random evolution question

[NLSoldier]

If at some point humans and other animals are all killed off due to nuclear war or natural disasters or whatever, but all the elements required to generate organic material and maybe even some simple organisms still existed, I assume that the process of evolution would start over?

How likely would it be for species similar to those currently existing on earth to exist again? And mainly, at what point would a species be classified as "intelligent life"? (basically at what point would we consider them essentially 2nd generation humans)