The three-domain system is a biological classification introduced by Carl Woese in 1990, that divides cellular life forms into archaea, bacteria, and eukaryote domains.

The Three Types of Learning. There is more than one type of learning. A committee of colleges, led by Benjamin Bloom, identified three domains of educational activities:

The Archaea are microorganisms very different from both bacteria and eukaryotes. Some biologists think they should be placed in a separate kingdom.

Three Domains of Life . Microbes are found in all three domains of life: bacteria, archaea, and eukaryotes. Diverse species of the three domains are explored in Microbial Biorealm.

A Molecular View of Microbial Diversity and the Biosphere. Read it. More details on Domains is found here.