"¹ The earliest life-like forms probably exchanged genetic material laterally in a manner that is analogous to lateral gene transfer amongst bacteria. For this and other reasons, the most recent common ancestor may have been a genetic pool rather than an organism."
In fact, I personally think that if abiogenesis is the ultimate origin of life on earth, then it is far more probable that the universal common ancestor is a gene pool rather than one individual organism that preempted all others (though the latter would hardly contravene the precept of abiogenesis either, much less the underpinnings of evolution). If instead some kind of deity were the first cause of terrestrial evolutionary development then it would be more efficient to just design the first, solitary replicating organism - since it would already contain all the necessary ingredients for everything that followed.
Leaving that aside, this was your initial question and my response:
Are you saying that it is possible all life may not have a common ancestor?
That is certainly possible and would not contravene the scientific underpinnings of evolution in the slightest.
Although we have no evidence of this and it appears fairly unlikely at this juncture, it is also possible that we have not yet discovered the extant remnant, if it exists, of any organisms that have descended from a different common ancestry than that of all known forms of terrestrial life. So, whereas we don't have any evidence of this, it is also possible that it's out there but we just haven't uncovered it, and if we did uncover it then it would definitely not contravene the scientific underpinnings of evolution in the slightest (but it would be a most fascinating subject for research!) any more so than discovering life on Europa or Titan would.
Speaking of which, another reason your statement is certainly possible is because you didn't specify all life on earth, but I knew that's what you meant and answered accordingly. If you had asked about "common ancestry" rather than a "common ancestor" then I would've said: There is no evidence or any reason to believe that any known life on earth originated apart from and outside of the common lineage.
"{"¹ The earliest life-like forms probably exchanged genetic material laterally in a manner that is analogous to lateral gene transfer amongst bacteria. For this and other reasons, the most recent common ancestor may have been a genetic pool rather than an organism."
This is why I don't know that life started with a single cell. For instance, mitochondria and the nucleus are thought to be from other cells that another ate or combined with. There is probably one common ancestor, but it is not clear there was just one cell at the start.
For many that's the point of the debate -- you believe, or want to believe, that the existence of God is impossible so you want that established as conventional wisdom.
if we did uncover it then it would definitely not contravene the scientific underpinnings of evolution in the slightest
Well, it would actually since the modern thesis demands a common ancestor. Now, understand, I'm not saying that evolution isn't responsible for a great deal of biodiversity -- just that in no way does it explain everything and there are those who insist that it does to the point of silliness.
What evidence would it take for you to believe in God?