The Three Domain System of Classification by Carl Woese (1977) based on variations in 16S rRNA sequence, divided the entire living organism in the biosphere into three major groups called Domains namely (1). Archaea, (2). Eubacteria (Bacteria) and (3). Eukarya or Eukaryota.
In the earlier systems of classifications, Archaea were treated as a unique type of bacteria called Archaebacteria and they were included in the Kingdom Monera along with true bacteria and Cyanobacteria (blue green algae). Now we are certain that Archaea possess distinct difference from true bacteria in their cellular structures and metabolic activities, and also they have a unique and separate evolutionary ancestry.
Archaea shows some characters similar to true bacteria where as some unique sets of characters they share between eukaryotes. Due to these peculiarities, the group Archaea is now recognized as a distinct domain of life.
The present post article describe what all are the similarities and difference between Archaea, Bacteria (eubacteria) and Eukarya (eukaryote) with a comparison table for easy understanding.
Similarities and Differences Between Bacteria, Archaebacteria and Eukaryotes: Comparison Table