Wednesday, January 21, 2015

Petrichor explained

Posted by Kirk Mona
If you're a doctor who fan like I am you know the word Petrichor. Author Neil Gaiman snuck the word into the episode The Doctor's Wife. The word was part of a telepathic passcode to open the hidden backup control room in the TARDIS. "Oh course," you say. "We are nerds, we know this!" You may also remember that Idris defined it as "the smell of dust after rain."

The word wasn't a fabrication of Gaiman, it was coined in 1964 by Australian researchers Bear and Thomas in the journal Nature. The posited that an oil extruded by plants in dry periods is somehow put into the air by the rain. The oil actually helps prevent other plants from germinating and thus helps the plants avoid competition. I would think this would also prevent their own seeds from germinating but perhaps that is discussed deeper in the research. To be fair to rain smells, Geosmin is also responsible for the smell of the earth after rain but until Gaiman works that into a Doctor Who episode I'm afraid that word will also remain obscure.

Deeply nerdy and linguistically savvy Doctor Who fans and biologists alike were excited when researchers from MIT recently presented evidence on how the compounds that comprise petrichor get into the air. They dropped raindrops on 28 different soil types hundreds of times and filmed the results with high speed cameras. You can see tiny particles become aerosolized and swept up in air currents as the result of the drops. The high speed footage has been released online and it is fascinating to see the particles launched into the air. It is fun to think of hundreds of trillions of raindrops hitting the earth in a storm, each releasing tiny particles into the air that we smell as fresh petrichor.




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