Bring May flowers...and take us back in time.\nOur noses have a way of sniffing out nostalgia. There's nothing quite like the scent of petrichor, that sweet earthy smell that fills the air evoking childhood memories of grabbing our boots to go out to jump in puddles and look for rainbows.\nThe 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 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."\nAnd then oh how the flowers did come in May.\nFrom the gardens waved the precocious sunny yellow of the Daffodils and the new vibrant hues of the pansies. And the royalty of the tall stalks and the deep purple blooms of the Iris. And the lilac trees. The gloriously fragrant lilacs that would be cut from the trees and then wrapped in a newspaper so we could take a bouquet to school for the teacher to be placed in a vase a window sill.\nWe're pretty obsessed with scent around here. Spring never fails to impress us with its heady offerings.\nChaucer had it right in the famous opening to the Canterbury Tales; \n"When April comes with his sweet, fragrant showers, which pierce the dry ground of March, and bathe every root of every plant in sweet liquid, then people desire to go on pilgrimages."