After a period of warm weather, it rains. And as it rains, it seems we can smell the rain. It is a smell that you can not miss but is hard to define. Some sense it as earthy, others as stony. But the smell does have a name in our wordy language. It is called petrichor. The first part of that word, explains Wikipedia, comes from the Greek word for stone, petros, and the second part, ichor, apparently names the blood of the gods in Greek mythology. (Christian mythology does not have a specific name for the blood of its god.) We have two Australian scientists to thank for this word, which entered the language in 1964 and describes "the distinctive scent which accompanies the first rain after a long warm dry spell."

MIT researchers recently figured out the source and mechanism of petrichor by using high-speed imaging. What they saw is that when a drop of rain, which has fallen from a cloud, hits the ground or a surface, it too forms a cloud—a cloud of particles. If a raindrop hits, say, a "natural environment," the tiny particles, aerosols, "may carry aromatic elements, along with bacteria and viruses stored in the soil." So, rain essentially smells like what it hits and disperses.