i would add that the greek septuagint puts the flood at around 3,3k bc which is shortly before civilizations all around the world jump into the bronze age almost simultaniously. also the word used for "earth" or "world" in the flood story also can mean simply "land", implying the levant. it says it covered the mountains with 15 cubits of water which is about 8 meters. the highest mountain in the levant is al-qurnat as-sauda with 3088m. if we then rise the waters 3095m on this map   we see that it is pretty much the entire world, but leaves a few places in asia, the americas etc. for some few to survive, repopulate and rebuilt giving rise to the many floodmyths around the world. so there is room to argue that some other people, maybe even non adamic ones, survived there, and subsequently intermixed with the noahites. and just to add: the sediment layers also could be simply dirt that fell off when everything was under water due to their different density. we also now know that there are huge water masses below the earth far bigger than the oceans giving explenation where the water came from   /2014/jun/13/earth-may-have-undergr ound-ocean-three-times-that-on-surf ace fountains of the great deep > 11in the six hundredth year of noah's life, in the second month, on the seventeenth day of the month, on the same day all the fountains of the great deep burst open, and the floodgates of the sky were opened.
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