I don't know the individual who wrote that. However, I found it compelling. If you do not, then how about the other half of the equation? You said "let's do the math". Let's means "let us", meaning now it is your turn. Show mathematically how the earth could have been repopulated to its current level solely by the people on Noah's Ark, in the time allotted. "Doing the math" was your idea, after all.
I don't think I'm smart enough. I'd just take the number 8 and double it. Then see how many times it takes by the same doubling to get to 6 billion. I think it's between 29 and 30. If that were generations of 40 years, then it would take c. 1200 years to get 6 billion. Maybe there are others who can help here.
I wasn't the one who asserted the impossibility. But I did ask for the math. So far I don't think anyone has supplied sufficient evidence to substantiate the impossibility of it all.
Mark is an intelligent, well read and reasoned person. He is not an evangelist in any sense of the word that I understand; he is simply concerned that evolution be expressed as truthfully as possible.