The Problem with Christians

[AJW333]

That would appear to make the whole atheist belief system somewhat tenuous. It would also mean that the declaration,  "God doesn't exist" cannot be made with any certainty.

Bingo!
That's why you'll find it difficult to find an atheist here that claims that.

I would say that every atheist here who says that there is no such thing as the supernatural is automatically ruling out the possibility of there being a God, since God is synonymous with the supernatural.

Observable means that it can be observed, but need not be, or have been, observed yet.
You should not confuse the unexplained with the unexplainable.
Unexplained is that which hasn't been explained yet.
Unexplainable is that which cannot be explained, no matter how we try. You seem to think that abiogenesis falls in this category when it doesn't seem to, at all!

So do we have an explanation of abiogenesis yet?

yes... history is full of stories.
And sometimes people guess correctly at what will happen. Sometimes, the guesses are vague enough to fit many things in there. Most times, however, the guesses are wrong and, as such, are cast away into oblivion. The good guesses, however, get recorded. Can you spot the problem with this mechanism?

Vagaries aside, there are certain instances that are quite precise. My wife had a prophetic dream of her grandfathers heart attack in the backyard of her parents house three weeks before it happened. It just so happens that her sister had the same dream, exactly.