There are more microbes on Earth than there are stars in the universe. They occupy every ecological niche, from deep-sea vents to the human gut. So you'd expect them to be staggeringly diverse. But the latest studies suggest there may be far less variation than thought.
David Wilkinson of Liverpool John Moores University in the UK says the diversity of microbes depends on the ease with which they are transported across geographical boundaries. "One of the reasons why there are so many species of big things is because of geographical isolation," he says. "But if you have widespread dispersal, one would guess that there would be fewer species."
To see how widely microbes could be dispersed, Wilkinson's team used computer models designed for studying the dispersal of dust particles. They modified the particles to be more like microbes - which tend to be bigger but less dense - and looked at what would happen if such particles were released from the southern tip of South America.