Pretty smart thinking on Noah’s part to send out birds. It would have been a mistake to open the door and check. And it definitely has to be divine intervention that the dove brings back an olive leaf. I would think it would just stay. I also wonder how high up this mountain did they sit? I imagine that it couldn’t be too high otherwise it would be difficult to get elephants and hippos down a mountainside.
In Genesis 8, we come to the sacrifice and God’s covenant. It would be slightly disappointing to be one of the animals sacrificed. You are one of a very few of your species to survive this flood and what is your reward for making it through this rough time. Well you get sacrificed. But at least it was pleasing to the Lord and he promised never to do it again. I think that this covenant is a big risk for God (though He knows the future). Basically He is saying that even if the future state of the world is worse off than it was, God will not destroy it. I guess there might be some loopholes, like He only said He won’t strike down every living creature, but I guess He could just wipe out mankind. You also see a very early declaration of total depravity when God says “the intention of man’s heart is evil from his youth.”