December 23, 2011
I was walking with my 6-year-old son in July and, just before it started to rain, he asked what that odor was. I was at a loss for an explanation. Do you know?
It's a question that we hear often. The pleasant smell that accompanies the onset of rain is known as petrichor, a word coined in a 1964 paper by two Australian researchers, I. Bear and R. Thomas. A single, compelling explanation for petrichor is lacking, but researchers are gradually closing in on an answer.
Petrichor seems to be the odor resulting from two organic substances that are released from the soil just as rain begins. During dry weather, some plants exude an oil that is absorbed onto surfaces like dry soil. Another substance already in the soil, geosmin, is produced by microbes that live there. Both geosmin and the oil are released by rain, combining to produce petrichor.
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