How does Anaerobic Bacteria fit into the whole evolution story?

Question

How does Anaerobic Bacteria fit into the whole evolution story?

Answer 1

well when the earth was still a new planet there was very little oxygen, so thats all that really could have survived at first.  

Answer 2

Both preceding answers are valid.  For the first two billion years of earth's history, there was no significant amount of free oxygen, and all life was anaerobic.  But photosynthesis gave life forms a powerful new source of energy, and eventually the resulting oxygenation of the planet permitted the evolution of an entirely new set of life forms that could deal with the oxygen atmosphere.  But it took another two billion years before much life moved from the sea onto land.

Answer 3

Long before oxygen was plentiful, all life was anaerobic.  

Some are hold overs before the Oxygen Catastrophe (the name of the sudden increase in atmospheric oxygen due to the evolution of Z scheme photosynthesis in cyanobacteria), others lost some of the mechanisms to cope with oxidative damage secondarily living in anaerobic environments.

Answer 4

They fit in just fine with evolution. There are many types of anerobic bacteria, so for the sake of convenience I'll speak in very general terms. All the classification of anerobe means is that they don't require oxygen (some can tollerate it - even use it under cetain conditions- some find oxygen toxic), but nothing about this conflicts with evolution in any way. All it means is they have evolved to fit certain niches.