Petrichor: Smell of the Earth
✿ A heavenly scent: Do you love the smell of soil after a fresh bout of rain? Are you a fan of the earthy smell of beets? There is a word for that: petrichor. It comes from the Greek petros, meaning stone and ichor, the fluid that flows in the veins of the gods. It is defined as “the distinctive scent which accompanies the first rain after a long warm dry spell”.
✿ Geosmin: After puzzling over the smell of soil for over a hundred years, scientists have pinned the source to Streptomyces, the soil bacterium that also gifts us with the most antibiotics. The bacteria release volatile compounds when disturbed, like the bicyclic alcohol, geosmin (named for “earthy smell”). Did you know that the human nose is incredibly sensitive to geosmin? We can detect as little as ten parts per trillion!
✿ One hump or two?: Bactrian camels are reputed to detect water from 50 miles away. The signature smell of Streptomyces is easily carried across the desert and picked up by the camel’s sensitive nose. In return, the bacterium probably benefits from having its spores spread around. The musty earth scent of some Cactus flowers is also due to a derivative of geosmin. It lures pollinating insects by a promise of water. This is known as floral mimicry. Unfortunately, fish that absorb minute amounts of geosmin from water don’t taste that great.
✿ This smelly chemistry post is a birthday present for our favorite Google+ chemist Siromi Samarasinghe! Check out other odoriferous posts in Sirome’s honor by Chad Haney (http://goo.gl/INUpXi , http://goo.gl/SN4WQs and http://goo.gl/XpVL9R).
Image: Streptomyces coelicolor http://microbewiki.kenyon.edu/index.php/Streptomyces
Source and Ref: http://www.bios.niu.edu/meganathan/smell_of_soil.shtml