I think that a meteorite could happen, but not soon. Hopefully, we will have found a way to live on Mars or somewhere by then. Also, with the way that we can see so far into space, we would have plenty of time to finish our bucket list.
Global warming won't end the world. It was always going to happen: we just sped it up. The world periodically goes through warming and cooling periods, and this has been going on ever since the beginning of time. After this warming period that we're in, there will be an ice age - maybe not on the scale of the Ice Age - that the Earth will use to try to dwindle the population of all living things, then start to heal herself.
Nuclear weapons are a definite possibility with some of the crazy dictators out there that like to watch things explode. Personally, I think watching things explode is fascinating too. (Just as a side note: I like harmless
explosions. Thank you for your time.)
Zombies are all science fiction and are good for movie plots. That is all.
The 'super-flu' won't cause the world to end. There is always that select group of people that survive to the end, then the communities always become closer for it.
As for what I think will end the Earth; I believe that God will end the Earth, and we probably wouldn't understand, even if he tried to explain it to us, how it would happen. Yes, I know what the Bible says, but how he will actually destroy the Earth then create a new one? I wouldn't be able to comprehend...
Here's to ignorance!