It’s Raining Bacteria! The Truth About Clouds Some clouds appear light and fluffy. Others dark and menacing. But are all clouds made of bacteria? Clouds contain dust and ice crystals and other atmospheric debris. But they also contain bacteria and other microscopic organisms. Scientists have done lab experiments showing that microbes can act as ice nuclei. And for a while scientists have suspected that microorganisms swept into the atmosphere end up as parts of clouds. Clouds, Alive? Now, thanks to an airborne mass spectrometer–an instrument that identifies the presence of elements and molecules–scientists know that clouds contain bacteria. In fact, they found that clouds are about a third biological material. Does this mean that clouds are somehow alive? Not necessarily, because it’s not yet clear if the microbes in clouds are living or dead. Climate And Weather Patterns What scientists do know is that the discovery will help develop new climate models. The more we know about how clouds form and what’s in them, the better we can understand their effect on climate and weather patterns. Clouds radiate sunlight back into space and also trap heat on earth. And, of course, clouds produce rain. Knowing that clouds harbor biological material adds another piece to the puzzle of how clouds work, and how they affect life on Earth.