I don't believe in God, I believe in Gravity

That's not really relevant to anything."Gravity" is just a name. Why should that be mentioned.I'm pretty sure you can find plenty of evidence that people understood that things fall. Science has singled out and studied that phenomenon, and given it the name "gravity". So the authors of genesis did not single that out and did not give it a name. But it doesn't follow that they did not know about it.Of course, they did not know nearly as much about it as today's science. But they would have been quite familiar with the phenomenon.To be clear, I am not defending Genesis. There's a lot of nonsense there. But, when we criticize it, let's not exaggerate its problems.

If it began that way, I would be more likely to think it was a modern forgery.

It had to make sense to the people at the time it was written. If not -- if it could only make sense to modern people -- then it would likely be a modern forgery. I am certainly not suggesting that you believe it. But I think you are finding artificial problems. There are plenty of problems without having to do that.