World Builders™                                                                 Session Four  --  Microbiology             


The Archaea may be the oldest life forms on earth.  They are prokaryotes.

    It is believed that the archaea may be the oldest life forms on earth, and that the bacteria and eukaryotes have evolved from them and  with them, at least in part.  The relationships are still being studied, and right now the scientists think that perhaps the early archaea and bacteria may have been the survivors of a pool of life forms that were all in the early stages of their evolution.  There may have been informal DNA (information) sharing in this pool, and organisms in each of the three domains share some DNA present in the other two.

                                Here is another look at the Three Domains diagram

     The Archaea have only recently been recognized as members of a separate domain.  The members of the archaea are tiny prokaryotes that look a lot like bacteria, and, until Dr. Carl Woese at the University of Illinois started studying their DNA sequences, no one had guessed that these little prokayrotes were a separate group of living things.

     Many of the archaea live in very challenging environments, which are perhaps similar to the environments on the early earth.  These hardy little organisms are called extremeophiles (because they like extreme conditions).  Recent widespread interest in extremeophiles pursues several lines of inquiry: 

  •  How, and under what conditions, did life begin on earth ?

  •  What are the environmental limits which make the development of life possible or impossible?    

  • How do archaea work, biochemicaly and structurally?

  • How are archea related to other life forms on earth?

  • How can more of these organisms be cultured in the laboratory?

     The space program, which has gathered so much information about our solar system, has also stimulated a lot of curiosity about whether or not there is life "out there".  NASA, and some universities, have begun the study of Astrobiology, and their scientists are naturally very interested in these extremophiles.

 Here are some environments in which archaea have been found.

In very salty water:  example:
the Great Salt Lake

Strongly alkaline or acidic water:  example: 
Pools in Yellowstone National Park

In very hot water:  example: 
pools in Yellowstone National Park

Near deep sea vents where hot water accompanies volcanic eruptions

In no oxygen (anoxic) environments:  example:  
lake bottoms. 

     Archaea have also been found floating amid the plankton in the open ocean and in hot, geothermally heated water under ground.  Others have been found in places that we would consider normal for living beings.  Not all archaea are extremeophiles.  They are amazingly adaptable organisms.

    Here is an interesting idea for you, which I came across in the book Rare Earth:  

Unicellular organisms deal with environmental change by adapting biochemically

Complex life forms (animals and plants) adapt morphologically, which means that they change the shapes of their bodies and modify their physical systems..

     An organism which is only one cell can make changes in its internal chemistry,  and can experiment with its chemical processes and how it uses its amino acids.

     However,  these kinds of changes are  impossible for a multicellular animal or plant to make.  The way that its cells work together make fundamental chemical changes too disruptive to be practical.  These complex organisms can change their sizes, the shapes of their bodies and limbs, how they manage body heat, and how they deal with hormones and supplies of water and food.  

    Thinking about this, it makes sense that the basic chemical plan of a life form has to be laid out fairly early in the evolutionary process.  What sorts of animals and plants might develop in an environment that was different from ours?  Given lots of time, could some of these extremeophiles evolve into complex life forms that are very different ones we know?

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  Sources:  Introduction to the Archaea. Oct. 29.2003 < http: //>
Todar, Kenneth.  MAJOR GROUPS OF PROKARYOTES.Oct. 29, 2003  (2002)  <>
Header graphic and Deep Sea Vent from NOAA Ocean Explorer

© 1996,1997, 1998, 1999, 2000, 2002, 2003.   Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at .