Prior to the work of scientists did not distinguish between members of the archaea and the bacteria.

Carl Woese

Explanation:

Earlier scientists used to divide organisms in two major groups, the prokaryotes which consisted of bacteria and the eukaryotes which consisted of all the other higher organisms. Carl Woese divided organisms in three groups: Bacteria, Archaea and Eukaryotes. He concluded that Archaea are more similar to eukaryotes than to bacteria. Previously Archaea were thought to inhabit only hostile extreme places but now they have also been discovered in other less hostile environment.

Archaea are similar to bacteria when it comes to morphology. But the process of translation and transcription is significantly different from bacteria and resembles eukaryotes more. Their cell membrane have unique ether linked lipids for more stability and they have some unique metabolic pathways like methanogenesis.