This guys says "For billions of years, life on Earth was single-celled and relatively simple"

Now, if earth is 4.5 billion years old, just wtf does he mean by this quoted statement?

And I'm supposed to believe the bulk of "scientific" estimations (which by definition, are NOT scientific), regarding astronomical numbers proven by what scientific method again?

"What if it's just us"

[link to www.forbes.com (secure)]

Gravity.