From the ICR’s URCall series of videos, hosted by Markus Lloyd. “How did we reach 7 Billion people?” (link)
How can we have a world population increase to over seven billion people today from only eight survivors from Noah’s flood, if the Earth is only a few thousand years old? Let’s assume one male and one female marry, and had children, and all their children marry and had children, and so on. Let’s assume, conservatively, that every 150 years the population doubles. After 32 doublings, or 4800 years, the population would reach almost 8.6 billion – which is more than we have now. On the other hand, if modern humans started 50000 years ago, at the same conservative population growth rate, even considering death rates, famine, wars etc, all the people could not even fit on the Earth. So if humans had really been around for millions of years, where did everybody go?
Let’s take a look at the equations. The ICR’s gloriously simplistic model can be written like this.