[Jiggymike]

If ALL life were to go extinct, I do not know if we could predict if life would rebegin/reevolve. No one is too sure how life first evolved and a lot of older theories don't hold as much water as they did maybe 10 years ago (primordial ooze, urea being formed from inorganic matter, etc.). Theoretically, if life were just abolished from the planet, I do not think it would evolve again in the current conditions but might once the planet heats up/cools down or whatever we foresee in the next billion years.

Let's say that life DOES occur again, however. Not long ago I went to a lecture about someone who described what life would be like on Mars if there were indeed Martians. Basically, he made some predictions based on constancies in life on our own planet. Things that have reevolved more than once include joints, skeletons and support structures, limbs for locomotion, and GENERAL forms of these things would probably reappear. However, other aspects would probably be so vastly different that we couldn't predict it. For instance, we all know that the reproductive and excretory system are combined in tetrapods. This is not some sort of "natural" state but just a coincidence that the creatures that eventually moved onto land had this system; they could easily be separate while other organ systems could have been combined. Its possible that totally unknown forms could evolve as well, things unlike anything seen today.

However, the odds against any organism that exists now reevolving from scratch is probably greater than the number of molecules in the universe, or some huge improbability like that. I don't really want to get onto intelligent life, though, as I havent' really thought about it before.