I sheltered beneath a large field maple tree, reframing my atti- tude to rain. Parking the grumbles and persuading myself instead how gleaming clean all the trees looked. Appreciating the gun-barrel-gran- ite skies. Remembering that a day in the rain is better than a day in the office. That kind of thing. One of my favourite smells is the air after a storm, the earthy scent of petrichor, from the Greek words petros (stone) and ichor (the blood of the gods). We tend to think that our sense of smell is something to be sniffed at compared with the animal world’s, but we are astonishing- ly adept at detecting geosmin, the chemical released by dead microbes that is responsible for the heady smells of petrichor and pools of water. We can smell geosmin at a level of five parts per trillion – that’s thou- sands of times more sensitive than sharks are to the scent of blood. We may be so sensitive to it because detecting water on the savannah where we evolved was a vital evolutionary advantage. 

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