Question

What is archaea? How it is our ancestor?

Answer 1

Archaea are a domain of single-celled microorganisms. They have no cell nucleus or any other organelles inside their cells. In the past Archaea were classified as an unusual group of bacteria and named archaebacteria, but since the Archaea have an independent evolutionary history and manifest numerous differences in their biochemistry from other forms of life.
Eukarya include the familiar plants, animals, and fungi, as well as protists, single-celled creatures such as microalgae. Their cells have an internal architecture based on membranes and the DNA is kept inside a nucleus. Organisms in the other two groups, Bacteria and Archaea, are all unicellular and lack this more complex internal structure.
Eukaryotes(us) arose directly from an Archaea. In other words, this means that the first Eukaryote was probably an Archaea that somehow acquired the cell structure present today only in Eukarya, perhaps by fusion with another cell. The implication of this alternative hypothesis is that we are members of the Archaea domain, and that there are only two, not three, domains of life
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