[gore3000]

If you see a planet full of life, such as the Earth, you can -- quite reasonably, based on our knowledge from chemistry and biology -- suggest that it developed over a long time from a pre-biotic soup.

No you cannot assume such a thing. You cannot prove the existence of something for which there is no evidence. You are making an assumption (that there is no God) and using it to prove that there is no God. Such reasoning is called a tautology in logic and sophistry in common speech.

[PatrickHenry]

No you cannot assume such a thing [pre-biotic soup].

I can; and I do. For the reasons I gave.

You cannot prove the existence of something for which there is no evidence.

That cuts two ways, doesn't it? Think about it. {Oh, I forgot to whom I'm speaking.)