Omg, we've done it before!!!
We messed it up before, causing fumingly hot temperatures that wiped out life, destroyed nearly all life, which then restarted, created land-animals, dinosaurs which were wiped out again by a meteor, then we got the chance for our species to strive, and now we are succeeding at it again, we are completing the cycle!!!
How many times have we destroyed the earth before? We must be getting pretty efficient at it by now right? It's the bloody Matrix!!
Ok all fun things aside, Lets get things in bloody perspective: We are COMPLETELY insignificant!!:
-- We can't diverge a meteor by sending Bruce Willis in a space shuttle to confront it (Armageddon 1998) (Ps .the space shuttle we scrapped because it was costing too much money to maintain, money we would rather use starting silly wars over living habits/religion).
-- We can't reignite the sun by nuking it.. (sunshine 2007) Think of it: If you line up a 100 earths its even smaller than the diameter of the sun. So do you really think that a nuke coming from earth is going to have an effect?
-- We can't create a black hole to suck up the earth, by making a grownups kid racing track under the mountains of Europe that collides stuff (Large Hadron Collider 2011) (really believe me on this, I did this when I was young, and it was a lot of fun, and I actually managed to break the window once by ramping the powered up racecar to jump, and it broke the window. But it never created a black hole..)
The only thing we do at the moment, is shit in our own bed. I am happy to discuss, how it is not smart to be shitting in your own bed, but concluding that we will end all life on earth for a million years is silly. We might be able to wipe ourselves out, but even that is pretty difficult, because next to roaches we might be one of the hardest species to exterminate: We are everywhere on this planet, and we can adapt to lots of different temperatures/threads/infections/diseases, so it probably will take something pretty nifty to destroy all of us..
And even if we do survive, is that our goal? To be some ever living organism on some planet? Maybe at some time we just got to make place for the new. Stop fighting it and embrace the inevitable, that's what evolution is about.... ;-)
One thing is pretty certain: The earth will be here, long after we are gone.