(Another hint: The Hebrew text of the Bible does not speak of a world-wide flood and neither did the people back then have any idea of what exactly the whole world was. The world-wide flood first appeared in scripture when the Latin word for "land" ("terra") changed its meaning to "world" and when the Germanic word "earth" changed its meaning from "land" to "the planet". But that is not exactly the oldest and most holy source.)
And with this mindset you have placed yourself in a box...when 1) the plain words of Scripture indicate that it was a world-wide Flood and 2) the Flood killed all of sinful humanity except only those on the Ark.
6 And he was six hundred years old, when the waters of the flood overflowed the earth. 7 And Noe went in and his sons, his wife and the wives of his sons with him into the ark, because of the waters of the flood. 8 And of beasts clean and unclean, and of fowls, and of every thing that moveth upon the earth, 9 Two and two went in to Noe into the ark, male and female, as the Lord had commanded Noe. 10 And after the seven days were passed, the waters of the flood overflowed the earth.
11 In the six hundredth year of the life of Noe, in the second month, in the seventeenth day of the month, all the fountains of the great deep were broken up, and the flood gates of heaven were opened: 12 And the rain fell upon the earth forty days and forty nights. 13 In the selfsame day Noe, and Sem, and Cham, and Japheth his sons: his wife, and the three wives of his sons with them, went into the ark: 14 They and every beast according to its kind, and all the cattle in their kind, and every thing that moveth upon the earth according to its kind, and every fowl according to its kind, all birds, and all that fly, 15 Went in to Noe into the ark, two and two of all flesh, wherein was the breath of life.
16 And they that went in, went in male and female of all flesh, as God had commanded him: and the Lord shut him in on the outside. 17 And the flood was forty days upon the earth, and the waters increased, and lifted up the ark on high from the earth. 18 For they overflowed exceedingly: and filled all on the face of the earth: and the ark was carried upon the waters. 19 And the waters prevailed beyond measure upon the earth: and all the high mountains under the whole heaven were covered. 20 The water was fifteen cubits higher than the mountains which it covered.
21 And all flesh was destroyed that moved upon the earth, both of fowl, and of cattle, and of beasts, and of all creeping things that creep upon the earth: and all men. 22 And all things wherein there is the breath of life on the earth, died. 23 And he destroyed all the substance that was upon the earth, from man even to beast, and the creeping things and fowls of the air: and they were destroyed from the earth: and Noe only remained, and they that were with him in the ark. 24 And the waters prevailed upon the earth a hundred and fifty days.
and 3) the fossil record itself indicates the flood covered the whole world as well.
The explanation is that the world before the Flood was very different from after the Flood. The continents were together and it was the devastating world-wide Flood, the subterranean volcanoes whose waters burst forth from the earth's crust, etc. that caused the so-called "ice Age" as well as the deep canyons of the world, the rock strata and layered fossils we find today, as well as the 46,000 mile long mountain range called the Mid-Oceanic Ridge that wraps around the earth of which most lies on the ocean floor, that we have the jig-saw fit of the continents.