Have you ever wondered why the earth smells so good after the rain? The answer is bacteria!

The smell of the earth just after the rain is very distinct, and many people think that it is a pleasant smell. It surely reminds some of us of springtime, or even autumn with the heavy rains. But have you ever wondered what causes this smell? I bet a lot of people thinks that it is the rain itself that causes the smell, but that’s not really the truth.

Image by Sérgio Valle Duarte, posted with the Creative Commons Attribution 3.0 Unported license.

Most of the “after the rain” earthy smell is caused by bacteria, more specifically bacteria from the call Actinobacteria. These bacteria behave more like fungi than other bacteria, and are found all over the world. They grow during damp and warm conditions, so they require a certain amount of rain in order to thrive. This means that they are dormant during dry periods, so when they soil begins to dry up the bacteria begins to produces spores. These spores can lie dormant in the soil for a long time, but will become active again once the soil becomes moist.

When the rain begins the soil begins to get wet, and the Actinobacteria spores will get shot up from the soil and into the air. During this phase we humans (and other animals) will breath these spores, and this is one of the phenomena that causes the “after the rain” smell we all love.

If the “after the rain” smell is unpleasant, it might be because of acidic rain

Bacteria are not the only reason why we get distinct smells when it is raining, and another of the reasons is because the rainwater is slightly acidic. This is especially true in urban environments, and could be one of the reasons why the forest smell better than the city during rainfall.

The acidic rainwater is just slightly more acidic than the regular water, but this is enough to get some chemical reactions going. Some of these chemical reactions that tend to happen in the soil when exposed to acidic water is very aromatic, and some of these smells can remind you of gasoline. What really happens is that the acidic water breaks apart soil and releases small mineral particles that are trapped to the soil particles, and these in turn react with the environment.

It's really cool that bacteria and chemical reactions in the soil is responsible for the distinct smell of rain, and I hope you enjoyed learning about this. Thanks for reading, and don't be afraid to leave a comment below!

About the author

Hi, I’m @valth! I live in Norway with my wife, our baby, and our two dogs; one of which is seen wearing a bow tie in the profile picture!

I am very passionate about nature and biology, and have been studying ecology for a few years now. My passions are mostly within conservation biology, mycology (the studies of mushrooms), botany, animal behavior and general microbiology. I really enjoy both the theoretical aspect, as well as the more practical aspect of biology, and I spend about as much time in front of biology textbooks as I do spend on finding and identifying plant, mushroom and animal species in the forests.

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