I am biased by my religious beliefs, but I've always struggled with the idea that abiogenesis could spontaneously occur in "just" a few billion years on earth. A few billion seems like not enough time. Even the simplest forms of life are mind bogglingly complex.
Of course, it's a few billion years scaled across >1 life-friendly planets (since it only has to happen on 1 of them), but still just seems like not enough monkeys and typewriters in the given timeframe to produce something as astonishingly complex as life, let alone Shakespeare.
Of course, it's a few billion years scaled across >1 life-friendly planets (since it only has to happen on 1 of them), but still just seems like not enough monkeys and typewriters in the given timeframe to produce something as astonishingly complex as life, let alone Shakespeare.