What is the smell before it rains?

What is it called? What causes it? Why does it happen?

Have you ever wondered what causes that distinct smell before a rain shower?

Scientists have too, and they uncovered what causes the curious smell! Petrichor, derived from the Greek words "petra" (stone) and "ichor" (blood of the gods), was discovered by the Australian scientists Isabel Bear and Richard Thomas in 1964.* It is defined as "a pleasant smell that frequently accompanies the first rain after a long period of warm, dry weather" (Oxford Dictionary). Eager to uncover the scientific reason behind the heady smell, the two took to experimentation.

So what exactly causes it?

Bear and Thomas found that when rocks and soils were subjected to high humidity, as water seeped into the pores of the rocks, a yellow oil was flushed out. This oil was responsible for the familiar smell! As the humidity increased in the air before a rain shower, the oils from the rocks and soil were flushed out and released into the air, causing the smell that we are familiar with. As the rain begins to fall, it helps to diffuse the smell.


The two scientists published their work in an Australian scientific journal, and we've used their work ever since to explain the not-so-mysterious smell. The scientists were awarded honors for their contributions.* Now when you come across this smell, you can explain what it is to all of your friends!

Now you know!

Class Activities:

(to be done before the lesson)

Activity #1

- Describe the smell in your own words. What does it smell like? Do you enjoy the smell? Do you notice it? Create a word cloud with words describing the smell.


Activity #2

- What do you think causes the smell? Do you think that smell is more prevalent in certain areas more so than others? Draw a diagram illustrating what you think causes the smell.


(to be done after the lesson)

Activity #3

- After learning about the smell, come up with a new name for it and explain its significance.