section_path: Life/Microbes
section_name: Microbes
paragraph_text: Microbes
  
  The first form of life to develop on the Earth were unicellular, and they remained the only form of life until about a billion years ago when multi-cellular organisms began to appear. Microorganisms are microscopic, and smaller than the human eye can see. Microorganisms can be single-celled, such as Bacteria, Archaea, many Protista, and a minority of Fungi.
  
  These life forms are found in almost every location on the Earth where there is liquid water, including in the Earth's interior. Their reproduction is both rapid and profuse. The combination of a high mutation rate and a horizontal gene transfer ability makes them highly adaptable, and able to survive in new environments, including outer space. They form an essential part of the planetary ecosystem. However, some microorganisms are pathogenic and can post health risk to other organisms.
  
  Viruses are infectious agents, but they are not autonomous life forms, as it is the case for viroids, satellites, DPIs and prions.