Carl Woese was a microbiologist who found important difference in the structure of ribosomes in prokaryotes (bacteria) and eukaryotes (eubacteria). He found that some single-cell organisms collected from mud flats around hot springs had an even simpler ribosome structure.
The most central ribosomal RNA (rRNA) surround the site where messenger RNA (mRNA) is decoded by matching the transfer RNA (tRNA) attached to the amino acids. The three-letter codon in mRNA (e.g., UUC) lines up with the three-letter anti-codon on the tRNA (AAG) and as the mRNA advance one step through the ribosome, the amino acid () is added to the growing polypeptide chain of a new protein/enzyme.
These most central and functionally active rRNA macromolecules were all the same, but the outer structures in bacteria and eubacteria were much larger.
Woese and his young colleague George Fox hypothesized that the smaller ribosomes were in cells that preceded the evolutionary development of all prokaryotes and eukaryotes, with their larger ribosomes. They called these cells Archaea and argued that the "tree of life" needed three branches from the origin of life, not just two.
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These most central and functionally active rRNA macromolecules were all the same, but the outer structures in bacteria and eubacteria were much larger.
Woese and his young colleague George Fox hypothesized that the smaller ribosomes were in cells that preceded the evolutionary development of all prokaryotes and eukaryotes, with their larger ribosomes. They called these cells Archaea and argued that the "tree of life" needed three branches from the 
