Why does rain have a smell?

Australian scientists Isabel Joy Bear and Richard Thomas coined the word petrichor in 1964, combining the Greek words for stone and the fluid in the veins of the gods. During dry spells, plants release oils that collect on rocks and soil, while Streptomyces bacteria produce a compound called geosmin. When rain falls, a 2015 study at MIT showed, drops hitting porous surfaces trap tiny air bubbles that burst and launch aerosols carrying these scents into the air. Humans are remarkably sensitive to geosmin, detecting it at around five parts per trillion. The sharp, clean smell before a thunderstorm is different: it is often ozone carried down by storm winds.