Trillions of bacteria, fungi, viruses and single-celled organisms travel the globe high in the atmosphere. Scientists are discovering they play a vital role in the weather and even our health.
Clouds are our lifelong companions. Sometimes they drift overhead as wispy filigrees. On other days, they darken the sky and dump rain on us. But for all our familiarity with these veils of water vapour, they have been keeping a secret from us. Clouds are actually floating islands of life, home to trillions of organisms from thousands of species.
Along with birds and dragonflies and dandelion seeds, a vast ocean of microscopic organisms travels through the air. The French chemist Louis Pasteur was among the first scientists to recognise what scientists now call the aerobiome in 1860. He held up sterile flasks of broth and allowed floating germs to settle into them, turning the clear broth cloudy. Pasteur captured germs on the streets of Paris, in the French countryside and even on top of a glacier in the Alps. But his contemporaries balked at the idea. “The world into which you wish to take us is really too fantastic,” one journalist told Pasteur at the time.
