World Population at the Time of Noah’s Flood
Bruce R. McConkie, The Promised Messiah, p. 607.
Our present interest in this chronology is to call attention to the great number of people who, in the very nature of things, saw their Lord in the early days of this earth's temporal existence. We do not know how many there were, and we do not say how many there were. But it is perfectly obvious there were “many, exceeding great many.” (Alma 13:12.) We do not know the population of the earth in the days before the flood. We do know that the childbearing years of women continued to great ages and that sufficient time was involved for great populations to arise. If the population of the earth had doubled every thirty-three years, from the day of Adam to the appearing of the Lord at Adam-ondi-Ahman, there would have been four and a half billion people on earth. We do not suppose for a moment that such was the case, but we cannot escape the conclusion that many people were then alive, and we do know that all the righteous among them saw the Lord.