The rain hasn’t stopped yet—so why can you already smell that earthy scent?
It has a name: petrichor. The word was coined by two Australian scientists in a 1964 paper published in Nature, combining Greek roots meaning “stone” and “the blood of the gods.” The star of the show is geosmin, a compound produced when soil-dwelling actinomycetes break down fallen leaves. It’s also what gives beets their earthy smell. The human nose is especially sensitive to it: we can detect it at concentrations of just five parts per trillion. You could say you know the moment the rain hits the ground.
How does the molecule get into the air? In 2015, MIT researchers captured it with a high-speed camera: when a raindrop hits the ground, it traps a tiny air bubble. The bubble rises to the surface of the drop and bursts, spraying geosmin and thousands of bacteria into a fine mist. They also made a counterintuitive discovery: light rain smells stronger than a downpour, because raindrops hit gently enough for the bubbles to form.
One hypothesis is that this is an evolutionary legacy: smelling it meant smelling water—and a chance to survive. If it rains tonight, step outside and take a sniff. See if you can catch that earthy scent.
It has a name: petrichor. The word was coined by two Australian scientists in a 1964 paper published in Nature, combining Greek roots meaning “stone” and “the blood of the gods.” The star of the show is geosmin, a compound produced when soil-dwelling actinomycetes break down fallen leaves. It’s also what gives beets their earthy smell. The human nose is especially sensitive to it: we can detect it at concentrations of just five parts per trillion. You could say you know the moment the rain hits the ground.
How does the molecule get into the air? In 2015, MIT researchers captured it with a high-speed camera: when a raindrop hits the ground, it traps a tiny air bubble. The bubble rises to the surface of the drop and bursts, spraying geosmin and thousands of bacteria into a fine mist. They also made a counterintuitive discovery: light rain smells stronger than a downpour, because raindrops hit gently enough for the bubbles to form.
One hypothesis is that this is an evolutionary legacy: smelling it meant smelling water—and a chance to survive. If it rains tonight, step outside and take a sniff. See if you can catch that earthy scent.