archaea

On Earth, there are only 2 kinds of autotrophic bacteria and archaea that may be independent from solar energy, the acetogenic bacteria and archaea and the methanogenic archaea.

Maybe the highlights would be Lynn Margulis and the endosymbiosis theory, and Carl Woese finding the Archaea in 1977.

These 2 kinds of bacteria and archaea need free hydrogen and most of them are killed by free oxygen.

A nitpick: Although similar in some aspects, archaea are not bacteria; they are classified under their own phylogenetic domain.

In bacteria or archaea it would be even easier -- just pick up the ancestral allele through horizontal gene transfer.

Perhaps arriving on the same comets that carry abundant hydrogen cyanide (though, no such archaea bearing asteroids have been observed, yet).

The eukaryotes are hybrids, mainly between some Archaea and some bacteria (the ancestors of mitochondria).

It is well known that the much less complex bacteria & archaea can live at much higher temperatures than any eukaryote.

But at least some species of Archaea were known long before, just inadequately classified.

Maybe a new sub-division in the multicellular kingdom but not a whole new branch at the same level as bacteria, archaea and multicellulars...

I've never heard of a study claiming B12 in animals in vivo is not synthesized by bacteria (or archaea).

For now, it is still not certain whether Archaea is the sister group of all Bacteria, or only of one branch of Bacteria.

If the hypothesis is false (it is widely believed that eukaryotes arose from a joining of archaea and bacteria, not archaea and virii) then "an archaeal ancestor" doesn't even have a referent.

I believe "archaeal cell" is referring to an Archaea, one of the three branches of life.

Note that an entire kingdom of life, the Archaea, was only identified in 1977[1].

[2] They are prokaryotes (lacking a nucleus and other membrane-bound organelles), and the two prokaryotic domains of life (Bacteria and Archaea) are composed entirely of microbes.