We're kind of obsessed with the connection between scent and memory around here. Our noses have a way of sniffing out nostalgia. Regardless of when you were born, you likely have noticed the scent of wet pavement after it rains on a warm day. It's called "petrichor." It's that sweet earthy smell that fills the air evoking childhood memories of playing in puddles.The word "petrichor" comes from the ancient Greek: it's a combination of ichor, the "ethereal essence" the Greeks believed flowed through the veins of their gods, and petros, the stones that form the surface of the Earth. \nThe earthy aroma we're smelling while it's storming can be traced to three chemical sources, says Joe Hansen in this episode of It's Okay To Be Smart. The first one thing we smell is ozone, which actually gets its name from the Greek word meaning "to smell". As storm clouds approach, the electrical charge of lightning splits the surrounding oxygen molecules into separate atoms, and some of those will reform into ozone. The wind sweeps the molecules downwards to the vicinity of our noses. Once the rain starts to fall and hit the soil we smell something new and different; the petrichor, \nHanson explains it this way. "When decomposed organic material is blown airborne from dry soil, it lands on dirt and rock where it's joined by minerals. And the whole mixture is cooked in this magical medley of molecules. Falling raindrops then send those chemicals airborne, right into your nostalgic nostrils."\nNow that April is here and with it spring showers, we're looking forward to playing in and smelling the magical medley of molecules in the rain.