A Circular Argument

I've had many debates with atheists about the existence of God, and I just wanted to post here an argument I made recently. The general consensus between them seemed to be that:

1) There was no evidence for the non-existence of God
2) They did not know how the universe came into being, nor how life started but that was not relevant
3) They were confident that scientists would one day know these answers.

To this I posed the following hypothesis:

Imagine if I were to declare that the earth was not really round without giving any evidence; saying that I didn't know what shape it was but that I knew it wasn't round; and that while I didn't know what shape it was, I felt sure that scientists would know one day.

Would my theory be given any credence?

Apparently it wasn't a valid argument :D