The earth's engine Microorganisms have been evolving for nearly 4 billion years and are capable of exploiting a vast range of energy sources and thriving in almost every habitat. For 2 billion years microbes were the only form of life on Earth. During this long history, all of the basic biochemistries of life evolved, and all life forms have developed from these microbial ancestors. Microorganisms represent by far the richest repertoire of molecular and chemical diversity in nature. They underlie basic ecosystem processes such as the biogeochemical cycles and food chains, as well as maintain vital and often elegant relationships between themselves and higher organisms.
Microbes provide the fundamental underpinning of all ecosystems.
Without microorganisms, all life on Earth would cease. Because microorganisms are small, they are least known, and this gap in knowledge is particularly apparent for bacteria and other small organisms. For bacteria there may be 300,000 to 1 million species on earth yet only 3,100 bacteria are described in Bergey's Manual, the treatise of described bacteria. Similarly low fractions of microorganisms have been cultured from fresh water and ocean environments. Hence, most microbes remain to be discovered.