The earthy smell of rain is called petrichor. The word was first coined by two Australian scientists in 1964 to describe the mix of water with certain organic compounds that we can smell when it rains.
During research into the “argillaceous odour”- which is how the smell was previously referred to - Isabel Bear and Dick Thomas, scientists from the CSIRO science agency, discovered the substance responsible for the smell. It was a yellow oil secreted by plants and found on rocks and in the soil.
The word petrichor comes from the Greek word “petra”, which means stone, and “ichor”, which refers to the golden fluid that flows in the veins of the immortals in Greek mythology, Met Office reports.
What is petrichor?
No you’re not imagining it, rain does have a smell and here’s why. Petrichor is the smell of water mixing with soil and certain compounds that bacteria and plants release in dry weather.
These organic compounds include aldehydes, ketones, alcohols, esters and acids - such as volatile plant oils, stearic acid and palmitic acid. They accumulate in the soil and on nearby rocks in dry weather.
A build up of these compounds signals to plants that they should hold off on growing their roots or sprouting seeds in dry conditions, the American Chemical Society states. When water droplets hit the ground, especially after a dry spell, these compounds are released into the air creating an earthy smell.
One of the other compounds that makes up the petrichor smell is produced by bacteria. Geosmin is a compound produced by actinomycetes, a type of bacteria in the soil. The compound is released when it rains and is the same compound that gives Beetroots their muddy flavour.
Compounds of petrichor also signal fish to spawn when they are washed into rivers and lakes, studies suggest. It may also help camels find water oases in the desert.
The CSIRO scientists first published their findings on petrichor in Nature journal. In the 58 years since then hundreds of studies featuring the effects of petrichor have been published.
Can you smell a thunderstorm?
Yes, ahead of a thunderstorm you may be able to smell ozone, O3, which some people associate with the petrichor smell. This is due to the electrical charge of lightning in approaching storm clouds that splits up O2 molecules, oxygen gas, into separate atoms that can reform into O3, ozone.
The smell of ozone is wafted down to us by downdrafts. The smell is often described as metallic, similar to chlorine, or compared to the smell of an electric spark.
Once rain begins, that’s when the smell of petrichor takes over. Most consider petrichor a pleasant and grounding smell and some scientists believe that we are hardwired to appreciate the aroma as our ancestors relied on rainfall for survival, Live Science reports.
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