The little things in life often are what make us the happiest. A hug from a loved one. The taste of homemade chocolate chip cookies. Wearing warm socks right after they come out of the dryer. And, of course, the earthy smell that overwhelms the air after it rains.
It’s not all in your head, either. That pleasant, earthy scent, known as petrichor, is caused by the release of specific chemicals when the rain reaches the ground. It’s as if the earth is rewarding everyone for putting up with terrifying thunderstorms and sudden downpours sans umbrella.
Soil-dwelling bacteria called Streptomyces secrete a molecule called geosmin, BBC reports. When rain hits the soil, the raindrops trap air bubbles containing geosmin. The bubbles move through the raindrop and burst out of it as aerosols, even smaller particles dispersed through the air. Once the geosmin gets off the ground and into the air, we’re able to smell it distinctly because human noses are extremely sensitive to it. According to Smithsonian Magazine, some people can smell it even when the concentration is as low as five parts per trillion. Check out these 8 other smells that are proven to make you happier.
Another contributing factor to petrichor is a combination of plant oils. Australian researchers Isabel Joy Bear and R. G. Thomas, who coined the term petrichor in 1964, discovered that some plants secret oils during times of drought. When it finally rains, the oils that had been accumulating are released into the air in the same way geosmin is.
And if the scent becomes especially strong—and oddly clean—after a thunderstorm, you can thank ozone. A bolt of lightning can split oxygen and nitrogen, which may recombine to form nitric oxide, one of the compounds needed to create ozone. That molecule is known for its pungent, chlorine-like odor. Here are more facts you never knew about thunderstorms.
So while the science behind petrichor isn’t all that romantic—who’d have guessed we’re actually smelling bacteria secretions and lightning?—the end result certainly is. Don’t miss these 18 other fun science facts you never learned in school.