Postlude

There are certain places on California’s Central Coast where the scent from stands of eucalyptus can penetrate your car even with the windows closed, although the smell is so inviting you are tempted to open them a bit.1 You can have equally interesting scent experiences driving east through the California and Nevada deserts after a rain when you can inhale the pungent smell of sage and creosote bush. Or consider the fact that sometimes you can smell rain before it comes, first from the ozone in the air produced by electrical discharges, and then, especially if you are in arid regions, from the smell of geosmin released from the earth. As Cynthia Barnett points out, you can inhale an especially intense version of earth odors in some rural areas of India, West Africa, or Australia that experience the climatic extremes of months of no rain followed by stretches of monsoon. Back in 1964 two Australian scientists discovered that a major source of this odor were geosmin, a soil-dwelling bacteria, and terpenes secreted by plants. These kinds of molecules are absorbed by rock and clay during hot dry periods, building up great quantities that are then released by the sudden rise in humidity. The scientists nicknamed the smell “petrichor,” from ...