Remember that there is a difference between what the Bible says and some people's interpretation.
Notice that there are two Adams. Gen 1 has both men and women as Adam. Gen 2 has Adam as male alone. If you combine them, then everyone is descended from Adam and Eve. If they are separate people (and in far separate times) then everyone is descended from Adam of chap 1, but only some are descended from Adam and Eve.
Similarly for the flood. The whole erets was flooded. It can be translated as earth, region or country. If it was region, then everyone in the region was killed, but others lived through it. Then, not everyone would be descended from noah, and through him, Adam and Eve. If it was region, you would expect that the Bible would mention that people discover an empty land to the east and move into it (Shinar/Sumer)
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