Few things are more invigorating, and quintessentially British, than stepping outside and inhaling the earthy aromas of a recent rainstorm. But the purpose of the unique scent, known as petrichor, has long been something of a mystery.... Now, however, scientists have found that geosmin, the chemical responsible for the smell, does have a use as it is made by soil microbes to fend off hungry worms. Dirt-dwelling bacteria, including toxic ones, produce the chemical to keep predators, such as worm