The world will end in five billion years when the sun becomes a red giant and boils all the water on Earth, and eventually burns the entire surface. It will possibly suck the Earth into it's gravitational pull, and it will collide with the sun, effectively destroying it. Now human's destroying what we know as Earth, that is an Earth where humans are the dominant species, I don't see it happening any time soon. Even with nuclear weapons, nuclear winter, what have you, people will survive in isolated areas. It's vain to think we have the power to destroy an entire planet, even an asteroid, or a polar shift can't destroy the Earth. They've happened before, and it's still here. The only things I can see causing mass human extermination are a particularly deadly virus, a massive asteroid strike which causes severe sun blockage due to particles in the atmosphere coupled with massive volcanic eruptions which also block out the sun with various particles. Even then, some life, humans included, will survive. Even if they don't, the world won't end. It will still exist, and go on as it has before, it may take millions of years until it has a plethora of flora and fauna, but it will continue until the sun destroys the entirety of the planet. And before it does, the planet will slowly boil and become a barren wasteland before it slowly succumbs to the heat and gravity of the sun. So in the end, I think T.S. Elliot was right. It will not end with a bang, but a whimper. Slowly boiling and getting pulled into the Sun until it's ripped apart by gravitational pull, probably turning into an asteroid belt. That's when the world will end, when it's nothing more than a bunch of rocks floating around a dying star.
