrops hit dry, loose ground, they trap little pockets of air. The bubbles rise and burst, like the fizz when you open a soft drink, flinging scented specks into the air.
This after-rain smell has its own name: petrichor. It is usually strongest when light rain falls on very dry ground; during long, heavy rain the smell is often weaker.
Where to see it in New Zealand
Some parts of New Zealand are quite dry in summer, such as the Canterbury Plains and Hawke's Bay. When the first rain falls after a long dry spell, the earthy smell can be very strong.
Try it together
Next time light rain starts or stops, go into a garden or park with an adult and sniff the air. Compare: does it smell the same before, during and after the rain? If you hear thunder, stay indoors.
Kids also ask
Is the 'rain is coming' smell before a storm the same thing?
Not quite. Before a thunderstorm you may notice a sharp, clean smell. That is often ozone made by lightning and carried ahead on the wind. The earthy smell after rain comes mainly from geosmin.
What is geosmin for?
Scientists are still finding out. One study found that tiny creatures called springtails are attracted to geosmin, and as they visit, they help the bacteria spread their spores.
In the game, “After-rain smell” is a nature card from the Sky set, and it can turn up on any island.
Your child finds this card by reaching the right place or meeting the right weather on the island, and lights it up by answering the question on the back. Tap the button below and the game shows your child which island it is on and how to find it. Mochi Isle is a browser learning game for ages 5 to 18; the main island and the daily lesson are free.
Find “After-rain smell” on the island ↗ All cards in the Sky set