ummm I'll answer this question with what I think you were asking about.
There are more worlds, because Earth can't be the only life baring planet in the universe. If our planet orbits a star, all the other stars we see probably have planets orbiting theirs as well. And in a universe full of infinite possibilities, we can only assume that the Earth isn't alone the only planet to be able to support life. Even Mars shows signs of once being able to support life. If you went to see the movie Knowing, the Earth was to be hit by a VERY strong solar flare. Some scientists believe that what destroyed Earth in the movie, was the same thing that happened to Mars. It destroyed Mars' atmoshpere, and all life with it. But that's simply a theory. Anway, I say that there are other worlds.
And if this was all just a science lesson that was irrelevant to what you were asking, it's cool to know right?