Had a non-believer mention that there was no way that 2 people could populate the Earth. After explaining how we'd need to restart after the flood, I of course set out to show just how it was possible and came up with the following estimate. Thought some might find it interesting.
Noah's three son's:
The children of Japheth: Gomer, Magog, Madai, Javan, Tubal, Meshek and Tiras were at least 7 and his grandchildren, per Genesis 10, were at least 7.
The children of Ham: Cush, and Mizraim, and Put, and Canaan were at least 4, and grandchildren were at least 5.
The children of Shem: Elam, and Asshur, and Arphaxad, and Lud, and Aram were at least 5.
Although only Arphaxad's and Aram's bloodlines are mentioned, we know there were Elamites, Luddites and Asshurites. So taking an average of 3 children per household (plus or minus), Shem's grandchildren would have numbered at least 15. Applying similar to Japeth and Ham, Noah would have had approximately 45 great grandchildren.
Again taking an average of 3 children per household, and multiplying exponentially using Shem's lineage, and applying similar to Japeth's and Ham's lineages, we end up with the following approximately 100 years after the flood, when Arphaxad was born until Abraham. According to Genesis 11, there were 390 years and 10 generations from Shem to Abraham .
Japeth's, Ham's and Shem's children (15 children at least multiplied by 3 children each): 45 children at time of Arphaxad's birth.
Arphaxad's children/year 135 (45 x 3): 135
Salah/year 165 (135 x 3): 405
Eber/year 199 (405 x 3): 1,215
Peleg/year 229 (1,215 x 3, etc.): 3,645
Reu/year 297: 10,935
Serug/year 327: 32,805
Nahor/year 356: 98,515
Terah/year 426: 295,245
Remember Noah lived another 350 years after the flood, plus his sons would still be living. At least 23 on earth within the first 135 years.
So we have approximately 300,000 on earth during Abraham's time, 390 years after the flood. Using Biblical events, it has been estimated that Abraham was born approximately 2001 B.C.
Continuing to year 500, or year 1,891 B.C., averaging 35 years til the next generation, there would be approximately 8 million people on earth. (Year 425: 885,735, year 460: 2,657,205, year 495/: 7,971,615)
The earth could be "filled" with at least 8 million people within 500 years of the flood, using only Japeth, Ham and Shem.
Each of Noahs son's lived hundreds of years and could have seen this many people in their lifetimes, and Noah seen at least tens of thousands in his.