Originally Posted by Caltex

The Sun won't explode, it is far too small to supernova.

What will happen is that the sun will slowly get bigger and heat up in the process of becoming a red giant. Eventually the earth will become scorched, and all the water will evaporate, then the H20 bonds will be broken, and the hydrogen will escape earth. All life will be long dead by this point. Eventually the expanding sun will engulf earth and burn up the planet.

We've probably got 2-3 billion years left of a good earth. Far longer than humans will last. If there was some intelligent life here when it does happen, they could in theory move out to mars and terriform the planet, and buy a few million for years, but it's only a matter of time until the sun scorches mars too.