Man like other animals has inherited a fine sense of smell from ancestors who did not have technology to know things that would help them survive. The environment gives out smells when something changes. Because we now mostly live indoors these smells do not come to our attention. However, they still exist.
Before it begins to rain the air falls and oil is released from the earth. A special odour is notable. CSIRO has named this smell "petrichor". It seems no one had given it a named before. The particular smell was made public in 1964 when Isabel Bear wrote a paper which was published in Nature journal. Mineralogists were first aware of it and mentioned the odour in text books but little was made of the smell.
Aboriginals would have know of it because oils given off before rain are stronger after drought. The word "mattiak ka attar" is used in Asia to describe the odour trapped in sandalwood oil to enhance the perfume.
Scientists at CSIRO identified a yellowish colored oil on soil and rocks that was created by moisture. Humidity is the trigger: water droplets form in crevices thus leaching the oil. It becomes stronger when it actually rains. The smell gets into the wind and is picked up by mammals.
✴ Chemistry by Ty Buchanan ✴