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Eubacteria and Archaebacteria: the oldest forms of life

Bacteria have an extremely important place in the evolution of life. Our knowledge of bacteria helps us understand, observe, and investigate evolution. This exhibits explains what we know about the origin of life on Earth and the role bacteria played and still play in this. As described in this Lecture on the Origin of Life all life originated from a common ancestor (Source: UTDallas). Our other exhibit explains how we can observe mutations in bacteria directly.

Archaeabacteria are a diverse group of bacteria (prokaryotes that do not have a nucleus) and are considered a major group unto themselves. This group is called the Archaea (from Greek, 'old') for short and to distinguish them from the other prokaryotes, all other bacteria are then called Eubacteria.

What are Archaea? (UCMP Berkeley). They are more similar to eukaryotes than to bacteria in several ways: their cell-wall does not contain peptidoglycan (a component of each bacterial cell). There are other characteristics that Archaea share with eukaryotes, however they do not have a nucleus (which all Eukaryotes have). They form a group by themselves.

The Kingdom Monera is the taxonomic kingdom that comprises all prokaryotes: Eubacteria and Archaebacteria (Source: Bartleby.com). Monera has been contrasted with the kingdoms of eukaryotic organisms (protists, fungi, plants, and animals).Archaebacteria emerged at least 3.5 billion years ago and are the oldest life forms. This diagram of the Kingdoms of Life (source: M. A. Kazlev) shows how archaea may be related to eubacteria and to the other kingdoms. However there are several theories about the exact phylogenetic relationship (what was derived from what) of archaea, eukaryotes, and eubacteria, as can be seen in two versions of the Tree-of-Life (Source: Tree of Life Web). New insights dictate that eubacteria and archaebacteria diverged from one another near the time of the origin of life, and that eukaryotes were derived from eubacteria. More about this subject (with many links to other sites on the subject) (Source: Geosciences.com).

Let's ignore the details. Important is that bacteria (Eu and Archae) have been on earth much longer than eukaryotes; they are probably the oldest forms of life and have populated Earth for most of the time our planet exists. Going back in evolutionary history, the Archaea evolved some 3500 million years ago. Fossiles are mostly not quite as old as that, but occasionally we do find bacterial fossiles (source:LasVegas Sun). Compare that to the age of the first eukaryotes, 1800 million years ago, or the first animals, 600 million years. Earth is truly the planet of bacteria in this respect!

Look at a cut-up prokaryote to see what is inside (Source: JoshuaBond)
You can imagine how important fossile records are in paleobiology (Source: Uni Berkeley).
Do you believe the scenario of "Jurassic Park" could come true? Maybe we can't generate dynosaures, but what about bacteria from "jurassic park" (Source: JC Brown).

The first inhabitants of Earth did not need oxygen to breath, in fact oxygen was toxic to them, and this gas was rare in the atmosphere in those days. However the cyanobacteria that inhabited Earth in the Precambrium produced oxygen as a waste gas and so helped establish an aerobic ecosystem. Read more about Cyanobacteria (Source:Uni Berkeley). They grew in shallow sea water where they formed mats, and used incoming sunlight for photosynthesis. When such a bacterial mat was covered by mud or sand, light could no longer penetrate and the organisms died. A new mat could form on top of this, and the fossilized buildup of millions of layers resulted in the formation of Stromatolites, which can be seen to this day.

There are three major known groups within the Archaebacteria: methanogens, halophiles, and thermophiles. The methanogens are anaerobic bacteria that produce methane. They are found in sewage treatment plants, bogs, and the intestinal tracts of ruminants. Ancient methanogens are the source of natural gas. Halophiles are bacteria that thrive in high salt concentrations such as those found in salt lakes or pools of sea water. Thermophiles are the heat-loving bacteria found near hydrothermal vents and hot springs. You can read more about these Extremophiles in another exhibit.

This lecture on Diversity of bacteria and archaeans explains the differences in more detail--and in more jargon. (Source: On-Line Biology Book)

The presence of Archaea and Bacteria changed Earth dramatically. They helped establish a stable atmosphere, and produced oxygen is such quantities that eventually life forms could evolve that needed oxygen in stead of producing it. The new atmospheric conditions calmed the weather so that the extremes were less severe. Life had created the conditions for new life to be formed. It is one of the great wonders of Nature that this could take place.

The content of this page is copyright of the Virtual Museum of Bacteria and was written by Dr. T. M. Wassenaar (curator), with support of the Foundation for Bacteriology.

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Page last modified: 08 Mar 2007

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