Question

Why are archaea in a different domain from bacteria apex?

Answer 1

Answer:

They are thought to have separate paths of evolutionary development. ~Apex    

Answer 2

The archaea are in a different domain from bacteria due to certain differences in their morphology and habitats, the Archaea are the separate domain of life in prokaryotes. For example; unlike bacteria, archaea cell walls do not contain peptidoglycan, they have different membrane lipid bonding from bacteria and eukarya.
Archaea is  considered as the different domain of life in prokaryotes, as they are the most primitive type and known as the ancient microbes found in extreme niches such as hydrothermal vents, higher salt concentration, high temperature, and pressure etc