> We don't know for certain that our understanding of gravity, for example is exactly correct. That does not mean, however, that the idea of Adam and Eve is tenable. It's not.
The idea of Adam and Eve is not tenable only if you are clinging to traditional and inadequate ways of perceiving Adam and Eve. So try not to jump to conclusions and make your mind up before gathering all the data. The Bible doesn't insist that Adam and Eve were the first, or even the only, hominids on the planet, but only those that God took from wherever they were and put in the garden (Gn. 2.8). It's very possible that these two were selected out from among to fulfill a particular function that God had in mind. That's not so untenable.
> Concordant with science
Maybe instead of continuing to go around in circles about science, let's talk specifics. What is it about the Bible's portrayal of science or some phenomenon on the earth that has ants in your pants? Specifics will yield a more productive conversation than mush contrived through generalities.
> Your whole religion fundamentally depends on this idea of Adam and Eve having really been the first two humans and the snake having really appeared to them and all of the stuff in that story being literally true, doesn't it?
No, that's the traditional take, but I don't take them that way. Adam and Eve weren't the first two humans, but were selected out from among the hominids at the time to represent the whole human race. It's very possible that as humans evolved to the point of being morally culpable and spiritually capable, that God chose them out to reveal Himself to them so they could be his priest and priestess to the rest (the language of Gen. 2.15 is priestly, not agricultural). As representatives of the human race they were disobedient, and so all of humanity was known to be incapable of a relationship with God unless God initiated all the dynamics of the relationship. We can talk about this theology more at length, but the Genesis account of chapter 2 I take to be an account of functionality, not of material origin. We can talk further.
As to the snake, first off, it may not have been a literal snake. The Hebrew word for serpent is nahash, which is indeed the common word for snake, but it also possibly means "able to stand upright." There are all kinds of verbal possibilities here. For instance, nahash is the same root as nehoset, which means "bronze". We see that the shiny, upright snake in Number 21.9 is the same root: it was a literal thing, but a spiritual symbol. "Snake" could also be a word play, because the Hebrew word for "deceive" is very close to it, and is the same root as for magic and divination. Snakes in the ancient world were very much associated with spiritual powers, magic, and cultic rituals. So maybe that's why it was a snake and not another animal.
Back to Genesis now. So what if this "thing" (the nahash) was a spiritual power, represented to the woman as a bright creature, speaking "spiritual wisdom", and yet was deceiving her—all of these can be expressed by the word for snake? Just a little bit of research could change the whole picture. Bible scholars are still working on this text. New archaeological data, as I have just explained, are motivating them to rethink what we thought we knew. So maybe that's why there was a snake in the first place—it was actually a spiritual power (same word group).
So maybe, as I said, this wasn't a snake at all (though logically that is the word used by their culture). Maybe it was a deceiviant (my own coined word. You like it?) upright spiritual being. That may have been why Adam & Eve didn't think it was weird to converse with it. After all, who would talk to a snake? The nahash distorted God's words, deceived them both, and was cursed by God for what he did. And, by the way, nahashim are often the object of curses in the ancient world, and the curse of Genesis 3.14 follows somewhat predictable patterns, conforming to the culture's expressions and forms. The word curse ('aror) also means "banned," so what was happening was that this spiritual being was being thrown out of the garden, so to speak, removed from God's presence (banned), and that was his curse. Maybe that's why God punished the spiritual being. It distorted God's words, deceived them both, and motivated them to rebel against God. You'll notice in the text that the serpent was cursed, but not the man or the woman. There were consequences for what they had done, but only the serpent and the ground were cursed.
In other words, you may be basing your critique of a foundation of sand. It's quite possible, with some thought and research, that the cornerstone upon which the entire Bible is based in more solid and not as scientifically ludicrous as you are assuming. Maybe, when it comes right down to it, the text isn't scientific at all, but theological. But there's nothing wrong with the science either, because there really isn't science in this text.