Is there a common ancestor between archaea, bacteria, and eukaryote?

Question

Is there a common ancestor between archaea, bacteria, and eukaryote?

Answer 1

Yes, the hypothetical, and aptly named last universal ancestor is the ancestor of all species on Earth.

Answer 2

Yes.  All of these life forms have a lot of similar biochemical processes.

This is evidence for a common ancestor.

Answer 3

Presumably, yes.  The Eukaryotes are the more recent clade, descended from Archaea.  Before that, the Archaea and true bacteria also share an ancestor.  They are all cells after all. The idea that lipid membranes evolved separately, but in such similar fashion, seems unlikely.  With early cells there is also the question of endosymbiosis.  Did cells swallow each other whole?  Even if they did, the cells involved still resulted from common ancestors.

Once you go back before the age of cells though, towards the era of abiogenesis, the very origin of life, things are a but more sticky.  There may have been separate origins of life.

Answer 4

Yes.  The near-universality of the genetic code (which codons specify which amino acids) is very good evidence for a single common ancestor for all modern life.

There may have been other kinds of life about four billion years ago, but it was either out-competed by our kind of life, or else it perished in the Oxygen Catastrophe.