We had a talk about this earlier over here. where there is a discussion of some other possible ‘doomsday’ events, including mega-volcano eruptions and nuclear war.
To be honest, the thing that worries me the most is us – humans – using up the earth’s resources and destroying its habitats, along with man-made global warming. Though these things aren’t likely to be the end of the world (as in ‘the end of life on the planet’), they are happening quickly and they are going to make a massive difference to the way humans live.
Even a nuclear weapon could not end the planet. It might end our civilisation if it turns into a nuclear war, but the planet would still be here.
To be honest, no matter what we do the planet will be here long after the human race has become extinct. Until the sun blows up into a red giant and incinerates the planet’s surface. But that’s not for another 5 billion years or so, so not anytime soon. I agree with Austin that we are doing a lot to damage the earth’s biosphere and probably changing it irrevocably. But I am an optimist and I believe that the earth has survived bigger extinction events than us, and will recover in time. The types of species that are around will change, but life will go on regardless.