how long will it take 2 people to make it to a population of 8 billion?
Do you mean: how many generations would take 2 people to become 8 billion?
If that's what you mean, then: Log(8 X 10^9) / Log(2)=33(rounded) generations. Because 2^33=8+ billion.
Can't answer that question without more information....what is the reproductive rate? (How many offspring can the two people have?) What is the life expectancy? What is the fertility rate? What is the ratio of women to men in the future offsprings? It also must assume that the original two people are a man and a woman of reproductive age and fertile.
