The realization that archaea are distinct from bacteria was a gradual process, but it can be traced back to the late 1970s.

Here's a breakdown of the key developments:

* 1970s: Carl Woese and George Fox were studying ribosomal RNA (rRNA) sequences, which are fundamental to the function of all cells. They noticed that some organisms, initially classified as bacteria, had significantly different rRNA sequences. This suggested a deeper evolutionary divergence than previously thought.

* 1977: Woese proposed a new system of classification that included three domains of life: Bacteria, Archaea, and Eukarya. This was revolutionary because it challenged the traditional two-kingdom system (plants and animals).

* 1980s and 1990s: Further studies on the biochemistry, genetics, and cell structure of archaea revealed more substantial differences from bacteria. These differences included:

* Cell wall composition: Archaea lack peptidoglycan, a key component of bacterial cell walls.

* Membrane lipids: Archaea have unique lipids with branched side chains, unlike the straight chains found in bacteria and eukaryotes.

* Gene expression: Archaea have their own distinct mechanisms for transcription and translation.

So, while the initial observations leading to the separation of archaea from bacteria were made in the 1970s, the full extent of their differences was revealed through ongoing research throughout the 1980s and 1990s.

It's important to note that the understanding of archaea continues to evolve as scientists discover new species and learn more about their biology.