Nobody really knows, there are several spiritual, religious and scientific theories of how the world will end and when, several times in the past there have been predictions of when the world will end, like the years 1000, 2000 and in the future, 2012. Scientifically though planet earth will be consumed when the sun grows to a red giant in a couple of billion years or so, whether or not humans are still around remains to be seen, more than likely we will either be extinct, evolved into another lifeform or no longer live on earth.