how much power does he have? how fast could he destroy the earth?

As I understand it. He has the same concussive energy as a Nuke stored within his head. At least, that is what Wolverine proclaimed. Of the three summers children, Cyclops is in my opinion, the weakest, although considering the upper limits of Havok and Vulcan, that isn't exactly an insult either. Cyclops can probably disentagrate a mountain if he really let loose. But he couldn't destroy the earth. His blasts would disappate after a few thousand meteres.

@IAMtheHERO:
cyclops as far as im know can have his optic blast at full power for around 20 minutes before needing a few minutes rest and of used in a wide spread effect goes like a small nuke so cyclops could in theory if he had full control of his powers which he doesnt which is holding him back in power would be able to easily destroy cities countries but not planet busting more like moon busting.

Its not so much his power, but his focus, intelligence and experience in using his power. though Cyke has taken out meteors without problem in rapid succession
if it helps guage. Likely if he were to turn and go after the planet, he would use tact rather than his optic blasts, and succeed before anyone knew what was up.

He is powerful but not ehough to like destroy a world

It seriously depends on the writer. Most of the time he's the weakest of the three Summer's brothers (though he used to be stronger than Havok before Havok got a huge upgrade) and has the power of a nuke. However, it has been stated that he can cut a planet in half. Again, though, it's based on the writer's discretion.

Actually fun fact: If Cyclops starts his attack with BEHOLD OPTIC BLAST! He can blast the moon apart, but it's such a ridiculous thing to say that he never does it.
 
(I just made that up I loved him in MVC2)

" @FadeToBlackBolt said:

" @Edamame:  Havok getting the power upgrade, Havok beating Vulcan, Vulcan putting up a fight against Black Bolt. All of it lol.   The whole X-Men/Cosmic Universe is great, so long as you know nothing about the backstories of the characters you're reading. "

I agree. "

He can punch a hole though ice with his fist. His eye beams have been known to... hurt people. One time he stared at Xavier so stoically, Xavier could not walk. He makes Wolverine smile like a school girl at an all boys boarding school because when he takes his visor off Wolverine's advanced sense can tell him that awesome is about to happen. He is so powerful that Mr Sinister is called Mr Sinister because of his sinister habit of watching Cyclops sleep and his tendency to collect DNA examples from Cyclops... the sinister way. 

" He can punch a hole though ice with his fist. His eye beams have been known to... hurt people. One time he stared at Xavier so stoically, Xavier could not walk. He makes Wolverine smile like a school girl at an all boys boarding school because when he takes his visor off Wolverine's advanced sense can tell him that awesome is about to happen. He is so powerful that Mr Sinister is called Mr Sinister because of his sinister habit of watching Cyclops sleep and his tendency to collect DNA examples from Cyclops... the sinister way.  "

" @TheCrowbar: True true, I can see Jean swinging both ways. In fact I often imagine that. Perhaps lets call that a past time of mine.  "

" @TheCrowbar: X-Men Forever pretty much confirmed that yes, Jean makes Emma look like a prude.  "